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BACKGROUND Trichogramma dendrolimi has been widely used in augmentative biocontrol of lepidopteran pests in China. In mass production of T. dendrolimi using Antheraea pernyi eggs as substitutive hosts, which are large in size, as clutch size is a parameter of importance to produce high quality parasitoids. Here, we aimed to determine the optimal clutch size for the bisexual Wolbachia-uninfected line (TdB) and Wolbachia-infected thelytokous line (TdT) of T. dendrolimi reared on A. pernyi eggs. RESULTS A medium clutch size of 42.75 to 62.27 for TdB and 52.93 to 57.14 for TdT was optimal to maximize fitness-correlated traits of parasitoid individual. The optimal clutch sizes with maximized parameters included adult emergence rate, adult body size, adult longevity, fecundity, and sum of fecundity of all females per brood were 58.31 (86.00%), 42.75 (231.11 μm), 50.92 (2.69 days), 62.27 (150.89 eggs), and 83.25 (7926.33 eggs) for TdB and 57.14 (94.54%), 52.93 (236.97 μm), 53.64 (2.62 days), 56.80 (161.01 eggs), and 70.10 (8579.71 eggs) for TdT. The TdT had a shorter adult longevity, longer development time, and higher adult emergence rate than did its non-infected bisexual counterpart. CONCLUSION A medium brood size in a A. pernyi egg host was optimal to produce offspring parasitoids with higher fitness parameters for both bisexual Wolbachia-uninfected and thelytokous Wolbachia-infected lines of T. dendrolimi. The determination of optimal clutch size for T. dendrolimi will provide the reference for the quality control of T. dendrolimi production and improvement of the field performance of the wasps. © 2020 Society of Chemical Industry.

Bemisia tabaci is one of notorious agricultural insect pests in China, and the strategies of management largely depend on application of insecticides. In order to assess levels of resistance in field populations of B. tabaci to six insecticides including abamectin, cyantraniliprole, pymetrozine, imidacloprid, chlorpyrifos and bifenthrin, we monitored the susceptibility to all tested insecticides in five field populations across China and the results indicated that field populations of B. tabaci have developed various levels of resistance to each chemical agent. Furthermore, para-type voltage gated sodium channel mutations (L925I and T929V) and acetylcholinesterase ace1 mutation (F331W) were confirmed, and expression levels of CYP6CM1, CYP4C64, GSTd7 and ABCG3 were detected for investigating mechanisms of imidacloprid resistance in the five field-collected populations. The results showed that, in all tested populations, frequencies of F331W were 100%, and the frequencies of the L925I and T929V were in the range of 28.5 to 47.0% and 11.0 to 53.5%, respectively. Moreover, CYP6CM1 and CYP4C64 were significantly overexpressed in two tested populations, respectively, and GSTd7 was significantly overexpressed in one population. No overexpression of ABCG3 was observed in all the populations. Above results provided valuable insight into the current status of insecticide resistance and could be contributed to design strategies of management for B. tabaci.

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC

Bemisia tabaci is a threat to agriculture worldwide because of its potential to cause devastating damage to various crops. β-asarone is a bioactive pesticidal chemical originating from Acorus calamus (or “Sweet Flag”) plants, and it displays significant lethal effects against insect pests. In this study, we established a baseline of susceptibility to β-asarone from China and patterns of cross-resistance to other popular insecticides. We found that all the 12 field-collected B. tabaci populations exhibited high susceptibility to β-asarone, and there was no cross-resistance detected for other tested insecticides. We subsequently evaluated the sublethal effects of β-asarone on physiology and biochemistry via LC25 treatment (4.7 mg/L). LC25 of β-asarone resulted in prolonged developmental duration and decreased survival rates in B. tabaci nymphs, pseudopupae, and adults. Significant reductions in oviposition duration, fecundity, and hatchability were also observed. Additionally, the metabolic enzyme activity and expression profiles of selected cytochrome P450 monooxygenase (P450) genes following the LC25 treatment of β-asarone suggest that enhanced detoxification via P450s could be involved in the observed sublethal effects. These findings demonstrate the strong toxicity and significant sublethal effects of β-asarone on B. tabaci and suggest that the induced overexpression of P450 genes could be associated with the response to β-asarone.

Bemisia tabaci, sweetpotato whitefly, is one notorious insect pest on a series of crops worldwide, and many populations show high resistance to various insecticides. The cyantraniliprole-resistant strain of B. tabaci SX-R (138.4-fold) was obtained by selections with an outdoor-collected cyantraniliprole resistant population. By crossing and repeated backcrossing to a susceptible MED-S strain, the trait of cyantraniliprole resistance from SX-R was moved into MED-S to establish one near-isogenic line (CYAN-R). MED-S and CYAN-R were utilized to build patterns of cross-resistance, CYAN-R strain exhibited 63.317-fold resistance to cyantraniliprole, but no cross-resistance to several other successfully commercialized chemical agents. After that significant inhibition of cyantraniliprole resistance by piperonyl butoxide (PBO) and increased cytochrome P450 (3.4-fold) were observed in CYAN-R strain, indicating putative involvement of P450 in detoxification. Furthermore, five published detoxification-related P450 genes in B. tabaci, CYP4C64, CYP6CM1, CYP6CX1, CYP6CX4, and CYP6DZ7 were selected and expression levels of them were measured for exploring mechanisms of cyantraniliprole resistance. Compare with MED-S, no significant overexpression of the five P450 genes was observed in the CYAN-R strain. Above results could be conductive to study on mechanism of cyantraniliprole resistance and will be very helpful for the management of whitefly.

Imidacloprid is a well-known pesticide and it is timely to evaluate its toxicity to earthworms (Eisenia fetida). In the present study, the effect of imidacloprid on reproduction, growth, acetylcholinesterase (AChE) and DNA damage in earthworms was assessed using an artificial soil medium. The median lethal concentration (LC50) and the median number of hatched cocoons (EC50) of imidacloprid to earthworms was 3.05 and 0.92 mg/kg respectively, the lowest observed effect concentration of imidacloprid about hatchability, growth, AChE activity and DNA damage was 0.02, 0.5, 0.1 and 0.5 mg/kg, respectively.

Beet armyworm, Spodoptera exigua (Hübner), is a worldwide pest of many crops. Chemical insecticides are heavily used for its control in China, and serious resistance has been evolved in the field to a variety of insecticides including emamectin benzoate. Through repeated backcrossing to a susceptible strain (WH-S) and selection with emamectin benzoate, the trait conferring resistance to emamectin benzoate in a field-collected population of S. exigua (moderately resistant to emamectin benzoate and strongly resistant to pyrethroids and indoxacarb) was introgressed into WH-S to generate a near-isogenic resistant strain (WH-EB). Compared with WH-S, the WH-EB strain developed a 1,110-fold resistance to emamectin benzoate and a high level of cross-resistance to abamectin (202-fold), with low levels of cross-resistance to cypermethrin (10-fold) and chlorfluazuron (7-fold), but no cross-resistance to representatives of another six different classes of insecticides (chlorantraniliprole, chlorfenapyr, indoxacarb, spinosad, tebufenozide, and chlorpyrifos). Resistance to emamectin benzoate in WH-EB was autosomal, incompletely dominant, and polygenic. Limited cross-resistance in WH-EB indicates that emamectin benzoate can be rotated with other classes of insecticides to which it does not show cross-resistance to delay the evolution of resistance in S. exigua. The incompletely dominant nature of resistance in S. exigua may explain the rapid evolution of resistance to emamectin benzoate in the field, and careful deployment of this chemical within a resistance management program should be considered.

The Bemisia tabaci (Gennadius) cryptic species complex comprises very destructive insect pests of agricultural crops worldwide and has been found to be resistant to various insecticides in China. Abamectin is one of the most widely used insecticides for insect pest control and the glutamate-gated chloride channel (GluCl) in insects was presumed to be the main target site of abamectin. In this study, a 1353 bp full-length cDNA encoding GluCl (named BtGluCl, GenBank ID: MF673854) was cloned and characterized from B. tabaci. BtGluCl encodes 450 amino acids, which shares 71–81% identity with other insect GluCl isoforms. Spatial and temporal expression revealed BtGluCl was highly expressed in the 4th nymphal instar and adult head, and the least expressed in the 1st nymphal instar and adult leg. Dietary ingestion of dsBtGluCl significantly reduced the mRNA level of BtGluCl in the treated adults by 62.9% and greatly decreased abamectin-induced mortality. Thus, our results could be conducive to further understanding the mechanisms of resistance to abamectin in arthropods.

Beet armyworm, Spodoptera exigua (Hubner), is a serious pest of vegetables in China, and its control is heavily dependent on chemical insecticides. The current resistance status of nine insecticides was investigated in 16 field populations collected from seven provinces of China during 2009–2012. Compared with the susceptible strain WH-S, some field populations evolved various levels of resistance to eight of the nine insecticides tested: emamectin benzoate (4- to 348-fold), indoxacarb (2- to 41-fold), spinosad (5- to 38-fold), chlorantraniliprole (2- to 44-fold), tebufenozide (2- to 87-fold), chlorfluazuron (3- to 31-fold), cypermethrin (79- to 1240-fold), and chlorpyrifos (8- to 3,080-fold), but no significant resistance was detected to chlorfenapyr (0.4- to 7-fold). This indicates that chlorfenapyr has no cross-resistance with these other currently used insecticides. Four consecutive years’ resistance screening at two places shows that resistance patterns were different between populations from Luhe (Jiangsu Province) and Fengxian (Shanghai), which are ≈300 km apart. Resistance levels to chlorpyrifos were much higher in populations from Luhe (877- to 3,080-fold) than from Fengxian (8- to 110-fold). Fengxian populations developed moderate levels of resistance to tebufenozide (13- to 87-fold), but no resistance in Luhe populations (2- to 6-fold). However, Luhe populations developed moderate levels of resistance to chlorfluazuron (21- to 31-fold), but there was no resistance in Fengxian populations (3- to 5-fold). It is suggested that local insecticide selection determined resistance patterns although S. exigua has long-distance migratory potential. Adaptive resistance management tactics (such as rotations) should be designed and implemented based on the resistance patterns of S. exigua for each geographic area.