Field‐evolved resistance to Bt maize in sugarcane borer (Diatraea saccharalis) in Argentina

BACKGROUND

Maize technologies expressing Bacillus thuringiensis (Bt) insecticidal proteins are widely used in Argentina to control sugarcane borer (Diatraea saccharalis Fabricius). Unexpected D. saccharalis damage was observed to Bt maize events TC1507 (expressing Cry1F) and MON 89034 × MON 88017 (expressing Cry1A.105 and Cry2Ab2) in an isolated area of San Luis Province. Diatraea saccharalis larvae were sampled from MON 89034 × MON 88017 fields in the area to generate a resistant strain (RR), which was subsequently characterized in plant and diet bioassays.

RESULTS

Survivorship of the RR strain was high on TC1507 leaf tissue, intermediate on MON 89034 × MON 88017, and low on MON 810 (expressing Cry1Ab). The RR strain had high resistance to Cry1A.105 (186.74‐fold) and no resistance to Cry2Ab2 in diet bioassays. These results indicate resistance to Cry1F and Cry1A.105 (and likely cross‐resistance between them) but not to Cry1Ab or Cry2Ab2. Resistance to MON 89034 × MON 88017 was functionally recessive. Reviews of grower records suggest that resistance initially evolved to Cry1F, conferring cross‐resistance to Cry1A.105, with low refuge compliance as the primary cause. A mitigation plan was implemented in San Luis that included technology rotation, field monitoring, and grower education on best management practices (BMPs) including refuges.

CONCLUSION

In the affected area, the resistance to Cry1F and Cry1A.105 is being managed effectively through use of MON 89034 × MON 88017 and MON 810 in combination with BMPs, and no spread of resistance to other regions has been observed. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Toxicity of δ‐phenothrin and resmethrin to non‐target insects

BACKGROUND: The susceptibility of adult house cricket, Acheta domesticus (L.), adult convergent lady beetle, Hippodamia convergens (Guérin‐Méneville), and larval fall armyworm, Spodoptera frugiperda (JE Smith), to resmethrin and δ‐phenothrin synergized with piperonyl butoxide (PBO) was evaluated in a laboratory bioassay procedure. RESULTS: The 1 day LC₅₀ values for resmethrin + PBO were 23.2, 32.08 and 307.18 ng cm^?2 for A. domesticus, H. convergens and S. frugiperda respectively. The 1 day LC₅₀ values for δ‐phenothrin + PBO were 26.9, 74.91 and 228.57 ng cm^?2 for A. domesticus, H. convergens and S. frugiperda respectively. The regression relationship between species mortality and concentration explained 51–81% of the variation for resmethrin + PBO and 72–97% of the variation for δ‐phenothrin + PBO. The LC₅₀ values decreased with time for these insecticides for all surrogate species. In terms of sensitivities among the insects to resmethrin + PBO and δ‐phenothrin + PBO, A. domesticus was most sensitive, followed by H. convergens and then S. frugiperda. CONCLUSION: The results indicate that resmethrin + PBO was generally more toxic than δ‐phenothrin + PBO. Based on the results, A. domesticus seems to be a good surrogate species for estimating potential non‐target terrestrial insect impacts from exposure to pyrethroids used in public health applications. Copyright © 2008 Society of Chemical Industry     

Inheritance of resistance to Bacillus thuringiensis Cry1Ac toxin in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from India

BACKGROUND: The cotton bollworm, Helicoverpa armigera (Hübner), is one of the most serious insect pests of cotton. It has developed resistance to almost all groups of chemical insecticides because of their intensive use. The failure of insecticides to control H. armigera has been a strong incentive for the adoption of transgenic cotton (Bt cotton). However, the value of Bt could be diminished by widespread resistance development to Bt toxins in insect populations. Therefore, understanding the genetic basis of resistance is essential for developing and implementing strategies to delay and monitor resistance. RESULTS: A resistant strain designated as BM‐R was obtained from the cross of adults from Bathinda () and Muktsar (), Punjab, India, which showed the highest survival (60.68%) and LC₅₀ value (1.396 µg mL^?1 diet). Similarly, a laboratory‐maintained strain from Hoshiarpur, Punjab, showed maximum susceptibility to Cry1Ac toxin with the lowest LC₅₀ value (0.087 µg mL^?1), and was designated as HP‐S. The genetic purity of both strains was confirmed by RAPD profile analysis at each generation, and genetic similarity reached more than 90% after the third generation. Continuous maintenance of the resistant BM‐R strain on Cry1Ac resulted in an increase in LC₅₀ from 0.531 µg mL^?1 in F₀ to 4.28 µg mL^?1 in F₁₄ and 7.493 µg mL^?1 in F₁₉, while the LC₅₀ values for HP‐S larvae on diet without Cry1Ac increased to 0.106 and 0.104 µg mL^?1, which lay within the fiducial limits of the baseline LC₅₀ value. The mode of inheritance of resistance was elucidated through bioassay response of resistant, susceptible heterozygotes and backcross progeny to Cry1Ac incorporated in semi‐synthetic diet. CONCLUSION: Based on dominance, degree of dominance and backcross values, resistance was inferred to be polygenic, autosomal and inherited as a recessive trait. Copyright © 2011 Society of Chemical Industry     

草地贪夜蛾对国产Bt玉米的抗性风险评估

为评估草地贪夜蛾Spodoptera frugiperda对国产Bt玉米的抗性风险,基于抗性风险分析模型对草地贪夜蛾在3种Bt玉米和2种庇护所条件下的抗性时间进行预测分析。结果显示,无论是采用种子混合庇护所还是结构化庇护所,草地贪夜蛾对Cry1Ab+Vip3Aa-玉米的抗性时间均远长于对Vip3Aa-玉米和Cry1Ab-玉米的抗性时间。在Bt与非Bt植株之间存在异花授粉和幼虫转移的条件下,采用种子混合庇护所的抗性时间较采用结构化庇护所的抗性时间大大缩短。以采用Cry1Ab+Vip3Aa-玉米和比例为0.20的庇护所为例,当异花授粉Bt显性度为0.5、幼虫转移概率为0.95时,采用结构化庇护所的抗性时间超过200代,而采用种子混合庇护所的抗性时间只有59代。结果表明,草地贪夜蛾对Cry1Ab-玉米的抗性风险远大于对Cry1Ab+Vip3Aa-玉米的抗性风险,而种子混合庇护所条件下的抗性风险远大于结构化庇护所条件下的抗性风险。     

基于转录组测序解析草地贪夜蛾对溴氰虫酰胺的解毒代谢分子机制

为阐明草地贪夜蛾Spodoptera frugiperda对溴氰虫酰胺的解毒代谢分子机制,通过LC₅₀的溴氰虫酰胺诱导草地贪夜蛾3龄幼虫后,利用酶活测定和转录组测序鉴定解毒代谢相关基因,并采用实时荧光定量PCR技术对细胞色素P450单加氧酶(cytochrome P450 monooxygenase,P450)基因进行验证分析。结果表明,经LC₅₀的溴氰虫酰胺处理后,草地贪夜蛾3龄幼虫体内3种解毒代谢酶活性较对照均有所升高,但仅P450活性较对照显著升高,而谷胱甘肽S-转移酶和羧酸酯酶与对照无显著差异。经LC₅₀的溴氰虫酰胺处理后草地贪夜蛾3龄幼虫转录组中共筛选到1 408个差异表达基因,其中上调表达的基因有935个,下调表达的基因有473个。药物代谢-细胞色素P450通路、药物代谢-其他酶通路及细胞色素P450对异生物质的代谢通路中有超过20个基因存在差异表达。在草地贪夜蛾转录组中筛选鉴定到121个P450基因,其中,属于CYP2、CYP3、CYP4以及Mito家簇的基因分别有9、45、58和9个,而经LC_5...     

Inheritance of resistance to a new non‐steroidal ecdysone agonist,fufenozide, in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is a cosmopolitan pest of cruciferous crops. Fufenozide, a novel non‐steroidal ecdysone agonist, exhibits good efficacy and plays an increasingly important role in the control of Lepidopterous pests in China. A laboratory strain of DBM was selected for resistance to fufenozide, and the genetic basis of resistance was studied. RESULTS: The resistant strain, selected under laboratory conditions, exhibited a higher level of resistance to fufenozide (302.8‐fold based on LC₅₀s) than the laboratory susceptible strain. Mortality data from the testing of F₁ progeny of reciprocal crosses of resistant and susceptible DBM indicated that resistance was autosomal and incompletely recessive with a degree of dominance of ?0.664. Chi‐square analysis from responses of a backcross of crossed F₁ progeny and the resistant strain and F₂ progeny were highly significant, suggesting that the resistance was probably controlled by more than one gene. The estimated realised heritability (h²) of fufenozide resistance was 0.08, indicating that diamondback moth may have a lower chance of developing resistance to fufenozide than other kinds of insecticide. CONCLUSION: The resistance of DBM to fufenozide might be autosomal and incompletely recessive, and the resistance is probably controlled by more than one gene. These results provide the basic information for pest management programmes. Copyright © 2009 Society of Chemical Industry     

Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India

BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007–2008 and 2008–2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2. RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non‐Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five‐day‐old larvae (LC₅₀) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC₅₀ for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population. CONCLUSIONS: The data reported here constitute the first evidence of field‐evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009–2010 growing season, which confirmed field‐evolved resistance to Cry1Ac in Amreli. The lack of cross‐resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac. Copyright © 2011 Society of Chemical Industry     

Impact of seed blend and structured maize refuge on Helicoverpa zea (Lepidoptera: Noctuidae) potential phenological resistance development parameters in pupae and adults

BACKGROUND

Helicoverpa zea, an economic pest in the south-eastern United States, has evolved practical resistance to Bacillus thuringiensis (Bt) Cry toxins in maize and cotton. Insect resistance management (IRM) programs have historically required planting of structured non-Bt maize, but because of its low adoption, the use of seed blends has been considered. To generate knowledge on target pest biology and ecology to help improve IRM strategies, nine field trials were conducted in 2019 and 2020 in Florida, Georgia, North Carolina, and South Carolina to evaluate the impact of Bt (Cry1Ab + Cry1F or Cry1Ab + Cry1F + Vip3A) and non-Bt maize plants in blended and structured refuge treatments on H. zea pupal survival, weight, soil pupation depth, adult flight parameters, and adult time to eclosion.

RESULTS

From a very large sample size and geography, we found a significant difference in pupal mortality and weight among treatments in seed blends with Vip3A, implying that cross-pollination occurred between Bt and non-Bt maize ears. There was no treatment effect for pupation depth, adult flight distance, and eclosion time.

CONCLUSION

Results of this study demonstrate the potential impact of different refuge strategies on phenological development and survival of an important pest species of regulatory concern. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Marker‐free,tissue‐specific expression of Cry1Ab as a safe transgenic strategy for insect resistance in rice plants

BACKGROUND: Rice is the major food resource for nearly half of the global population; however, insect infestation could severely affect the production of this staple food. To improve rice insect resistance and reduce the levels of Bt toxin released into the environment, the Cry1Ab gene was conjugated to the rice rbcS promoter to express Bt toxin in specific tissues of transgenic plants. RESULTS: Eight marker‐free, T₂ lines were separated from the T₀ cotransformants. Using RT‐PCR, high levels of Cry1Ab expression were detected in the leaf but not in the seed. The Cry1Ab protein level ranged from 1.66 to 3.31 µg g^?1 in the leaves of four transgenic lines, but was barely detectable in their seeds by ELISA. Bioassays showed that the mortality rate of silkworm larvae feeding on mulberry leaves dipped in transgenic rice flour and pollen was less than that of the positive control (KMD), and that their average weight was higher than that of KMD, suggesting that the Cry1Ab protein was not expressed in the seed and pollen. CONCLUSION: The transgene conferred a high level of resistance to insects and biosafety to the rice plants, which could be directly used in rice breeding. Copyright © 2012 Society of Chemical Industry     

Bioassay‐guided isolation of potent aphicidal Erythrina alkaloids against Aphis gossypii from the seed of Erythrina crista‐galli L

BACKGROUND

The cotton aphid (Aphis gossypii Glover) is one of the most invasive pests of cotton. Many botanical phytochemicals have a long history as a source of insecticides, and as templates for new insecticides. This study was undertaken to isolate aphicidal compounds from the seeds of Erythrina crista‐galli L. using the bioassay‐guided isolation method.

RESULTS

Three novel and 11 known Erythrina alkaloids were isolated. Erysodine ( 9 ), erysovine ( 10 ), erysotrine ( 8 ) and erythraline ( 11 ) showed moderate to excellent aphicidal activity with LD₅₀ values of 7.48, 6.68, 5.13 and 4.67 ng aphid^–1, respectively. The Potter spray tower bioassay gave corresponding LC₅₀ values of 186.81, 165.35, 163.74 and 112.78 µg ml^–1. A unique substructure, which presents an sp³ methylene at C‐8, a non‐oxygenated site at N‐9 and a conjugated dienes group (Δ^1,2 and Δ^6,7), plays a crucial role in the aphicidal activity. Application of erythraline ( 11 ) led to different increases in the activities of superoxide dismutase, catalase and glutathione S‐transferase.

CONCLUSION

The study demonstrated that the Erythrina alkaloids erysodine ( 9 ), erysovine ( 10 ), erysotrine ( 8 ) and erythraline ( 11 ) have potential use as botanical aphicides for commercial application, or as templates for the development of new insecticides. © 2017 Society of Chemical Industry     

草地贪夜蛾病原微孢子虫的鉴定及其致病力分析

为明确从田间采集草地贪夜蛾 Spodoptera frugiperda幼虫体内发现的一种微孢子虫的分类地位和致病性,利用传统形态学观察和分子生物学技术对该微孢子虫进行鉴定,同时采用室内生物活性测定法对其致病性进行分析。结果显示,该微孢子虫的形态学特征与家蚕微孢子虫 Nosemabombycis相近,具有典型微孢子虫超微组成结构,孢子壁厚度为195.00~205.15 nm,极丝盘旋于孢子后极内侧10~12圈;其基因组的基因间隔区（intergenic spacer, ITS）和小亚基核糖体RNA（smallsubunit ribosomal RNA, SSU）序列与已报道的家蚕微孢子虫相关序列的相似度分别达94.34%和99.50%,系统发育树显示该微孢子虫属于微孢子虫属 Nosema,与家蚕微孢子虫亲缘关系最近。该微孢子虫侵染草地贪夜蛾1龄和2龄幼虫5 d时的LC50分别为2.51×10⁷孢子/mL和2.48×10⁷孢子/mL;侵染3龄幼虫10 d时的LC₅₀为3.79×10⁷孢子/mL;侵染4龄幼虫15 d时的LC50为3.98×10⁷孢子/mL;且当微孢子虫浓度为1.0×10⁸孢子/mL时,草地贪夜蛾1至4龄幼虫的LT₅₀分别为3.04、 3.86、 7.47和10.43 d。表明该微孢子虫隶属微孢子虫属,对草地贪夜蛾不同龄期幼虫均有较强的致病力,具有良好的开发应用潜力。     

Efficacy of Bacillus thuringiensis Cry3Aa protoxin and protease inhibitors against coleopteran storage pests

BACKGROUND: Environmental impacts and resistance to insecticides pose serious challenges to stored‐product insect and other types of pest control. Insect‐resistant transgenic grain is a potential alternative to fumigants, but candidate control proteins are needed, especially for coleopterans. Therefore, we evaluated the efficacy of a coleopteran‐active toxin, Bacillus thuringiensis Cry3Aa, with or without protease inhibitors, in laboratory feeding assays against coleopteran storage pests. RESULTS: In a comparison of the toxicity of Cry3Aa protoxin towards three species of coleopteran storage pests, Tenebrio molitor L. was found to be most sensitive, Tribolium castaneum (Herbst.) was most refractory and Rhyzopertha dominica F. displayed an intermediate response. For R. dominica, Cry3Aa combined with 3500 mg potato carboxypeptidase inhibitor or 5000 mg aprotinin kg^?1 diet resulted in both delayed development and increased mortality. Potato carboxypeptidase inhibitor and bovine aprotinin reduced the LC₅₀ of Cry3Aa for R. dominica two‐ and threefold respectively. Cry3Aa treatment resulted in fewer progeny from R. dominica, and progeny was further reduced when the protoxin was combined with potato carboxypeptidase inhibitor. CONCLUSIONS: These data support the hypothesis that a combination of Cry3Aa protoxin and protease inhibitors, particularly a potato carboxypeptidase inhibitor, may have applications in control strategies for preventing damage to stored products and grains by coleopteran pests. Published 2011 by John Wiley & Sons, Ltd.     

Old and new association of Cotesia icipe (Hymenoptera: Braconidae) with alien invasive and native Spodoptera species and key stemborer species: implication for their management

BACKGROUND

Maize production in Africa is hindered by a myriad of biotic challenges, key among them being invasive and native lepidopteran stemborers. Recent invasion of the continent by fall armyworm, Spodoptera frugiperda, has further exacerbated the situation. Fortunately, Cotesia icipe was found to be very promising against S. frugiperda. However, the co-occurrence and interaction between S. frugiperda and the stemborers (Busseola fusca, Sesamia calamistis, and Chilo partellus) in maize agroecosystem may jeopardize the efficiency of C. icipe as a biocontrol agent of S. frugiperda. This study investigated the performance of C. icipe on S. frugiperda, Spodoptera littoralis and the stemborers. Specifically, the preference and acceptability of C. icipe to the host insects, the physiological suitability of the hosts for its development, and the effect of these hosts on the fitness parameters of the offspring were assessed.

RESULTS

Cotesia icipe accepted all the tested hosts, albeit with higher preference for Spodoptera species than for stemborers under multiple-choice tests. Also, the highest parasitism of up to 97% was recorded on S. frugiperda compared with parasitism on the stemborers of 43% in B. fusca. Moreover, physiological suitability and fitness traits (except for per cent female offspring) varied with host species, again being optimal on Spodoptera species.

CONCLUSION

Cotesia icipe demonstrated strong potential to control S. frugiperda in maize due to its high affinity for parasitization and developmental success in this host; and despite its non-specific parasitization, the presence of other hosts may not prevent its maximum control of S. frugiperda. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

两株虫生真菌对草地贪夜蛾的致病力及高毒力菌株与卵寄生蜂的相容性

为有效防控新入侵我国的重大农业害虫草地贪夜蛾 Spodoptera frugiperda,采用浸叶法测定球孢白僵菌 Beauveria bassiana菌株Bb1237、 Bb201017、 Bb20091317及金龟子绿僵菌 Metarhiziumanisopliae菌株Ma189和莱氏绿僵菌 M. rileyi菌株MrCDTLJ1对草地贪夜蛾3龄幼虫的致病力,筛选对草地贪夜蛾3龄幼虫有较强致病力的菌株,并测定该菌株对草地贪夜蛾3龄幼虫的致病力和对其天敌的致死率。结果显示,球孢白僵菌Bb20091317和莱氏绿僵菌MrCDTLJ1对草地贪夜蛾3龄幼虫的累计校正死亡率显著高于其他菌株,分别为95.59%和97.06%,致死中时LT₅₀分别为3.42 d和5.72 d, LC₅₀分别为7.05×10⁶个/mL和2.25×10⁵个/mL。2种菌在高浓度1×10⁸个/mL下对草地贪夜蛾天敌夜蛾黑卵蜂 Telenomus remus和玉米螟赤眼蜂 Trichogramma ostriniae成蜂的致死率也仅介于15%~20%之间。表明球孢白僵菌Bb20091317和莱氏绿僵菌MrCDTLJ1不仅对草地贪夜蛾有高致病力,同时与夜蛾黑卵蜂和玉米螟赤眼蜂有较好的相容性。     

转Cry1Ab-ma基因玉米CM8101对草地贪夜蛾1龄和2龄幼虫的抗性

为明确转Bt基因玉米对草地贪夜蛾Spodoptera frugiperda的抗性,采用室内玉米离体组织生测法测定取食转Cry1Ab-ma基因抗虫玉米CM8101心叶、花丝和籽粒后草地贪夜蛾1龄和2龄幼虫存活数量、存活幼虫的体重、蛹重、化蛹和羽化等参数,分析转Cry1Ab-ma基因抗虫玉米CM8101三种组织对草地贪夜蛾1龄和2龄幼虫的抗性。结果显示,转Cry1Ab-ma基因玉米CM8101心叶可完全杀死草地贪夜蛾1龄幼虫,2龄幼虫有存活,存活率为10.0%,但不能化蛹与羽化;花丝可杀死大部分草地贪夜蛾1龄幼虫,存活率为3.3%,并阻断其生活史,但对2龄幼虫杀伤力弱,存活率为73.3%,存活幼虫化蛹率和羽化率分别为20.0%和13.3%;籽粒可完全杀死草地贪夜蛾1龄幼虫,2龄幼虫有存活,存活率为13.3%,有少量可化蛹,化蛹率为3.3%、有少量羽化,羽化率为3.3%。表明转Cry1Ab-ma基因玉米CM8101在短期内对草地贪夜蛾1龄和2龄幼虫有良好的控制作用。     

Inheritance mode and realized heritability of resistance to imidacloprid in the brown planthopper,Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: The brown planthopper, Nilaparvata lugens (Stål), is a serious pest that causes enormous losses to the rice crop in Asia. The genetic basis of imidacloprid resistance was investigated in N. lugens. RESULTS: The resistant strain, selected for imidacloprid resistance from a field population of N. lugens collected from Nanjing, Jiangsu Province, China, showed a 964‐fold resistance compared with the laboratory strain. Progenies of reciprocal crosses (F₁ and F₁′) showed similar dose–mortality responses (LC₅₀) to imidacloprid, and also exhibited a similar degree of dominance (D), 0.58 for F₁ and 0.63 for F₁′. Chi‐square analyses of self‐bred and backcross progenies (F₂, F₂′ and BC respectively) rejected the hypothesis for a single gene control of the resistance. The estimated realized heritability (h²) of imidacloprid resistance was 0.1141 in the resistant strain of N. lugens. CONCLUSION: The results showed that imidacloprid resistance in N. lugens was autosomal and was expressed as an incompletely dominant trait, probably controlled by multiple genes. Copyright © 2009 Society of Chemical Industry     

Being exposed to low concentrations of pirimiphos-methyl and chlorfenapyr has detrimental effects on the mobility of Trogoderma granarium

BACKGROUND

Sublethal effects of insecticides may negatively affect several biological and behavioral traits of insects. The lethal effects of pirimiphos-methyl and chlorfenapyr have been previously showed on Trogoderma granarium, but little knowledge is available about their sublethal effects at low concentrations on both sexes. Herein, the sublethal effects of pirimiphos-methyl and chlorfenapyr on the mobility of T. granarium males and females were investigated.

RESULTS

Lethal concentration (LC) values of pirimiphos-methyl and chlorfenapyr were lower for T. granarium females than males. LC values on males were LC₁₀ = 0.000788 and 0.00139 mg active ingredient (a.i.) cm⁻², LC₃₀ = 0.00350 and 0.00535 mg a.i. cm⁻², and LC₅₀ = 0.00986 and 0.0136 mg a.i. cm⁻² for pirimiphos-methyl and chlorfenapyr respectively. LC on females were LC₁₀ = 0.000704 and 0.00110 mg a.i. cm⁻², LC₃₀ = 0.00323 and 0.00428 mg a.i. cm⁻², and LC₅₀ = 0.00925 and 0.0110 mg a.i. cm⁻² for pirimiphos-methyl and chlorfenapyr respectively. The walking duration of beetles exposed to LC₃₀ of pirimiphos-methyl was significantly lower than the individuals exposed to LC₁₀ and LC₃₀ of both insecticides and control ones. Pirimiphos-methyl LC₃₀-exposed males remained more time on their back (101.7 s) than females (46.9 s), while the latter stayed immobile longer than males (381.7 s versus 371.9 s). The highest speed was recorded for control beetles (14.17 mm s⁻¹ females vs. 12.44 mm s⁻¹ males), while the lowest speed was observed in pirimiphos-methyl LC₃₀-treated males (8.36 mm s⁻¹) and females (9.66 mm s⁻¹).

CONCLUSIONS

Overall, males and females exposed to low concentrations of pirimiphos-methyl and chlorfenapyr showed reduced motility. This knowledge can be exploited further to unlock behavioral effects of insecticides for effective pest management programs in warehouses. © 2023 Society of Chemical Industry.     

Genetic analysis of abamectin resistance in Tetranychus cinnabarinus

The carmine spider mite is the most serious crop mite pests in China. Abamectin has been used to control insects and mites worldwide but carmine spider mites, Tetranychus cinnabarinus, had developed resistance to it. Genetic research on insecticide resistance has been fundamental for understanding the resistance development, studying resistance mechanisms, and designing appropriate resistance management strategies to control insect pests. A resistant colony of T. cinnabarinus, RRG42, was established to examine the inheritance of abamectin resistance in T. cinnabarinus. The females of T. cinnabarinus were selected for bioassay using a slide dip method. After 42 generations of selection, the RRG42 strain was 8.7-fold resistant to abamectin compared with the susceptible strain (SS). The logarithm (log) concentration–probit response curve for F₁s from reciprocal crosses, of F₁RS and F₁SR, were inclined to that for SS and the degree of dominance (D) values for F₁s were −0.81 and −0.17. There was a significant difference in values of LC₅₀ and slope of log concentration–probit lines between F₁RS and F₁SR. The observed mortalities of BC1 (F₁RS♀ × RRG42♂) and BC1′ (F₁SR♀ × SS♂) were significantly different from the expected mortalities based on a monogenic resistance in the chi-square tests. The inheritance of abamectin resistance in T. cinnabarinus is incompletely recessive and may be controlled by more than one gene. The maternal or cytoplasmic effect may exist in the inheritance of resistance to abamectin in T. cinnabarinus.     

Mendelian inheritance of rust resistance to Melampsora larici‐epitea in crosses between Salix sachalinensis and S. viminalis

Two F₁, two F₂ and two backcross (BC) full‐sib families of Salix sachalinensis × S. viminalis were tested for resistance to two pathotypes of Melampsora larici‐epitea in leaf‐disc inoculation experiments. Two single‐pustule isolates, VM and ST, belonging to pathotypes LET1 and LET5, respectively, were used in the tests. Disease was scored based on the number of uredinia, uredinial diameter and inoculum densities. Both F₁ families were completely resistant to both VM and ST. Resistance to VM segregated at a 9:6:1 ratio in the F₂ families and at a 1:2:1 ratio in the BC families, suggesting that two independently segregating genes controlled rust resistance, with resistance dominant over susceptibility. This also indicates incomplete dominance of the resistance alleles over the susceptibility to VM. For ST, the equivalent ratios were 3:1 and 1:1, showing that a single dominant gene was responsible for rust resistance. The broad sense heritabilities were >0·91 for uredinial diameter and 0·1–0·33 for the number of uredinia. There were significant overall correlations between data from inoculations with VM and those from inoculations with ST in the number of uredinia, uredinial diameter and disease scores (Spearman’s rank correlation coefficients = 0·31–0·75).     

The effects of diet on the detection of resistance to Cry1Ac toxin in Australian Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

The effects of raw or heat-denatured soybean flour in an artificial diet on the detection of Cry1Ac resistance in Helicoverpa armigera were examined. Resistant neonate larvae reared on denatured soybean flour diet showed resistance factors of 7980 and 16,901 at the LC₅₀ and LC_99.9 levels, respectively. By comparison, resistance could not be detected in neonate larvae reared on raw flour diet. Third instar larvae reared on denatured flour diet showed resistance factors of 322 and 21,190 at the LC₅₀ and LC_99.9 levels. Resistance was not detected in third instar larvae reared on raw flour diet. There was 68% survival of resistant neonate larvae on Bollgard II cotton leaf feeding assays, compared to 100% mortality in a susceptible strain. We conclude that detection of CRY1Ac resistance in H. armigera from Australia can be masked, if an artificial diet gives chronic exposure to potent, protease inhibitors present in raw soy flour.