Effects of triflumuron on the two-spotted spider mite,Tetranychus urticae (Acari: Tetranichydae)

The effects of triflumuron on the mortality, fecundity, and fertility of the two-spotted spider mite, Tetranychus urticae, were evaluated in the laboratory. No differences in toxicity for larvae, protonymphs and deutonymphs were observed, but immature stages were 3.8-times more susceptible than adults at the LC₅₀. The compound exhibited a direct contact ovicidal activity influenced by eggs age. 48–72 hold eggs were significantly more sensitive than eggs of the other age classes. No hatch inhibition was observed in eggs laid by treated adult females using a sublethal dose at two physiological times (<12 and 48–72h old). However, fecundity decreased in younger treated females, but it increased in the older-ones. The toxicity for immatures and eggs, and the sublethal effects described suggest that triflumuron could be an interesting incorporation in integrated pest programs of T. urticae. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acaricidal activity and sublethal effects of an oxymatrine-based biopesticide on two-spotted spider mite (Acari: Tetranychidae)

Lethal and sublethal effects of the biopesticide Kingbo (oxymatrine 0.2 % + psoralen 0.4 %) on the two-spotted spider mite (Tetranychus urticae Koch) were investigated in laboratory bioassays. The biopesticide was applied to bean leaf discs or primary leaves by using a Potter spray tower. Acute toxicity tests showed no significant ovicidal action: toxic effect (LC₅₀ = 55.49 μl/l) was the result of a residual activity against larvae that hatched from the treated eggs. Preovipositional females and female teleiochrysales showed similar susceptibility (LC₅₀ = 52.68 and 59.03 μl/l, respectively), whereas larvae, protonymphs and female deutonymphs were the most susceptible stages (LC₅₀ = 6.88, 13.03, and 8.80 μl/l, respectively). In a choice test, females preferred the untreated halves of leaves over the halves treated with 2,000, 1,000, and 500 μl/l in the first 24 h, and their oviposition in those treatments was significantly greater on the untreated halves after 24 and 48 h, as well as the summed oviposition over 72 h. Viability and reproduction of survivors, as well as population growth, were strongly affected after the treatments of preovipositional females and female teleiochrysales with 100, 50 and 25 μl/l. On the other hand, sublethal effects on the females that survived treatment at the egg stage or reached adulthood from the eggs laid on the treated surface (treatments with 50 and 25 μl/l) were significantly weaker. Acaricidal and sublethal effects of the biopesticide Kingbo were discussed as a starting point for further research aimed to improve management of T. urticae populations. Regulatory issues and safety concerns regarding further commercialization of this biopesticide are addressed as well.     

Repellency and toxicity of extract from Francoeria crispa (Forsk.) to Eutetranychus orientalis (Klein) (Acari: Tetranychidae)

Laboratory bioassays were conducted to characterise the activity of the extract Francoeria crispa (Forsk.) (Family: Compositae) against the citrus brown mite, Eutetranychus orientalis (Klein). Ethyl acetate was tested for preparing the crude extract of F. crispa. The extract was tested for its toxicity against eggs and adult females of the pest E. orientalis. Ethyl acetate extract of F. crispa affected the behaviour, toxicity and fecundity of females under laboratory conditions. The extract had similar toxic effects on egg stage and adult females of E. orientalis (LC₅₀ = 0.00050 g/ml), respectively. Leaf discs treated with increasing concentrations of ethyl acetate extract of F. crispa showed a high percentage of repellency (97.45%), respectively. Treated females with LC₅₀ concentration of ethyl acetate extract showed a higher remarkable percentage of mortality as well as a reduction in the total number of eggs laid during 7 days. Ten isolated fractions of ethyl acetate crude extract from F. crispa were detected. The results clearly indicate that the isolate number (10) was the most toxic isolate on eggs and females of E. orientalis (LC₅₀ = 0.00014 and 0.000125 g/ml), respectively.     

Sublethal effects of spirodiclofen on the demographic parameters of Tetranychus urticae Koch (Acari: Tetranychidae)

Abstract

The two-spotted spider mite, Tetranychus urticae Koch is one of the most common pests of agricultural crops. The use of sublethal doses can reduce the need of pesticides and prevent pests’ resistance, which is an important step in integrated pest management and safely controlling this pest. The sublethal effects (LC₅, LC₁₅ and LC₃₅) of spirodiclofen on demographic parameters of T. urticae based on the age-stage, two-sex life table theory were investigated under laboratory conditions [25?±?2?°C, 60?±?5% RH and 16:8 (L:D) h]. The longevity, total life span, oviposition period and total fecundity reduced after exposure to LC₁₅ and LC₃₅. Oviposition period ranged from 5.64 to 10.92?days. The gross reproduction rate (GRR), net reproductive rate (R₀) and the finite rate of increase (λ) of the mites treated with LC₁₅ and LC₃₅ were inferior to the results when treated with LC_5, and control. The values of intrinsic rate of increase (r) was 0.2209?day^?1 in the control and this was reduced to 0.1714?day^?1 in LC₃₅. Based on these results, considering the negative impact of spirodiclofen on the population growth of T. urticae, this acaricide can be helpful to achieve an efficient control for T. urticae in frame of integrated pest management.     

Predation-related odours reduce oviposition in a herbivorous mite

When adult females of the herbivorous mite, Tetranychus urticae, were exposed to the predatory mite, Phytoseiulus persimilis, they laid fewer eggs than females that had not been exposed to P. persimilis when transferred onto a new leaf patch. However, when T. urticae females were exposed to either products of P. persimilis or artificially damaged conspecific eggs on a leaf patch, the number of T. urticae eggs on a new leaf patch did not differ significantly from the control. The reduced oviposition was neither due to the feeding activity on the leaf patch with P. persimilis nor to that on the new leaf patch. There was also no significant difference between the number of T. urticae eggs produced on a new leaf patch following exposure to the odours of a neighbouring leaf patch where there had previously been either P. persimilis or T. urticae adults. However, female T. urticae that had been exposed to odours from neighbouring leaf patches on which both T. urticae and P. persimilis had been placed produced significantly fewer eggs on a new leaf patch than those that had not been exposed to such odours. Neither odours from neighbouring intact leaf patches on which T. urticae eggs were preyed on by P. persimilis, nor odours from a neighbouring Parafilm patch on which T. urticae was preyed on by P. persimilis affected the oviposition of T. urticae. These data suggest that the presence of T. urticae, P. persimilis and a leaf patch are needed for the emission of odours to reduce oviposition in T. urticae.     

Functional response ofAllothrombium pulvinum deutonymphs (Acari: Trombidiidae) on two-spotted spider mites (Acari: Tetranychidae)

Functional responses of deutonymphs of the predatory mite,Allothrombium pulvinum Ewing, on eggs and adult females of two-spotted spider mite,Tetranychus urticae Koch, were determined in the laboratory. Predation experiments were conducted on lima bean leaf discs over a 24-h period at 25±2°C, 30–50% RH and 24L: 0D photoperiod. Prey densities ranged from 10 to 120T. urticae eggs per disc or 2 to 32 adult females per disc.Allothrombium pulvinum deutonymphs were more effective againstT. urticae eggs than its adult females. The role ofA. pulvinum deutonymphs in integrated and biological pest control is discussed.     

Sublethal effects of spirodiclofen on life history and life-table parameters of two-spotted spider mite (<Emphasis Type="Italic">Tetranychus urticae</Emphasis>)

Laboratory bioassays were conducted to evaluate the effects of spirodiclofen on life history and life-table parameters of two-spotted spider mite (Tetranychus urticae Koch) females treated at pre-ovipositional period with a series of acaricide concentrations starting with the concentration discriminative for eggs and immatures i.e. the lowest concentration that causes 100% mortality of those stages. After a 24 h exposure, the proportion of females that survived treatments was 0.71 (6 mg/l), 0.51 (12 mg/l), 0.41 (24 mg/l), 0.30 (48 mg/l) and 0.25 (96 mg/l). At the end of the trial, the survival rate of females treated with the lowest concentration was significantly lower than the survival rate of untreated females but it remained above that of females treated with higher concentrations. Total fecundity/fertility significantly decreased as concentrations of spirodiclofen increased. Viable eggs were laid by females treated with 6, 12 and 24 mg/l, and total fertility was reduced by 42, 84 and 97%, respectively. Compared with control, the gross fecundity/fertility of the treated females was significantly reduced throughout the trial, except in females treated with 6 mg/l. All concentrations caused a significant reduction in the net fecundity/fertility throughout the trial. The females treated with 12 mg/l had significantly reduced net reproductive rate (R ₀ = 6.45), compared to females treated with 6 mg/l (R ₀ = 23.35) and to untreated females (R ₀ = 28.92); there was no significant difference between the last two treatments. The intrinsic rate of increase (r _m ) and finite rate of increase (λ) were significantly reduced in treated females (r _m = 0.141, λ = 1.156 and r _m = 0.214, λ = 1.232; 12 and 6 mg/l, respectively), compared to control (r _m = 0.251, λ = 1.276). The reduction was significantly greater in females treated with the highest concentration. As a result of the lowered r _m , the doubling time in treated females was significantly extended. Sublethal effects of spirodiclofen and its impact on T. urticae management are discussed.     

Predator avoidance in phytophagous mites: response to present danger depends on alternative host quality

We studied whether volatiles released by putative host plants affect the antipredator response of an herbivorous mite, Tetranychus urticae, when the patch was invaded by Phytoseiulus persimilis. Tetranychus urticae laid a lower number of eggs on tomato leaves than on lima bean leaves, suggesting that lima bean is a preferred host food source for T. urticae. In addition, T. urticae preferred lima bean plant volatiles to tomato plant volatiles in a Y-tube olfactometer test. To investigate the antipredator response of T. urticae, we examined the migration of T. urticae from a lima bean leaf disc to a neighbouring leaf disc (either a tomato or lima bean leaf disc) when ten predators were introduced into the original lima bean disc. A Parafilm bridge allowed for migration between the leaf discs. No migrations occurred between leaf discs when there were no predators introduced to the original leaf disc. However, when predators were introduced migrations did occur. When the neighbouring leaf disc was upwind of the original disc, the migration rate of the mite from original lima bean leaf disc to a neighbouring tomato leaf disc was significantly lower than that to a neighbouring lima bean leaf disc. By contrast, when the neighbouring leaf disc was downwind of the original leaf disc, there was no difference in the migration rates between lima bean leaf discs and tomato leaf discs. The number of T. urticae killed by P. persimilis for each treatment was not different, and this clearly shows that the danger was the same in all treatments regardless of the decision made by T. urticae. From these results, we conclude that T. urticae change their antipredator response by evaluating the difference in host plant volatiles in the patch they inhabit.     

Phytochemical,acaricidal and biological activity of Dodonaea viscosa L. against the two spotted spider mite Tetranychus urticae Koch

Alcohol extract, saponins and flavones fractionated from Dodonaea viscosa leaves were tested for their acaricidal activity against the adult females of Tetranychus urticae Koch. It was found that crude alcohol extract was more potent than the isolates obtained. At LC₅₀ and LC₉₀ levels, the crude extract ranked the first. All the biotic factors are significantly affected. The fecundity was seriously reduced however, the hatchability of eggs was not affected. Two flavonoids were identified as Querectin 3–0-glucose 7-0-rhamnoside and the other as Querectin 3-0 arabinose 7-0 rhammoside from the ethyl acetate fraction of the alcohol extract.     

Functional response of Neoseiulus barkeri Hughes on two-spotted spider mite (Acari: Tetranychidae)

Generalist predatory mites are the common phytoseiid fauna in many agroecosystems, but little attention has been paid to their potential as biological control agents. In this study, we determined the functional responses of adult females of the generalist predator Neoseiulus barkeri Hughes on eggs, larvae, and adults of the two-spotted spider mite, Tetranychus urticae Koch, in the laboratory. Predation experiments were conducted on pepper leaf discs over a 24 h period at 25±1°C, 70–80% RH and 16L:8D photoperiod. Prey densities ranged 5 to 80 eggs, or 5 to 40 larvae, or 1 to 8 female adults of T. urticae per disc. The predation rate of N. barkeri adult females on T. urticae eggs was the same as on its larvae, but the predation rate on adult females was much lower. The role of generalist predatory mites in integrated and biological control of greenhouse pests was discussed.     

Effects of B-azolemiteacrylic on life-history traits and demographic parameters of two-spotted spider mite,Tetranychus urticae (Acari: Tetranychidae)

The present study was conducted to evaluate sublethal effects of B-azolemiteacrylic on the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Female adults of T. urticae were exposed to LC₁₀ and LC₃₀ of the acaricide, and the effects on treated females and their offspring were evaluated. The results showed that the fecundity of F₀ female adults treated with LC₁₀ and LC₃₀ of B-azolemiteacrylic was reduced by 30.9 and 39.2%, respectively. Longevity and oviposition period of the females were significantly reduced as well. The developmental duration of egg and deutonymph stage of the F₁ generation were not significantly different from that of the control. The protonymph stage after LC₃₀ treatment lasted significantly longer, whereas the larva, deutonymph and female stage were significantly shorter than the control. The oviposition period of the F₁ generation was significantly shortened, the fecundity of each female decreased significantly, and the ratio of female-to-male was reduced too. Moreover, the average generation period of T. urticae after LC₁₀ and LC₃₀ treatments was shorter than that of the control, and the net production rate (R₀), intrinsic rate of increase (r_m) and finite rate of increase (λ) were all reduced by 33.3, 7.5 and 1.9% (LC₁₀ treatment) and by 51.3, 14.8 and 3.6% (LC₃₀ treatment), respectively. The population doubling time was prolonged by 7.5 and 14.8% after LC₁₀ and LC₃₀ treatments, respectively, compared with the control. These results indicate that B-azolemiteacrylic may effectively inhibit the development rate of the F₀ and F₁ populations of T. urticae, which will help design integrated strategies for the comprehensive control of T. urticae and rational use of pesticides in the field.

     

Sublethal effects of essential oil of Cinnamomum zeylanicum Blume on life expectancy (ex) and age-specific fertility (mx) of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

Two-spotted spider mite, Tetranychus urticae Koch, is one of the most important pests of agricultural products that have a global distribution. Now, the control is dependent on the use of chemical pesticides. The effects of the sublethal concentrations (LC₁₀ and LC₂₅) of the essential oil of Cinnamomum zeylanicum were evaluated on some parameters of the life table of the pest, at the constant temperature of 30?°C, relative humidity of 40?±?5% and photoperiod of 16L: 8D. Our results showed that the essential oil of cinnamon is effective on female adult stage. Lethal concentration at which 50% mortality (LC₅₀) for the essential oils is from C. zeylanicum on female adult mite was 23.39?μl/L air. Sublethal concentrations of the essential oil of C. zeylanicum also impair the natural biology of the mite. Concentrations of sublethal of essential oil decreased age-specific fertility (m_x) of T. urticae compared with the control. Sublethal concentrations (LC₁₀ and LC₂₅) have reduced the life expectancy (e_x) in egg stage. Sublethal effects of the essential oil of C. zeylanicum and its impact on T. urticae management are discussed.     

Sublethal effects of Thymus vulgaris essential oil on life-table parameters of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

Sublethal effects of Thymus vulgaris were investigated on life-table parameters of Tetranychus urticae Koch (Acari: Tetranychidae) in the laboratory conditions at 25?±?1?°C, 70?±?10% RH and a 14:10?h (L:D) photoperiod. Bioassay was conducted to assess the effect of different concentrations of T. vulgaris essential oil on two-spotted spider mite. LC₅₀ and LC₂₀ of T. vulgaris on T. urticae were calculated as 18.86 and 6.24?μl/litre air for 24?h after treatment. In the sublethal effects, after 24?h exposure to LC₅₀ concentration, mortality, fecundity and longevity of the females that survived from treatment were determined. Results showed that T. vulgaris caused significant reductions in fecundity and longevity of adults. Life-table assay indicated that the intrinsic rate of increase (r _m), net reproductive rate (R ₀), finite rate of increase (λ), mean generation time (T), significantly reduced in treated females compared to control. These results suggest that T. vulgaris could be incorporated in integrated pest management programmes of T. urticae.     

八种杀虫剂对韭菜迟眼蕈蚊发育和繁殖的亚致死效应

用胃毒触杀法确定8种常用杀虫剂对韭菜迟眼蕈蚊Bradysiaodoriphaga 3龄幼虫的LC₂₀和LC₅₀剂量后,以其LC₂₀分别处理3龄幼虫,将存活幼虫正常饲养,测定该剂量药剂对韭菜迟眼蕈蚊化蛹率、蛹重、羽化率,成虫存活率、雌雄比、单雌产卵量及卵孵化率等指标的影响。结果表明:毒死蜱等4种药剂的影响较显著,其影响程度由高到低依次为毒死蜱＞辛硫磷＞阿维菌素溴虫腈;而另4种药剂丙硫克百威、灭多威、丁硫克百威和吡虫啉则影响不显著。此外也测定了用后4种药剂LC₅₀剂量处理的存活试虫的上述生物学指标,结果表明：除化蛹率和羽化率较对照降低且差异显著外,其他生物学指标与对照处理无明显变化。     

The Predatory Mite Phytoseiulus persimilis Adjusts Patch-leaving to Own and Progeny Prey Needs

Integration of optimal foraging and optimal oviposition theories suggests that predator females should adjust patch leaving to own and progeny prey needs to maximize current and future reproductive success. We tested this hypothesis in the predatory mite Phytoseiulus persimilis and its patchily distributed prey, the two-spotted spider mite Tetranychus urticae. In three separate experiments we assessed (1) the minimum number of prey needed to complete juvenile development, (2) the minimum number of prey needed to produce an egg, and (3) the ratio between eggs laid and spider mites left when a gravid P. persimilis female leaves a patch. Experiments (1) and (2) were the pre-requirements to assess the fitness costs associated with staying or leaving a prey patch. Immature P. persimilis needed at least 7 and on average 14±3.6 (SD) T. urticae eggs to reach adulthood. Gravid females needed at least 5 and on average 8.5±3.1 (SD) T. urticae eggs to produce an egg. Most females left the initial patch before spider mite extinction, leaving prey for progeny to develop to adulthood. Females placed in a low density patch left 5.6±6.1 (SD) eggs per egg laid, whereas those placed in a high density patch left 15.8±13.7 (SD) eggs per egg laid. The three experiments in concert suggest that gravid P. persimilis females are able to balance the trade off between optimal foraging and optimal oviposition and adjust patch-leaving to own and progeny prey needs.     

Some factors affecting reproduction and sex-ratio of the predacious mite Amblyseius deleoni (Muma and Denmark) (Acari: Phytoseiidae)

Abstract

Several factors were examined to determine their effect on the reproduction and sex ratio in the predacious mite Amblyseius deleoni (Muma and Denmark), in the laboratory. The factors investigated included multiple matings, duration of copulation, capacity of male for mating in excess of females and age of mating females and males. The factors included also, the host plant leaf texture, food deprivation during immature and adult stages, and prey (Tetranychus urticae Koch) density. The results indicated that females of A. deleoni require multiple matings to maximize their reproductive potential, also when copulation was allowed for increasing periods of time, there was a gradual increase in total egg production and oviposition period. A male showed a high reproductive ability for more than 15 days and was able to mate more than once in excess of females. Age of females has an influence on fecundity and sex ratio; old females decreased egg production and produced proportionally more male progeny compared with young females. Similarly, the highest number of eggs deposited per female A. deleoni was reported, when female mated with a young male (0-day old). In addition, males of A. deleoni (at any age) were able to inseminate the females. Results from host plant leaf texture indicated that guava leaf gave the highest reproduction rate, while the fig leaf gave the least female fecundity. Neither the reproductive rate nor the sex ratio of the progeny of females crossed by normal or experimental males had been influenced by the food deprivation during immature stages. A significant lower fecundity was recorded on female's A. deleoni when exposed to different food deprivation programmes during adult stage. The number of eggs laid by the predator female increased with increasing prey density of T. urtice to a maximum of 2.04 eggs deposited per day at a prey density of 30 protonymphs of T. urticae as a prey. As the level of prey density was increased, there was a shift in sex ratio towards an increased proportion of females.     

Sublethal effects of abamectin on the biological performance of the predatory mite, <Emphasis Type="Italic">Phytoseius plumifer</Emphasis> (Acari: Phytoseiidae)

Traditionally estimating pesticide effects by measuring only lethal effect may underestimate the total negative effect on beneficial arthropods and sublethal effects should be assessed to estimate the total effect of their applications. In this study, sublethal effect of the acaricide abamectin (Vermectin^® 1.8% EC, Giah, Iran) on the predatory mite Phytoseius plumifer (Canestrini &; Fanzago) (Acari: Phytoseiidae) fed on Tetranychus urticae Koch was assessed in laboratory conditions. The adult predators were exposed to the residues of the acaricide on fig leaves and the LC₅₀ value was determined based on a concentration–response analysis. The results showed that sublethal concentrations (LC₁₀, LC₂₀ and LC₃₀) of abamectin severely affected the fecundity and longevity of the treated females of P. plumifer. Furthermore, reproductive and life table parameters of the subsequent generation were affected. The results indicated that adverse effects of abamectin on population growth of P. plumifer were significant, so the results from this study can be used to develop approximate guidelines for the use of abamectin in order to minimize their impact on P. plumifer and related natural enemies.     

Antipredator responses in Tetranychus urticae differ with predator specialization

The behavioural response of Tetranychus urticae to chemical cues from specialist predatory mites, Phytoseiulus persimilis, or generalist predatory bugs, Orius majusculus, on either bean or strawberry was studied in experimental arenas. Predators were placed on the leaf disc for 24 h and removed before T. urticae females were introduced. After 24 h, prey fecundity (number of eggs laid) and dispersal (number of prey drowned in the water barrier) were assessed. Chemical cues from the specialist predator resulted in reduced prey fecundity, significantly different from the generalist predator and control treatments. No interaction effect was found between plant species and prey fecundity, while significantly more eggs were laid on bean than on strawberry. Predator cues irrespective of predator specialization resulted in more prey dispersal than in the control. Findings emphasize the importance of specialization in the predator species complex for the degree and type of antipredator responses and resulting biological control.     

Survival,fecundity and reproductive recovery period of Neoseiulus californicus (McGregor) during long-term preservation on maize pollen and after switch to Tetranychus urticae Koch

Immature stages of the predacious mite, Neoseiulus californicus (McGregor) were reared on eggs of Tetranychus urticae Koch and gravid females were preserved on pollen of maize, Zea mays L. for 30, 45, 60 and 80?days. Afterwards, pollen was shifted to prey eggs for 15?days to evaluate their survival, fecundity and reproductive recovery period. All adult females of N. californicus survived the different maintenance periods and the following 15?days after pollen switch to the prey. Furthermore, predator females consuming pollen produced relatively few eggs during the preservation experiments, while they laid the majority of eggs during 15?days after pollen change to T. urticae without a second mating. The fecundity during the conservation periods significantly increased with increasing the maintenance period, whereas the reverse occurred subsequent to the shift to the prey. Moreover, the reproductive recovery period after the switch to T. urticae was inversely associated with the preservation period. Therefore, maize pollen is a useful alternative food for long-term survival and for maintaining fecundity of N. californicus females to exhibit an adequate numerical response to T. urticae at a subsequent time.     

Sublethal effects of hexaflumuron on development and reproduction of the diamondback moth,Plutella xylostella (Lepidoptera: Yponomeutidae)

Abstract Effects of hexaflumuron at 10% lethal concentration (LC₁₀) and LC₂₅ on development and reproduction parameters of the diamondback moth, Plutella xylostella (Linnaeus, 1753) (Lep.: Yponomeutidae) were investigated. Estimated LC₅₀, LC₁₀ and LC₂₅ values of leaf dip bioassay of hexaflumuron on the third instar larvae of the P. xylostella were 1.48, 0.59 and 0.91 mg/L, respectively. Hexaflumuron decreased pupal weight in the parent generation at sublethal concentrations but in the offspring generation, this effect was not observed. Sublethal concentrations increased egg, first and second larval instar and pupa developmental time and shortened life span of adults, but did not change the third and fourth larval instars and pre‐pupa developmental period. Also fecundity of females reduced significantly but hatchability of treatments and control were similar. Survival rate of pre‐adult stages declined significantly at LC₂₅ concentration. Reproduction parameters such as reproductive rate (R₀) and intrinsic rate of increase in sublethal concentrations were significantly lower compared with control, but gross reproduction rate (GRR) at the LC₁₀ concentration was increased and it could be hormoligosis. Also hexaflumuron significantly increased doubling time (Dt). We conclude that the sublethal effects of hexaflumuron might exhibit significant effects on the population dynamics of P. xylostella.