Susceptibility of oriental fruit moth (Lepidoptera: Tortricidae) to two pyrethroids and a proposed diagnostic dose of esfenvalerate for field detection of resistance

Laboratory colonies of oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), were reared on 'Gala' apples (Malus pumila Mill.) and lima bean (Phaseolus lunatus L.) diet. Neonates were placed on wheat germ diet containing a range of concentrations of esfenvalerate or lambda-cyhalothrin; mortality was assessed after 96 h. For a long-term laboratory colony, LC50 values of esfenvalerate and lambda-cyhalothrin were 0.35 and 0.12 ppm, respectively, for progeny of insects reared on apples. For a colony established from Calhoun Co., IL, in 2007, LC50 values of esfenvalerate and lambda-cyhalothrin were 0.37 and 0.10 ppm, respectively, for progeny of insects reared on apples. LC50 values of these insecticides did not differ significantly for either colony when progeny of insects reared on lima bean diet were tested. We observed no consistent evidence of pyrethroid resistance in the Calhoun colony after laboratory culture for 21-23 generations. We described the dose-response relationship for esfenvalerate applied topically in 1 microl of acetone to male moths from the long-term laboratory colony and estimated the LD99 to be 0.022 microg per moth. Application of 0.022 microg of esfenvalerate per moth to approximately 600 male moths from two putatively susceptible populations resulted in mean survivorship approximately equal to the expected level of 1.0%. Application of the same dose to 374 field-captured moths from two Calhoun Co. orchards with histories of pyrethroid use resulted in mean survivorship of 9.4 and 82%. We propose that 0.022 microg of esfenvalerate in 1 microl of acetone can be used as a diagnostic dose for monitoring pyrethroid resistance in oriental ruit moth in the field.     

Toxicity of thiamethoxam and mixtures of chlorantraniliprole plus acetamiprid, esfenvalerate, or thiamethoxam to neonates of oriental fruit moth (Lepidoptera: Tortricidae)

To assess the toxicity ofthiamethoxam and three mixtures of insecticides to oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), we added the insecticides to diet and fed it to neonates of two laboratory colonies; mortality was assessed after 96 h. Thiamethoxam was much less toxic than insecticides previously tested. Five of six analyses of the joint action of chlorantraniliprole plus acetamiprid, esfenvalerate, or thiamethoxam indicated that toxicity was not independent and not correlated. For chlorantraniliprole plus acetamiprid, mortality was slightly lower than expected at low concentrations and greater than expected at high concentrations. For chlorantraniliprole plus esfenvalerate, mortality was less than expected at nearly all concentrations, suggesting antagonism despite the two compounds' different modes of action. For chlorantraniliprole plus thiamethoxam, observed mortality exceeded expected mortality at low concentrations, but this trend did not continue at higher concentrations. Although the null hypothesis of independent and uncorrelated toxicity was rejected for chlorantraniliprole plus acetamiprid and chlorantraniliprole plus thiamethoxam in three of four analyses, differences between observed and expected mortality were minor and inconsistent over the range of concentrations tested. We do not expect these mixtures to exhibit significant synergism or antagonism in the field. Apparent antagonism between chlorantraniliprole and esfenvalerate is particularly relevant because these insecticides (or chlorantraniliprole plus a different pyrethroid) may be used together in apples or peaches for control of oriental fruit moth and hemipteran pests. The effectiveness of each insecticide against oriental fruit moth might be reduced in such applications.     

Life stage toxicity and residual activity of insecticides to codling moth and oriental fruit moth (Lepidoptera: Tortricidae)

The codling moth, Cydia pomonella (L.), and oriental fruit moth, Grapholita molesta (Busck), are two key pests of apple (Malus domestica Borkh.) in North Carolina. Growers extensively relied on organophosphate insecticides, primarily azinphosmethyl, for > 40 yr to manage these pests. Because of organophosphate resistance development and regulatory actions, growers are transitioning to management programs that use new, reduced-risk, and OP-replacement insecticides. This study evaluated the toxicity of a diversity of replacement insecticides to eggs, larvae, and adults, as well as an assessment of their residual activity, to codling moth and oriental fruit moth. Laboratory-susceptible strains of both species were used for all bioassays. Fresh field-harvested apples were used as a media for assessing the ovicidal activity of insecticides. For larval studies, insecticides were topically applied to the surface of lima bean-based diet, onto which neonates were placed. Toxicity was based on two measures of mortality; 5-d mortality and development to adult stage. Ovicidal bioassays showed that oriental fruit moth eggs were generally more tolerant than codling moth eggs to insecticides, with novaluron, acetamiprid, and azinphoshmethyl having the highest levels of toxicity to eggs of both species. In contrast, codling moth larvae generally were more tolerant than oriental fruit moth to most insecticides. Methoxyfenozide and pyriproxyfen were the only insecticides with lower LC50 values against codling moth than oriental fruit moth neonates. Moreover, a number of insecticides, particularly the IGRs methoxyfenozide and novaluron, the anthranilic diamide chlorantriliprole, and the spinosyn spinetoram, provided equal or longer residual activity against codling moth compared with azinphosmethyl in field studies. Results are discussed in relation to their use in devising field use patterns of insecticides and for insecticide resistance monitoring programs.     

Prevalence and stability of insecticide resistances in field population of Spodoptera litura (Lepidoptera: Noctuidae) from Huizhou,Guangdong Province,China

The field population of Spodoptera litura from Huizhou, Guangdong Province, China was evaluated for resistance to 21 insecticides, including conventional and new chemistry insecticides. Extreme levels of resistance were observed to metaflumizone and emamectin benzoate with resistance factors of 234.1 and 183.3, respectively. Resistance to abamectin was also high (perhaps extremely high) and over 71.9-fold. The Huizhou population of S. litura possessed high resistance to deltamethrin (96.5-fold) and moderate resistance to beta cyfluthrin and lambda cyhalothrin but remained susceptible to bifenthrin. Moderate resistance to chlorantraniliprole (22.3-fold), endosulfan (22.2-fold), tebufenozide (10.7-fold) and thiodicarb (14.3-fold), and low-level resistance to fipronil, indoxacarb and spinosad were also reported in this population. This field population remained susceptible to acetamiprid, chlorfenapyr, chlorfluazuron, hexaflumuron, chlorpyrifos, pyridalyl and spinetoram. The stabilities of resistance to metaflumizone, emamectin benzoate, deltamethrin, chlorantraniliprole and endosulfan were evaluated, the resistance level decreased when the insecticide stress was removed, suggesting stop of the application of insecticides with high level resistance could be implemented into the resistance management. Because S. litura from Huizhou developed resistance to multiple insecticides, integration of different control practices, especially the rotation of insecticides with biocontrol agents, should be performed in the management of this pest. The results suggested the suspension of the application of insecticide to which S. litura had developed high level of resistance in order to mitigate the resistance status, and the use of the insecticides to which this pest remained sensitive, including spinetoram, pyridalyl, indoxacarb, hexaflumuron, chlorfluazuron, chlorfenapyr and bifenthrin, could be incorporated into the alternating application for resistance management.     

Host plant-induced changes in detoxification enzymes and susceptibility to pesticides in the twospotted spider mite (Acari: Tetranychidae)

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on lima bean plants were moved to cucumber, maize, or new lima bean plants (the latter being a control) and evaluated after 24 h or 7 d for changes in susceptibility to three pesticides and in levels of related detoxification enzymes. The largest and most consistent changes were observed in mites feeding on cucumber. Susceptibility of mites on cucumber to the synthetic pyrethroids bifenthrin and lambda-cyhalothrin was greater than that of mites reared on lima bean and maize after only 24 h on the plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to the organophosphate dimethoate than were mites on lima bean, but only after 7 d on the host. Susceptibility was inversely related to activities of both general esterase and glutathione S-transferase (GST) in mites on cucumber; general esterase and GST activities were 60 and 25% lower, respectively, than activities of twospotted spider mite on lima bean after 7 d of feeding. Mites on maize were slightly but significantly more susceptible than those on lima bean to bifenthrin, but not to lambda-cyhalothrin, after 7 d and to dimethoate after 24 h but not after 7 d. General esterase and GST activities in twospotted spider mite fed on maize for 24 h were 20 and 16% higher, respectively, than activities in twospotted spider mite on lima bean, but general esterase activity was 30% lower than lima bean-fed mites and GST was not different after 7 d. Thus, plant-induced changes in general esterase activity, perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in susceptibility of twospotted spider mite to several pesticides, particularly the synthetic pyrethroids. General esterases appear to play less of a role in the detoxification of the organophosphate insecticide dimethoate.     

玉米种子丸粒化包衣处理对草地贪夜蛾的防治效果

本研究明确了乙基多杀菌素和氯虫苯甲酰胺丸粒化包衣后对玉米种子的安全性和玉米幼苗对草地贪夜蛾的防治效果,为玉米苗期草地贪夜蛾防治提供新技术。首先在室内验证了乙基多杀菌素和氯虫苯甲酰胺拌土后对草地贪夜蛾的防治效果,又进行了种子丸粒化包衣处理,测定了丸粒化包衣方式下药剂对种子萌发的影响和对草地贪夜蛾的防治效果。结果表明,250 mg/kg的乙基多杀菌素和氯虫苯甲酰胺拌土处理后,草地贪夜蛾对14天的玉米苗的取食率分别为1.67%、5.01%,与对照组取食率27.02%差异显著。药种比为1:100和1:200的乙基多杀菌素和氯虫苯甲酰胺丸粒化包衣处理组与对照组的发芽率之间无显著差异。乙基多杀菌素和氯虫苯甲酰胺丸粒化包衣处理组在播种后第7天对草地贪夜蛾广州种群防治效果显著,其中药种比为1:100的乙基多杀菌素丸粒化包衣处理组致死率最高为89%;两药剂丸粒化包衣处理组在播种后第21天对草地贪夜蛾云南种群仍有较好防治效果,两个浓度的乙基多杀菌素丸粒化包衣处理对草地贪夜蛾的致死率均达100%。本研究表明玉米种子丸粒化包衣技术可有效防控玉米苗期草地贪夜蛾的危害。     

Laboratory rearing of lesser appleworm (Lepidoptera: Tortricidae)

The lesser appleworm, Cydia prunivora (Walsh), was reared successfully in the laboratory. Larvae of various instars were collected in the field from hawthorn fruit, Crataegus spp. Initially, immature apples served as the food source for the larvae in the laboratory. Rearing was conducted in a greenhouse and later in combination with a controlled environment room at 25 degrees C, 50-60% RH, and a photoperiod of 18:6 (L:D) h. Under these conditions, a generation required approximately 30 d. Fifty-six adult lesser appleworm moths emerged from the original field collected hawthorn fruits. After a decline in the number of the F1 generation to 39 moths, the colony on mature apples, increased to in excess of 10,000 moths by the fifth generation with a mean survival rate to adult of 68.0%. When production on immature apples was compared with that on four artificial diets, the most promising of the artificial diets was the lima bean-based diet currently used to rear the oriental fruit moth, Cydia molesta (Busck), with a mean survival rate of 46.4%. The other bean-based diets tested were not as satisfactory. Pear foliage was the preferred oviposition substrate of those tested, including apple and hawthorn foliage. No eggs were deposited on plain waxed paper or glass microscope slides; however, large numbers of eggs were deposited on waxed paper treated with a water extract of pear foliage and immature apples.     

马尾松毛虫抗阿维菌素种群的抗性机制及交互抗性

为探讨阿维菌素防治马尾松毛虫的抗性风险和抗性机制,本研究采用叶片浸药法测定了马尾松毛虫抗阿维菌素种群(AV)对多种杀虫剂的交互抗性及增效剂胡椒基丁醚(PBO)、磷酸三苯酯(TPP)和顺丁烯二酸二乙酯(DEM)对马尾松毛虫AV种群、秦岭接官亭种群(JGT)和敏感种群(S)的增效作用,并使用分光光度计测定了AV、JGT和S种群的羧酸酯酶(CarE)、谷胱甘肽转移酶(GST)和多功能氧化酶系(MFOs)活性。结果表明: 马尾松毛虫AV种群与甲氨基阿维菌素苯甲酸盐(抗性倍数RR₅₀=25.0)、毒死蜱(RR₅₀=19.0)和高效氯氟氰菊酯(RR₅₀=15.4)存在中等水平交互抗性,与溴虫腈存在低水平交互抗性(RR₅₀=8.1),与乙基多杀菌素、多杀菌素和氯虫苯甲酰胺不存在交互抗性。增效剂PBO与TPP对马尾松毛虫AV、JGT和S种群均有显著增效作用,DEM对马尾松毛虫AV、JGT和S种群均无显著增效作用。马尾松毛虫AV种群MFOs中细胞色素P₄₅₀含量(3.5倍)、细胞色素b₅含量(3.1倍)、O-脱甲基酶活性(4.1倍)和CarE活性(2.2倍)均显著高于S种群,AV种群GST活性与S种群不存在显著性差异。MFOs及CarE活性增强是马尾松毛虫对阿维菌素产生抗性的重要生化机制,推荐乙基多杀菌素、多杀菌素和氯虫苯甲酰胺与阿维菌素轮换使用防治马尾松毛虫。     

Functional and genetic characteristics of Chlorantraniliprole resistance in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth (Plutella xylostella) is a globally distributed and important economic pest, and it has developed resistance to all conventional insecticide classes used in the field. Chlorantraniliprole is a new chemical class of insecticide that acts as a conformation‐sensitive activator of the insect ryanodine receptor (RyR). In the present study, a field strain (16.3‐fold resistance to chlorantraniliprole) was collected in Korea and lab‐selected with chlorantraniliprole for more than one year. The resulting strain presented 2,157‐fold resistance to chlorantraniliprole. A point mutation (G4946E) in the RyR gene was observed at a high frequency in the resistant strain. Enzyme assays indicated that glutathione S‐transferase (GST) and P450 activity in the resistant strain were 2.4‐ and 1.96‐times higher than that of the susceptible strain, respectively. The expression of the RyR, GST (sigma, omega, and zeta) and CYP321E1 gene was higher in the resistant strain than in the susceptible strain. The F₁ progeny resulting from reciprocal crosses did not reveal maternal effects or a diamide‐susceptible phenotype, which suggests an autosomal nearly recessive mode of inheritance. In addition, we surveyed the susceptibility to 13 insecticides (3 diamides, 2 synthetic pyrethroids, 2 spinosyns, 1 organophosphate, 1 oxadiazine, 1 avermectin, and 3 others) in the chlorantraniliprole‐resistant strain. The resistant strain exhibited high cross‐resistance to flubendiamide (5,910 fold) and showed no cross‐resistance to spinetoram, spinosad, indoxacarb, and metaflumizone. These results can serve as an important basis for guiding the use of insecticides in the field.     

Susceptibility of Chrysochus auratus,a natural enemy of spreading dogbane,to insecticides used in wild blueberry production

Insect pest management in wild blueberry (Vaccinium angustifolium Aiton) usually involves insecticidal sprays, which may have detrimental effects on non‐target beneficial insects. Dogbane beetle (Chrysochus auratus Fabricius) (Coleoptera: Chrysomelidae) feeds almost exclusively on spreading dogbane (Apocynum androsaemifolium L.), an increasing weed problem in wild blueberry production. Because C. auratus is an important natural enemy of spreading dogbane, we assessed its susceptibility to several insecticides it may be exposed to during insect pest management. In laboratory bioassays, we found adult dogbane beetles were highly susceptible to field rates of phosmet (Imidan) and acetamiprid (Assail) by direct topical contact and ingestion of treated foliage, whereas no mortality was seen with spirotetramat (Movento) and chlorantraniliprole (Altacor). Topical applications of spinetoram (Delegate) did not cause significant mortality of beetles, but high mortality to beetles was found when they ingested spinetoram‐treated foliage. The results suggest that while some insecticides used in blueberry management will be hazardous to C. auratus, options are available that will cause little harm to this natural enemy.     

Insecticide susceptibility level and control failure likelihood estimation of Sub-Saharan African populations of tomato leafminer: Evidence from Burkina Faso

The South American tomato pinworm, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is a leafminer species currently considered as one of the major pests of fresh tomatoes around the world. The species settled in north Africa in 2007, before being observed in the entire continent. Widespread insecticide use has led to the emergence of resistant populations in South America and Europe, but no large-scale insecticide resistance assessment has been performed in Sub-Saharan Africa so far. In this study, we collected T. absoluta larvae from locations widely distributed in Burkina Faso, where the pest was first detected in 2016. Acute toxicity of the all available molecules in Burkina Faso was evaluated in the laboratory on F1 individuals, including acetamiprid, abamectin, spinosad, cypermethrin, chlorpyrifos, λ-cyhalothrin, deltamethrin, and Bacillus thuringiensis. No LC50 differences among T. absoluta populations were highlighted, except for Bacillus thuringiensis. Insects were still highly susceptible to abamectin [LC50 < 0.4 mg/L; Control failure likelihood (CFL) = −25%], spinosad (LC50 < 0.6 mg/L; CFL = 25%) and chlorpyrifos-ethyl (LC50 between 254 and 458 mg/L; CFL = −15%), but were less susceptible to acetamiprid (CFL ranging from 72% to 91%), cypermethrin (CFL = 80%), λ-cyhalothrin (CFL =79%), and deltamethrin (CFL ranging from 51% to 66%), with LC50 values for these insecticides ranging between 100 and 525 mg/L. Pending a proper communication strategy, we hope this work could help producers avoiding the most inefficient active substances.     

Direct trade-off between cyanogenesis and resistance to a fungal pathogen in lima bean (Phaseolus lunatus L.)

1.  Plants are simultaneously attacked by multiple herbivores and pathogens. While some plant defences act synergistically, others trade-off against each other. Such trade-offs among resistances to herbivores and pathogens are usually explained by the costs of resistance, i.e. resource limitations compromising a plant's overall defence.
2.  Here, we demonstrate that trade-offs can also result from direct negative interactions among defensive traits. We studied cyanogenesis (release of HCN) of lima bean (Fabaceae: Phaseolus lunatus ) and effects of this efficient anti-herbivore defence on resistance to a fungal pathogen (Melanconiaceae: Colletotrichum gloeosporioides ).
3.  Leaf tissue destruction by fungal growth was significantly higher on high cyanogenic (HC) lima bean accessions than on low cyanogenic (LC) plants. The susceptibility of HC accessions to the fungal pathogen was strongly correlated to reduced activity of resistance-associated polyphenol oxidases (PPOs) in leaves of these plants. LC accessions, in contrast, showed high PPO activity, which was correlated with distinct resistance to C. gloeosporioides .
4.  Experimentally applied, gaseous HCN reduced PPO activity and significantly increased the size of lesions caused by C. gloeosporioides in LC leaves.
5.  Field observations of a wild lima bean population in Mexico revealed a higher infection rate of HC compared to LC plant individuals. The types of lesions observed on the different cyanogenic plants in nature were similar to those observed on HC and LC plants in the laboratory.
6.   Synthesis. We suggest that cyanogenesis of lima bean directly trades off with plant defence against fungal pathogens and that the causal mechanism is the inhibition of PPOs by HCN. Our findings provide a functional explanation for the observed phenomenon of the low resistance of HC lima beans in nature.     

Insecticide,sugar, and diet effects on feeding and mortality in Rhagoletis indifferens (Dipt., Tephritidae)

The effects of spinosad bait and various insecticides, the presence of sugar in insecticides, and diet on feeding responses and mortality in western cherry fruit fly, Rhagoletis indifferens Curran (Dipt., Tephritidae), were determined. Numbers of feeding events on insecticides with sugar were greater than on insecticides alone, but there was only a small effect of diet on feeding responses to insecticides with sugar. Feeding durations on imidacloprid, thiamethoxam and acetamiprid with sugar were shorter than on sugar water and spinosad bait, as the neonicotinoids paralysed flies quickly. Flies that fed on sugar only (nitrogen‐starved) suffered higher mortalities when exposed to spinosad, thiamethoxam and azinphos‐methyl than to imidacloprid, acetamiprid and indoxacarb, and mortality in between these two groups of treatments when exposed to spinosad bait. Mortalities were greater when sugar was added to insecticides, and were higher in nitrogen‐starved than fully‐fed (yeast extract + sugar fed) flies. Flies that fed once on thiamethoxam were killed more quickly than those that fed once on spinosad bait and spinosad. Results suggest that thiamethoxam is comparable to spinosad in its effects on mortality, and that using it with sugar in bait may also have similar results as using spinosad bait or spinosad. One benefit of using thiamethoxam with sugar may be that it kills flies more quickly, before they can oviposit, than spinosad bait, although whether a fly will feed on it may depend on how much sugar or nitrogenous food it has eaten.     

Experience with methyl salicylate affects behavioural responses of a predatory mite to blends of herbivore-induced plant volatiles

Many natural enemies of herbivorous arthropods use herbivore‐induced plant volatiles to locate their prey. These foraging cues consist of mixtures of compounds that show a considerable variation within and among plant–herbivore combinations, a situation that favours a flexible approach in the foraging behaviour of the natural enemies. In this paper, we address the flexibility in behavioural responses of the predatory mite Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseiidae) to herbivore‐induced plant volatiles. In particular, we investigated the effect of experience with one component of a herbivore‐induced volatile blend: methyl salicylate (MeSA). We compared the responses of three groups of predatory mites: (1) those reared from egg to adult on Tetranychus urticae Koch (Acari: Tetranychidae) on lima bean plants (Phaseolus lunatus L. that produces MeSA), (2) those reared on T. urticae on cucumber (Cucumus sativus L. that does not produce MeSA), and (3) those reared on T. urticae on cucumber in the presence of synthetic MeSA. Exposure to MeSA during the rearing period (groups 1 and 3) resulted in an attraction to the single compound MeSA in a Y‐tube olfactometer. Moreover, exposure to MeSA affected the choice of predatory mites between two volatile blends that were similar, except for the presence of MeSA. Predators reared on lima bean plants preferred the volatile blend from T. urticae‐induced lima bean (including MeSA) to the volatile blend from jasmonic‐acid induced lima bean (lacking MeSA), but predators reared on cucumber preferred the volatile blend from the latter. Predatory mites reared on cucumber in the presence of synthetic MeSA did not discriminate between these two blends. Exposure to MeSA for 3 days in the adult phase, after rearing on cucumber, also resulted in attraction to the single compound MeSA. We conclude that a minor difference in the composition of the volatile blend to which a predatory mite is exposed can explain its preferences between two odour sources.     

Genetic, biochemical, and physiological characterization of spinosad resistance in Plutella xylostella (Lepidoptera: Plutellidae)

Bioassays (at generation G2) with a newly collected field population (designated MN) of Plutella xylostella (L.) (Lepidoptera: Plutellidae) from Multan, Pakistan, indicated resistance to spinosad, indoxacarb, deltamethrin, abamectin, and acetamiprid. At G2 the field-derived population was divided into two subpopulations, one was selected (G2 to G11) with spinosad (Spino-SEL), whereas the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G12, indicating that the observed resistance to each insecticide was unstable. For Spino-SEL, bioassays at G12 found that selection with spinosad gave a resistance ratio of 283 compared with MN at G2. The resistance to indoxacarb and acetamiprid in the Spino-SEL population increased to 13- and 67-fold, respectively, compared with MN at G2. The toxicity of deltamethrin to Spino-SEL was similar to its toxicity to the MN population at G2. This suggests that spinosad selection maintained the otherwise unstable resistance to the compound. In contrast, resistance to abamectin decreased significantly from G2 to G12 in Spino-SEL. Logit regression analysis of F1 reciprocal crosses between Spino-SEL and the susceptible Lab-UK indicated that resistance to spinosad was inherited as an autosomal, incompletely recessive trait. The spinosad resistance allele significantly delays the developmental time, reduced pupal weight, number of eggs laid, and number of eggs hatched compared with Lab-UK. Further analysis suggests Spino-SEL exhibited a significantly lower intrinsic rate of population increase (r(m)) to all other populations tested.     

Toxicity of seventeen insecticides to Camponotus sericeus (Hymenoptera: Formicidae)

The success of chemical control depends on toxicity of insecticides against insect pests. Camponotus sericeus is an important urban pest with the ability to cause substantial damage to wooden structures, but there is a lack of information on toxicity of insecticides against C. sericeus. To determine the insecticide toxicity, workers of C. sericeus were exposed to 17 insecticides from different classes: carbamate (methomyl, bendiocarb), organophosphate (chlorpyrifos, profenofos, temephos), pyrethroid (bifenthrin, deltamethrin, permethrin), neonicotinoid (acetamiprid, imidacloprid, thiamethoxam), avermectin (abamectin, emamectin), pyrrole (chlorfenapyr), phenylpyrazole (fipronil), and spinosyn (spinosad and spinetoram), via residual bioassay method. The LC₅₀ ranged from: 0.15 to 0.20 µg/vial for carbamates, 0.09 to 0.27 µg/vial for organophosphates, 0.09 to 0.44 µg/vial for pyrethroids, 0.02 to 0.67 µg/vial for neonicotinoids, 0.54 to 0.82 µg/vial for avermectins, 0.78 µg/vial for pyrrole, 0.62 µg/vial for phenylpyrazole, and 1.96 to 2.05 µg/vial for spinosyns. Overall, acetamiprid was the most toxic one among the tested insecticides followed by permethrin, temephos, profenofos, bendiocarb and methomyl, while spinosad and spinetoram were the least toxic insecticides. Considering the potential toxicity of different insecticides against C. sericeus, future studies could investigate the practical application of these insecticides in order to design an effective management plan.     

Mortality of a wireworm, Agriotes obscurus (Coleoptera: Elateridae), after topical application of various insecticides

Ten insecticides representing seven chemical groups were applied at various concentrations topically by using a Potter Spray Tower to evaluate their relative toxicities on the European wireworm Agriotes obscurus L. (Coleoptera: Elateridae). Wireworms were stored at 15 degrees C after exposure to organophosphate (OP) (chlorpyrifos, diazinon), pyrethroid (tefluthrin), thianicotinoid (thiamethoxam, clothianidin), chloronicotinoid (imidacloprid, acetamiprid), phenyl pyrazole (fipronil), organochlorine (lindane), and spinosyn (spinosad) insecticides, and their postapplication health was evaluated weekly for up to 301 d. LC50, LC90, LT50, and LT90 values were calculated for each chemical except acetamiprid, and compared with those of lindane, clothianidin, and chlorpyrifos. Wireworms exposed to OPs died or recovered more quickly (LT50 < 20 d, LT90 < 50 d), than those exposed to all other insecticides tested except tefluthrin (LT50 = 25.5 d, LT90 = 66.5 d). Wireworms exposed to sublethal concentrations of all neonicotinoids quickly became moribund after application but made a full recovery. Wireworms exposed to fipronil at concentrations near the LC90 value showed no intoxication symptoms for up to 35 d, and they did not recover after symptoms developed. For each chemical, increasing the concentration increased the time required for wireworms to recover but decreased the time required to kill wireworms. Fipronil was highly toxic to wireworms (LC50 = 0.0001%), but acetamiprid (LC50 = 1.82%), imidacloprid (LC50 = 0.83%), tefluthrin (LC50 = 0.23%), diazinon (LC50 = 0.54%), and spinosad (LC50 = 0.51%) were not. The toxicity of both clothianidin (LC50 = 0.07%) and thiamethoxam (LC50 = 0.17%) were similar to those oflindane (LC50 = 0.06%) and chlorpyrifos (LC50 = 0.10%).     

The interaction between host and host plant influences the oviposition and performance of a generalist ectoparasitoid

The successful development of parasitoids of herbivores depends on the quality of their host, which is often affected by the host plant. Therefore, a parasitoid’s oviposition decisions will directly depend on the host, but also on plant quality. Here, we investigated the direct effects of host species and the indirect effects of the host’s food plant on the oviposition decisions and performance of the gregarious ectoparasitoid Euplectrus platyhypenae Howard (Hymenoptera: Eulophidae). With a series of no‐choice experiments, we determined the oviposition and performance of the parasitoid on: (1) two caterpillar species, fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), and velvet armyworm, Spodoptera latifascia Walker, reared on maize (Zea mays L., Poaceae), (2) the same caterpillars reared on maize, bean (Phaseolus vulgaris L., Fabaceae), or squash (Cucurbita pepo L., Cucurbitaceae) leaves, and (3) S. latifascia caterpillars reared on leaves of wild and cultivated lima bean, Phaseolus lunatus L. All these insects and plants originate from Mesoamerica where they have coexisted for thousands of years in the traditional agricultural system known as Milpa in which maize, beans, and squash are planted together. We found that the preferred and best combination of host and host plant for parasitoid performance was S. frugiperda on maize. Parasitoids laid larger clutches, had higher survival, and more females and larger adults emerged from S. frugiperda reared on maize. However, when both caterpillar species were reared on squash, S. latifascia was the better host. Contrary to the literature, S. frugiperda was not able to develop on bean plants. Results from the lima bean experiment showed that parasitoid performance was best when S. latifascia was reared on leaves of cultivated compared to wild lima bean. These findings are discussed in the context of mixed cropping in which the ability of generalist parasitoids to switch among hosts and host plant species could be advantageous for pest management.     

High levels of resistance to chlorantraniliprole evolved in field populations of Plutella xylostella

Chlorantraniliprole is the first commercial insecticide from a new class of chemistry, the anthranilic diamides. Chlorantraniliprole provides an effective alternative insecticide for control of Plutella xylostella (L.) populations resistant to other insecticides. Baseline susceptibility to chlorantraniliprole for P. xylostella was surveyed previously from 16 geographical populations sampled from China during 2008-2009, and the median lethal concentrations (LC50s) varied among populations from 1.8- to 8.9-fold higher than the LC50 of a susceptible strain (Roth). In the present work, 20 field populations of P. xylostella sampled in 2010-2011 from China were tested with laboratory bioassays to determine if resistance to chlorantraniliprole had evolved in the field. The LC50s of the 14 populations from northern China ranged from 1.7- to 5.4-fold compared with the LC50 of Roth, which indicates these populations remain reasonably susceptible to chlorantraniliprole. However, the LC50s of the six populations from southern China (Guangdong Province) were 2.6-, 12-, 18-, 81-, 140-, and 2,000-fold higher than the LC50 of Roth. The results showed that high levels of resistance to chlorantraniliprole had evolved in field populations from Guangdong Province of southern China. Intensive use and misuse of chlorantraniliprole may be responsible for the rapid evolution of high-level resistance in P. xylostella in this region. The implementation of resistance monitoring plans and resistance management strategies is urgently needed in China to preserve susceptibility to chlorantraniliprole in P. xylostella.     

Laboratory studies to elucidate the residual toxicity of eight insecticides to Anystis baccarum (Acari: Anystidae)

Anystis baccarum (L.) [=Anystis agilis (Banks)] (Acari: Anystidae) is a common predatory mite recently identified in apple (Malus spp.) orchards and in vineyards (Vitus spp.) in Québec, Canada. Studies of its susceptibility to pesticides used in these crops need to be carried out to encourage integrated pest management programs. A laboratory evaluation of methoxyfenozide, acetamiprid, thiamethoxam, imidacloprid, spinosad, phosmet, carbaryl, and lambda-cyhalothrin showed that residues of lambda-cyhalothrin, phosmet, and carbaryl were highly toxic in 48-h petri dish bioassays. The field rate of lambda-cyhalothrin is 0.0184 g (AI) /liter, which is 26-fold the estimated LC50 of 0.0007 g (AI) /liter) for this predator. The field rate for phosmet is 0.6000 g (AI) /liter, which is 118-fold the LC50 for phosmet, which is 0.0051 g (AI) /liter), and the field rate for carbaryl is 1.960 g (AI) /liter, which is 784-fold the estimated LC50 of 0.0025 g (AI) /liter). Five other insecticides, methoxyfenozide, acetamiprid, thiamethoxam, imidacloprid, and spinosad, were evaluated and found to be nontoxic.