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Evaluation of Two Commercial Strains of Phytoseiuluspersimilis Athias-Henriot (Acarina: Phytoseiidae) and Laboratory-Selected, Pyrethroid-Resistant and Susceptible Strains of Amblyseius fallacis (Garman) (Acarina: Phytoseiidae) for Pesticide Resistance on Greenhouse Cucumber
1. Asia-Pacific Entomol. 4 (2) : 165 ~ 169 (2001) www.entomology.or.kr
Evaluation of Two Commercial Strains of Phytoseiulus persimilisAthias-Henriot (Acarina: Phytoseiidae) and Laboratory-Selected, Pyrethroid-Resistant and Susceptible Strains of Amblyseius fallacis (Garman) (Acarina: Phytoseiidae) for Pesticide Resistance on Greenhouse CucumberSang-Cuei Lee*, J. Les Shipp' and K. Wang' National Institute of Agricultural Science and Technology, RDA, Suwon 441-707, Korea 1 Greenhouse Processing Crop Research Centre, AAFC, Harrow, Ontario, Canada
Abstract To evaluate the pesticide resistance of two commercial strains of Phytoseiulus persimilis Athias -Henriot (Koppert, strain A; Applied Bio-Nomics, strain B) and two strains of Amblyseiusfallacis (Garman) (resistant and susceptible), residual toxicity trials were conducted on greenhouse cucumber crops that were sprayed with two pesticides (pyridaben and dicofol), respectively. Strain A had significantly higher mortalities than strain B when exposed to foliage residues of pyridaben and dicofol. Strain B showed 3-18% higher survivorship than strain A when exposed to 7- to 14-day foliage residues of pyridaben at 213 and 426 ppm. When exposed to 1- and 8-day foliage residues of dicofol at 152 and 303 ppm, strain A exhibited 8-10% higher mortalities as compared to strain B. Residual toxicity of both pesticides to P. persimilis decreased significantly at the lower concentrations and over time under greenhouse conditions. Mortalities of both strains of P. persimilis were reduced by 50% when exposed to the l-week residues of both pesticides at the lowest concentrations. With the treatment of dicofol (303 ppm), mortalities for the two strains of P. persimilis decreased from 53.54- 42.68% at l-day residues to 28.18-21.21 % at 8-day residues. At 500 ppm of dicofol, mortalities decreased from 60.09~ 60.90% at l-day residue to 35.75-34.14% at 22-day residues. However, with dicofol (1000 ppm), mortalities were as high as 61.73% at 22~day residue. The resistant strain of A. fallacies showed significantly lower mortality, as compared to the susceptible strain, when exposed to 1- and 7-day foliage residue of pyridaben at 213 and 426 ppm concentrations. Mortality of A. fallacis to pyridaben was lower than that of P. persimilis. This suggests that A. fallacis may be more compatible with the application of this pesticide to greenhouse crops than that of P. persimilis. In "Corresponding author. E-mail: [email protected] Tel: 031-290-0467; Fax: 031-290-0479 (Received June 20, 2001; Accepted October 31, 2001)
addition, strain B of P. persimilis may be more advantageous after the application of these pesticides in a greenhouse rPM program than strain A. Key words Phytoseiulus persimilis, Amblyseius fallaeis, pesticide resistance, greenhouse trials
Introduction Natural enemies are used successfully for biological control of a number of insect and mite pests, but on many crops, the use of non-selective chemicals will often reduce or eliminate natural enemy populations. Resistance to pesticides has been developed only rarely in natural enemies (Croft and Morse, 1979), but those few species that have acquired pesticide resistance have provided effective biological control of secondary pests when pesticides are used for control of the major pests (Croft, 1977). The predatory mites, Phytoseiulus persimilis AthiasHenriot and Amblyseius fallacis (Garman), are effective biological control agents for control of the two-spotted spider mite, Tetranychus urticae Koch. These agents have been used on cucumber, sweet pepper, berry, and fruit crops in the greenhouse (Elliott 1993; Van Lenteren et al., 1997). Also, P. persimilis can be an effective predator on other crops such as strawberry, small fruit crops, watermelon, and ornamentals (Malais and Ravensberg, 1992). However, biological control in the greenhouse can be difficult at times without the periodic use of pesticides for controlling pest outbreaks (Hayashi, 1996) and for clean up of the crop at the end of the season (Howard et al., 1994). Biological control of T urticae using predatory mites such as P. persimilis is effective only against low population densities of the pest (Pralavorio et al., 1985). When the population density is too high, an acaricide treatment is needed to reduce the pest pop-
166 J. Asia-Pacific Entomol. Vol. 4 (2001)
ulation before the release of beneficial mites (Malezieux et al., 1992) or sometimes after releases. As a result, biological control of T urticae is sometimes integrated with chemical control measures. To integrate the use of pesticides with biological control agents of T urticae in the greenhouse, several factors need to be considered (Shipp et al., 2000). First, physiologically selective acaricidesthat are specific to particular pest species should be used to adjust prey/predatorratios only when necessary. Several studies have been conducted to evaluate pesticides that are toxic to specific pests but not harmful to their control agents such as natural enemies (Zhang and Sanderson, 1990; Malezieux et al., 1992; Spollen and Isman, 1996). This approach allows producers to choose the least harmful pesticides, but unfortunately few such pesticides are commercially available (Malezieux et al., 1992). Second, naturally-or artificially-selected natural enemies that are resistant to pesticides can be used (Hoy, 1990; Rathman et a1., 1990). Several studies have been conducted to select pesticide-resistant strains of parasitoids and predators (Schulten and van de Klashort, 1979; Hoy and Ouyang, 1989). Lee et al. (2001) reported differences in insecticide resistance for the phytoseiid predatory mite, P. persimilis from each of three commercial companies strains to several insecticides and acaricides in laboratory trials. Amblyseius fallacis has been selected for pyrethroid resistance in the laboratory and mass produced for commercial release in several regions (Whalon et al., 1982; Thistlewood et al., 1995). To apply pesticide-resistant strains of predatory mites with other biological control agents against T urticae in greenhouse IPM programs, the resistance of these predatory mites must be determined in conjunction with the application of pesticides or acaricides under greenhouses conditions. To date, few studies have documented the resistance of different strains of predatory mites in greenhouses where a pesticide has been applied. In this study, the resistance of two commercial strains of P. persimilis (Koppert and Applied Bio-Nomics strains) and two strains of A. fallacis (resistant and susceptible) was evaluated on greenhouse cucumber crops that were sprayed with two strains ofpesticides (pyridaben and dicofol), respectively.
Materials and Methods Experimental Greenhouses Experiments were conducted from January to March 2001 in two greenhouses (9.0 by 7.3 m) at the Greenhouse and Processing Crops Research Centre, Harrow, Ontario, Canada. Commercial cucumbercultivar 'Bodega'
Sang-Guei Lee, J. Les Shipp and K. Wang
grown in rockwool slabs (90 by 20 by 7.5 em, FIBRgro®, Fibrex Insulations Inc.) at the 20 leaf stage were used as host plants. Day/night temperatures for the greenhouses were kept at 24/22°C. Relative humidity was maintained at 75% throughout the trial period. The plants were irrigated and fertilized using the Harrow Fertigation Manager" (Labbate Climate Control Systems, Leamington, Ontario, Canada) and were maintained according to standard commercial recommendations by Ontario Ministry of Agriculture and Food. Greenhouse climate was monitored and maintained by Argus Controls" System (Argus Control Systems Ltd, White Rock, British Columbia, Canada).
Pesticide Application Solutions of dicofol (35% WP) (Rohm and Haas Canada Inc.) and pridaben (75% WP) (Plant Products Co. Ltd.) were prepared by dissolving the pesticide in water at the required rates and then sprayed on a cucumber crop under greenhouse production conditions. Treatment rates were designated as 152, 303, 500 and 1000 ppm for dicofol, and 213 and 426 ppm for pyridaben, respectively, according to the recommended rates for the two pesticide products against the two spotted spider mite (303 ppm for dicofol and 213 ppm for pyridaben). Sprays were applied, using a high pressure C02 sprayer (11.6 kPa), to both leaf surfaces until runoff. Water was sprayed only for the control treatment. At least 12 fully expanded leaves per plant were sprayed.
Maintenance of Predatory Mites P. persimilis mites from Koppert B.V. (The Nether-
lands) (strain A) and Applied Bio-Nomics Ltd. (Canada)
Table 1. Mortalities' (Mean ± SE) of two commercial strains of P. persimilis exposed to different time periods of foliage residues for pyridaben
Concentration (ppm)
Residual time (days)
7
14
213
426
A
54.19±8.53a
53.39±7.20a
B
41.45±3.53a
54.12±3.35a
A
23.49±4.24a
44.05 ± 2.74a
B
15_65±2.lla
26.33±3.05b
A
12.69±1.13a
23.68±2.86a
B
9.29±2.34a
16.93±2.56a
Within columns for each residual-til~~e, means followed by the same letter are not significantly different at P "> 0.05 based on LSD lest. Data were arcsin. square root transformed before ANOYA. "Corrected mortality by Abbott' s formulat Abbott, 1925). 1,'1 wo commercial strains of Phytosetulus persnnrlls (Strain A-Kopper1~ Strain fl-Applicd Bio-Nomics strain).
Evaluation of Predatory Mites for Pesticide Resistance
167
Table 2. Mortalities' (Mean±SE) of two commercial strains of P. persimilis exposed to different time periods of foliage residues for dicofol Residual time (days)
8
15
22
Strainb
Concentration (ppm) 152
A
29.95±4.31a
B
21.00± 1.82a
A
14.32±2.48a
B
6.53± 1.33b
303
500
1000
53.54±3.4la 42.68 ± 2.25b
60.09±2.91a 60.90 ± 3.07a
94.50 ± 1.55a
28.18±5.20a 21.21 ±3.81a
57.85±2.26a 52.70±5.56a
82.95±2.l6b
62.04 ± 4.06a 30.48± l.72b
86.40 ± 1.58a 74.44±3.l6b
35.75±6.0la 34.l4±5.49a
64.43±4.10a
A
B A
B
93.59 ± 1.76a 93.04± 1.44a
61.73±2.50a
Within columns for each residual time, means followed by the same letter are not significantly different at P > 0.05 based on LSD test. Data were arcsine square root transformed before ANOVA. "Corrected mortality by Abbott's formula/Abbott, 1925). bTwo commercial strains of Phytoseiulus persimilis (Strain A-Koppelt; Strain B-Applied Bio-Nomics strain).
(strain B) were used in the greenhouse trials for comparison of pesticide resistance to P. persimilis. TIle mites were shipped from the suppliers and stored separately in their shipping bottle in a controlled enviromnent chamberat WaC, 70 % RH, and 16:8h (L:D) photoperiod until needed. Resistant and susceptible strains ofA. fallacis were supplied by the Southern Crop Protection and Food Research Centre (Vineland), Agriculture and AgriFood Canada, where the resistant strain has been maintained since 1989 under the selective pyrethroid pesticide (deltamethrin) pressure. Amblyseius fallacis colonies were maintained in the laboratory at 26 ± r'c, 70% RH, and a photoperiod of 16:8 h (L:D) according to the methods of Thistlewood et al. (1992). The predatory mites along with T urticae as a food source were confined on a cucumber leaf disk that was placed at the center of a water-soaked sponge within a plastic box (15 X 20 x 0 ern), Both predators and preys were confined on the leaf disk by keeping a sufficient water bath surrounding the leaf edge. Cucumber leaves infested with T urticae were added three times every week and, at the same time, the dried leaves were removed. The colony of T urticae was maintained on cucumber plants in a controlled environment chamber at 24 ± I°C, 70% RH, and a photoperiod of 16:8 h (L:D).
Release of Predatory Mites The P. pesimilis mites were exposed to different residue times by confming the mites onto sprayed leaves I, 7 and 15 days for pyridaben, and 1, 8, 15 and 22 days for dicofol after pesticide application using leaf cages, respectively. Approximately 30 adult females from each test strain along with 60 T urticae as a
food source were confined to the lower surface of treated leaves using leaf cages (diameter 5 em X height 0.5 em, with a hole of 3 em diameter in the cage bottom, which was covered with nylon cloth for ventilation, with a same size plastic plate on the back of the cage). Eight replicates were conducted for each residual time treatment and the untreated control. After 48 h exposure, the mites were returned to the laboratory and recorded as live and dead using a dissecting microscope. For the A-fallacis mites, the same method was used as for P. persimilis except that only 20 predator mites from each of the two strains along with 50 T urticae were used for each replicate. Each treatment was repeated twice due to the limited number of available A. fallacis. In addition, A. fallacis was exposed to only 1 and 7 day residues.
Data Analysis For each replicate, mite mortality after a 48-h exposure period was expressed as a percentage, corrected by Abbott's formula (Abbott, 1925). ANOVA (pesticide X residue time period x strain) was conducted on the arcsine square root transformed mortality data. When significant differences in mortalities were found, the means were separated using LSD test (SAS Institute, 1990). Strain mortalities of P. persimilis that were exposed to different residual time periods of the pesticides at different concentrations were further compared using probit analysis with Gompertz distribution (SAS Institute, 1990). Paired t-test was used to compare the mortalities of resistant and susceptible strains of A. fallacies that were caused by 1- and 7-clay pyridaben residual toxicity.
168 J. Asia-Pacific Entomol. Vol. 4 (2001)
Sang-Guei Lee, J. Les Shipp and K. Wang
Results A three-way ANaYA was performed on the adult mortality data using the factors pesticide, residue ages, and strains. Generally, strain A had significantly higher mortalities than strain B when exposed to foliage residues of pyridaben (F = 15.93; 4/ = 1,79; P < 0.01) and dicofol (F = 34.32; df= 1,218; P < 0.01), respectively. Strain B showed 3 to 18% higher survivorship than strain A when exposed to 7- to 14-d ay foliage residues of pyridaben at 213 and 426 ppm with the exception that strain B had slightly lower survivorship than strain A when exposed to I-day residues at 426 ppm (Table I). When exposed to land 8-day foliage residues of dicofol at 152 and 303 ppm, strain A exhibited 7-11% higher mortalities when compared to strain B. However, both mortalities at 152 and 303 ppm were less then 29% when exposed to S-day foliage residues (Table 2). Residual toxicity of both pesticides to P. persimilis decreased significantly at the lower concentrations (F= 21.2; df =1,79; P
50\
/g
I
40 " ;R
g t:: '" 0
30
I
201:
--
::;;
-
--
10 \ ' 0
Resistant 0 Susceptible
\/ 1
426 Day 1
213
-----
.
i
U'
-'
._ ...•
~
c:=J --
c:=J
426
213
Day 7
Concentration (ppm)
Fig. 1. Mortalities of resistant and susceptible strains of A, fallacies when exposed to 1- and 7-day foliage residues or pyridaben with spray concentrations of 426 and 213 ppm.
at 22-day residue. The resistant strain of A. fallacies showed significanily lower mortality (F=1.77, dj=14 P=O 049), as compared to the susceptible strain, when exposed to 1- and 7-day foliage residue of pyridaben at 213 and 426 ppm (Fig. I).
Discussion When using pyridaben and dicofol, mortality for strain A was greater than that for strain B. Furthermore, residual toxicity to strain A was longer than that to strain B. The mortality trends in the greenhouse were similar to the laboratory trials by Lee et al, (2001). However, mortality values in the greenhouse were lower than in the laboratory. Shipp et al. (1999) reported that two factors may be contributing to this result. First, individuals in the greenhouse trial had the opportunity to avoid contact with the leaf surface bearing the toxic residues by resting on the inner surface of the petri dishes. However, in the laboratory trials, the mites were constantly in contact with the toxic residues because the leaf disks were surrounded by water to prevent predator escapes from the leaf disk. Second, residues on the petri dish may have dissipated more slowly than those on the leaves. The exposure to sunlight in the greenhouses can result in quicker dissipation of residues (Lasota and Dybas, 1991). This study has quantified the relationship between pesticide residues at different time periods and the morities caused by these residues using probit analysis and also, has estimated the residue thresholds for pyridaben against two strains of commercially produced P. persimilis under greenhouse conditions. Our results indicated that the susceptibility of strain A to these pesticides was greater than that of the strain S, and that the susceptibility of P. persimilis to pyridaben was much greater than that of A. fallacis. In conjunction with the information of pesticide resistance against predatory mite strains and species under greenhouse production conditions, additional useful information would be to determine the best pesticide-resistant mite strains or species and the optimal time period after pesticide application before release of the predatory mites. This information will be used to improve the integration of the use of pesticides with biological control measures for environmentally-friendly crop production. In summary, the mortality of both pesticides was higher to strain A than to strain B. The mortality ofthe pesticide-resistant strain ofA. fallacis to pyridaben was lower than that of the susceptible strain. Mortality of A. fallacis to pyridaben was also lower than that
Evaluation of Predatory Mites for Pesticide Resistance
of P. persimilis. This suggests that A. fallacis may be more compatible with the application of this pesticide to greenhouse crops than that of P. persimilis. In addition, strain B of P. persimilis may be more advantageous after application of these pesticides in a greenhouse IPM program than strain A, even if the mortalities between strain A and B of P. persimilis are only slightly different to both pesticide at the recommended rate. Acknowledgments This study was made possible by a Cooperative Research Agreement between Agriculture and Agri-Food Canada (AAFC), Canada and the NationalInstitute of Agricultural Science and Technology (NIAST), RDA, Korea. The authors would like to thank D. Gagnier and T. Lomond, GPCRC, Harrow, for their technical assistance.
Literature Cited Abbott, W.S. 1925. A method for computing the effectiveness of an insecticide. J. Econ. Entomol. 18: 265-267. Croft, B. A. and .I. G. Morse. 1979. Research advances on pesticide resistance in natural enemies. Entomophaga 24: 3-11. Croft, B.A 1977. Resistance in arthropod predators and parasite. pp. 52-56, in Pesticide management and insecticide resistance, Eds. D.L. Watson and AW.A Brown. 638pp. Acad. Press, New York. Elliott, D. 1993. Biological Technical Manual, Applied BioNomics Ltd. pp.200-20 I. Hayashi, H. 1996. Side effects of pesticides on Encarsia formosa Gahan. Bull. Hiroshima Prefectural Agric. Res. Ctr. 64: 33-43. Howard, R. J., J. A Garland and W.L. Seaman. 1994. Diseases and Pest of Vegetable Crops in Canada. 578pp. M. O. M. Printing Ltd., Ottawa, Canada. Hoy, M.A. 1990. Pesticide resistance in arthropod natural enemies: Variability and selection responses. pp. 203-236, in Pesticide Resistance in Arthropods, Eds. R.T. Roush and B.E. Tabashnik. Chapman & Hall, New York. Hoy, M. A and Y-L. Ouyang. 1989. Selection of the western predatory mite, Metaseiulus occidentalis (Acari: Phytoseiidae), for resistance to abamectin, J. Econ. Entomol. 82: 35-40. Lasota, J. A. and R. A. Dybas. 1991. Avermectins, a novel class of compounds: Implications for use in arthropod pest control. Annu. Rev. Entomol. 36: 91-117.
169
Lee S. G., S. A. Hilton, A. B. Broadbent and J. H. Kim. 200 I. Identity insecticide resistance of phytopseiid predatory mites, Phytoseiulus persimilis Athias-Henriot and Amblyseius cucumeris Oudemans (Acarina: Phytosciidac). 17 pp. NIAST/AAFC Report. Malais, M. and W. J. Ravensberg. 1992. The biology ofglasshouse pests and their natural enemies. 109 pp. Knowing and Recognizing. B. V. Koppert, the Netherlands. Malezieux, S., L. Lapchin, M. Pralavorio, J. C. Moulin and D. Fournier. 1992. Toxicity of pesticide residues to a beneficial arthropod, Phytoseiulus persimilis (Acari: Phytoseiidae). J. Econ. Entomol, 85: 2077-2081. Pralavorio, M., P. Millor and D. Fournier. 1985. Biological control of greenhouse spider mites in southern France. pp J 25-128 in Biological Pest control: The Glasshouse Experience. Eds. N. W. Hussey and N. Scopes. Cornell Univ. Press, Ithaca, NY. Rathman, R. J., M. W. Johnson, J. A Rosenheim and B. E. Tabashink. 1990. Carbamate and pyrethroid resistance in the leatininer parasitoid Diglyphus begini (Hymenoptera: Eulophidae). J. Econ. Entomol. 83: 2153-2158. SAS Institute. 1990. SAS/STAT users guide, release 6.04 cd. SAS Institute. Cary, North Carolina. Schulten, G. G. M., and G. Van de Klashorsl. 1979. Genetics of resistance to parathion and dcmcthon-Svmcthyl in Phytoselulus persimilis A. H. pp 519-524, in Proceedings of the 4th International Congress of Acarology. Eds. E. Plffl., Saalfeden, Austria. Shipp, J. L., K. Wang and G. Ferguson. 1999. Residual toxicity of Avermectin bl and pyridaben to eight commercially produced beneficial arthropod species used for COntrol of greenhouse pests. Biol, Control 17: 125-131. Spollen, K. M. and M. B. lsman. 1996. Acute and sublethal effects of a neem insecticide on the comcrcial biological control agents Phytoseiulus perslmills, Amblyselus cucumeris (Acari: Phytoseiidae) and Aphidoletes aphidimyza (Diptera: Cecidomyiidae). .I. Econ. Entomol. 89: 1379-1386. Thistlewood, I-L M. A, D . .I. Pree and L A Crawford. 1995. Selection and genetic analysis of permethrin resistance in Amblyseius fallacis (Garman) (Acari: Phytoseiidae) from Ontario apple orchards. Exp. Appl. Acarol. 19: 707-721. Van Lenteren, J.V., M. M. Roskam and R. Timmer. 1997. Commercial mass production and pricing of organisms for biological control of pests in Europe. Biol. Control 10: 143-149. Whalon, M. E., B. A. Croft and T. M. MOWlY. 1982. Introduction and survival of susceptible and pyrethroid- resistant strains of Amblyseius fallacis (Acari: Phytoseiidae) in Michigan apple orchard. Environ. Entomol. 11: 1096-1099. Zhang, Z. Q. and J. P. Sanderson. 1990. Relative toxicity of abamectine to the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidac) and two spotted spider mite (Acari: Tctranychidae). J. Econ. Entomol. 83: 1783-1790.
Evaluation of Two Commercial Strains of Phytoseiulus persimilisAthias-Henriot (Acarina: Phytoseiidae) and Laboratory-Selected, Pyrethroid-Resistant and Susceptible Strains of Amblyseius fallacis (Garman) (Acarina: Phytoseiidae) for Pesticide Resistance on Greenhouse CucumberSang-Cuei Lee*, J. Les Shipp' and K. Wang' National Institute of Agricultural Science and Technology, RDA, Suwon 441-707, Korea 1 Greenhouse Processing Crop Research Centre, AAFC, Harrow, Ontario, Canada
Abstract To evaluate the pesticide resistance of two commercial strains of Phytoseiulus persimilis Athias -Henriot (Koppert, strain A; Applied Bio-Nomics, strain B) and two strains of Amblyseiusfallacis (Garman) (resistant and susceptible), residual toxicity trials were conducted on greenhouse cucumber crops that were sprayed with two pesticides (pyridaben and dicofol), respectively. Strain A had significantly higher mortalities than strain B when exposed to foliage residues of pyridaben and dicofol. Strain B showed 3-18% higher survivorship than strain A when exposed to 7- to 14-day foliage residues of pyridaben at 213 and 426 ppm. When exposed to 1- and 8-day foliage residues of dicofol at 152 and 303 ppm, strain A exhibited 8-10% higher mortalities as compared to strain B. Residual toxicity of both pesticides to P. persimilis decreased significantly at the lower concentrations and over time under greenhouse conditions. Mortalities of both strains of P. persimilis were reduced by 50% when exposed to the l-week residues of both pesticides at the lowest concentrations. With the treatment of dicofol (303 ppm), mortalities for the two strains of P. persimilis decreased from 53.54- 42.68% at l-day residues to 28.18-21.21 % at 8-day residues. At 500 ppm of dicofol, mortalities decreased from 60.09~ 60.90% at l-day residue to 35.75-34.14% at 22-day residues. However, with dicofol (1000 ppm), mortalities were as high as 61.73% at 22~day residue. The resistant strain of A. fallacies showed significantly lower mortality, as compared to the susceptible strain, when exposed to 1- and 7-day foliage residue of pyridaben at 213 and 426 ppm concentrations. Mortality of A. fallacis to pyridaben was lower than that of P. persimilis. This suggests that A. fallacis may be more compatible with the application of this pesticide to greenhouse crops than that of P. persimilis. In "Corresponding author. E-mail: [email protected] Tel: 031-290-0467; Fax: 031-290-0479 (Received June 20, 2001; Accepted October 31, 2001)
addition, strain B of P. persimilis may be more advantageous after the application of these pesticides in a greenhouse rPM program than strain A. Key words Phytoseiulus persimilis, Amblyseius fallaeis, pesticide resistance, greenhouse trials
Introduction Natural enemies are used successfully for biological control of a number of insect and mite pests, but on many crops, the use of non-selective chemicals will often reduce or eliminate natural enemy populations. Resistance to pesticides has been developed only rarely in natural enemies (Croft and Morse, 1979), but those few species that have acquired pesticide resistance have provided effective biological control of secondary pests when pesticides are used for control of the major pests (Croft, 1977). The predatory mites, Phytoseiulus persimilis AthiasHenriot and Amblyseius fallacis (Garman), are effective biological control agents for control of the two-spotted spider mite, Tetranychus urticae Koch. These agents have been used on cucumber, sweet pepper, berry, and fruit crops in the greenhouse (Elliott 1993; Van Lenteren et al., 1997). Also, P. persimilis can be an effective predator on other crops such as strawberry, small fruit crops, watermelon, and ornamentals (Malais and Ravensberg, 1992). However, biological control in the greenhouse can be difficult at times without the periodic use of pesticides for controlling pest outbreaks (Hayashi, 1996) and for clean up of the crop at the end of the season (Howard et al., 1994). Biological control of T urticae using predatory mites such as P. persimilis is effective only against low population densities of the pest (Pralavorio et al., 1985). When the population density is too high, an acaricide treatment is needed to reduce the pest pop-
166 J. Asia-Pacific Entomol. Vol. 4 (2001)
ulation before the release of beneficial mites (Malezieux et al., 1992) or sometimes after releases. As a result, biological control of T urticae is sometimes integrated with chemical control measures. To integrate the use of pesticides with biological control agents of T urticae in the greenhouse, several factors need to be considered (Shipp et al., 2000). First, physiologically selective acaricidesthat are specific to particular pest species should be used to adjust prey/predatorratios only when necessary. Several studies have been conducted to evaluate pesticides that are toxic to specific pests but not harmful to their control agents such as natural enemies (Zhang and Sanderson, 1990; Malezieux et al., 1992; Spollen and Isman, 1996). This approach allows producers to choose the least harmful pesticides, but unfortunately few such pesticides are commercially available (Malezieux et al., 1992). Second, naturally-or artificially-selected natural enemies that are resistant to pesticides can be used (Hoy, 1990; Rathman et a1., 1990). Several studies have been conducted to select pesticide-resistant strains of parasitoids and predators (Schulten and van de Klashort, 1979; Hoy and Ouyang, 1989). Lee et al. (2001) reported differences in insecticide resistance for the phytoseiid predatory mite, P. persimilis from each of three commercial companies strains to several insecticides and acaricides in laboratory trials. Amblyseius fallacis has been selected for pyrethroid resistance in the laboratory and mass produced for commercial release in several regions (Whalon et al., 1982; Thistlewood et al., 1995). To apply pesticide-resistant strains of predatory mites with other biological control agents against T urticae in greenhouse IPM programs, the resistance of these predatory mites must be determined in conjunction with the application of pesticides or acaricides under greenhouses conditions. To date, few studies have documented the resistance of different strains of predatory mites in greenhouses where a pesticide has been applied. In this study, the resistance of two commercial strains of P. persimilis (Koppert and Applied Bio-Nomics strains) and two strains of A. fallacis (resistant and susceptible) was evaluated on greenhouse cucumber crops that were sprayed with two strains ofpesticides (pyridaben and dicofol), respectively.
Materials and Methods Experimental Greenhouses Experiments were conducted from January to March 2001 in two greenhouses (9.0 by 7.3 m) at the Greenhouse and Processing Crops Research Centre, Harrow, Ontario, Canada. Commercial cucumbercultivar 'Bodega'
Sang-Guei Lee, J. Les Shipp and K. Wang
grown in rockwool slabs (90 by 20 by 7.5 em, FIBRgro®, Fibrex Insulations Inc.) at the 20 leaf stage were used as host plants. Day/night temperatures for the greenhouses were kept at 24/22°C. Relative humidity was maintained at 75% throughout the trial period. The plants were irrigated and fertilized using the Harrow Fertigation Manager" (Labbate Climate Control Systems, Leamington, Ontario, Canada) and were maintained according to standard commercial recommendations by Ontario Ministry of Agriculture and Food. Greenhouse climate was monitored and maintained by Argus Controls" System (Argus Control Systems Ltd, White Rock, British Columbia, Canada).
Pesticide Application Solutions of dicofol (35% WP) (Rohm and Haas Canada Inc.) and pridaben (75% WP) (Plant Products Co. Ltd.) were prepared by dissolving the pesticide in water at the required rates and then sprayed on a cucumber crop under greenhouse production conditions. Treatment rates were designated as 152, 303, 500 and 1000 ppm for dicofol, and 213 and 426 ppm for pyridaben, respectively, according to the recommended rates for the two pesticide products against the two spotted spider mite (303 ppm for dicofol and 213 ppm for pyridaben). Sprays were applied, using a high pressure C02 sprayer (11.6 kPa), to both leaf surfaces until runoff. Water was sprayed only for the control treatment. At least 12 fully expanded leaves per plant were sprayed.
Maintenance of Predatory Mites P. persimilis mites from Koppert B.V. (The Nether-
lands) (strain A) and Applied Bio-Nomics Ltd. (Canada)
Table 1. Mortalities' (Mean ± SE) of two commercial strains of P. persimilis exposed to different time periods of foliage residues for pyridaben
Concentration (ppm)
Residual time (days)
7
14
213
426
A
54.19±8.53a
53.39±7.20a
B
41.45±3.53a
54.12±3.35a
A
23.49±4.24a
44.05 ± 2.74a
B
15_65±2.lla
26.33±3.05b
A
12.69±1.13a
23.68±2.86a
B
9.29±2.34a
16.93±2.56a
Within columns for each residual-til~~e, means followed by the same letter are not significantly different at P "> 0.05 based on LSD lest. Data were arcsin. square root transformed before ANOYA. "Corrected mortality by Abbott' s formulat Abbott, 1925). 1,'1 wo commercial strains of Phytosetulus persnnrlls (Strain A-Kopper1~ Strain fl-Applicd Bio-Nomics strain).
Evaluation of Predatory Mites for Pesticide Resistance
167
Table 2. Mortalities' (Mean±SE) of two commercial strains of P. persimilis exposed to different time periods of foliage residues for dicofol Residual time (days)
8
15
22
Strainb
Concentration (ppm) 152
A
29.95±4.31a
B
21.00± 1.82a
A
14.32±2.48a
B
6.53± 1.33b
303
500
1000
53.54±3.4la 42.68 ± 2.25b
60.09±2.91a 60.90 ± 3.07a
94.50 ± 1.55a
28.18±5.20a 21.21 ±3.81a
57.85±2.26a 52.70±5.56a
82.95±2.l6b
62.04 ± 4.06a 30.48± l.72b
86.40 ± 1.58a 74.44±3.l6b
35.75±6.0la 34.l4±5.49a
64.43±4.10a
A
B A
B
93.59 ± 1.76a 93.04± 1.44a
61.73±2.50a
Within columns for each residual time, means followed by the same letter are not significantly different at P > 0.05 based on LSD test. Data were arcsine square root transformed before ANOVA. "Corrected mortality by Abbott's formula/Abbott, 1925). bTwo commercial strains of Phytoseiulus persimilis (Strain A-Koppelt; Strain B-Applied Bio-Nomics strain).
(strain B) were used in the greenhouse trials for comparison of pesticide resistance to P. persimilis. TIle mites were shipped from the suppliers and stored separately in their shipping bottle in a controlled enviromnent chamberat WaC, 70 % RH, and 16:8h (L:D) photoperiod until needed. Resistant and susceptible strains ofA. fallacis were supplied by the Southern Crop Protection and Food Research Centre (Vineland), Agriculture and AgriFood Canada, where the resistant strain has been maintained since 1989 under the selective pyrethroid pesticide (deltamethrin) pressure. Amblyseius fallacis colonies were maintained in the laboratory at 26 ± r'c, 70% RH, and a photoperiod of 16:8 h (L:D) according to the methods of Thistlewood et al. (1992). The predatory mites along with T urticae as a food source were confined on a cucumber leaf disk that was placed at the center of a water-soaked sponge within a plastic box (15 X 20 x 0 ern), Both predators and preys were confined on the leaf disk by keeping a sufficient water bath surrounding the leaf edge. Cucumber leaves infested with T urticae were added three times every week and, at the same time, the dried leaves were removed. The colony of T urticae was maintained on cucumber plants in a controlled environment chamber at 24 ± I°C, 70% RH, and a photoperiod of 16:8 h (L:D).
Release of Predatory Mites The P. pesimilis mites were exposed to different residue times by confming the mites onto sprayed leaves I, 7 and 15 days for pyridaben, and 1, 8, 15 and 22 days for dicofol after pesticide application using leaf cages, respectively. Approximately 30 adult females from each test strain along with 60 T urticae as a
food source were confined to the lower surface of treated leaves using leaf cages (diameter 5 em X height 0.5 em, with a hole of 3 em diameter in the cage bottom, which was covered with nylon cloth for ventilation, with a same size plastic plate on the back of the cage). Eight replicates were conducted for each residual time treatment and the untreated control. After 48 h exposure, the mites were returned to the laboratory and recorded as live and dead using a dissecting microscope. For the A-fallacis mites, the same method was used as for P. persimilis except that only 20 predator mites from each of the two strains along with 50 T urticae were used for each replicate. Each treatment was repeated twice due to the limited number of available A. fallacis. In addition, A. fallacis was exposed to only 1 and 7 day residues.
Data Analysis For each replicate, mite mortality after a 48-h exposure period was expressed as a percentage, corrected by Abbott's formula (Abbott, 1925). ANOVA (pesticide X residue time period x strain) was conducted on the arcsine square root transformed mortality data. When significant differences in mortalities were found, the means were separated using LSD test (SAS Institute, 1990). Strain mortalities of P. persimilis that were exposed to different residual time periods of the pesticides at different concentrations were further compared using probit analysis with Gompertz distribution (SAS Institute, 1990). Paired t-test was used to compare the mortalities of resistant and susceptible strains of A. fallacies that were caused by 1- and 7-clay pyridaben residual toxicity.
168 J. Asia-Pacific Entomol. Vol. 4 (2001)
Sang-Guei Lee, J. Les Shipp and K. Wang
Results A three-way ANaYA was performed on the adult mortality data using the factors pesticide, residue ages, and strains. Generally, strain A had significantly higher mortalities than strain B when exposed to foliage residues of pyridaben (F = 15.93; 4/ = 1,79; P < 0.01) and dicofol (F = 34.32; df= 1,218; P < 0.01), respectively. Strain B showed 3 to 18% higher survivorship than strain A when exposed to 7- to 14-d ay foliage residues of pyridaben at 213 and 426 ppm with the exception that strain B had slightly lower survivorship than strain A when exposed to I-day residues at 426 ppm (Table I). When exposed to land 8-day foliage residues of dicofol at 152 and 303 ppm, strain A exhibited 7-11% higher mortalities when compared to strain B. However, both mortalities at 152 and 303 ppm were less then 29% when exposed to S-day foliage residues (Table 2). Residual toxicity of both pesticides to P. persimilis decreased significantly at the lower concentrations (F= 21.2; df =1,79; P
50\
/g
I
40 " ;R
g t:: '" 0
30
I
201:
--
::;;
-
--
10 \ ' 0
Resistant 0 Susceptible
\/ 1
426 Day 1
213
-----
.
i
U'
-'
._ ...•
~
c:=J --
c:=J
426
213
Day 7
Concentration (ppm)
Fig. 1. Mortalities of resistant and susceptible strains of A, fallacies when exposed to 1- and 7-day foliage residues or pyridaben with spray concentrations of 426 and 213 ppm.
at 22-day residue. The resistant strain of A. fallacies showed significanily lower mortality (F=1.77, dj=14 P=O 049), as compared to the susceptible strain, when exposed to 1- and 7-day foliage residue of pyridaben at 213 and 426 ppm (Fig. I).
Discussion When using pyridaben and dicofol, mortality for strain A was greater than that for strain B. Furthermore, residual toxicity to strain A was longer than that to strain B. The mortality trends in the greenhouse were similar to the laboratory trials by Lee et al, (2001). However, mortality values in the greenhouse were lower than in the laboratory. Shipp et al. (1999) reported that two factors may be contributing to this result. First, individuals in the greenhouse trial had the opportunity to avoid contact with the leaf surface bearing the toxic residues by resting on the inner surface of the petri dishes. However, in the laboratory trials, the mites were constantly in contact with the toxic residues because the leaf disks were surrounded by water to prevent predator escapes from the leaf disk. Second, residues on the petri dish may have dissipated more slowly than those on the leaves. The exposure to sunlight in the greenhouses can result in quicker dissipation of residues (Lasota and Dybas, 1991). This study has quantified the relationship between pesticide residues at different time periods and the morities caused by these residues using probit analysis and also, has estimated the residue thresholds for pyridaben against two strains of commercially produced P. persimilis under greenhouse conditions. Our results indicated that the susceptibility of strain A to these pesticides was greater than that of the strain S, and that the susceptibility of P. persimilis to pyridaben was much greater than that of A. fallacis. In conjunction with the information of pesticide resistance against predatory mite strains and species under greenhouse production conditions, additional useful information would be to determine the best pesticide-resistant mite strains or species and the optimal time period after pesticide application before release of the predatory mites. This information will be used to improve the integration of the use of pesticides with biological control measures for environmentally-friendly crop production. In summary, the mortality of both pesticides was higher to strain A than to strain B. The mortality ofthe pesticide-resistant strain ofA. fallacis to pyridaben was lower than that of the susceptible strain. Mortality of A. fallacis to pyridaben was also lower than that
Evaluation of Predatory Mites for Pesticide Resistance
of P. persimilis. This suggests that A. fallacis may be more compatible with the application of this pesticide to greenhouse crops than that of P. persimilis. In addition, strain B of P. persimilis may be more advantageous after application of these pesticides in a greenhouse IPM program than strain A, even if the mortalities between strain A and B of P. persimilis are only slightly different to both pesticide at the recommended rate. Acknowledgments This study was made possible by a Cooperative Research Agreement between Agriculture and Agri-Food Canada (AAFC), Canada and the NationalInstitute of Agricultural Science and Technology (NIAST), RDA, Korea. The authors would like to thank D. Gagnier and T. Lomond, GPCRC, Harrow, for their technical assistance.
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