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A potential threat to tomato, a congener crop to potato from invaded potato tuber moth, Phthorimaea operculella (Zeller)
Journal of Asia-Pacific Entomology 22 (2019) 77–82
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A potential threat to tomato, a congener crop to potato from invaded potato tuber moth, Phthorimaea operculella (Zeller) Sunil Aryala,c, Chuleui Junga,b,
T
⁎
a
Department of Bioresource Sciences, Graduate school, Andong National University, Andong, GB, South Korea Agricultural Science and Technology Research Institute, Andong National University, Andong, GB, South Korea. c Entomology Division, Nepal Agricultural Research Council (NARC), Kathmandu, Nepal b
ARTICLE INFO
ABSTRACT
Keywords: Invasion Climate change Host expansion Antixenosis Preference
Potato tuber moth (PTM) is a primary pest of potato which had invaded into Korea in 1968 and its distribution was restricted in the southern part of the peninsula. Possibly due to the climate change, its distribution expanded toward the Northern part of South Korea including Gyounggi and Gangwon province where tomato production is high. Host expansion and damage potential of PTM was evaluated on tomato, a congeneric crop of potato. Three commercial varieties of tomato (Dafnis, Bangul and Jujube) and a potato (Superior-Sumi) were subjected to PTM larvae. The results showed that host suitability of tomato to PTM was lower than potato, but PTM could completely develop and reproduce on tomato leaves or fruits. Development time was varied relative to tomato varieties and plant age. PTM showed lower performance on the leaves and fruits of cherry type tomatoes. Higher survival was observed in the large sized fruit of tomato varieties. This study showed substantial evidence that the invaded PTM could damage the tomato cultivation.
Introduction Potato tuber moth (PTM) as a cosmopolitan insect pest (Kroschel et al., 2013; CABI, 2018) has a range of host plants mostly in the solanaceous crops (Cunningham, 1969). Though, its major host is potato (Solanum tuberosum L.) it also can cause damage to tomato (Solanum lycopersicon L.), and tobacco (Nicotiana tabacum L.) (Das and Raman, 1994). PTM is a primary pest of potato which had invaded into Korea in 1968 (Aryal and Jung, 2015) and its distribution was restricted in the southern part of the peninsula (Choe and Park, 1980) but now expanded toward 200 km in three decades to the North including Gyounggi and Gangwon province (Kwon et al., 2017). Recently PTM has shown its flight activity not only on potato field but also in the area of tomato field (Unpublished data, S. Aryal). Tomato area harvest, yield and production has been in increasing trend from 1095 to 7070 ha, 110,685 to 707,157 hg/ha and 12,120 to 499,960 tons during the period of 1961 to 2014 respectively (Faostat, 2017) (Fig. 1). With the increase in the temperature insect can increase rapid development and also can increase its population fast, where Raza et al. (2014) stated that the green stink bug (Acrosternum hilare Say) shifts range of 185 miles north in 25 years with increase of 2 °C and can facilitate the population outbreaks for some invasive insect species (Ju et al., 2011). With this change in climate the insect's generation per ⁎
year also can be increased and can create considerable range expansion (Bale, 2002). So this unpredicted climate pattern, host condition and insect pests' population also led to investigate and adopt resistance mechanism that will provide a general insect tolerance to the crop (Woods et al., 2010). Host shift includes situations where new host plant is colonized by insect population and will also continue to use previous host plants which are more properly referred as host range expansion. This host range expansion is specially takes place due to ecological fitting where host shifts by herbivores onto novel plants and these host shifts occurs, because new host traits have related phytochemical (Bernays and Graham, 1988) and nutritional resource to use by pests such as carbon, nitrogen, and defensive metabolites (Awmack and Simon, 2002). This will tend to lead to shifts to those hosts which are phylogenetically related because and tend to contain the same or highly similar resources (Agosta, 2006). Another mechanism for host shifts is evolutionary where is can occur over relatively short time scales if herbivore have capacity to utilize novel host rapidly for which genetic changes in insects chemosensory system should occur (Opitz et al., 2012). Earlier we showed that the PTM can survive on harsh winter climatic condition and its credible adaptabilityin lower temperature (Aryal and Jung, 2018). Climate of the Korea has been in vulnerable stage of being warmer day by day. With the highest cold adaptability
Corresponding author: Department Plant Medicals, Andong National University, Andong 36729, Republic of Korea. E-mail address: [email protected] (C. Jung).
https://doi.org/10.1016/j.aspen.2018.12.008 Received 2 August 2018; Received in revised form 1 December 2018; Accepted 6 December 2018 Available online 07 December 2018 1226-8615/ © 2018 Korean Society of Applied Entomology. Published by Elsevier B.V. All rights reserved.
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sufficient eggs for experiments (Maharjan and Jung, 2011). Oviposition on leaves Choice test Leaf rachis with 3 to 4 terminal leaflets from the compound leaves of three cultivar of tomato and a potato leaves were dipped in vial containing water to maintain the leaflet turgidity and keep inside acrylic cage (40 × 40 × 40 cm) at four corners. Four cages were used at a time and repeated 5 times. One pair with mated female of PTM was released inside each cage to choose among the varieties for oviposition. Female PTM has choice to oviposit on the leaves of the varieties of their choice either three variety of tomato or a potato leaves. If the female fail to lay egg, new pair will be replaced as and when required. Number of eggs laid on tomato as well as potato was counted on both the sides of the leaves until day 4. The positions of the different varieties inside the cages were changed daily. A 5% sugar solution was applied in a cotton wick twice daily in the morning and evening and placed inside the cage as a food for adult moths.
Fig. 1. Tomato and potato area harvest during the period of 1960 to 2014 in Korea. (Source: Faostat, 2017).
and unpredicted climate patterns in Korean peninsula, PTM may shift its host to tomato than potato since both crops are under similar genus which can trigger PTM to shift rapidly in climate change scenario. It has been reported from various countries that PTM is infesting tomato (Yathom, 1986; Gilboa and Podoler, 1994; Gurr and McGrath, 2001; Gurr and McGrath, 2002; Mulatu et al., 2006a, 2006b; Juvik et al., 1982). We investigated the preferential damage among tomatoes with potato as a reference standard. Since this pest also can inflict damage on other solanaceous crop like tobacco and tomato, we tested the possible host expansion and damage potential on the varieties of tomato by invaded PTM and look for the resistant cultivar.
No choice test Leaf rachis with 3 to 4 terminal leaflets from the compound leaves were dipped in water containing vial of the three cultivars of tomato and a potato and kept inside individual container (72 × 72 × 100 mm, SPL life sciences). Ten containers were used for each variety, with a total of forty containers. One pair of mated female along with male of PTM was released inside each cage. The female has only one variety as a choice for oviposition. Number of eggs laid on tomato or potato leaves on both the sides and the eggs laid inside the wall of the container was counted up to day 4. A 5% sugar solution was applied in a cotton wick twice daily in the morning and evening and place inside cage. The number of egg laid where converted in percentage before subjected to analysis. Condition of the experimental environment were 25 ± 1 °C and RH of 65 ± 5% and photo period maintained was 16 L:8D.
Materials and methods Host plant Three varieties (Dafnis, Bangul and Jujube) of tomatoes with different growth habit, leaf type, fruit color, shape, size, type were selected for the study. Dafnis were large size fruit, and Bangul and Jujube cherry were small having regular leaf type. Potato variety ‘Sumi’ was selected for the introduction of PTM as these varieties occupies highest area of cultivation in Korea. One month old seedlings of tomato were transplanted on March 2016 and the experiment started from the April for one month and July 2016 for three month old plants. Almost all the plants grow equally. All the plants were cultivated in a greenhouse in a plastic pot (Iljin, 10 L, Korea) filled with peat (Dong Woo Bio, Korea).
Larval development on the potato and tomato leaves Choice test Larval preference was also compared between 1 and 3 month old leaves of tomatoes but the potato leaves were of 2 month old. Leaflets of tomatoes (three varieties) and potato were placed in equidistance on the single Petri dishes. Five one day old larvae were released on the middle of the petri dishes (150 × 20 mm, Crystel-Grade Polystyrene disposable; SPL life science) each time. Nine petri dishes used at a time and were repeated 3 times. Larvae were allowed freely to choose among the host plant leaflet as per their preference. The cut ends of the petiole of the leaflets were covered with the cotton soaked water to maintain the leaves turgidity After 72 h, number of leaf mine and larvae inside were observed under stereo microscope (SZ61, Olympus). The numbers of mines were summed up for each experiment for each variety and converted into percentage and subject to analysis.
Insects Potato tuber moth (PTM) used in bioassays was obtained from High Land Research Institute, Pyeongchang, Gangwon-do and maintained at the Insect Ecology Laboratory, Andong National University. The potato tubers were placed in container boxes (40 × 40 × 40 cm) with fine sterilized sand at the bottom and incubated at 25 ± 1 °C with relative humidity (RH) 65 ± 5% and 16 L:8D condition. Dry sand served as pupation medium. When the larvae had completed the larval stage, the pupae (with their cocoons) were harvested through sieving (2.0 mm mesh width). Cocoons were removed and pupae surface-sterilized by washing them in a sodium hypochlorite solution (0.3%) (Sporleder et al., 2004). The collected pupae were air-dried and placed in a cylindrical plastic container (∅ 12 cm × 14 cm depth), which was covered with a mesh cloth. After adult emergence, a filter paper was placed on the mesh cloth as oviposition medium. Adults were fed with 5% sugar solution, which was dropped on the edges of the filter paper. Eggs were let to hatch and used for experiments or for further rearing. In this way rearing cycle was continued to multiply the PTM for providing
No choice test The tomatoes were grown in a greenhouse and maintained at 27 ± 1 °C with a relative humidity of 65 ± 1 °C with natural photoperiod system. The cut ends of the petiole of the leaflets were covered with the cotton soaked water. The cotton wicks were watered daily to maintain the turgidity of leaves. Three to four leaflets from compound leaves of three tomato varieties and potato variety were kept in petridish (100 × 40 mm, SPL life sciences, mesh size 0.053 mm) separately as a no-choice test and a day old neonate larvae was released. Total of 20 leaflets were maintained for each varieties. Leaves were checked 78
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daily and replace with new ones whenever needed until pupa formation. Number of mines after 48 h was observed to insure the damage potential for this pest. Other biological parameters such as larval, adult and pupal survival, longevity, Larval and pupal weight were evaluated from this experiment. Mean temperature and relative humidity were 25 ± 0.07 °C and 55.8 ± 0.55% during the experiment period recorded with data logger (EL-USB-2, Lascar Electronics Ltd., Salisbury, UK) and photo period maintained was 16 L:8D during the both choice and no choice experiment for oviposition experiments. Larval development on the potato tubers and tomato fruits Ten cups (120 × 80 mm, SPL life sciences, mesh size 0.053 mm) with ventilation were maintained for each variety with sufficient food and inoculated with 5 one day old larvae. As PTM mostly feed on the central core of the tomato (placenta) (Mulatu et al., 2006b), we supplied the fruits of tomato to be sufficient for 5 larvae in each cup. Larval, adult and pupal survival, longevity, Larval and pupal weight, Head capsule width of 4th instar larvae were evaluated. Mean temperature and relative humidity were 26.3 ± 0.04 °C and 53.08 ± 0.11% during the experiment period recorded with data logger which was adjusted to record for half an hour and the photo period maintained was 16 L:8D. Statistical analysis A two way ANOVA was conducted to compare the main effects of crop varieties and age, the interaction effect between the varieties and age on number and proportion of egg laying on both choice and no choice condition respectively. The feeding bioassays, longevity and other parameter were analyzed using one way ANOVA followed by SNK or Tukey's test for mean separation. Relation between the % mine and survival to adult for PTM were conducted for one and three month old leaves using spread sheet for four varieties. The ANOVA analysis was performed using SAS 9.4 (SAS Institute, 2013).
Fig. 2. Oviposition preference of the potato tuber moth when supplied with three varieties of tomato (one month old) with a potato leaves in choice condition (A) and no choice condition (B).Bar represent the standard error. The same letter above bars do not have any significant difference in mean (Tukey's test, P < .05).
Results
(7.4%)in both ages of plant whereas potato leaves where most preferred (59.3%) in two month old plant.There was significant different in mine proportion to leaves from one moth (F3,8 = 64.87, p < .001)and three month (F3,8 = 78.09, p < .00) old plants 1(Fig. 3). Larva to adult development time was longest in Jujube variety in both one month (F3, 46 = 14.59, p < .001) and three month old leaves (F3, 46 = 26.9, p < .001) while it was shortest in case of potato leaves (Table 1). Pupal weight varied among varieties in either fed with leaves of one (F3, 48 = 10.13, p < .001) or 3 month old (F3, 46 = 33.03, p < .001) plants. In the first experiment with one month old plants the PTM fed with potato leaves have highest pupal weight of 8 mg whereas the lowest was found on the Dafnis tomato variety. But in the second experiment with the three month old plants pupal weight of the PTM was 9.05 mg for the potato leaves and least in Bangul varieties (6.8 mg) (Fig. 4). Relation between the mine percent on 48 h and total survival percent to adulthood was positively correlated for the PTM fed with leaves of one month old and three month old as described by R-squared value of 0.86 and 0.99 respectively (Fig. 5).
Oviposition on leaves Choice test There is significant difference in proportion of total egg laying on leaves of tomato and potato varieties (F3, 152 = 397.11, p < .001) in choice test. Similarly the egg laying between the ages (F1, 152 = 19.55, p < .001) and interaction between variety and age for the oviposition was found to be significant (F3, 152 = 2.98, p < .03) (Fig. 2A, Table 3). No choice test Two way analysis of ANOVA on no-choice egg laying conditionshowed that there was significant difference in proportion of total egg laying on leaves of tomato and potato varieties (F3, 72 = 81.49, p < .0001) and interaction between varieties and age of the plants (F3, 72 = 3.52, p < .02) (Table 3) whereas the age of the plant does not have any particular preferences and was insignificant (F1,72 = 0.12, p < .73, Table 1). Whereas, in case of the egg laying, inside container there was significant differences among varieties (F3,72 = 14.33, P < .0001) were highest number of egg on the container surface was highest in Bangul (91.94%) variety of one month old leaves and lowest in the container containing potato leaves (Fig. 2B). There was not significant interaction among variety and age of the plant (F3,72 = 0.18, P < .90) and between the age of the plant (F3,72 = 0.55, p = .45) in terms of egg laying in container.
Larval development on the potato tubers and tomato fruits Larval development duration took about average of 18.4 days in the variety Bangul followed by Jujube variety (F3, 110 = 136.56, p < .001. Adult development time was also longest in Bangul variety followed by Jujube variety (F3, 106 = 124.85, p < .001. Shortest developmental time was found in potato (Table 2). Percent larva (F3, 36 = 9.96, p < .001) and pupa (F3, 106 = 9.75, p < .001) survived was very low in Jujube and Bangul variety when compared to potato or Normal
Larval development on the potato and tomato leaves A Jujube variety was least preferred in terms of proportion of mine 79
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Table 1 Development period (day, Mean ± SE) of immature Phthorimaea operculella fed on different age of varieties of tomato and potato leaves. Developmental duration (d)
Host plant Tomato, Dafnis Tomato, Bangul Tomato, Jujube Potato, (sumi)
Larvae
Prepupae
Pupae
Total immature
Larvae
Prepupae
Pupae
Total immature
One month old 15.60( ± 0.21)a 14.25 ( ± 0.45)b 16.00 ( ± 0.18)a 13.05 ( ± 0.39)c
2.10( ± 0.10)a 1.94( ± 0.06)a 1.67( ± 0.21)a 1.85( ± 0.13)a
7.10 7.50 7.33 7.60
24.80 23.75 25.00 22.50
Three 15.50 18.17 20.50 12.75
2.07( ± 0.12)a 1.83( ± 0.11)a 2.00( ± 0.00)a 2.10( ± 0.10)a
7.57 ( ± 0.25)a 7.17( ± 0.20)a 7.33( ± 0.33)a 7.25( ± 0.14)a
25.14( ± 0.39)b 27.17( ± 0.87)b 29.75( ± 0.85)a 22.10 ( ± 0.19)c
( ± 0.15)a ( ± 0.42)a ( ± 0.13)a ( ± 0.25)a
( ± 0.39)a ( ± 0.25)b ( ± 0.51)a ( ± 0.22)c
month old ( ± 0.38)c ( ± 0.82)b ( ± 0.86)a ( ± 0.12)d
Numbers in parenthesis are standard errors( ± SE); the same letters within the column indicate no significant difference among the varieties.
Fig. 3. Larval preference on choice condition toward the leaves of tomato and potato varieties on one and three month old leaves. Bar represent the standard error. The same letters above bars do not have any significant difference in mean (Tukey's test, P < .05). Fig. 5. Relation between the proportion of mined leaves and survival of the PTM to the adults for the PTM fed with tomato leaves from one month old plant (dark line) and three month old plant (dashed line). The points are the observed data. Tomato (V1-Dafnis, V2- Bangul, V3-Jujube) and potato (V4-Sumi).
Discussion Host suitability of herbivorous insect can be determined by the nutritional requirements and antibiosis and antixenois (Bernays and Graham, 1988; Awmack and Simon, 2002). Potato tube moth, Phthorimaea operculella (Zeller) as being the major host of potato also can inflict damage on other solanaceous crop like tomato. There are some reports that PTM can cause extensive damage to tomato rather than potato in some parts of the world (Juvik et al., 1982; Yathom, 1986; Gilboa and Podoler, 1994; Mulatu et al., 2006a, 2006b). When tomato leaves with potato were given as a choice for egg laying, the PTM preferred potato, nevertheless oviposition occurred on the leaves of tomato as found by the Mulatu et al. (2007). In no choice condition where we provide the tomato leaves for oviposition most of the eggs were laid on the interior of the container rather than in leaves of tomatoes. But some eggs are still laid on the surface of tomato. In case of potato, leaves were preferred for oviposition while in case of tomato container were preferred to lay eggs which Varela and Bernays, 1988 also observed during their experiments that soil was preferred for tobacco and tomato and foliage was preferred for potato. In the choice test, mostly PTM choose potato leaves for laying eggs except a few cases. Similar observation was made by other scientific study (Mulatu et al., 2007). In no choice test also PTM showed the same trend. They choose interior part of the container instead of tomato leaves provided. Difference in the oviposition may be due to the capability of female insects in detection of small variation of host plant related cues such as volatiles (Karlsson et al., 2009; Proffit et al., 2011) whereas trichome
Fig. 4. Pupal weight of Phthorimeaoperculella fed with leaves of difference crop varieties of either tomato or potato. Bar represent the standard error. The same letters above bars do not have any significant difference in mean.
(Dafnis) tomato varieties, percent larvae survived, percent pupation in Jujube variety was found to be 40, 38 and 36% respectively (Table 2). Fourth instar head capsule size did not differ significantly but found to wider in potato tuber fed PTM of 1.3 mm (F3, 36 = 1.27, p < .29) (Fig. 6A). Fourth instar wondering larval weight was significantly different among the variety, heaviest being the potato fed larva of about average of 11.2 mg followed by Bangul and Jujube (F3, 36 = 3.3, p < .001). Similarly weight of the pupa was also found significantly different among the variety heaviest being the potato fed larva of about average of 10.8 mg, lightest pupa being of Jujube (F3, 36 = 14.23, p < .001 (Fig. 6B).
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Table 2 Development period (day, Mean ± SE) of immature Phthorimaea operculella fed on different varieties of tomato fruits and potato tuber. Varieties
L duration
P duration
Total immature
L survival
P survival
Dafnis Bangul Jujube Potato (sumi)
15.06 18.37 17.65 13.44
7.32 7.37 7.57 7.16
24.09 27.58 27.11 22.44
68( ± 1.97)a 48( ± 2.38)b 40( ± 2.98)b 72( ± 1.46)a
64( ± 2.23)ab 48( ± 2.23)bc 38( ± 2.23)c 72( ± 2.23)a
( ± 0.39)c ( ± 0.27)a ( ± 0.31)b ( ± 0.24)d
( ± 0.18)a ( ± 0.20)a ( ± 0.23)a ( ± 0.16)a
( ± 0.39)c ( ± 0.32)a ( ± 0.26)b ( ± 0.21)d
Numbers in parenthesis are standard errors ( ± SE).The same letters within the column indicate no significant difference among the varieties; L = Larval, P-Pupal.
tomato. It occurred because some common volatile may trigger PTM to lay eggs on tomato (Bernays and Graham, 1988) leaves. An investigation of volatiles emitted by the tested host plants is important factors in oviposition preferences. In free choice for larval feeding most of the mines were found on potato leaflet followed by Dafnis variety in both one and three month old leaves. The Jujube, Cherry cultivar fed with the 3 months old leaves have longest development time with reduced pupal weight which may be due to the high amount of volatiles like tomatine which has insecticidal properties (Chowanski et al., 2016) and high number of trichome on older leaves (Gurr and McGrath, 2001). If herbivorous insects find better food, they can enhance their survival rates and shorten development times which are the indicators for better food quality (Awmack and Simon, 2002; Greenberg et al., 2002; Pereyra and Sanchez, 2006). Both larval and larva to adult development time on potato leaves were found shorter than on tomato leaves and it is in agreement with several other reports (Lopes and Vendramim, 2001; Mulatu et al., 2007). Our results showed that the older leaves have better larval performance on tomato leaves because young leaves have high saponin content than older leaves which has deterrent effect (Badenes-Perez et al., 2014). In fruit feeding bioassay, the performance for cherry type tomato (Jujube and Bangul) is inferior to potato and fresh market type tomato (Dafnis) and the high survival of PTM larvae was found in potato and onDafnis variety which is fresh market cultivar. The fresh market cultivar possesses the largest fruit, which might have provided more core tissue for the developing PTMlarva. This affords the developing larvae the opportunity to remain and complete their development within a single fruit. Leonardi et al. (2000) reported that cultivar, ripening stage and growing condition play a pivotal role in determining the amount of glycoalkaloid in tomato fruits. The longest duration to complete life cycle was for the cherry tomato where tomato glycoalkaloids called αtomatine could act as antibiosis component and wasfound in higher amount than in fresh market tomato (Mulatu et al., 2006b). In conclusion larvae could choose tomato leaves and complete its lifecycle on them in laboratory condition. Though, the performance of PTM on tomato was lower than potato, it could complete life cycle feeding tomato leaves or fruits. There is great threat of host shift and has damage potential to attack tomato variety.The possibility could manifest by the facts that the distribution of PTM has been expanded toward northern part of South Korea partly because of the change of climates in the peninsular and the cultivation area of tomato has increased for last few decades while potato cultivation is in declining. Potato tuber moths were caught in the pheromone traps installed in the area of tomato plantation where no potato was grown (Unpublished data, Aryal and Jung). Further careful monitoring of the host expansion of PTM would be required in tomato fields with its biochemical interaction.
Table 3 Two way analysis of variance on the oviposition choice of the PTM on crop variety and age of the crops. Source Choice condition Variety Plant age Interaction No choice condition Variety Plant age Interaction
Oviposition on leaves
Oviposition on container
0.0001 0.0001 0.0334
NA NA NA
0.0001 ns 0.0193
0.0001 Ns ns
Three tomato varieties and one potato variety, two age of plant leaves (one and three month, in case of potato one and two month), NA = Not available; ns = not significant (P ≤.005).
Fig. 6. Fourth instar head capsule size (A) and weight of the larvae and pupa (B) fed with different fruits of tomato and potato. Bar represent the standard error. The same letters above bars do not have any significant difference in mean.
Acknowledgement This work was supported by Basic Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (NRF-2018R1A6A1A03024862). SA would thank to Nepal Agricultural Research Council for the study leave.
and other leaves physical parameter also play role as antixenosis. Antixenosis refers modified behavior of an insect pest and usually is expressed as non-preference of the insect for a resistant plant compared with a susceptibleone. Some of the eggs still deposited on leaves of the 81
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Conflict of interest
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None. References Agosta, S.J., 2006. On ecological fitting, plant-insect associations, herbivore host shifts, and host plant selection. Oikos 114 (3). Aryal, S., Jung, C., 2015. A Review on the Ecological Characteristics of Potato Tuber Moth, Phthorimaeaoperculella(Zeller) (Lepidoptera: Gelechiidae). Korean J. Soil Zool. 19, 35–41. Aryal, S., Jung, C., 2018. Cold tolerance characteristics of Korean population of potato tuber moth, Phthorimaeaoperculella (Zeller), (Lepidoptera: Gelechiidae): Cold tolerance of the potato tuber moth. Entomol. Res. 48, 300–307. Awmack, C.S., Simon, L., 2002. Host plant quality and fecundity in herbivores Insects. Annu. Rev. Entomol. 47, 817–844. Badenes-Perez, F.R., Gershenzon, J., Heckel, D.G., 2014. Insect attraction versus plant defense: young leaves high in glucosinolates stimulate oviposition by a specialist herbivore despite poor larval survival due to high saponin content. PLoS One 9 (4), e95766. Bale, J.S., 2002. Insects and low temperatures: from molecular biology to distributions and abundance. Phil. Trans. R. Soc. Lond. B. Biol. Sci. 357, 849–862. Bernays, E., Graham, M., 1988. On the evolution of host specificity in phytophagous arthropods. Ecology 69, 886–892. CABI, 2018. https://www.cabi.org/isc/datasheet/40686 Retrieved on 6 March 2018. Choe, K.R., Park, J.S., 1980. Distribution of the Potato Tuber Moth, Phthorimaeaoperculella (Zeller) (Lepidoptera: Gelechiidae). Korea. Korean J. of Plant Protec. 19, 103–107. Chowanski, S., Adamski, Z., Marciniak, P., Rosinski, G., Buyükgüzel, E., Buyukguzel, K., Falabella, P., Scrano, L., Ventrella, E., Lelario, F., Bufo, S.A., 2016. A review of bioinsecticidal activity of Solanaceae Alkaloids. Toxins. 8, 1–28. Cunningham, I.C., 1969. Alternative host plants of tobacco leaf-miner. Phthorimaeaaperculella (Zell.). Queensland J. Agric. Animal Sci. 26, 107–111. Das, G.P., Raman, K.V., 1994. Alternate hosts of the potato tuber moth, Phthorimaeaoperculella (Zeller). Crop Protec. 13, 83–86. Faostat, 2017. http://www.fao.org/faostat/en/#home Retrieved on 15 Sep 2017. Gilboa, S., Podoler, H., 1994. Population dynamics of the potato tuber moth on processing tomatoes in Israel. Entomol. Exp. Appl. 72, 197–206, 1994. Greenberg, S.M., Sappington, T.W., Setamou, M., Liu, T.X., 2002. Beet armyworm (Lepidoptera: Noctuidae) host plant preferences for oviposition. Environ. Entomol. 31, 142–148. Gurr, G.M., McGrath, D., 2001. Effect of plant variety, plant age and photoperiod on glandular pubescence and host-plant resistance to potato moth (Phthorimaeaoperculella) in Lycopersicon spp. Ann. appl. Biol. 138, 221–230. Gurr, G.M., McGrath, D., 2002. Foliar pubescence and resistance to potato moth, Phthorimaeaoperculella, in Lycopersiconhirsutum. Entomol. Exp. Appl. 103, 35–41. Ju, R.T., Zhu, H.Y., Gao, L., Zhou, X.H., Li, B., 2011. Increases in both temperature means and extremes likely facilitate invasive herbivore outbreaks. Nature 5, 15715. Juvik, J.A., Berlinger, M.J., Ben-David, T., Rudich, J., 1982. Resistance among accessions of the genera Lycopersicon and Solanum to four of the main insect pests of tomato in Israel. Phytoparasitica 10, 145–156.
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Journal of Asia-Pacific Entomology journal homepage: www.elsevier.com/locate/jape
A potential threat to tomato, a congener crop to potato from invaded potato tuber moth, Phthorimaea operculella (Zeller) Sunil Aryala,c, Chuleui Junga,b,
T
⁎
a
Department of Bioresource Sciences, Graduate school, Andong National University, Andong, GB, South Korea Agricultural Science and Technology Research Institute, Andong National University, Andong, GB, South Korea. c Entomology Division, Nepal Agricultural Research Council (NARC), Kathmandu, Nepal b
ARTICLE INFO
ABSTRACT
Keywords: Invasion Climate change Host expansion Antixenosis Preference
Potato tuber moth (PTM) is a primary pest of potato which had invaded into Korea in 1968 and its distribution was restricted in the southern part of the peninsula. Possibly due to the climate change, its distribution expanded toward the Northern part of South Korea including Gyounggi and Gangwon province where tomato production is high. Host expansion and damage potential of PTM was evaluated on tomato, a congeneric crop of potato. Three commercial varieties of tomato (Dafnis, Bangul and Jujube) and a potato (Superior-Sumi) were subjected to PTM larvae. The results showed that host suitability of tomato to PTM was lower than potato, but PTM could completely develop and reproduce on tomato leaves or fruits. Development time was varied relative to tomato varieties and plant age. PTM showed lower performance on the leaves and fruits of cherry type tomatoes. Higher survival was observed in the large sized fruit of tomato varieties. This study showed substantial evidence that the invaded PTM could damage the tomato cultivation.
Introduction Potato tuber moth (PTM) as a cosmopolitan insect pest (Kroschel et al., 2013; CABI, 2018) has a range of host plants mostly in the solanaceous crops (Cunningham, 1969). Though, its major host is potato (Solanum tuberosum L.) it also can cause damage to tomato (Solanum lycopersicon L.), and tobacco (Nicotiana tabacum L.) (Das and Raman, 1994). PTM is a primary pest of potato which had invaded into Korea in 1968 (Aryal and Jung, 2015) and its distribution was restricted in the southern part of the peninsula (Choe and Park, 1980) but now expanded toward 200 km in three decades to the North including Gyounggi and Gangwon province (Kwon et al., 2017). Recently PTM has shown its flight activity not only on potato field but also in the area of tomato field (Unpublished data, S. Aryal). Tomato area harvest, yield and production has been in increasing trend from 1095 to 7070 ha, 110,685 to 707,157 hg/ha and 12,120 to 499,960 tons during the period of 1961 to 2014 respectively (Faostat, 2017) (Fig. 1). With the increase in the temperature insect can increase rapid development and also can increase its population fast, where Raza et al. (2014) stated that the green stink bug (Acrosternum hilare Say) shifts range of 185 miles north in 25 years with increase of 2 °C and can facilitate the population outbreaks for some invasive insect species (Ju et al., 2011). With this change in climate the insect's generation per ⁎
year also can be increased and can create considerable range expansion (Bale, 2002). So this unpredicted climate pattern, host condition and insect pests' population also led to investigate and adopt resistance mechanism that will provide a general insect tolerance to the crop (Woods et al., 2010). Host shift includes situations where new host plant is colonized by insect population and will also continue to use previous host plants which are more properly referred as host range expansion. This host range expansion is specially takes place due to ecological fitting where host shifts by herbivores onto novel plants and these host shifts occurs, because new host traits have related phytochemical (Bernays and Graham, 1988) and nutritional resource to use by pests such as carbon, nitrogen, and defensive metabolites (Awmack and Simon, 2002). This will tend to lead to shifts to those hosts which are phylogenetically related because and tend to contain the same or highly similar resources (Agosta, 2006). Another mechanism for host shifts is evolutionary where is can occur over relatively short time scales if herbivore have capacity to utilize novel host rapidly for which genetic changes in insects chemosensory system should occur (Opitz et al., 2012). Earlier we showed that the PTM can survive on harsh winter climatic condition and its credible adaptabilityin lower temperature (Aryal and Jung, 2018). Climate of the Korea has been in vulnerable stage of being warmer day by day. With the highest cold adaptability
Corresponding author: Department Plant Medicals, Andong National University, Andong 36729, Republic of Korea. E-mail address: [email protected] (C. Jung).
https://doi.org/10.1016/j.aspen.2018.12.008 Received 2 August 2018; Received in revised form 1 December 2018; Accepted 6 December 2018 Available online 07 December 2018 1226-8615/ © 2018 Korean Society of Applied Entomology. Published by Elsevier B.V. All rights reserved.
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sufficient eggs for experiments (Maharjan and Jung, 2011). Oviposition on leaves Choice test Leaf rachis with 3 to 4 terminal leaflets from the compound leaves of three cultivar of tomato and a potato leaves were dipped in vial containing water to maintain the leaflet turgidity and keep inside acrylic cage (40 × 40 × 40 cm) at four corners. Four cages were used at a time and repeated 5 times. One pair with mated female of PTM was released inside each cage to choose among the varieties for oviposition. Female PTM has choice to oviposit on the leaves of the varieties of their choice either three variety of tomato or a potato leaves. If the female fail to lay egg, new pair will be replaced as and when required. Number of eggs laid on tomato as well as potato was counted on both the sides of the leaves until day 4. The positions of the different varieties inside the cages were changed daily. A 5% sugar solution was applied in a cotton wick twice daily in the morning and evening and placed inside the cage as a food for adult moths.
Fig. 1. Tomato and potato area harvest during the period of 1960 to 2014 in Korea. (Source: Faostat, 2017).
and unpredicted climate patterns in Korean peninsula, PTM may shift its host to tomato than potato since both crops are under similar genus which can trigger PTM to shift rapidly in climate change scenario. It has been reported from various countries that PTM is infesting tomato (Yathom, 1986; Gilboa and Podoler, 1994; Gurr and McGrath, 2001; Gurr and McGrath, 2002; Mulatu et al., 2006a, 2006b; Juvik et al., 1982). We investigated the preferential damage among tomatoes with potato as a reference standard. Since this pest also can inflict damage on other solanaceous crop like tobacco and tomato, we tested the possible host expansion and damage potential on the varieties of tomato by invaded PTM and look for the resistant cultivar.
No choice test Leaf rachis with 3 to 4 terminal leaflets from the compound leaves were dipped in water containing vial of the three cultivars of tomato and a potato and kept inside individual container (72 × 72 × 100 mm, SPL life sciences). Ten containers were used for each variety, with a total of forty containers. One pair of mated female along with male of PTM was released inside each cage. The female has only one variety as a choice for oviposition. Number of eggs laid on tomato or potato leaves on both the sides and the eggs laid inside the wall of the container was counted up to day 4. A 5% sugar solution was applied in a cotton wick twice daily in the morning and evening and place inside cage. The number of egg laid where converted in percentage before subjected to analysis. Condition of the experimental environment were 25 ± 1 °C and RH of 65 ± 5% and photo period maintained was 16 L:8D.
Materials and methods Host plant Three varieties (Dafnis, Bangul and Jujube) of tomatoes with different growth habit, leaf type, fruit color, shape, size, type were selected for the study. Dafnis were large size fruit, and Bangul and Jujube cherry were small having regular leaf type. Potato variety ‘Sumi’ was selected for the introduction of PTM as these varieties occupies highest area of cultivation in Korea. One month old seedlings of tomato were transplanted on March 2016 and the experiment started from the April for one month and July 2016 for three month old plants. Almost all the plants grow equally. All the plants were cultivated in a greenhouse in a plastic pot (Iljin, 10 L, Korea) filled with peat (Dong Woo Bio, Korea).
Larval development on the potato and tomato leaves Choice test Larval preference was also compared between 1 and 3 month old leaves of tomatoes but the potato leaves were of 2 month old. Leaflets of tomatoes (three varieties) and potato were placed in equidistance on the single Petri dishes. Five one day old larvae were released on the middle of the petri dishes (150 × 20 mm, Crystel-Grade Polystyrene disposable; SPL life science) each time. Nine petri dishes used at a time and were repeated 3 times. Larvae were allowed freely to choose among the host plant leaflet as per their preference. The cut ends of the petiole of the leaflets were covered with the cotton soaked water to maintain the leaves turgidity After 72 h, number of leaf mine and larvae inside were observed under stereo microscope (SZ61, Olympus). The numbers of mines were summed up for each experiment for each variety and converted into percentage and subject to analysis.
Insects Potato tuber moth (PTM) used in bioassays was obtained from High Land Research Institute, Pyeongchang, Gangwon-do and maintained at the Insect Ecology Laboratory, Andong National University. The potato tubers were placed in container boxes (40 × 40 × 40 cm) with fine sterilized sand at the bottom and incubated at 25 ± 1 °C with relative humidity (RH) 65 ± 5% and 16 L:8D condition. Dry sand served as pupation medium. When the larvae had completed the larval stage, the pupae (with their cocoons) were harvested through sieving (2.0 mm mesh width). Cocoons were removed and pupae surface-sterilized by washing them in a sodium hypochlorite solution (0.3%) (Sporleder et al., 2004). The collected pupae were air-dried and placed in a cylindrical plastic container (∅ 12 cm × 14 cm depth), which was covered with a mesh cloth. After adult emergence, a filter paper was placed on the mesh cloth as oviposition medium. Adults were fed with 5% sugar solution, which was dropped on the edges of the filter paper. Eggs were let to hatch and used for experiments or for further rearing. In this way rearing cycle was continued to multiply the PTM for providing
No choice test The tomatoes were grown in a greenhouse and maintained at 27 ± 1 °C with a relative humidity of 65 ± 1 °C with natural photoperiod system. The cut ends of the petiole of the leaflets were covered with the cotton soaked water. The cotton wicks were watered daily to maintain the turgidity of leaves. Three to four leaflets from compound leaves of three tomato varieties and potato variety were kept in petridish (100 × 40 mm, SPL life sciences, mesh size 0.053 mm) separately as a no-choice test and a day old neonate larvae was released. Total of 20 leaflets were maintained for each varieties. Leaves were checked 78
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daily and replace with new ones whenever needed until pupa formation. Number of mines after 48 h was observed to insure the damage potential for this pest. Other biological parameters such as larval, adult and pupal survival, longevity, Larval and pupal weight were evaluated from this experiment. Mean temperature and relative humidity were 25 ± 0.07 °C and 55.8 ± 0.55% during the experiment period recorded with data logger (EL-USB-2, Lascar Electronics Ltd., Salisbury, UK) and photo period maintained was 16 L:8D during the both choice and no choice experiment for oviposition experiments. Larval development on the potato tubers and tomato fruits Ten cups (120 × 80 mm, SPL life sciences, mesh size 0.053 mm) with ventilation were maintained for each variety with sufficient food and inoculated with 5 one day old larvae. As PTM mostly feed on the central core of the tomato (placenta) (Mulatu et al., 2006b), we supplied the fruits of tomato to be sufficient for 5 larvae in each cup. Larval, adult and pupal survival, longevity, Larval and pupal weight, Head capsule width of 4th instar larvae were evaluated. Mean temperature and relative humidity were 26.3 ± 0.04 °C and 53.08 ± 0.11% during the experiment period recorded with data logger which was adjusted to record for half an hour and the photo period maintained was 16 L:8D. Statistical analysis A two way ANOVA was conducted to compare the main effects of crop varieties and age, the interaction effect between the varieties and age on number and proportion of egg laying on both choice and no choice condition respectively. The feeding bioassays, longevity and other parameter were analyzed using one way ANOVA followed by SNK or Tukey's test for mean separation. Relation between the % mine and survival to adult for PTM were conducted for one and three month old leaves using spread sheet for four varieties. The ANOVA analysis was performed using SAS 9.4 (SAS Institute, 2013).
Fig. 2. Oviposition preference of the potato tuber moth when supplied with three varieties of tomato (one month old) with a potato leaves in choice condition (A) and no choice condition (B).Bar represent the standard error. The same letter above bars do not have any significant difference in mean (Tukey's test, P < .05).
Results
(7.4%)in both ages of plant whereas potato leaves where most preferred (59.3%) in two month old plant.There was significant different in mine proportion to leaves from one moth (F3,8 = 64.87, p < .001)and three month (F3,8 = 78.09, p < .00) old plants 1(Fig. 3). Larva to adult development time was longest in Jujube variety in both one month (F3, 46 = 14.59, p < .001) and three month old leaves (F3, 46 = 26.9, p < .001) while it was shortest in case of potato leaves (Table 1). Pupal weight varied among varieties in either fed with leaves of one (F3, 48 = 10.13, p < .001) or 3 month old (F3, 46 = 33.03, p < .001) plants. In the first experiment with one month old plants the PTM fed with potato leaves have highest pupal weight of 8 mg whereas the lowest was found on the Dafnis tomato variety. But in the second experiment with the three month old plants pupal weight of the PTM was 9.05 mg for the potato leaves and least in Bangul varieties (6.8 mg) (Fig. 4). Relation between the mine percent on 48 h and total survival percent to adulthood was positively correlated for the PTM fed with leaves of one month old and three month old as described by R-squared value of 0.86 and 0.99 respectively (Fig. 5).
Oviposition on leaves Choice test There is significant difference in proportion of total egg laying on leaves of tomato and potato varieties (F3, 152 = 397.11, p < .001) in choice test. Similarly the egg laying between the ages (F1, 152 = 19.55, p < .001) and interaction between variety and age for the oviposition was found to be significant (F3, 152 = 2.98, p < .03) (Fig. 2A, Table 3). No choice test Two way analysis of ANOVA on no-choice egg laying conditionshowed that there was significant difference in proportion of total egg laying on leaves of tomato and potato varieties (F3, 72 = 81.49, p < .0001) and interaction between varieties and age of the plants (F3, 72 = 3.52, p < .02) (Table 3) whereas the age of the plant does not have any particular preferences and was insignificant (F1,72 = 0.12, p < .73, Table 1). Whereas, in case of the egg laying, inside container there was significant differences among varieties (F3,72 = 14.33, P < .0001) were highest number of egg on the container surface was highest in Bangul (91.94%) variety of one month old leaves and lowest in the container containing potato leaves (Fig. 2B). There was not significant interaction among variety and age of the plant (F3,72 = 0.18, P < .90) and between the age of the plant (F3,72 = 0.55, p = .45) in terms of egg laying in container.
Larval development on the potato tubers and tomato fruits Larval development duration took about average of 18.4 days in the variety Bangul followed by Jujube variety (F3, 110 = 136.56, p < .001. Adult development time was also longest in Bangul variety followed by Jujube variety (F3, 106 = 124.85, p < .001. Shortest developmental time was found in potato (Table 2). Percent larva (F3, 36 = 9.96, p < .001) and pupa (F3, 106 = 9.75, p < .001) survived was very low in Jujube and Bangul variety when compared to potato or Normal
Larval development on the potato and tomato leaves A Jujube variety was least preferred in terms of proportion of mine 79
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Table 1 Development period (day, Mean ± SE) of immature Phthorimaea operculella fed on different age of varieties of tomato and potato leaves. Developmental duration (d)
Host plant Tomato, Dafnis Tomato, Bangul Tomato, Jujube Potato, (sumi)
Larvae
Prepupae
Pupae
Total immature
Larvae
Prepupae
Pupae
Total immature
One month old 15.60( ± 0.21)a 14.25 ( ± 0.45)b 16.00 ( ± 0.18)a 13.05 ( ± 0.39)c
2.10( ± 0.10)a 1.94( ± 0.06)a 1.67( ± 0.21)a 1.85( ± 0.13)a
7.10 7.50 7.33 7.60
24.80 23.75 25.00 22.50
Three 15.50 18.17 20.50 12.75
2.07( ± 0.12)a 1.83( ± 0.11)a 2.00( ± 0.00)a 2.10( ± 0.10)a
7.57 ( ± 0.25)a 7.17( ± 0.20)a 7.33( ± 0.33)a 7.25( ± 0.14)a
25.14( ± 0.39)b 27.17( ± 0.87)b 29.75( ± 0.85)a 22.10 ( ± 0.19)c
( ± 0.15)a ( ± 0.42)a ( ± 0.13)a ( ± 0.25)a
( ± 0.39)a ( ± 0.25)b ( ± 0.51)a ( ± 0.22)c
month old ( ± 0.38)c ( ± 0.82)b ( ± 0.86)a ( ± 0.12)d
Numbers in parenthesis are standard errors( ± SE); the same letters within the column indicate no significant difference among the varieties.
Fig. 3. Larval preference on choice condition toward the leaves of tomato and potato varieties on one and three month old leaves. Bar represent the standard error. The same letters above bars do not have any significant difference in mean (Tukey's test, P < .05). Fig. 5. Relation between the proportion of mined leaves and survival of the PTM to the adults for the PTM fed with tomato leaves from one month old plant (dark line) and three month old plant (dashed line). The points are the observed data. Tomato (V1-Dafnis, V2- Bangul, V3-Jujube) and potato (V4-Sumi).
Discussion Host suitability of herbivorous insect can be determined by the nutritional requirements and antibiosis and antixenois (Bernays and Graham, 1988; Awmack and Simon, 2002). Potato tube moth, Phthorimaea operculella (Zeller) as being the major host of potato also can inflict damage on other solanaceous crop like tomato. There are some reports that PTM can cause extensive damage to tomato rather than potato in some parts of the world (Juvik et al., 1982; Yathom, 1986; Gilboa and Podoler, 1994; Mulatu et al., 2006a, 2006b). When tomato leaves with potato were given as a choice for egg laying, the PTM preferred potato, nevertheless oviposition occurred on the leaves of tomato as found by the Mulatu et al. (2007). In no choice condition where we provide the tomato leaves for oviposition most of the eggs were laid on the interior of the container rather than in leaves of tomatoes. But some eggs are still laid on the surface of tomato. In case of potato, leaves were preferred for oviposition while in case of tomato container were preferred to lay eggs which Varela and Bernays, 1988 also observed during their experiments that soil was preferred for tobacco and tomato and foliage was preferred for potato. In the choice test, mostly PTM choose potato leaves for laying eggs except a few cases. Similar observation was made by other scientific study (Mulatu et al., 2007). In no choice test also PTM showed the same trend. They choose interior part of the container instead of tomato leaves provided. Difference in the oviposition may be due to the capability of female insects in detection of small variation of host plant related cues such as volatiles (Karlsson et al., 2009; Proffit et al., 2011) whereas trichome
Fig. 4. Pupal weight of Phthorimeaoperculella fed with leaves of difference crop varieties of either tomato or potato. Bar represent the standard error. The same letters above bars do not have any significant difference in mean.
(Dafnis) tomato varieties, percent larvae survived, percent pupation in Jujube variety was found to be 40, 38 and 36% respectively (Table 2). Fourth instar head capsule size did not differ significantly but found to wider in potato tuber fed PTM of 1.3 mm (F3, 36 = 1.27, p < .29) (Fig. 6A). Fourth instar wondering larval weight was significantly different among the variety, heaviest being the potato fed larva of about average of 11.2 mg followed by Bangul and Jujube (F3, 36 = 3.3, p < .001). Similarly weight of the pupa was also found significantly different among the variety heaviest being the potato fed larva of about average of 10.8 mg, lightest pupa being of Jujube (F3, 36 = 14.23, p < .001 (Fig. 6B).
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Table 2 Development period (day, Mean ± SE) of immature Phthorimaea operculella fed on different varieties of tomato fruits and potato tuber. Varieties
L duration
P duration
Total immature
L survival
P survival
Dafnis Bangul Jujube Potato (sumi)
15.06 18.37 17.65 13.44
7.32 7.37 7.57 7.16
24.09 27.58 27.11 22.44
68( ± 1.97)a 48( ± 2.38)b 40( ± 2.98)b 72( ± 1.46)a
64( ± 2.23)ab 48( ± 2.23)bc 38( ± 2.23)c 72( ± 2.23)a
( ± 0.39)c ( ± 0.27)a ( ± 0.31)b ( ± 0.24)d
( ± 0.18)a ( ± 0.20)a ( ± 0.23)a ( ± 0.16)a
( ± 0.39)c ( ± 0.32)a ( ± 0.26)b ( ± 0.21)d
Numbers in parenthesis are standard errors ( ± SE).The same letters within the column indicate no significant difference among the varieties; L = Larval, P-Pupal.
tomato. It occurred because some common volatile may trigger PTM to lay eggs on tomato (Bernays and Graham, 1988) leaves. An investigation of volatiles emitted by the tested host plants is important factors in oviposition preferences. In free choice for larval feeding most of the mines were found on potato leaflet followed by Dafnis variety in both one and three month old leaves. The Jujube, Cherry cultivar fed with the 3 months old leaves have longest development time with reduced pupal weight which may be due to the high amount of volatiles like tomatine which has insecticidal properties (Chowanski et al., 2016) and high number of trichome on older leaves (Gurr and McGrath, 2001). If herbivorous insects find better food, they can enhance their survival rates and shorten development times which are the indicators for better food quality (Awmack and Simon, 2002; Greenberg et al., 2002; Pereyra and Sanchez, 2006). Both larval and larva to adult development time on potato leaves were found shorter than on tomato leaves and it is in agreement with several other reports (Lopes and Vendramim, 2001; Mulatu et al., 2007). Our results showed that the older leaves have better larval performance on tomato leaves because young leaves have high saponin content than older leaves which has deterrent effect (Badenes-Perez et al., 2014). In fruit feeding bioassay, the performance for cherry type tomato (Jujube and Bangul) is inferior to potato and fresh market type tomato (Dafnis) and the high survival of PTM larvae was found in potato and onDafnis variety which is fresh market cultivar. The fresh market cultivar possesses the largest fruit, which might have provided more core tissue for the developing PTMlarva. This affords the developing larvae the opportunity to remain and complete their development within a single fruit. Leonardi et al. (2000) reported that cultivar, ripening stage and growing condition play a pivotal role in determining the amount of glycoalkaloid in tomato fruits. The longest duration to complete life cycle was for the cherry tomato where tomato glycoalkaloids called αtomatine could act as antibiosis component and wasfound in higher amount than in fresh market tomato (Mulatu et al., 2006b). In conclusion larvae could choose tomato leaves and complete its lifecycle on them in laboratory condition. Though, the performance of PTM on tomato was lower than potato, it could complete life cycle feeding tomato leaves or fruits. There is great threat of host shift and has damage potential to attack tomato variety.The possibility could manifest by the facts that the distribution of PTM has been expanded toward northern part of South Korea partly because of the change of climates in the peninsular and the cultivation area of tomato has increased for last few decades while potato cultivation is in declining. Potato tuber moths were caught in the pheromone traps installed in the area of tomato plantation where no potato was grown (Unpublished data, Aryal and Jung). Further careful monitoring of the host expansion of PTM would be required in tomato fields with its biochemical interaction.
Table 3 Two way analysis of variance on the oviposition choice of the PTM on crop variety and age of the crops. Source Choice condition Variety Plant age Interaction No choice condition Variety Plant age Interaction
Oviposition on leaves
Oviposition on container
0.0001 0.0001 0.0334
NA NA NA
0.0001 ns 0.0193
0.0001 Ns ns
Three tomato varieties and one potato variety, two age of plant leaves (one and three month, in case of potato one and two month), NA = Not available; ns = not significant (P ≤.005).
Fig. 6. Fourth instar head capsule size (A) and weight of the larvae and pupa (B) fed with different fruits of tomato and potato. Bar represent the standard error. The same letters above bars do not have any significant difference in mean.
Acknowledgement This work was supported by Basic Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (NRF-2018R1A6A1A03024862). SA would thank to Nepal Agricultural Research Council for the study leave.
and other leaves physical parameter also play role as antixenosis. Antixenosis refers modified behavior of an insect pest and usually is expressed as non-preference of the insect for a resistant plant compared with a susceptibleone. Some of the eggs still deposited on leaves of the 81
Journal of Asia-Pacific Entomology 22 (2019) 77–82
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Conflict of interest
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