- Email: [email protected]
Lethal and sublethal effects of imidacloprid and buprofezin on the sweetpotato whitefly parasitoid Eretmocerus mundus (Hymenoptera: Aphelinidae)
Crop Protection 45 (2013) 98e103
Contents lists available at SciVerse ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Lethal and sublethal effects of imidacloprid and buprofezin on the sweetpotato whitefly parasitoid Eretmocerus mundus (Hymenoptera: Aphelinidae) Fariba Sohrabi a, *, Parviz Shishehbor a, Moosa Saber b, Mohammad Said Mosaddegh a a b
Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University, Ahvaz, Iran Department of Plant Protection, Faculty of Agriculture, University of Maragheh, Maragheh, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 June 2012 Received in revised form 23 November 2012 Accepted 30 November 2012
The parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is one of the key natural enemies of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Lethal and sublethal effects of imidacloprid and buprofezin on emergence and key biological and population parameters of E. mundus exposed during different developmental stages were studied. Doseeresponse bioassays were carried out on adult wasps using a leaf dipping method. The emergence rates of adults were reduced significantly by the field-recommended concentrations of the insecticides. However, the emergence rates were not affected either by the stage of the parasitoid at the time of exposure (larval and pupal stages), and there was no interaction between treatments and time of exposure. No significant mortality of E. mundus adults was observed following buprofezin treatment. The LC50 of imidacloprid on adults was 4.75 ppm. The results showed that the longevity and fecundity of E. mundus adults were reduced significantly by the two insecticides, though the sex ratio of E. mundus offspring was not affected. Population parameters of the parasitoid such as R0, rm and T were also significantly reduced by the insecticides. Our results indicated that, in addition to lethal effects, sublethal effects should also be considered when these insecticides are applied in IPM programs for this pest. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Bemisia tabaci Demographic toxicology Eretmocerus mundus Insecticides Lethal effects
1. Introduction The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a serious pest of cotton, legume and vegetable crops worldwide (Mound and Halsey, 1978; Byrne and Bellows, 1991). Biotype determination of Iranian populations of B. tabaci indicated that the B biotype predominates in Iran (Rajaei Shoorcheh et al., 2008). It causes damage through direct feeding, excretion of honeydew and transmission of more than 100 plant viruses (Jones, 2003). Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is a solitary parasitoid wasp and one of the key natural enemies of B. tabaci (Urbaneja and Stansly, 2004; Urbaneja et al., 2007). Because E. mundus is not always able to maintain whitefly populations below an economically acceptable level, supplementary chemical treatments are often needed in crops (Stansly et al., 2004,
* Corresponding author. Current address: Department of Plant Breeding, Faculty of Agriculture, Persian Gulf University, Bushehr, Iran. Tel.: þ98 9173708661; fax: þ98 7713531534. E-mail address: [email protected] (F. Sohrabi). 0261-2194/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cropro.2012.11.024
2005). Selective insecticides that are more toxic to insect pests than to natural enemies can be useful tools for integrated pest management (IPM) programs (Croft, 1990; Hopper, 2003). Knowledge about the impact of insecticides on the natural enemies of a pest species is important for the integration of biological control and chemical applications. Assessment of the lethal and sublethal effects of insecticides on natural enemies is necessary to recognize the total effect of insecticide applications (Desneux et al., 2007). Sublethal effects are defined as effects on individuals that survive exposure to a pesticide (Desneux et al., 2007). Sublethal effects may be manifested as reductions in life span, developmental rates, fecundity, changes in sex ratio and/or changes in behaviour (Haynes, 1988; Croft, 1990; Salerno et al., 2002; Stark and Banks, 2003; Desneux et al., 2004a, 2004b; Bayram et al., 2010a, 2010b). Demographic toxicology has been suggested as an important tool to evaluate the total effects of toxicants (Stark and Banks, 2003). The intrinsic rate of increase (rm) has been recommended to assess overall effects of pesticides since this statistic is based on both survivorship and fecundity parameters (Stark and Wennergren, 1995). The chloronicotinyl insecticide imidacloprid and the insect growth regulator (IGR) buprofezin are two relatively new insecticides
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
for controlling whiteflies in Iran (Talebi-Jahromi, 2007). Imidacloprid is effective against a broad range of insects, in particular homopterous insect pests, and can be applied as both foliar and soil treatments as well as via seed treatment (Horowitz et al., 1998). Buprofezin, an inhibitor of chitin synthesis, is generally considered to have a relatively narrow spectrum of activity which is limited to homopterous insects (Kanno et al., 1981). The purpose of this study was to assess the lethal and sublethal effects of imidacloprid and buprofezin on adult and preimaginal stages of E. mundus in order to gain a deeper understanding of their total effects on this parasitoid. 2. Materials and methods 2.1. Whitefly and parasitoid cultures B. tabaci adults were originally collected from cucumber fields in Ahvaz (Iran) in October 2009. Whiteflies were cultured at 16e25 C, 40e50% RH and a photoperiod of 14:10 (L:D) in a muslin-walled cage (120 60 60 cm) containing cucumber plants (cultivar Superdominus). E. mundus used in this study was collected in a greenhouse in Ahvaz in October 2010, on cucumber plants, and reared on cucumber plants infested with B. tabaci nymphs. The rearing conditions were identical to those for whiteflies. Each week new cucumber plants harbouring nymphal stages of sweetpotato whitefly were added to the cages. 2.2. Insecticides tested Imidacloprid 350 g/l SC (ConfidorÒ 35 SC, Gyah, Iran) and buprofezin 400 g/l SC (ApplaudÒ 40 SC, Syngenta, Switzerland) were obtained as formulated products. All treatments included 500 ppm Tween 20 as a non-ionic surfactant. 2.3. Effect of insecticides on the emergence rate of E. mundus Effects of imidacloprid and buprofezin on the emergence rate of E. mundus were separately examined with parasitised whitefly nymphs containing parasitoids in either the larval or pupal stage. Groups of approximately 50 adult whiteflies from our laboratory culture were each confined in clip cages to the lower surface of a cucumber leaf on a potted plant for a 24 h synchronised oviposition period. After oviposition, the adult whiteflies were removed. The plants, now harbouring whitefly eggs, were incubated under conditions of 25 1 C, 70 5% RH, and a photoperiod of 14:10 (L:D) for egg hatching and subsequent nymphal development to the second nymphal instar (appropriate for parasitisation). Thereafter, groups of 5e6 parasitoid females (plus 2e3 males), collected with an aspirator from the laboratory colony, were each confined in clip cages placed over the areas of leaf where the whitefly nymphs were situated. The parasitoids were removed after a 24 h synchronised parasitisation period. Parasitized nymphs were incubated under similar conditions as above to obtain different preimaginal stages of the parasitoid. Ten-day- and thirteen-day-old parasitoids approximately correspond to the larval and pupal stages of E. mundus, respectively. Then, 25e30 parasitized nymphs at these two different developmental stages were marked on each of 5 leaves per treatment by circling with a felt pen. Thereafter, each leaf was dipped in the field-recommended concentration of formulated insecticide for 10 s. The control groups were treated with distilled water. The concentrations used were 1000 and 2000 ppm for imidacloprid and buprofezin, respectively (Heidari, 2004; TalebiJahromi, 2007). Parasitoid emergence was evaluated 10 days after the treatment.
99
The experiment comprised a 3 2 factorial design with the treatment (three levels: control, imidacloprid and buprofezin) and stage treated (two levels: larvae and pupae) as main factors. An arcsin square root transformation was performed on percent emergence before data analysis. The emergence data were subjected to a two-way analysis of variance (ANOVA) and the means were separated using Fisher’s protected Least Significant Difference (LSD) test at P ¼ 0.05 where applicable (SAS Institute, 2003). 2.4. Effect of insecticides on the adult parasitoids The toxicity of imidacloprid and buprofezin to adult parasitoids was assessed using a leaf dipping method (Prabhaker et al., 2007). Leaves were dipped into insecticide solutions diluted to the required concentration for l0 s, and air dried for 1 h. The control samples were dipped into distilled water. Adult parasitoids were confined to the leaf discs from treated leaves placed with their adaxial side on a thin layer of 1% agar (2e3 mm) in exposure cages. The exposure cages consisted of a round plastic container (52 mm tall, 40 mm diameter) with four lateral screened holes (10 mm diameter) in order to facilitate ventilation. The parasitoids in the test cages were supplied with a thin strip of honey placed on the underside of each container lid as food. Five concentrations of the insecticide, determined by preliminary experiments, were used to obtain LC90, LC50 and LC10 data for parasitoid adults. Each concentration had three replicates with a total of 15e20 adults per replicate. Each experiment was repeated three times (i.e., totally nine replicates for each insecticide concentration). The cages were kept in an incubator (25 1 C, 70 5% RH, and a photoperiod of 14:10 (L:D)). The number of dead and live wasps was counted 48 h after initial exposure to the insecticide residue. Mortality data were analysed using PROC PROBIT (SAS Institute, 2003) to compute lethal concentration values (LC90, LC50 and LC10) and associated 95% fiducial limits (FL). As the mortality of E. mundus adults at buprofezin treatment was too low to compute an LC50 value, the data were subjected to analysis of variance (ANOVA). To determine which treatments differed after the ANOVA test, the Fisher’s protected Least Significant Difference (LSD) test (P ¼ 0.05) was undertaken (SAS Institute, 2003). No data transformation was performed before analysis because there was no evidence of nonnormality within the data. 2.5. Life history parameter measurements 2.5.1. Life history of parasitoids treated at the adult stage Sublethal effects of insecticides on the life history parameters of adults treated with the LC25 of imidacloprid (1 ppm) and the fieldrecommended concentration of buprofezin (2000 ppm) or distilled water (control) were studied. In demographic studies, concentrations below the LC30 value are usually used by researchers to investigate the sublethal effects of pesticides (Biddinger and Hull, 1999; Salerno et al., 2002; Rafiee Dastjerdi et al., 2009; Bayram et al., 2010a). With buprofezin, as the mortality of E. mundus adults at toxicity bioassays was too low, the field-recommended concentration of this insecticide was used for life history studies. Forty to 50 pairs of emerged young adults (<24 h old) were exposed to cucumber leaves treated with insecticides for 48 h. The technique, conditions and cages used for exposing adults were as described in the preceding section. Thereafter, 20 live pairs were selected randomly and transferred individually to clip cages on fresh, undipped leaves infested with 50 s instar hosts for oviposition. Infested leaves were replaced daily until death of females occurred. Daily and total number of parasitized B. tabaci, adult longevity and offspring sex ratio were recorded.
100
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
Table 1 Mean (SE) emergence of E. mundus exposed to field-recommended concentrations of insecticides at larval and pupal stages of the parasitoid.a Treatment
Mean percentage of adult parasitoid emergence from parasitized host nymphs treated at different preimaginal stages Larvae
Pupae
Control Imidacloprid Buprofezin
79.80 (6.21)Aa 37.00 (4.10)Bb 62.00 (8.07)Aa
75.80 (2.58)Aa 48.40 (2.64)Ab 66.40 (6.66)Aa
a
Means in a column followed by different lower case letters, or in a row by different upper case letters differ significantly (Fisher’s protected LSD; P < 0.05).
2.5.2. Life history of parasitoids treated at preimaginal (larval and pupal) stages In this experiment, adult parasitoids that emerged from B. tabaci nymphs treated with either the insecticides or with distilled water (control) at the larval (10 days after parasitism) and pupal (13 days after parasitism) stages of the parasitoid were used for the life history studies. Preliminary experiments with each insecticide were performed to determine the concentrations that resulted in at least 30e40% parasitoid emergence when applied to parasitoid larvae or pupae. With buprofezin, cucumber leaves bearing parasitized whitefly nymphs at both larval and pupal stages of the parasitoid were dipped in a 2000 ppm (field-recommended concentration) solution for l0 s. The imidacloprid concentrations were 1000 ppm (field-recommended concentration) and 500 ppm for treatment of E. mundus larvae and pupae, respectively. Subsequently, 20 parasitoid pairs (<24 h old) that emerged from each experiment were selected randomly and placed individually in clip cages on leaves with fresh hosts, and their survival and fecundity were examined as described for the preceding experiment. Time from oviposition to emergence, adult parasitoid survivorship rates, daily fecundity, and sex ratio of offspring at each treatment were used to construct lxmx life tables from which demographic parameters were calculated. Mean demographic parameters and pseudo-replicates for the net reproductive rate (R0), intrinsic rate of increase (rm), finite rate of increase (l), mean generation time (T), and doubling time (DT) were generated using the bootstrap method (Pilkington and Hoddle, 2006). Mean bootstrap estimates of demographic parameters were compared across treatments using analysis of variance (ANOVA). Mean adult longevity, offspring sex ratio, and fecundity data in each experiment were analysed by ANOVA and means compared using Fisher’s LSD test (P < 0.05). Data which required normalization were transformed prior to analysis. The percentage data were arcsin square root-transformed and the count data were square root-transformed (Zar, 1984). A 3 3 factorial
analysis of variance (ANOVA) was applied to study the possible effects of insecticides on biological parameters of adult parasitoids exposed to insecticides at larval, pupal, and adult stages. This analysis of variance model included main effects of stage, treatment, and the interaction of the main effects. 3. Results 3.1. Effect of insecticides on the emergence rate of E. mundus Adult E. mundus emergence from B. tabaci nymphs, following exposure to the field-recommended concentrations of imidacloprid and buprofezin at larval and pupal stages, was significantly reduced by the insecticides (F ¼ 21.07, df ¼ 2, 24, P < 0.0001). However, the emergence rate was not affected either by the time of insecticide exposure relative to parasitoid preimaginal development (F ¼ 0.78, df ¼ 1, 24, P ¼ 0.3858), or the interaction between treatments and time of exposure (F ¼ 1.00, df ¼ 2, 24, P ¼ 0.3828). These results indicate that imidacloprid is toxic to the preimaginal (larval and pupal) stages of the parasitoid, and is significantly more toxic to parasitoid larvae than to pupae (Table 1). 3.2. Effect of insecticides on the adult parasitoids The mean percentage mortality rates observed for adult parasitoids for untreated control and buprofezin at concentrations of 2000, 8000 and 10,000 ppm were 17, 12, 17 and 18%, respectively. No significant difference was found between mortality of E. mundus adults following buprofezin treatments and control (P > 0.05). Imidacloprid was toxic to adult parasitoids. The LC90, LC50 and LC10 values and 95% fiducial limits (FL) were estimated to be 95.8 (58.97e 182.01), 4.75 (2.93e7.13) and 0.23 (0.08e0.5) ppm, respectively. 3.3. Life history parameter measurements Sublethal effects of imidacloprid and buprofezin on biological and demographic parameters of adult E. mundus exposed to insecticides at adult and preimaginal (larval and pupal) stages are summarized in Tables 2 and 3. For parasitoids exposed to imidacloprid during the adult stage, their longevity (F ¼ 11.76, df ¼ 2, 57, P < 0.0001), total fecundity (F ¼ 13.92, df ¼ 2, 57, P < 0.0001), and mean daily fecundity (F ¼ 7.20, df ¼ 2, 57, P ¼ 0016) were significantly lower than those for both control and buprofezin (Table 2). The offspring sex ratio was not affected significantly by either of the two insecticides (P > 0.05) (Table 2). For parasitoids exposed to imidacloprid and buprofezin during the larval stage, the longevity (F ¼ 16.35, df ¼ 2, 57, P < 0.0001), and
Table 2 The mean rates of biological parameters (SE) of E. mundus exposed to different concentrations of imidacloprid and buprofezin at the larval, pupal, and adult stages in comparison with untreated control insects.a Treatments Larval treatments Control Imidacloprid Imidacloprid Pupal treatments Control Imidacloprid Buprofezin Adult treatments Control Imidacloprid Buprofezin a
Concentration (ppm)
Longevity (days)
Total fecundity
Eggs/day
Sex ratio (proportion female)
Distilled water 1000 1000
7.10 (0.40)a 3.40 (0.34)b 3.40 (0.34)b
100.44 (9.60)a 35.20 (5.90)c 35.20 (5.90)c
13.50 (0.66)a 9.62 (0.58)b 9.62 (0.58)b
0.54 (0.02)a 0.51 (0.00)a 0.51 (0.00)a
Distilled water 500 2000
4.35 (0.17)a 4.15 (0.26)a 5.30 (0.56)a
65.85 (6.05)a 44.75 (6.43)b 40.85 (5.49)b
15.30 (1.30)a 9.88 (0.75)b 7.30 (0.37)c
0.49 (0.01)a 0.50 (0.02)a 0.51 (0.04)a
Distilled water 1 2000
7.20 (0.34)a 5.15 (0.23)b 6.80 (0.43)a
62.40 (2.91)a 32.45 (4.14)b 60.40 (5.90)a
12.47 (0.64)a 9.62 (0.76)b 12.40 (0.33)a
0.50 (0.02)a 0.54 (0.02)a 0.47 (0.02)a
Means in a column for each developmental stage followed by the same letter do not differ significantly (P > 0.05).
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
101
Table 3 The mean rates of stable population parameters (SE) of E. mundus exposed to different concentrations of imidacloprid and buprofezin at the larval, pupal, and adult stages in comparison with untreated control insects.a Treatments Larval treatments Control Imidacloprid Buprofezin Pupal treatments Control Imidacloprid Buprofezin Adult treatments Control Imidacloprid Buprofezin a
Concentration (ppm)
R0
rm
l
T
DT
Distilled water 1000 2000
49.50 (6.54)a 17.95 (1.47)b 40.34 (2.25)a
0.22 (0.00)a 0.17 (0.00)c 0.21 (0.00)b
1.25 (0.01)a 1.18 (0.00)b 1.23 (0.00)a
17.75 (0.36)a 16.71 (0.17)b 17.31 (0.09)a
3.15 (0.07)b 4.17 (0.10)a 3.32 (0.04)b
Distilled water 500 2000
32.40 (1.01)a 24.18 (4.41)a 20.41 (1.13)b
0.21 (0.00)a 0.18 (0.01)b 0.17 (0.00)b
1.24 (0.00)a 1.20 (0.01)b 1.18 (0.00)b
16.10 (0.03)b 17.10 (0.33)a 17.69 (0.23)a
3.26 (0.05)c 3.82 (0.21)b 4.11 (0.04)a
Distilled water 1 2000
31.2 (0.71)a 16.20 (0.48)c 29.33 (1.47)b
0.18 (0.00)a 0.15 (0.00)b 0.18 (0.00)a
1.20 (0.00)a 1.16 (0.00)b 1.19 (0.00)a
18.49 (0.11)a 18.12 (0.05)b 18.57 (0.07)a
3.82 (0.04)b 4.69 (0.05)a 3.89 (0.04)b
Means in a column for each developmental stage followed by the same letter are not significantly different (P > 0.05).
total fecundity (F ¼ 10.07, df ¼ 2, 57, P ¼ 0.0002) were significantly lower than those for the control population (Table 2). Imidacloprid significantly decreased the mean daily fecundity of E. mundus adults (F ¼ 4.04, df ¼ 2, 57, P ¼ 0.0228). The offspring sex ratio was not affected significantly by either of the two insecticides (P > 0.05) (Table 2). Insecticides did not significantly affect the mean longevity of parasitoids exposed to imidacloprid or buprofezin at the pupal stage (P > 0.05). However, the total fecundity (F ¼ 5.85, df ¼ 2, 57, P ¼ 0.0049), and mean daily fecundity (F ¼ 22.65, df ¼ 2, 57, P < 0.0001) of parasitoids exposed to imidacloprid and buprofezin at the pupal stage were significantly lower than those for the control population (Table 2). There were no differences observed in sex ratio between the treatments and the control (P > 0.05) (Table 2). Two-way analysis of variance (ANOVA) indicated that treatment (F ¼ 18.97, df ¼ 2, 171, P < 0.0001), developmental stage of the parasitoid at the time of exposure (F ¼ 16.68, df ¼ 2, 171, P < 0.0001), and also interaction between treatment and the time of exposure (F ¼ 6.88, df ¼ 4, 171, P < 0.0001) had a significant effect on adult longevity. ANOVA analysis revealed that treatment (F ¼ 18.77, df ¼ 2, 171, P < 0.0001), stage (F ¼ 5.67, df ¼ 2, 171, P ¼ 0.0041), and treatment stage interaction (F ¼ 3.37, df ¼ 4, 171, P ¼ 0.0110) effects on the total fecundity were also significant. Daily fecundity of E. mundus was not significantly affected by the stage (P > 0.05), but it was the effects of treatment (F ¼ 17.02, df ¼ 2, 171, P < 0.0001) and treatment stage interaction (F ¼ 7.46, df ¼ 4, 171, P < 0.0001) that were significant. A two-way ANOVA indicated that neither the treatment nor the treatment stage interaction had a significant effect on offspring sex ratio (P > 0.05), whereas the stage of the parasitoid at the time of exposure significantly influenced the offspring sex ratio (F ¼ 2.95, df ¼ 2, 171, P ¼ 0.05). Effects of imidacloprid and buprofezin on the life history parameters of E. mundus are shown in Table 3. For parasitoids exposed to insecticides at the adult stage, the R0 (F ¼ 210.63, df ¼ 2, 57, P < 0.0001) was significantly influenced by insecticide treatment. The values of the rm (F ¼ 152.26, df ¼ 2, 57, P < 0.0001), l (F ¼ 114.67, df ¼ 2, 57, P < 0.0001), and T (F ¼ 9.60, df ¼ 2, 57, P ¼ 0.0021) of parasitoids exposed to imidacloprid at the adult stage were all significantly lower than those for both water control and buprofezin. Maximal DT was observed following imidacloprid treatment, which was significantly different from the control and buprofezin (F ¼ 62.73, df ¼ 2, 57, P < 0.0001) (Table 3). For parasitoids exposed to insecticides at the larval stage, the R0 (F ¼ 16.76, df ¼ 2, 57, P ¼ 0.0003), rm (F ¼ 100.16, df ¼ 2, 57, P < 0.0001), l (F ¼ 56.89, df ¼ 2, 57, P < 0.0001), T (F ¼ 6.39, df ¼ 2, 57, P ¼ 0.0129), and DT (F ¼ 32.98, df ¼ 2, 57, P < 0.0001) were significantly influenced by insecticide treatment (Table 3).
The R0 (F ¼ 15.48, df ¼ 2, 57, P ¼ 0.0005), rm (F ¼ 32.04, df ¼ 2, 57, P < 0.0001), and l (F ¼ 31.36, df ¼ 2, 57, P < 0.0001) values of parasitoids exposed to imidacloprid and buprofezin at the pupal stage were significantly influenced by insecticide treatment. T (F ¼ 15.55, df ¼ 2, 57, P ¼ 0.0005), and DT (F ¼ 28.32, df ¼ 2, 57, P < 0.0001) were significantly increased by insecticide treatment (Table 3). 4. Discussion The present study shows that the field-recommended concentration of imidacloprid (1000 ppm) severely affected the preimaginal stages of the parasitoid, reducing adult emergence when applied to either parasitoid larvae or pupae (Table 1). Similarly, reduction in emergence rate was reported in Encarsia inaron (Walker) after treatment with imidacloprid (Hoseini, 2010; Sohrabi et al., 2012). Regarding the adverse effect of imidacloprid on preimaginal stages, it should be noted that in the present study, the parasitized host nymphs were completely dipped in the insecticide solution. Consequently, the nymphs received a large amount of the insecticide. Under field conditions, parasitized host nymphs live on the underside of the leaves, and are therefore likely to receive a lower concentration of the insecticide. Our results further reveal that imidacloprid had a more significant adverse effect on parasitoid emergence during the larval stage compared to the pupal stage. Similarly, Uygun et al. (1994) found that the timing of exposure to pesticides had a differential effect on the survival of Eretmocerus debachi Rose. The field-recommended concentration of buprofezin (2000 ppm) had no significant effect on the emergence of E. mundus when the parasitoid was treated during either the larval or pupal stages. Similar results have been reported for a number of other aphelinid parasitoids (Rill et al., 2008; Sugiyama et al., 2011). In contrast, buprofezin showed toxicity to preimaginal stages of Encarsia luteola Howard (Gerling and Sinai, 1994) and to E. inaron (Sohrabi et al., 2012). Imidacloprid was highly toxic to adult E. mundus with an LC50 value of 4.75 ppm. Imidacloprid also led to significant mortality of E. mundus, Eretmocerus eremicus, Encarsia formosa (Sugiyama et al., 2011) and E. inaron adults (Sohrabi et al., 2012). The present study further indicated a low impact of buprofezin on E. mundus adults, as reported on other aphelinid parasitoids in several studies (Gerling and Sinai, 1994; Hoddle et al., 2001; Heidari, 2004; Sugiyama et al., 2011; Sohrabi et al., 2012). We further investigated the sublethal effects of imidacloprid and buprofezin on female adult longevity, fecundity, offspring sex ratio, and stable population parameters of E. mundus that had been exposed as larvae, pupae and adults to different concentrations of the insecticides. The results showed that the application of
102
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
imidacloprid at larval and adult stages, significantly affected all of the biological and stable population parameters of E. mundus except it did not affect the sex ratio of offspring. Furthermore, imidacloprid applied to pupae significantly affected fecundity and all of the stable population parameters of E. mundus except it did not affect the R0 value. There are a few studies reporting sublethal effects of imidacloprid on the biological and population parameters of parasitoids. A recent study showed that longevity, fecundity, sex ratio and some life history parameters of E. inaron were significantly affected by applying imidacloprid at the larval, pupal and adult stages (Sohrabi et al., 2012). However, Saber (2011) reported that treatment of Trichogramma cacoeciae Marchal pupae with imidacloprid had no significant effect on longevity, fecundity or population life table parameters of the parasitoid. As stated by Smilanick et al. (1996), percentage emergence of parasitoids from treated hosts is not an adequate measure of ecological selectivity of an insecticide. When interpreting data on emergence rate from insecticide treated hosts, it is also important to consider the fitness of the parasitoids that emerge (Smilanick et al., 1996; Saber et al., 2004, 2005; Bayram et al., 2010b; Saber, 2011). In this study, buprofezin treatment at the larval stage had adverse effects on longevity, total fecundity and rm of E. mundus females. Furthermore, buprofezin applied to pupae significantly affected fecundity and all of the stable population parameters of the parasitoid. However, treatment of E. mundus adults with buprofezin had no significant effect on the biological and stable population parameters of E. mundus although R0 was significantly reduced compared to the control. A previous study showed that buprofezin treatment had no influence on the longevity and total fecundity of E. inaron females when the parasitoid was treated during either the larval, pupal or adult stages (Sohrabi et al., 2012). However, buprofezin had significant effects on daily fecundity and sex ratio of E. inaron offspring (Sohrabi et al., 2012). Furthermore, buprofezin treatment at larval and adult stages of E. inaron had no significant effect on the stable population parameters of E. inaron, however it significantly affected R0, T, and DT when pupae were treated (Sohrabi et al., 2012). The different responses of E. mundus and E. inaron to the same insecticide at the pupal stage treatment may be related to the concentration of insecticide parasitoids had been exposed to, and the species differences in physiological responses to the insecticides. Jones et al. (1998) found no adverse effects of buprofezin on reproduction of E. mundus and Eretmocerus tejanus Rose and Zolnerowich when applied to either parasitoids larvae or pupae, but buprofezin applied to pupae significantly reduced longevity of surviving E. tejanus adults. In a similar study, Heidari (2004) found that treatment of E. formosa pupae with buprofezin had no significant effect on population parameters of the parasitoid except that it reduced R0 of the parasitoid compared to the control. In view of the possible detrimental sublethal effects of imidacloprid (in addition to its significant lethal effects on preimaginal and adult stages) and buprofezin on biological and population parameters of E. mundus, the use of these insecticides in crops should be avoided in situations where biological control by this parasitoid is important. Semi-field and field studies aiming to evaluate the efficacy of the combined use of insecticides and E. mundus are needed in order to obtain more applicable results under field conditions. Acknowledgements The authors would like to thank the receiving editor, Dr. Jerry Cross and two anonymous reviewers for their valuable and helpful comments on earlier drafts of this manuscript. We also thank Dr. Ahmet Bayram (Faculty of Agriculture, Department of Plant Protection, Dicle University, 21280 Diyarbakir, Turkey) for statistical
assistance as well as Karen O’ Hanlon (Biotech Research and Innovation Centre, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen 2200, Denmark) for editorial and language assistance. Financial support provided by the research deputy of Shahid Chamran University is gratefully acknowledged. References Bayram, A., Salerno, G., Onofri, A., Conti, E., 2010a. Sub-lethal effects of two pyrethroids on biological parameters and behavioral responses to host cues in the egg parasitoid Telenomus busseolae. Biol. Control 53, 153e160. Bayram, A., Salerno, G., Onofri, A., Conti, E., 2010b. Lethal and sublethal effects of preimaginal treatments with two pyrethroids on the life history of the egg parasitoid Telenomus busseolae. BioControl 55, 697e710. Biddinger, D.J., Hull, L.A., 1999. Sublethal effects of selected insecticides on growth and reproduction of a laboratory susceptible strain of tufted apple bud moth (Lepidoptera: Tortricidae). J. Econ. Entomol. 90, 314e324. Byrne, D.N., Bellows, T.S., 1991. Whitefly biology. Annu. Rev. Entomol. 36, 31e457. Croft, B.A., 1990. Arthropod Biological Control Agents and Pesticides. Wiley, New York, p. 723. Desneux, N., Fauvergue, E.X., Privet, S., Kaiser, L., 2004a. Oviposition behaviour and patch-time allocation in two aphid parasitoids exposed to deltamethrin residues. Entomol. Exp. Appl. 112, 227e235. Desneux, N., Pham-Delegue, M.H., Kaiser, L., 2004b. Effect of sub-lethal and lethal dose of lambda-cyhalothrin on oviposition experience and host searching behaviour of a parasitic wasp, Aphidius ervi. Pest Manag. Sci. 60, 381e389. Desneux, N., Decourtye, A., Delpuech, J.M., 2007. The sublethal effects of pesticides on beneficial arthropods. Annu. Rev. Entomol. 52, 81e106. Gerling, D., Sinai, P., 1994. Buprofezin effects on two parasitoid species of whitefly (Homoptera: Aleyrodidae). J. Econ. Entomol. 87, 842e846. Haynes, H.F., 1988. Sublethal effects of neurotoxic insecticides on insect behavior. Ann. Rev. Entomol. 33, 149e168. Heidari, A., 2004. Effects of Insect Growth Regulators on the Bionomic of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) and its Parasitoid Wasp, Encarsia formosa (Hymenoptera: Aleyrodidae) in the Laboratory Conditions. Ph.D. thesis, Tarbiat Modares University, Tehran, Iran, 137 pp. Hoddle, M.S., van Driesche, R.G., Lyon, S.M., Sanderson, J.P., 2001. Compatibility of insect growth regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for whitefly (Homoptera: Aleyrodidae) control on poinsettias. l. Laboratory assays. Biol. Control 20, 122e131. Hopper, K.R., 2003. United States Department of AgricultureeAgricultural Research Service research on biological control of arthropods. Pest Manag. Sci. 59, 643e 653. Horowitz, A.R., Mendelson, Z., Weintraub, P.G., Ishaaya, I., 1998. Comparative toxicity of foliar and systemic applications of acetamiprid and imidacloprid against the cotton whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae). Bull. Entomol. Res. 88, 437e442. Hoseini, S.A., 2010. Study the Effects of Two Insecticides Commonly Used in Greenhouses on Survival and Capability of the Parasitoid E. inaron (Walker) in Control Trialeurodes vaporariorum (Westwood) Under Greenhouse Conditions. M.Sc. thesis, University of Urmia, Iran, 88 pp. Jones, W.A., Ciomperlik, M.A., Wolfenbarger, D.A., 1998. Lethal and sublethal effects of insecticides on two parasitoids attacking Bemisia argentifolii (Homoptera: Aleyrodidae). Biol. Control 11, 70e76. Jones, D.R., 2003. Plant viruses transmitted by whiteflies. Eur. J. Plant Pathol. 109, 195e219. Kanno, H.K., Asi, T., Maekawa, S., 1981. 2-tert-butylimino-3-isopropyl-perhydro1,3,5-thaidiazin-4-one (NNI 750), a new insecticide. In: Proceedings, Brighton Crop Protection Conference. Pests and Diseases, Brighton, England, pp. 56e69. Mound, L.A., Halsey, S.H., 1978. Whitefly of the World. Wiley and Sons, New York, 340 pp. Pilkington, L.J., Hoddle, M.S., 2006. Reproductive and developmental biology of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), an egg parasitoid of Homalodisca coagulata (Hemiptera: Cicadellidae). Biol. Control 37, 266e275. Prabhaker, N., Morse, J.G., Castle, S.J., Naranjo, S.E., Henneberry, T.J., Toscano, N.C., 2007. Toxicity of seven foliar insecticides to four insect parasitoids attacking citrus and cotton pests. J. Econ. Entomol. 100, 1053e1061. Rafiee Dastjerdi, H., Hejazi, M.J., Nouri Ganbalani, G., Saber, M., 2009. Sublethal effects of some conventional and biorational insecticides on ectoparasitoid, Habrobracon hebetor Say (Hymenoptera: Braconidae). J. Entomol. 6, 82e89. Rajaei Shoorcheh, H., Kazemi, B., Manzari, S., Brown, J.K., Sarafrazi, A., 2008. Genetic variation and mtCOI phylogeny for Bemisia tabaci (Hemiptera, Aleyrodidae) indicate that the ‘B’ biotype predominates in Iran. J. Pest Sci. 81, 199e206. Rill, S.M., Grafton-Cardwell, E.E., Morse, J.G., 2008. Effects of two insect growth regulators and a neonicotinoid on various life stages of Aphytis melinus (Hymenoptera: Aphelinidae). Biocontrol 53, 579e587. Saber, M., Hejazi, M.J., Hassan, S.A., 2004. The effects of Azadirachtin/Neemazal on different stages and adult life-table parameters of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae). J. Econ. Entomol. 97, 905e910. Saber, M., Hejazi, M.J., Kamali, K., Moharramipour, S., 2005. Lethal and sublethal effects of fenitrothion and deltamethrin residues on the egg parasitoid Trissolcus grandis (Hymenoptera: Scelionidae). J. Econ. Entomol. 98, 35e40.
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103 Saber, M., 2011. Acute and population level toxicity of imidacloprid and fenpyroximate on an important egg parasitoid, Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae). Ecotoxicology 20, 1476e1484. Salerno, G., Colazza, S., Conti, E., 2002. Sub-lethal effects of deltamethrin on walking behaviour and response to host kairomone of egg parasitoid Trissolcus basalis. Pest Manag. Sci. 58, 663e668. SAS Institute, 2003. The SAS System for Windows, Release 9.0. SAS, Institute, Cary, NC. Smilanick, J.M., Zalom, F.G., Ehler, L.E., 1996. Effect of metamidophos residue on the pentatomid egg parasitoids Trissolcus basalis and T. utahensis (Hym.: Scelionidae). Biol. Control 6, 193e201. Sohrabi, F., Shishehbor, P., Saber, M., Mosaddegh, M.S., 2012. Lethal and sublethal effects of buprofezin and imidacloprid on the whitefly parasitoid Encarsia inaron (Hymenoptera: Aphelinidae). Crop Prot. 32, 83e89. Stansly, P.A., Sanchez, P.A., Rodriguez, J.M., Canizares, F., Nieto, A., Lopez Leyva, M.J., Fajardo, M., Suarez, V., Urbaneja, A., 2004. Prospects for biological control of Bemisia tabaci (Homoptera: Aleyrodidae) in greenhouse tomatoes of southern Spain. Crop Prot. 23, 701e712. Stansly, P.A., Calvo, F.J., Urbaneja, A., 2005. Release rates for control of Bemisia tabaci (Homoptera: Aleyrodidae) biotype “Q” with Eretmocerus mundus
103
(Hymenoptera: Aphelinidae) in greenhouse tomato and pepper. Biol. Control 35, 124e133. Stark, J.D., Wennergren, U., 1995. Can population effects of pesticides be predicted from demographic toxicological studies? J. Econ. Entomol. 88, 1089e1096. Stark, J.D., Banks, J.E., 2003. Population-level effects of pesticides and other toxicants on arthropods. Ann. Rev. Entomol. 48, 505e519. Sugiyama, K., Katayama, H., Saito, T., 2011. Effect of insecticides on the mortalities of three whitefly parasitoid species, Eretmocerus mundus, Eretmocerus eremicus and Encarsia formosa (Hymenoptera: Aphelinidae). Appl. Entomol. Zool. 46, 311e317. Talebi-Jahromi, K., 2007. Pesticides Toxicology. University of Tehran Publication, Tehran, 492 pp. Urbaneja, A., Stansly, P.A., 2004. Host suitability of different instars of the whitefly Bemisia tabaci ‘biotype Q’ for Eretmocerus mundus. Biocontrol 49, 153e161. Urbaneja, A., Sanchez, E., Stansly, P.A., 2007. Life history of Eretmocerus mundus, a parasitoid of Bemisia tabaci, on tomato and sweet pepper. BioControl 52, 25e39. Uygun, N., Sengonca, C., Ulusoy, M.R., Kersting, U., 1994. Toxicity of some pesticides to Eretmocerus debachi (Hymenoptera: Aphelinidae), an important parasitoid of Parabemisia myricae (Homoptera: Aleyrodidae). Bull. Entomol. Res. 84, 119e122. Zar, J.H., 1984. Biostatistical Analysis. Prentice-Hall, Inc, Englewood Cliffs, NJ, p. 130.
Contents lists available at SciVerse ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Lethal and sublethal effects of imidacloprid and buprofezin on the sweetpotato whitefly parasitoid Eretmocerus mundus (Hymenoptera: Aphelinidae) Fariba Sohrabi a, *, Parviz Shishehbor a, Moosa Saber b, Mohammad Said Mosaddegh a a b
Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University, Ahvaz, Iran Department of Plant Protection, Faculty of Agriculture, University of Maragheh, Maragheh, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 June 2012 Received in revised form 23 November 2012 Accepted 30 November 2012
The parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is one of the key natural enemies of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Lethal and sublethal effects of imidacloprid and buprofezin on emergence and key biological and population parameters of E. mundus exposed during different developmental stages were studied. Doseeresponse bioassays were carried out on adult wasps using a leaf dipping method. The emergence rates of adults were reduced significantly by the field-recommended concentrations of the insecticides. However, the emergence rates were not affected either by the stage of the parasitoid at the time of exposure (larval and pupal stages), and there was no interaction between treatments and time of exposure. No significant mortality of E. mundus adults was observed following buprofezin treatment. The LC50 of imidacloprid on adults was 4.75 ppm. The results showed that the longevity and fecundity of E. mundus adults were reduced significantly by the two insecticides, though the sex ratio of E. mundus offspring was not affected. Population parameters of the parasitoid such as R0, rm and T were also significantly reduced by the insecticides. Our results indicated that, in addition to lethal effects, sublethal effects should also be considered when these insecticides are applied in IPM programs for this pest. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Bemisia tabaci Demographic toxicology Eretmocerus mundus Insecticides Lethal effects
1. Introduction The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a serious pest of cotton, legume and vegetable crops worldwide (Mound and Halsey, 1978; Byrne and Bellows, 1991). Biotype determination of Iranian populations of B. tabaci indicated that the B biotype predominates in Iran (Rajaei Shoorcheh et al., 2008). It causes damage through direct feeding, excretion of honeydew and transmission of more than 100 plant viruses (Jones, 2003). Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is a solitary parasitoid wasp and one of the key natural enemies of B. tabaci (Urbaneja and Stansly, 2004; Urbaneja et al., 2007). Because E. mundus is not always able to maintain whitefly populations below an economically acceptable level, supplementary chemical treatments are often needed in crops (Stansly et al., 2004,
* Corresponding author. Current address: Department of Plant Breeding, Faculty of Agriculture, Persian Gulf University, Bushehr, Iran. Tel.: þ98 9173708661; fax: þ98 7713531534. E-mail address: [email protected] (F. Sohrabi). 0261-2194/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cropro.2012.11.024
2005). Selective insecticides that are more toxic to insect pests than to natural enemies can be useful tools for integrated pest management (IPM) programs (Croft, 1990; Hopper, 2003). Knowledge about the impact of insecticides on the natural enemies of a pest species is important for the integration of biological control and chemical applications. Assessment of the lethal and sublethal effects of insecticides on natural enemies is necessary to recognize the total effect of insecticide applications (Desneux et al., 2007). Sublethal effects are defined as effects on individuals that survive exposure to a pesticide (Desneux et al., 2007). Sublethal effects may be manifested as reductions in life span, developmental rates, fecundity, changes in sex ratio and/or changes in behaviour (Haynes, 1988; Croft, 1990; Salerno et al., 2002; Stark and Banks, 2003; Desneux et al., 2004a, 2004b; Bayram et al., 2010a, 2010b). Demographic toxicology has been suggested as an important tool to evaluate the total effects of toxicants (Stark and Banks, 2003). The intrinsic rate of increase (rm) has been recommended to assess overall effects of pesticides since this statistic is based on both survivorship and fecundity parameters (Stark and Wennergren, 1995). The chloronicotinyl insecticide imidacloprid and the insect growth regulator (IGR) buprofezin are two relatively new insecticides
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
for controlling whiteflies in Iran (Talebi-Jahromi, 2007). Imidacloprid is effective against a broad range of insects, in particular homopterous insect pests, and can be applied as both foliar and soil treatments as well as via seed treatment (Horowitz et al., 1998). Buprofezin, an inhibitor of chitin synthesis, is generally considered to have a relatively narrow spectrum of activity which is limited to homopterous insects (Kanno et al., 1981). The purpose of this study was to assess the lethal and sublethal effects of imidacloprid and buprofezin on adult and preimaginal stages of E. mundus in order to gain a deeper understanding of their total effects on this parasitoid. 2. Materials and methods 2.1. Whitefly and parasitoid cultures B. tabaci adults were originally collected from cucumber fields in Ahvaz (Iran) in October 2009. Whiteflies were cultured at 16e25 C, 40e50% RH and a photoperiod of 14:10 (L:D) in a muslin-walled cage (120 60 60 cm) containing cucumber plants (cultivar Superdominus). E. mundus used in this study was collected in a greenhouse in Ahvaz in October 2010, on cucumber plants, and reared on cucumber plants infested with B. tabaci nymphs. The rearing conditions were identical to those for whiteflies. Each week new cucumber plants harbouring nymphal stages of sweetpotato whitefly were added to the cages. 2.2. Insecticides tested Imidacloprid 350 g/l SC (ConfidorÒ 35 SC, Gyah, Iran) and buprofezin 400 g/l SC (ApplaudÒ 40 SC, Syngenta, Switzerland) were obtained as formulated products. All treatments included 500 ppm Tween 20 as a non-ionic surfactant. 2.3. Effect of insecticides on the emergence rate of E. mundus Effects of imidacloprid and buprofezin on the emergence rate of E. mundus were separately examined with parasitised whitefly nymphs containing parasitoids in either the larval or pupal stage. Groups of approximately 50 adult whiteflies from our laboratory culture were each confined in clip cages to the lower surface of a cucumber leaf on a potted plant for a 24 h synchronised oviposition period. After oviposition, the adult whiteflies were removed. The plants, now harbouring whitefly eggs, were incubated under conditions of 25 1 C, 70 5% RH, and a photoperiod of 14:10 (L:D) for egg hatching and subsequent nymphal development to the second nymphal instar (appropriate for parasitisation). Thereafter, groups of 5e6 parasitoid females (plus 2e3 males), collected with an aspirator from the laboratory colony, were each confined in clip cages placed over the areas of leaf where the whitefly nymphs were situated. The parasitoids were removed after a 24 h synchronised parasitisation period. Parasitized nymphs were incubated under similar conditions as above to obtain different preimaginal stages of the parasitoid. Ten-day- and thirteen-day-old parasitoids approximately correspond to the larval and pupal stages of E. mundus, respectively. Then, 25e30 parasitized nymphs at these two different developmental stages were marked on each of 5 leaves per treatment by circling with a felt pen. Thereafter, each leaf was dipped in the field-recommended concentration of formulated insecticide for 10 s. The control groups were treated with distilled water. The concentrations used were 1000 and 2000 ppm for imidacloprid and buprofezin, respectively (Heidari, 2004; TalebiJahromi, 2007). Parasitoid emergence was evaluated 10 days after the treatment.
99
The experiment comprised a 3 2 factorial design with the treatment (three levels: control, imidacloprid and buprofezin) and stage treated (two levels: larvae and pupae) as main factors. An arcsin square root transformation was performed on percent emergence before data analysis. The emergence data were subjected to a two-way analysis of variance (ANOVA) and the means were separated using Fisher’s protected Least Significant Difference (LSD) test at P ¼ 0.05 where applicable (SAS Institute, 2003). 2.4. Effect of insecticides on the adult parasitoids The toxicity of imidacloprid and buprofezin to adult parasitoids was assessed using a leaf dipping method (Prabhaker et al., 2007). Leaves were dipped into insecticide solutions diluted to the required concentration for l0 s, and air dried for 1 h. The control samples were dipped into distilled water. Adult parasitoids were confined to the leaf discs from treated leaves placed with their adaxial side on a thin layer of 1% agar (2e3 mm) in exposure cages. The exposure cages consisted of a round plastic container (52 mm tall, 40 mm diameter) with four lateral screened holes (10 mm diameter) in order to facilitate ventilation. The parasitoids in the test cages were supplied with a thin strip of honey placed on the underside of each container lid as food. Five concentrations of the insecticide, determined by preliminary experiments, were used to obtain LC90, LC50 and LC10 data for parasitoid adults. Each concentration had three replicates with a total of 15e20 adults per replicate. Each experiment was repeated three times (i.e., totally nine replicates for each insecticide concentration). The cages were kept in an incubator (25 1 C, 70 5% RH, and a photoperiod of 14:10 (L:D)). The number of dead and live wasps was counted 48 h after initial exposure to the insecticide residue. Mortality data were analysed using PROC PROBIT (SAS Institute, 2003) to compute lethal concentration values (LC90, LC50 and LC10) and associated 95% fiducial limits (FL). As the mortality of E. mundus adults at buprofezin treatment was too low to compute an LC50 value, the data were subjected to analysis of variance (ANOVA). To determine which treatments differed after the ANOVA test, the Fisher’s protected Least Significant Difference (LSD) test (P ¼ 0.05) was undertaken (SAS Institute, 2003). No data transformation was performed before analysis because there was no evidence of nonnormality within the data. 2.5. Life history parameter measurements 2.5.1. Life history of parasitoids treated at the adult stage Sublethal effects of insecticides on the life history parameters of adults treated with the LC25 of imidacloprid (1 ppm) and the fieldrecommended concentration of buprofezin (2000 ppm) or distilled water (control) were studied. In demographic studies, concentrations below the LC30 value are usually used by researchers to investigate the sublethal effects of pesticides (Biddinger and Hull, 1999; Salerno et al., 2002; Rafiee Dastjerdi et al., 2009; Bayram et al., 2010a). With buprofezin, as the mortality of E. mundus adults at toxicity bioassays was too low, the field-recommended concentration of this insecticide was used for life history studies. Forty to 50 pairs of emerged young adults (<24 h old) were exposed to cucumber leaves treated with insecticides for 48 h. The technique, conditions and cages used for exposing adults were as described in the preceding section. Thereafter, 20 live pairs were selected randomly and transferred individually to clip cages on fresh, undipped leaves infested with 50 s instar hosts for oviposition. Infested leaves were replaced daily until death of females occurred. Daily and total number of parasitized B. tabaci, adult longevity and offspring sex ratio were recorded.
100
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
Table 1 Mean (SE) emergence of E. mundus exposed to field-recommended concentrations of insecticides at larval and pupal stages of the parasitoid.a Treatment
Mean percentage of adult parasitoid emergence from parasitized host nymphs treated at different preimaginal stages Larvae
Pupae
Control Imidacloprid Buprofezin
79.80 (6.21)Aa 37.00 (4.10)Bb 62.00 (8.07)Aa
75.80 (2.58)Aa 48.40 (2.64)Ab 66.40 (6.66)Aa
a
Means in a column followed by different lower case letters, or in a row by different upper case letters differ significantly (Fisher’s protected LSD; P < 0.05).
2.5.2. Life history of parasitoids treated at preimaginal (larval and pupal) stages In this experiment, adult parasitoids that emerged from B. tabaci nymphs treated with either the insecticides or with distilled water (control) at the larval (10 days after parasitism) and pupal (13 days after parasitism) stages of the parasitoid were used for the life history studies. Preliminary experiments with each insecticide were performed to determine the concentrations that resulted in at least 30e40% parasitoid emergence when applied to parasitoid larvae or pupae. With buprofezin, cucumber leaves bearing parasitized whitefly nymphs at both larval and pupal stages of the parasitoid were dipped in a 2000 ppm (field-recommended concentration) solution for l0 s. The imidacloprid concentrations were 1000 ppm (field-recommended concentration) and 500 ppm for treatment of E. mundus larvae and pupae, respectively. Subsequently, 20 parasitoid pairs (<24 h old) that emerged from each experiment were selected randomly and placed individually in clip cages on leaves with fresh hosts, and their survival and fecundity were examined as described for the preceding experiment. Time from oviposition to emergence, adult parasitoid survivorship rates, daily fecundity, and sex ratio of offspring at each treatment were used to construct lxmx life tables from which demographic parameters were calculated. Mean demographic parameters and pseudo-replicates for the net reproductive rate (R0), intrinsic rate of increase (rm), finite rate of increase (l), mean generation time (T), and doubling time (DT) were generated using the bootstrap method (Pilkington and Hoddle, 2006). Mean bootstrap estimates of demographic parameters were compared across treatments using analysis of variance (ANOVA). Mean adult longevity, offspring sex ratio, and fecundity data in each experiment were analysed by ANOVA and means compared using Fisher’s LSD test (P < 0.05). Data which required normalization were transformed prior to analysis. The percentage data were arcsin square root-transformed and the count data were square root-transformed (Zar, 1984). A 3 3 factorial
analysis of variance (ANOVA) was applied to study the possible effects of insecticides on biological parameters of adult parasitoids exposed to insecticides at larval, pupal, and adult stages. This analysis of variance model included main effects of stage, treatment, and the interaction of the main effects. 3. Results 3.1. Effect of insecticides on the emergence rate of E. mundus Adult E. mundus emergence from B. tabaci nymphs, following exposure to the field-recommended concentrations of imidacloprid and buprofezin at larval and pupal stages, was significantly reduced by the insecticides (F ¼ 21.07, df ¼ 2, 24, P < 0.0001). However, the emergence rate was not affected either by the time of insecticide exposure relative to parasitoid preimaginal development (F ¼ 0.78, df ¼ 1, 24, P ¼ 0.3858), or the interaction between treatments and time of exposure (F ¼ 1.00, df ¼ 2, 24, P ¼ 0.3828). These results indicate that imidacloprid is toxic to the preimaginal (larval and pupal) stages of the parasitoid, and is significantly more toxic to parasitoid larvae than to pupae (Table 1). 3.2. Effect of insecticides on the adult parasitoids The mean percentage mortality rates observed for adult parasitoids for untreated control and buprofezin at concentrations of 2000, 8000 and 10,000 ppm were 17, 12, 17 and 18%, respectively. No significant difference was found between mortality of E. mundus adults following buprofezin treatments and control (P > 0.05). Imidacloprid was toxic to adult parasitoids. The LC90, LC50 and LC10 values and 95% fiducial limits (FL) were estimated to be 95.8 (58.97e 182.01), 4.75 (2.93e7.13) and 0.23 (0.08e0.5) ppm, respectively. 3.3. Life history parameter measurements Sublethal effects of imidacloprid and buprofezin on biological and demographic parameters of adult E. mundus exposed to insecticides at adult and preimaginal (larval and pupal) stages are summarized in Tables 2 and 3. For parasitoids exposed to imidacloprid during the adult stage, their longevity (F ¼ 11.76, df ¼ 2, 57, P < 0.0001), total fecundity (F ¼ 13.92, df ¼ 2, 57, P < 0.0001), and mean daily fecundity (F ¼ 7.20, df ¼ 2, 57, P ¼ 0016) were significantly lower than those for both control and buprofezin (Table 2). The offspring sex ratio was not affected significantly by either of the two insecticides (P > 0.05) (Table 2). For parasitoids exposed to imidacloprid and buprofezin during the larval stage, the longevity (F ¼ 16.35, df ¼ 2, 57, P < 0.0001), and
Table 2 The mean rates of biological parameters (SE) of E. mundus exposed to different concentrations of imidacloprid and buprofezin at the larval, pupal, and adult stages in comparison with untreated control insects.a Treatments Larval treatments Control Imidacloprid Imidacloprid Pupal treatments Control Imidacloprid Buprofezin Adult treatments Control Imidacloprid Buprofezin a
Concentration (ppm)
Longevity (days)
Total fecundity
Eggs/day
Sex ratio (proportion female)
Distilled water 1000 1000
7.10 (0.40)a 3.40 (0.34)b 3.40 (0.34)b
100.44 (9.60)a 35.20 (5.90)c 35.20 (5.90)c
13.50 (0.66)a 9.62 (0.58)b 9.62 (0.58)b
0.54 (0.02)a 0.51 (0.00)a 0.51 (0.00)a
Distilled water 500 2000
4.35 (0.17)a 4.15 (0.26)a 5.30 (0.56)a
65.85 (6.05)a 44.75 (6.43)b 40.85 (5.49)b
15.30 (1.30)a 9.88 (0.75)b 7.30 (0.37)c
0.49 (0.01)a 0.50 (0.02)a 0.51 (0.04)a
Distilled water 1 2000
7.20 (0.34)a 5.15 (0.23)b 6.80 (0.43)a
62.40 (2.91)a 32.45 (4.14)b 60.40 (5.90)a
12.47 (0.64)a 9.62 (0.76)b 12.40 (0.33)a
0.50 (0.02)a 0.54 (0.02)a 0.47 (0.02)a
Means in a column for each developmental stage followed by the same letter do not differ significantly (P > 0.05).
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
101
Table 3 The mean rates of stable population parameters (SE) of E. mundus exposed to different concentrations of imidacloprid and buprofezin at the larval, pupal, and adult stages in comparison with untreated control insects.a Treatments Larval treatments Control Imidacloprid Buprofezin Pupal treatments Control Imidacloprid Buprofezin Adult treatments Control Imidacloprid Buprofezin a
Concentration (ppm)
R0
rm
l
T
DT
Distilled water 1000 2000
49.50 (6.54)a 17.95 (1.47)b 40.34 (2.25)a
0.22 (0.00)a 0.17 (0.00)c 0.21 (0.00)b
1.25 (0.01)a 1.18 (0.00)b 1.23 (0.00)a
17.75 (0.36)a 16.71 (0.17)b 17.31 (0.09)a
3.15 (0.07)b 4.17 (0.10)a 3.32 (0.04)b
Distilled water 500 2000
32.40 (1.01)a 24.18 (4.41)a 20.41 (1.13)b
0.21 (0.00)a 0.18 (0.01)b 0.17 (0.00)b
1.24 (0.00)a 1.20 (0.01)b 1.18 (0.00)b
16.10 (0.03)b 17.10 (0.33)a 17.69 (0.23)a
3.26 (0.05)c 3.82 (0.21)b 4.11 (0.04)a
Distilled water 1 2000
31.2 (0.71)a 16.20 (0.48)c 29.33 (1.47)b
0.18 (0.00)a 0.15 (0.00)b 0.18 (0.00)a
1.20 (0.00)a 1.16 (0.00)b 1.19 (0.00)a
18.49 (0.11)a 18.12 (0.05)b 18.57 (0.07)a
3.82 (0.04)b 4.69 (0.05)a 3.89 (0.04)b
Means in a column for each developmental stage followed by the same letter are not significantly different (P > 0.05).
total fecundity (F ¼ 10.07, df ¼ 2, 57, P ¼ 0.0002) were significantly lower than those for the control population (Table 2). Imidacloprid significantly decreased the mean daily fecundity of E. mundus adults (F ¼ 4.04, df ¼ 2, 57, P ¼ 0.0228). The offspring sex ratio was not affected significantly by either of the two insecticides (P > 0.05) (Table 2). Insecticides did not significantly affect the mean longevity of parasitoids exposed to imidacloprid or buprofezin at the pupal stage (P > 0.05). However, the total fecundity (F ¼ 5.85, df ¼ 2, 57, P ¼ 0.0049), and mean daily fecundity (F ¼ 22.65, df ¼ 2, 57, P < 0.0001) of parasitoids exposed to imidacloprid and buprofezin at the pupal stage were significantly lower than those for the control population (Table 2). There were no differences observed in sex ratio between the treatments and the control (P > 0.05) (Table 2). Two-way analysis of variance (ANOVA) indicated that treatment (F ¼ 18.97, df ¼ 2, 171, P < 0.0001), developmental stage of the parasitoid at the time of exposure (F ¼ 16.68, df ¼ 2, 171, P < 0.0001), and also interaction between treatment and the time of exposure (F ¼ 6.88, df ¼ 4, 171, P < 0.0001) had a significant effect on adult longevity. ANOVA analysis revealed that treatment (F ¼ 18.77, df ¼ 2, 171, P < 0.0001), stage (F ¼ 5.67, df ¼ 2, 171, P ¼ 0.0041), and treatment stage interaction (F ¼ 3.37, df ¼ 4, 171, P ¼ 0.0110) effects on the total fecundity were also significant. Daily fecundity of E. mundus was not significantly affected by the stage (P > 0.05), but it was the effects of treatment (F ¼ 17.02, df ¼ 2, 171, P < 0.0001) and treatment stage interaction (F ¼ 7.46, df ¼ 4, 171, P < 0.0001) that were significant. A two-way ANOVA indicated that neither the treatment nor the treatment stage interaction had a significant effect on offspring sex ratio (P > 0.05), whereas the stage of the parasitoid at the time of exposure significantly influenced the offspring sex ratio (F ¼ 2.95, df ¼ 2, 171, P ¼ 0.05). Effects of imidacloprid and buprofezin on the life history parameters of E. mundus are shown in Table 3. For parasitoids exposed to insecticides at the adult stage, the R0 (F ¼ 210.63, df ¼ 2, 57, P < 0.0001) was significantly influenced by insecticide treatment. The values of the rm (F ¼ 152.26, df ¼ 2, 57, P < 0.0001), l (F ¼ 114.67, df ¼ 2, 57, P < 0.0001), and T (F ¼ 9.60, df ¼ 2, 57, P ¼ 0.0021) of parasitoids exposed to imidacloprid at the adult stage were all significantly lower than those for both water control and buprofezin. Maximal DT was observed following imidacloprid treatment, which was significantly different from the control and buprofezin (F ¼ 62.73, df ¼ 2, 57, P < 0.0001) (Table 3). For parasitoids exposed to insecticides at the larval stage, the R0 (F ¼ 16.76, df ¼ 2, 57, P ¼ 0.0003), rm (F ¼ 100.16, df ¼ 2, 57, P < 0.0001), l (F ¼ 56.89, df ¼ 2, 57, P < 0.0001), T (F ¼ 6.39, df ¼ 2, 57, P ¼ 0.0129), and DT (F ¼ 32.98, df ¼ 2, 57, P < 0.0001) were significantly influenced by insecticide treatment (Table 3).
The R0 (F ¼ 15.48, df ¼ 2, 57, P ¼ 0.0005), rm (F ¼ 32.04, df ¼ 2, 57, P < 0.0001), and l (F ¼ 31.36, df ¼ 2, 57, P < 0.0001) values of parasitoids exposed to imidacloprid and buprofezin at the pupal stage were significantly influenced by insecticide treatment. T (F ¼ 15.55, df ¼ 2, 57, P ¼ 0.0005), and DT (F ¼ 28.32, df ¼ 2, 57, P < 0.0001) were significantly increased by insecticide treatment (Table 3). 4. Discussion The present study shows that the field-recommended concentration of imidacloprid (1000 ppm) severely affected the preimaginal stages of the parasitoid, reducing adult emergence when applied to either parasitoid larvae or pupae (Table 1). Similarly, reduction in emergence rate was reported in Encarsia inaron (Walker) after treatment with imidacloprid (Hoseini, 2010; Sohrabi et al., 2012). Regarding the adverse effect of imidacloprid on preimaginal stages, it should be noted that in the present study, the parasitized host nymphs were completely dipped in the insecticide solution. Consequently, the nymphs received a large amount of the insecticide. Under field conditions, parasitized host nymphs live on the underside of the leaves, and are therefore likely to receive a lower concentration of the insecticide. Our results further reveal that imidacloprid had a more significant adverse effect on parasitoid emergence during the larval stage compared to the pupal stage. Similarly, Uygun et al. (1994) found that the timing of exposure to pesticides had a differential effect on the survival of Eretmocerus debachi Rose. The field-recommended concentration of buprofezin (2000 ppm) had no significant effect on the emergence of E. mundus when the parasitoid was treated during either the larval or pupal stages. Similar results have been reported for a number of other aphelinid parasitoids (Rill et al., 2008; Sugiyama et al., 2011). In contrast, buprofezin showed toxicity to preimaginal stages of Encarsia luteola Howard (Gerling and Sinai, 1994) and to E. inaron (Sohrabi et al., 2012). Imidacloprid was highly toxic to adult E. mundus with an LC50 value of 4.75 ppm. Imidacloprid also led to significant mortality of E. mundus, Eretmocerus eremicus, Encarsia formosa (Sugiyama et al., 2011) and E. inaron adults (Sohrabi et al., 2012). The present study further indicated a low impact of buprofezin on E. mundus adults, as reported on other aphelinid parasitoids in several studies (Gerling and Sinai, 1994; Hoddle et al., 2001; Heidari, 2004; Sugiyama et al., 2011; Sohrabi et al., 2012). We further investigated the sublethal effects of imidacloprid and buprofezin on female adult longevity, fecundity, offspring sex ratio, and stable population parameters of E. mundus that had been exposed as larvae, pupae and adults to different concentrations of the insecticides. The results showed that the application of
102
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103
imidacloprid at larval and adult stages, significantly affected all of the biological and stable population parameters of E. mundus except it did not affect the sex ratio of offspring. Furthermore, imidacloprid applied to pupae significantly affected fecundity and all of the stable population parameters of E. mundus except it did not affect the R0 value. There are a few studies reporting sublethal effects of imidacloprid on the biological and population parameters of parasitoids. A recent study showed that longevity, fecundity, sex ratio and some life history parameters of E. inaron were significantly affected by applying imidacloprid at the larval, pupal and adult stages (Sohrabi et al., 2012). However, Saber (2011) reported that treatment of Trichogramma cacoeciae Marchal pupae with imidacloprid had no significant effect on longevity, fecundity or population life table parameters of the parasitoid. As stated by Smilanick et al. (1996), percentage emergence of parasitoids from treated hosts is not an adequate measure of ecological selectivity of an insecticide. When interpreting data on emergence rate from insecticide treated hosts, it is also important to consider the fitness of the parasitoids that emerge (Smilanick et al., 1996; Saber et al., 2004, 2005; Bayram et al., 2010b; Saber, 2011). In this study, buprofezin treatment at the larval stage had adverse effects on longevity, total fecundity and rm of E. mundus females. Furthermore, buprofezin applied to pupae significantly affected fecundity and all of the stable population parameters of the parasitoid. However, treatment of E. mundus adults with buprofezin had no significant effect on the biological and stable population parameters of E. mundus although R0 was significantly reduced compared to the control. A previous study showed that buprofezin treatment had no influence on the longevity and total fecundity of E. inaron females when the parasitoid was treated during either the larval, pupal or adult stages (Sohrabi et al., 2012). However, buprofezin had significant effects on daily fecundity and sex ratio of E. inaron offspring (Sohrabi et al., 2012). Furthermore, buprofezin treatment at larval and adult stages of E. inaron had no significant effect on the stable population parameters of E. inaron, however it significantly affected R0, T, and DT when pupae were treated (Sohrabi et al., 2012). The different responses of E. mundus and E. inaron to the same insecticide at the pupal stage treatment may be related to the concentration of insecticide parasitoids had been exposed to, and the species differences in physiological responses to the insecticides. Jones et al. (1998) found no adverse effects of buprofezin on reproduction of E. mundus and Eretmocerus tejanus Rose and Zolnerowich when applied to either parasitoids larvae or pupae, but buprofezin applied to pupae significantly reduced longevity of surviving E. tejanus adults. In a similar study, Heidari (2004) found that treatment of E. formosa pupae with buprofezin had no significant effect on population parameters of the parasitoid except that it reduced R0 of the parasitoid compared to the control. In view of the possible detrimental sublethal effects of imidacloprid (in addition to its significant lethal effects on preimaginal and adult stages) and buprofezin on biological and population parameters of E. mundus, the use of these insecticides in crops should be avoided in situations where biological control by this parasitoid is important. Semi-field and field studies aiming to evaluate the efficacy of the combined use of insecticides and E. mundus are needed in order to obtain more applicable results under field conditions. Acknowledgements The authors would like to thank the receiving editor, Dr. Jerry Cross and two anonymous reviewers for their valuable and helpful comments on earlier drafts of this manuscript. We also thank Dr. Ahmet Bayram (Faculty of Agriculture, Department of Plant Protection, Dicle University, 21280 Diyarbakir, Turkey) for statistical
assistance as well as Karen O’ Hanlon (Biotech Research and Innovation Centre, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen 2200, Denmark) for editorial and language assistance. Financial support provided by the research deputy of Shahid Chamran University is gratefully acknowledged. References Bayram, A., Salerno, G., Onofri, A., Conti, E., 2010a. Sub-lethal effects of two pyrethroids on biological parameters and behavioral responses to host cues in the egg parasitoid Telenomus busseolae. Biol. Control 53, 153e160. Bayram, A., Salerno, G., Onofri, A., Conti, E., 2010b. Lethal and sublethal effects of preimaginal treatments with two pyrethroids on the life history of the egg parasitoid Telenomus busseolae. BioControl 55, 697e710. Biddinger, D.J., Hull, L.A., 1999. Sublethal effects of selected insecticides on growth and reproduction of a laboratory susceptible strain of tufted apple bud moth (Lepidoptera: Tortricidae). J. Econ. Entomol. 90, 314e324. Byrne, D.N., Bellows, T.S., 1991. Whitefly biology. Annu. Rev. Entomol. 36, 31e457. Croft, B.A., 1990. Arthropod Biological Control Agents and Pesticides. Wiley, New York, p. 723. Desneux, N., Fauvergue, E.X., Privet, S., Kaiser, L., 2004a. Oviposition behaviour and patch-time allocation in two aphid parasitoids exposed to deltamethrin residues. Entomol. Exp. Appl. 112, 227e235. Desneux, N., Pham-Delegue, M.H., Kaiser, L., 2004b. Effect of sub-lethal and lethal dose of lambda-cyhalothrin on oviposition experience and host searching behaviour of a parasitic wasp, Aphidius ervi. Pest Manag. Sci. 60, 381e389. Desneux, N., Decourtye, A., Delpuech, J.M., 2007. The sublethal effects of pesticides on beneficial arthropods. Annu. Rev. Entomol. 52, 81e106. Gerling, D., Sinai, P., 1994. Buprofezin effects on two parasitoid species of whitefly (Homoptera: Aleyrodidae). J. Econ. Entomol. 87, 842e846. Haynes, H.F., 1988. Sublethal effects of neurotoxic insecticides on insect behavior. Ann. Rev. Entomol. 33, 149e168. Heidari, A., 2004. Effects of Insect Growth Regulators on the Bionomic of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) and its Parasitoid Wasp, Encarsia formosa (Hymenoptera: Aleyrodidae) in the Laboratory Conditions. Ph.D. thesis, Tarbiat Modares University, Tehran, Iran, 137 pp. Hoddle, M.S., van Driesche, R.G., Lyon, S.M., Sanderson, J.P., 2001. Compatibility of insect growth regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for whitefly (Homoptera: Aleyrodidae) control on poinsettias. l. Laboratory assays. Biol. Control 20, 122e131. Hopper, K.R., 2003. United States Department of AgricultureeAgricultural Research Service research on biological control of arthropods. Pest Manag. Sci. 59, 643e 653. Horowitz, A.R., Mendelson, Z., Weintraub, P.G., Ishaaya, I., 1998. Comparative toxicity of foliar and systemic applications of acetamiprid and imidacloprid against the cotton whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae). Bull. Entomol. Res. 88, 437e442. Hoseini, S.A., 2010. Study the Effects of Two Insecticides Commonly Used in Greenhouses on Survival and Capability of the Parasitoid E. inaron (Walker) in Control Trialeurodes vaporariorum (Westwood) Under Greenhouse Conditions. M.Sc. thesis, University of Urmia, Iran, 88 pp. Jones, W.A., Ciomperlik, M.A., Wolfenbarger, D.A., 1998. Lethal and sublethal effects of insecticides on two parasitoids attacking Bemisia argentifolii (Homoptera: Aleyrodidae). Biol. Control 11, 70e76. Jones, D.R., 2003. Plant viruses transmitted by whiteflies. Eur. J. Plant Pathol. 109, 195e219. Kanno, H.K., Asi, T., Maekawa, S., 1981. 2-tert-butylimino-3-isopropyl-perhydro1,3,5-thaidiazin-4-one (NNI 750), a new insecticide. In: Proceedings, Brighton Crop Protection Conference. Pests and Diseases, Brighton, England, pp. 56e69. Mound, L.A., Halsey, S.H., 1978. Whitefly of the World. Wiley and Sons, New York, 340 pp. Pilkington, L.J., Hoddle, M.S., 2006. Reproductive and developmental biology of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), an egg parasitoid of Homalodisca coagulata (Hemiptera: Cicadellidae). Biol. Control 37, 266e275. Prabhaker, N., Morse, J.G., Castle, S.J., Naranjo, S.E., Henneberry, T.J., Toscano, N.C., 2007. Toxicity of seven foliar insecticides to four insect parasitoids attacking citrus and cotton pests. J. Econ. Entomol. 100, 1053e1061. Rafiee Dastjerdi, H., Hejazi, M.J., Nouri Ganbalani, G., Saber, M., 2009. Sublethal effects of some conventional and biorational insecticides on ectoparasitoid, Habrobracon hebetor Say (Hymenoptera: Braconidae). J. Entomol. 6, 82e89. Rajaei Shoorcheh, H., Kazemi, B., Manzari, S., Brown, J.K., Sarafrazi, A., 2008. Genetic variation and mtCOI phylogeny for Bemisia tabaci (Hemiptera, Aleyrodidae) indicate that the ‘B’ biotype predominates in Iran. J. Pest Sci. 81, 199e206. Rill, S.M., Grafton-Cardwell, E.E., Morse, J.G., 2008. Effects of two insect growth regulators and a neonicotinoid on various life stages of Aphytis melinus (Hymenoptera: Aphelinidae). Biocontrol 53, 579e587. Saber, M., Hejazi, M.J., Hassan, S.A., 2004. The effects of Azadirachtin/Neemazal on different stages and adult life-table parameters of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae). J. Econ. Entomol. 97, 905e910. Saber, M., Hejazi, M.J., Kamali, K., Moharramipour, S., 2005. Lethal and sublethal effects of fenitrothion and deltamethrin residues on the egg parasitoid Trissolcus grandis (Hymenoptera: Scelionidae). J. Econ. Entomol. 98, 35e40.
F. Sohrabi et al. / Crop Protection 45 (2013) 98e103 Saber, M., 2011. Acute and population level toxicity of imidacloprid and fenpyroximate on an important egg parasitoid, Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae). Ecotoxicology 20, 1476e1484. Salerno, G., Colazza, S., Conti, E., 2002. Sub-lethal effects of deltamethrin on walking behaviour and response to host kairomone of egg parasitoid Trissolcus basalis. Pest Manag. Sci. 58, 663e668. SAS Institute, 2003. The SAS System for Windows, Release 9.0. SAS, Institute, Cary, NC. Smilanick, J.M., Zalom, F.G., Ehler, L.E., 1996. Effect of metamidophos residue on the pentatomid egg parasitoids Trissolcus basalis and T. utahensis (Hym.: Scelionidae). Biol. Control 6, 193e201. Sohrabi, F., Shishehbor, P., Saber, M., Mosaddegh, M.S., 2012. Lethal and sublethal effects of buprofezin and imidacloprid on the whitefly parasitoid Encarsia inaron (Hymenoptera: Aphelinidae). Crop Prot. 32, 83e89. Stansly, P.A., Sanchez, P.A., Rodriguez, J.M., Canizares, F., Nieto, A., Lopez Leyva, M.J., Fajardo, M., Suarez, V., Urbaneja, A., 2004. Prospects for biological control of Bemisia tabaci (Homoptera: Aleyrodidae) in greenhouse tomatoes of southern Spain. Crop Prot. 23, 701e712. Stansly, P.A., Calvo, F.J., Urbaneja, A., 2005. Release rates for control of Bemisia tabaci (Homoptera: Aleyrodidae) biotype “Q” with Eretmocerus mundus
103
(Hymenoptera: Aphelinidae) in greenhouse tomato and pepper. Biol. Control 35, 124e133. Stark, J.D., Wennergren, U., 1995. Can population effects of pesticides be predicted from demographic toxicological studies? J. Econ. Entomol. 88, 1089e1096. Stark, J.D., Banks, J.E., 2003. Population-level effects of pesticides and other toxicants on arthropods. Ann. Rev. Entomol. 48, 505e519. Sugiyama, K., Katayama, H., Saito, T., 2011. Effect of insecticides on the mortalities of three whitefly parasitoid species, Eretmocerus mundus, Eretmocerus eremicus and Encarsia formosa (Hymenoptera: Aphelinidae). Appl. Entomol. Zool. 46, 311e317. Talebi-Jahromi, K., 2007. Pesticides Toxicology. University of Tehran Publication, Tehran, 492 pp. Urbaneja, A., Stansly, P.A., 2004. Host suitability of different instars of the whitefly Bemisia tabaci ‘biotype Q’ for Eretmocerus mundus. Biocontrol 49, 153e161. Urbaneja, A., Sanchez, E., Stansly, P.A., 2007. Life history of Eretmocerus mundus, a parasitoid of Bemisia tabaci, on tomato and sweet pepper. BioControl 52, 25e39. Uygun, N., Sengonca, C., Ulusoy, M.R., Kersting, U., 1994. Toxicity of some pesticides to Eretmocerus debachi (Hymenoptera: Aphelinidae), an important parasitoid of Parabemisia myricae (Homoptera: Aleyrodidae). Bull. Entomol. Res. 84, 119e122. Zar, J.H., 1984. Biostatistical Analysis. Prentice-Hall, Inc, Englewood Cliffs, NJ, p. 130.