Note: Systemic effects of a spinosad insecticide onLiriomyza huidobrensis Larvae

In an effort to expand the spectrum of larvicides effective againstLiriomyza huidobrensis (Blanchard), the effect of spinosad was studied on the mortality of the leafminer under laboratory conditions. Bean plants infested with various leafminer stages (egg through third instar) were treated by dipping leaves in a liter of water containing 24, 48 or 96 mg a.i. spinosad or by drenching the soil of plants with 200 ml of water containing 12 mg, 24 mg or 48 mg a.i. spinosad. In general, leaf dipping was more efficacious and adverse effects were observed sooner than with soil drench. All concentrations of spinosad significantly reduced the number of adults that emerged except leaf dip of third instar; only the highest concentration caused significant reduction of pupae and adults. Spinosad would likely be a valuable insecticide for control of the pea leafminer,L. huidobrensis. http://www.phytoparasitica.org posting Nov. 4, 2005.     

3种环境友好型药剂对西花蓟马的室内毒力与田间防效

测定了3种杀虫剂对西花蓟马的室内毒力和田间防效。室内生物测定结果表明,多杀菌素、甲氨基阿维菌素苯甲酸盐、阿维菌素对西花蓟马成虫的LC50值为0.050～2.887mg/L,对西花蓟马若虫的LC50值为0.040～0.457mg/L;田间药效试验表明,田间防治西花蓟马时推荐使用剂量(防效>80%)分别为:2.5%多杀菌素悬浮剂30～60g/667m2,1%甲氨基阿维菌素苯甲酸盐乳油30～60g/667m2,1.8%阿维菌素乳油不可低于75g/667m2。     

Note: Toxicity of some insecticides onBracon hebetor under laboratory conditions

Insecticides which were environmentally friendly and the least toxic, were screened against a laboratory strain ofBracon hebetor (Say) (Hymenoptera: Braconidae) for their suitability for release in IPM of cotton. Concentrations ranging from 1 to 1000 ppm of the formulated insecticides in acetone were applied in glass vials and also by a leaf method, whereby cotton leaves were dipped in aqueous solutions of the same concentrations of insecticides. Adult parasitoids were exposed in both methods. According to the LC₅₀ at 24 h exposure, Λ-cyhalothrin and spinosad were the most (7 and 5 ppm) and least (263 and 225 ppm) toxic in the vial and the leaf method, respectively, toB. hebetor. The possible use of the parasitoid for IPM of cotton is discussed. http://www.phytoparasitica.org posting July 20, 2006.     

Laboratory and field evaluation of spinosad against the gypsy moth,Lymantria dispar

The toxicity of the naturally derived insecticide spinosad was tested against the gypsy moth, Lymantria dispar. Bioassays using red oak leaf disks, treated with spinosad in a Potter spray tower, yielded an LC₅₀ value of 0.0015 µg AI cm⁻² (3‐day exposure; 13‐day evaluation; 2nd instar larvae). Applied to foliage to run‐off in the laboratory (potted red oak seedlings) and the field (4 m‐tall birch trees), spinosad effectively controlled 2nd instar larvae at concentrations ranging from 3 to 50 mg litre⁻¹. Toxicity in the laboratory, and efficacy and persistence in the field, were comparable to those achieved with the insecticide permethrin. Laboratory studies supported field observations that control was achieved in part by knockdown due to paralysis. In addition, laboratory results demonstrated that crawling contact activity may play an important role in field efficacy; 50% of treated larvae were paralyzed 16 h after a 2‐min crawling exposure to glass coated with a 4 mg litre⁻¹ spinosad solution. © 2000 Society of Chemical Industry     

Activity of abamectin against larval stages of Spodoptera littoralis boisduval and Heliothis armigera hübner (Lepidoptera: Noctuidae) and possible mechanisms determining differential toxicity

Marked changes in the relative toxicity of topically-applied abamectin were found between larval instars of Spodoptera littoralis, toxicity decreasing up to the fifth instar but increasing over 500-fold (at LD₅₀ level) in the sixth instar. By contrast, the toxicity of abamectin remained constant from fifth to sixth instar Heliothis armigera and there was an increase in the toxicity of two chemically unrelated insecticides, malathion (4-fold) and lambda-cyhalothrin (2.5-fold), from fifth to sixth instar S. littoralis. Prior topical application or injection of the microsomal oxidase inhibitor, piperonyl butoxide (PB) increased the toxicity of abamectin (6–8 and 16-fold respectively) against fifth instar S. littoralis, while topically-applied PB increased the proportion of radioactivity present as abamectin in the ventral nerve cord of this instar following topical application with [³H]abamectin. Topically-applied PB also enhanced the toxicity of abamectin against third (4-fold) and fourth instar (5-fold) S. littoralis but had no significant effect on sixth instar S. littoralis, fifth instar H. armigera, or on the toxicity of malathion and lambda-cyhalothrin against fifth instar S. littoralis. Topical application of the esterase inhibitor, S,S,S-tributyl phosphorothioate (DEF) significantly increased the toxicity of abamectin at the LD₅₀ level (3-fold) against fifth instar S. littoralis. The toxicity of injected abamectin against fifth instar S. littoralis was greater (20-fold) than with topical application but injected abamectin was less toxic (2-fold) against sixth instar S. littoralis and had no significant effect on fifth instar H. armigera. It is suggested that differential toxicity of abamectin is due in part to greater metabolism and reduced penetration in fifth instar S. littoralis than in sixth instar S. littoralis or fifth instar H. armigera.     

Topical and residual toxicity of six pesticides to <Emphasis Type="BoldItalic">Orius majusculus</Emphasis>

The toxicity of six pesticides (four insecticides and two fungicides) to Orius majusculus (Reuter) (Hemiptera: Anthocoridae) adults and nymphs was determined using different exposure methods. Mortality upon topical exposure to abamectin, endosulfan and spinosad at recommended field doses ranged from 56% to 100% after 24 h. However, in leaf residue tests, toxicity to both life stages decreased significantly, ranging from 0% to 33% mortality. Benomyl and copper salts + mancozeb (fungicides) were much less toxic to O. majusculus, with less than 15% mortality of either adults or nymphs in topical and residue bioassays. In persistent toxicity tests, insects were exposed to the same three insecticides for 4 days; mortality varied from 38% to 100%. Egg hatching was not significantly affected when abamectin, endosulfan and spinosad were topically applied. Number of eggs laid per female in choice and no-choice tests did not differ significantly from the control. The insecticides did not show considerable repellent effect in the choice tests. Topical, residue and systemic uptake methods were also compared to determine the differences in the toxicity levels of imidacloprid, a systemic insecticide. However, 100% mortality occurred with all methods.     

不同药剂对甜菜夜蛾幼虫毒力和田间应用效果研究

利用浸渍法分别测定虫螨腈等不同药剂对甜菜夜蛾3龄及5龄幼虫的毒力，结果表明：不同药剂对甜菜夜蛾幼虫的毒力存在明显差异，一些特异杀虫剂对甜菜夜蛾幼虫的毒力普遍高于试验用常规化学杀虫剂的毒力；同一药剂对不同龄期幼虫毒力的差异程度也不同，如虫螨腈、氟啶脲、氟铃脲、甲胺基阿维菌素、阿维菌素、虫酰肼等药剂对甜菜夜蛾3龄及5龄幼虫毒力的差异程度明显低于顺式氯氰菊酯、丙溴磷、灭多威等化学药剂。同时，作者还对12种药剂分别稀释1000倍对甜菜夜蛾5龄幼虫不同时间的毒力进行了观察，除常规化学农药出现中毒现象较快外，虫螨腈、甲胺基阿维菌素也表现较快中毒症状，田间药效试验进一步验证防治甜菜夜蛾宜选用虫螨腈、氟啶脲、氟铃脲、甲胺基阿维菌素、阿维菌素、虫酰肼等药剂。     

多杀霉素亚致死浓度对棉铃虫幼虫生理及代谢的影响

为明确田间使用多杀霉素亚致死浓度对棉铃虫Helicoverpa armigera幼虫的影响,用含多杀霉素亚致死浓度LC₂₅的人工饲料持续饲喂棉铃虫3龄幼虫,并对饲喂后其体重、取食量、累计蛹化率、蛹发育历期和蛹重等生长发育及脂肪体内甘油三脂（triglyceride,TG）含量和相关基因SREBP、FAS和HSL表达情况进行测定。结果表明,多杀霉素对棉铃虫的亚致死浓度LC₂₅为0.21 mg/kg;多杀霉素亚致死浓度处理4~6 d后,棉铃虫3龄幼虫体重分别为0.065、0.263和0.329 g,较对照显著降低;处理6 d后,其取食量为0.082 g,较对照显著降低;处理4~7 d后,其累计化蛹率分别为60.90%、63.20%、65.50%和65.50%,较对照显著降低。多杀霉素亚致死浓度处理后,棉铃虫蛹发育历期由对照9.89 d显著延长至10.74 d,单头蛹重为0.274 g,显著低于对照的0.324 g;其脂肪体TG含量较对照显著降低。多杀霉素亚致死浓度处理24~72 h后,参与脂肪酸合成信号通路中重要基因SREBP和FAS的相对表达量较对照均显著下调,而参与脂肪代谢的重要基因HSL则较对照显著上调。     

多杀菌素等新杀虫剂对粘虫的杀虫活性

浸叶法证明，多杀菌素(spinosad)、乙酰氨基阿维菌素和虫螨腈比阿维菌素对粘虫表现出更高的杀虫活性。其杀虫活性分别比阿维菌素高5倍、8倍和3．7倍。     

Cross-resistance and biochemical mechanisms of abamectin resistance in the western flower thrips, Frankliniella occidentalis

Abamectin resistance was selected in the western flower thrips [Frankliniella occidentalis (Pergande)] under the laboratory conditions, and cross-resistance patterns and possible resistance mechanisms in the abamectin-resistant strain (ABA-R) were investigated. Compared with the susceptible strain (ABA-S), the ABA-R strain displayed 45.5-fold resistance to abamectin after 15 selection cycles during 18 generations. Rapid reversion of abamectin resistance was observed in the ABA-R strain in the absence of the insecticide selection pressure. Moderate and low levels of cross-resistance to chlorpyrifos (RR 11.4) and lambda-cyhalothrin (3.98) were observed in the ABA-R strain, but no significant cross-resistance was found to spinosad (2.00), acetamiprid (1.47) and chlorfenapyr (0.26). Our studies also showed that the esterase inhibitor S,S,S-tributyl phosphorotrithioate (DEF) and glutathione S-transferase inhibitor diethyl maleate (DEM) were not able to synergize the toxicity of abamectin, whereas the oxidase inhibitor piperonyl butoxide (PBO) conferred a significant synergism on abamectin in the ABA-R strain (SR 3.00). Biochemical analysis showed that cytochrome P450 monooxygenase activity of the ABA-R strain was 6.66-fold higher than that of the ABA-S strain. It appears that enhanced oxidative metabolism mediated by cytochrome P450 monooxygenases was a major mechanism for abamectin resistance in the western flower thrips.     

15种杀虫剂对草地贪夜蛾卵的毒力测定

采用浸卵法测定了15种杀虫剂对草地贪夜蛾卵的毒力,并比较了不同杀虫剂的毒力水平。结果表明:100 mg/L处理后48 h,甲氨基阿维菌素苯甲酸盐(甲维盐)和灭多威对草地贪夜蛾卵孵化抑制率最高,达到100%,其LC 50分别为12.67 mg/L和16.95 mg/L;而200 mg/L的氯虫苯甲酰胺、多杀霉素、阿维菌素、高效氯氰菊酯、虱螨脲、辛硫磷和杀螟丹分别处理后72 h对草地贪夜蛾卵的孵化抑制率次之,在69.6%~87.65%之间,其LC 50分别为44.1、50.9、78.37、79.0、98.15、126.8 mg/L和137.7 mg/L。依据毒力测定的结果和高效低毒类杀虫剂优先选用的原则,推荐选择甲维盐、氯虫苯甲酰胺、多杀霉素、阿维菌素和高效氯氰菊酯作为防治草地贪夜蛾卵的主要药剂。     

丽蚜小蜂寄生对Q型烟粉虱生长发育的影响

为明确丽蚜小蜂寄生对Q型烟粉虱的影响,通过室内饲养观察不同龄期Q型烟粉虱被丽蚜小蜂寄生后的生长发育,并比较了被寄生后烟粉虱若虫的个体大小及死亡率。结果表明,2龄、3龄和4龄烟粉虱若虫被寄生后均能继续发育,2龄若虫蜕皮进入3龄和3龄若虫蜕皮进入4龄的时间与对照间无显著差异,而被寄生若虫的4龄期显著延长。对于同一龄期的烟粉虱若虫,丽蚜小蜂偏向于选择较大的个体寄生,2龄和3龄被寄生若虫发育后期个体比未被寄生个体大,但4龄时被寄生的个体在发育后期略小于未被寄生个体,显示丽蚜小蜂对不同龄期若虫的生长发育影响不同。2龄若虫死亡率为61.64%,显著高于3龄和4龄若虫;4龄若虫褐蛹率最高,为48.84%。表明无论寄生哪一发育阶段的烟粉虱若虫,丽蚜小蜂的寄生均为容性寄生,田间应用丽蚜小蜂防治Q型烟粉虱时在其若虫3~4龄时释放更适宜。     

枸杞木虱啮小蜂寄生生物学研究

枸杞木虱啮小蜂(Tamarixia lyciumiYang)(新种)是枸杞木虱(Paratrioza sinicaYangLi)若虫期的重要寄生性天敌。第1~3日龄的木虱啮小蜂寄生寄主的能力较强。最喜寄生枸杞木虱4龄若虫,其次为5龄和3龄若虫。1头蜂一般一次只产1粒卵,寄生1头寄主,对已被寄生的寄主具有明显的辨别能力。在试验条件下,不能在沙枣木虱和柽柳木虱等其他寄主上产卵寄生,只寄生于枸杞木虱。对不同龄期(3、4、5龄)枸杞木虱若虫的功能反应均符合HollingⅡ型反应,相同寄主密度下,4龄时寄生数量最大,拟合的圆盘方程为:Na=0.560 9N/(1+0.027 1N)。枸杞木虱啮小蜂具有较强的种内干扰作用,随自身密度(P)的增加,对枸杞木虱4龄若虫的发现域(a)随之降低,用Hassell-Varley模型拟合为:a=0.122 2P-0.464 1。     

龟纹瓢虫对柑橘木虱的捕食功能反应及猎物偏好性

为评估龟纹瓢虫Propylea japonica对柑橘木虱Diaphorina citri的生物防治潜能,在实验室条件下测定龟纹瓢虫1~4龄幼虫和成虫对柑橘木虱5龄若虫的捕食功能反应、搜寻效应、自身密度干扰反应以及捕食偏好性。结果表明,龟纹瓢虫1~4龄幼虫和成虫对柑橘木虱5龄若虫的捕食功能反应均符合Holling II型功能反应类型,其各虫态龟纹瓢虫的瞬时攻击率分别为0.313、0.610、0.234、0.585和0.675,处理时间分别为0.088、0.077、0.013、0.008和0.016 d,龟纹瓢虫4龄幼虫对柑橘木虱5龄若虫的捕食能力最大,为73.125,龟纹瓢虫成虫、3龄幼虫、2龄幼虫、1龄幼虫次之,捕食能力分别为42.188、18.000、7.922和3.557。各虫态龟纹瓢虫对柑橘木虱5龄若虫的搜寻效应随柑橘木虱5龄若虫密度升高而下降;在柑橘木虱5龄若虫密度一定的条件下,各虫态龟纹瓢虫对柑橘木虱5龄若虫的捕食率随自身密度升高而下降,其自身密度干扰方程为E=0.421P^-0.52;当柑橘木虱5龄若虫和豆蚜Aphis craccivora 4龄若虫2种猎物共存时,龟纹瓢虫成虫对其食物选择性指数均小于1,表明龟纹瓢虫成虫对这2种猎物无捕食偏好性。表明龟纹瓢虫对柑橘木虱5龄若虫有较强的防控潜能。     

Effects of photoperiod on the development and growth of <Emphasis Type="Italic">Podisus nigrispinus</Emphasis>, a predator of cotton leafworm

The effects of photoperiod on nymphal development, growth and adult size in Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) were studied. Predators were collected in cotton fields in Patos (7°S, 37°W), Paraíba State, Brazil. A randomized block experimental design was used, with treatments consisting of photoperiods of 10L:14D, 11L:13D, 12L:12D, 13L:11D, 14L:10D, 15L:9D and 16L:8D (LD, in h), at a constant temperature of 28 ± 1°C and relative air humidity of 70 ± 10%. Treatments were distributed in four replications, with each experimental unit composed of 40 nymphs. The development period for each instar of P. nigrispinus varied according to the photoperiod exposure. Regardless of the photophase (PhP), the 5th instar nymphs exhibited the longest development period, except for the 15-h PhP, in which the development period of 2nd instar nymphs (4.13 days) was as long as that of the 5th instar nymphs (4.23 days). In the 1st, 3rd and 5th instars of P. nigrispinus, the development period was inversely proportional to the increase in light period in which the nymphs developed, for the PhP intervals of 10–14 h, 12–14 h, and 12–15 h, respectively. Predators exposed to a 14-h PhP developed a wider pronotum than those exposed to extreme PhP’s (of 10 h, 11 h and 16 h). Conditions from 14 h to 15 h of light resulted in higher daily growth rates in P. nigrispinus than those obtained with the other PhP’s tested. P. nigrispinus females exhibited faster daily growth rates than did males.     

Systemic effects of a neem insecticide onLiriomyza huidobrensis larvae

In an effort to expand the spectrum of larvicides effective against the pea leafminer,Liriomyza huidobrensis (Blanchard), we studied the effects of a neem-based insecticide (Neemix-45) on the development of the leafminer under laboratory conditions. Bean plants were treated with a soil drench of 1, 5, 10 or 25 ppm azadirachtin or by dipping leaves in 1 or 15 ppm azadirachtin at various times before or during the development of the leafminer. Treating the plants with the neem insecticide before exposure to egg-laying adults had a greater effect on inhibiting the development of pupae and adult eclosion than treatment at the 1st-instar larval stage. The systemic effects from a soil drench had a greater adverse effect on pupation and adult eclosion than leaf dipping. Drenching plants with 1 ppm azadirachtin 24 h before exposure to adults had a greater effect (0% adult eclosion) than leaf dipping at the same time period and concentration (15. 6% adult eclosion). Similar results were obtained when drenching plants infested with lst-instar larvae with 1 ppm azadirachtin (11. 7% eclosion)vs dipping leaves at the same time period and concentration (44. 7% eclosion).     

Toxicity of butene-fipronil,in comparison with seven other insecticides,in <Emphasis Type="Italic">Leptinotarsa decemlineata</Emphasis> and <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The speed of toxic action of an insecticide is an indicator for control efficacy and has considerable practical importance. For agricultural pest control, fast-acting is an important feature for an insecticide to consistently reduce the amount of feeding damage. Butene-fipronil is a novel compound obtained via the structural modification of fipronil. However, information about the toxicity and speed of toxic action is still limited. In the present paper, we compared the toxic feature of butene-fipronil with seven other insecticides, of which imidacloprid and abamectin are slow-acting insecticides, and acephate, endosulfan, methomyl, α-cypermethrin and spinosad are fast-acting insecticides. We found that the contact and stomach toxicities of butene-fipronil were among the highest ever estimated to Leptinotarsa decemlineata and Drosophila melanogaster. The speed of toxic action of butene-fipronil was determined using median lethal time (LT₅₀) at a dose (concentration) equivalent to LD₈₀ values. For L. decemlineata, the values for butene-fipronil, imidacloprid, abamectin, acephate, endosulfan, methomyl, cypermethrin and spinosad were calculated to be 39.9, 36.5, 37.5, 20.2, 22.4, 23.8, 16.4 and 23.1 h, respectively. Those for D. melanogaster were 29.8, 31.5, 29.4, 14.0, 20.3, 18.1, 13.5, and 20.1 h, respectively. ANOVA analysis showed that butene-fipronil, imidacloprid, abamectin had similar LT₅₀ values, whereas acephate, endosulfan, methomyl, spinosad and cypermethrin had comparable LT₅₀ values. Thus, butene-fipronil belongs to slow-acting insecticides. Our results provide more empirical information for butene-fipronil potential application.     

Effects of a Chenopodium-based botanical insecticide/acaricide on Orius insidiosus (Hemiptera: Anthocoridae) and Aphidius colemani (Hymenoptera: Braconidae)

UDA-245 is a Chenopodium-based natural insecticide. Forty-eight hours after treatment with this compound, Orius insidiosus (Say) and Aphidius colemani Viereck showed slight contact toxicity at 5 g AI liter(-1). There was no residual toxicity to A colemani. These two beneficials are currently used in commercial flower and vegetable greenhouses for the management of thrips, spider mites, aphids and small caterpillars. In contrast, abamectin and insecticidal soap were toxic by contact to both species. UDA-245 did not reduce the number of eggs laid by treated O insidiosus. The eclosion of these eggs was also not adversely affected by UDA-245. The other two insecticides, abamectin and insecticidal soap had no effect on the emergence of A colemani from treated aphid mummies. However, abamectin decreased the percentage of aphid parasitism by A colemani following a residual treatment. The LC50 for UDA-245 for the two beneficials is slightly over twice the recommended field dose.     

Lethal and sublethal side-effect assessment supports a more benign profile of spinetoram compared with spinosad in the bumblebee Bombus terrestris

BACKGROUND: This study was undertaken to identify the potential side effects of the novel naturalyte insecticide spinetoram in comparison with spinosad on the bumblebee Bombus terrestris L. The potential lethal effects together with the ecologically relevant sublethal effects on aspects of bumblebee reproduction and foraging behaviour were evaluated. Bumblebee workers were exposed via direct contact with wet and dry residues under laboratory conditions to spinetoram at different concentrations, starting from the maximum field recommended concentration (MFRC) and then different dilutions (1/10, 1/100, 1/1000 and 1/10 000 of the MFRC), and compared with spinosad. In addition, the side effects via oral exposure in supplemented sugar water were assessed. RESULTS: Direct contact of B. terrestris workers with wet residues of spinosad and spinetoram showed spinetoram to be approximately 52 times less toxic than spinosad, while exposure to dry residues of spinetoram was about 8 times less toxic than exposure to those of spinosad. Oral treatment for 72 h (acute) indicated that spinetoram is about 4 times less toxic to B. terrestris workers compared with spinosad, while exposure for a longer period (i.e. 11 weeks) showed spinetoram to be 24 times less toxic. In addition, oral exposure to the two spinosyns resulted in detrimental sublethal effects on bumblebee reproduction. The no observed effect concentration (NOEC) for spinosad was 1/1000 of the MFRC, and 1/100 of the MFRC for spinetoram. Comparison between the chronic exposure bioassays assessing the sublethal effects on nest reproduction, with and without allowing for foraging behaviour, showed that the respective NOEC values for spinosad and spinetoram were similar over the two bioassays, indicating that there were no adverse effects by either spinosyn on the foraging of B. terrestris workers. CONCLUSION: Overall, the present results indicate that the use of spinetoram is safer for bumblebees by direct contact and oral exposure than the use of spinosad, and therefore it can be applied safely in combination with B. terrestris. Another important conclusion is that the present data provide strong evidence that neither spinosyn has a negative effect on the foraging behaviour of these beneficial insects. However, before drawing final conclusions, spinetoram and spinosad should also be evaluated in more realistic field‐related situations for the assessment of potentially deleterious effects on foraging behaviour with the use of queenright colonies of B. terrestris. Copyright © 2011 Society of Chemical Industry     

Characterisation of abamectin resistance in a field‐evolved multiresistant population of Plutella xylostella

BACKGROUND: Plutella xylostella (L.) has evolved resistance to various kinds of insecticide in the field. Reversion and selection, cross‐resistance, inheritance and mechanisms of abamectin resistance were characterised in a field‐derived multiresistant population of P. xylostella from China. RESULTS: Compared with a susceptible Roth strain, the field‐derived TH population showed ～5000‐fold resistance to abamectin. Rapid reversion of abamectin resistance was observed in the TH population when kept without insecticide selection. The TH‐Abm strain, selected from the TH population with abamectin, developed 23 670‐fold resistance to abamectin, a high level of cross‐resistance to emamectin benzoate and low levels of cross‐resistance to spinosad and fipronil. Genetic analyses indicated that abamectin resistance in the TH‐Abm strain was autosomal, incompletely dominant and polygenic. P450 monooxygenase activities in the TH‐Abm strain were significantly elevated compared with the TH strain. Piperonyl butoxide (PBO) inhibited a small part of abamectin resistance in the TH‐Abm strain. CONCLUSION: Field‐evolved high‐level resistance to abamectin in the TH population was not stable. Selection of the TH population with abamectin resulted in an extremely high level of cross‐resistance to emamectin benzoate and low levels of cross‐resistance to spinosad and fipronil. Enhanced oxidative metabolism was involved in, but may not be the major mechanism of, polygenic abamectin resistance in the TH‐Abm strain. Copyright © 2009 Society of Chemical Industry