Baseline toxicity and field efficacy of metaflumizone on Colorado potato beetle (Coleoptera: Chrysomelidae)

Control efficacy and joint toxicity of metaflumizone mixed with chlorantraniliprole or indoxacarb against the fall armyworm, Spodoptera frugiperda

BACKGROUND

The fall armyworm (FAW), Spodoptera frugiperda is the main destructive pest of grain crops, and has led to substantial economic losses worldwide. Chemical pesticides are the most effective way to manage FAW. Here, a laboratory test using an artificial diet-incorporated assay was conducted to determine the toxicity of five insecticides and the joint effect of the binary combination insecticides to FAW larvae. A field plot test using foliar spray was carried out to assess the control efficacy of metaflumizone mixed with chlorantraniliprole or indoxacarb against FAW.

RESULTS

The bioassay results showed that metaflumizone had a stronger insecticidal effect than indoxacarb toward FAW larvae. Furthermore, the mixture of metaflumizone and chlorantraniliprole in a volume ratio of 3:7 had the strongest synergistic effect against FAW, with a co-toxicity coefficient (CTC) of 317.18. The best synergistic effect for mixtures of metaflumizone and indoxacarb was observed at a 1:9 volume ratio, with a CTC of 185.98. However, there was an antagonistic effect of metaflumizone mixed with emamectin benzoate and with lufenuron, because the co-toxic factor was less than -20 at volume ratios of 8:2 and 9:1, respectively. According to the results of the field trial, metaflumizone mixed with chlorantraniliprole or indoxacarb at a 50% reduction of the application rate can effectively control FAW with efficacy ranging from 77.73% to 94.65% 1-7 days postapplication.

CONCLUSION

Overall, our findings suggest that metaflumizone and its binary combination insecticides can be utilized in FAW integrated pest management programs. © 2022 Society of Chemical Industry.

Genome resequencing reveals rapid, repeated evolution in the Colorado potato beetle

Insecticide resistance and rapid pest evolution threatens food security and the development of sustainable agricultural practices, yet the evolutionary mechanisms that allow pests to rapidly adapt to control tactics remains unclear. Here we examine how a global super-pest, the Colorado potato beetle (CPB), Leptinotarsa decemlineata, rapidly evolves resistance to insecticides. Using whole genome resequencing and transcriptomic data focused on its ancestral and pest range in North America, we assess evidence for three, non-mutually exclusive models of rapid evolution: pervasive selection on novel mutations, rapid regulatory evolution, and repeated selection on standing genetic variation. Population genomic analysis demonstrates that CPB is geographically structured, even among recently established pest populations. Pest populations exhibit similar levels of nucleotide diversity, relative to non-pest populations, and show evidence of recent expansion. Genome scans provide clear signatures of repeated adaptation across CPB populations, with especially strong evidence of selection on insecticide resistance genes in different populations. Analyses of gene expression show that constitutive upregulation of candidate insecticide resistance genes drives distinctive population patterns. CPB evolves insecticide resistance repeatedly across agricultural regions, leveraging similar genetic pathways but different genes, demonstrating a polygenic trait architecture for insecticide resistance that can evolve from standing genetic variation. Despite expectations, we do not find support for strong selection on novel mutations, or rapid evolution from selection on regulatory genes. These results suggest that integrated pest management practices must mitigate the evolution of polygenic resistance phenotypes among local pest populations, in order to maintain the efficacy and sustainability of novel control techniques.

Regional differences in gene regulation may underlie patterns of sensitivity to novel insecticides in Leptinotarsa decemlineata

BACKGROUND

Agricultural insect pests frequently exhibit geographic variation in levels of insecticide resistance, which are often presumed to be due to the intensity of insecticide use for pest management. However, regional differences in the evolution of resistance to novel insecticides suggests that other factors are influencing rates of adaptation. We examined median lethal concentration (LC₅₀ ) bioassay data spanning 15 years and six insecticides (abamectin, imidacloprid, spinosad, cyantraniliprole, chlorantraniliprole, and metaflumizone) for evidence of regional differences in Leptinotarsa decemlineata baseline sensitivity to insecticides as they became commercially available.

RESULTS

We consistently found that larvae from Colorado potato beetle populations from the northwestern USA had the highest baseline sensitivity to novel insecticides, while populations from the eastern USA had the lowest. Comparisons of gene expression between populations from these regions revealed constitutively elevated expression of an array of detoxification genes in the East, but no evidence of additional induction when exposed to imidacloprid.

CONCLUSIONS

Our results suggest a mechanism for geographic variation in rates of adaptation to insecticides, whereby baseline levels of gene expression determine a population's response to novel insecticides. These findings have implications for the regional development of insecticide resistance management strategies and for the fundamental question of what determines the rate of adaptation to insecticides. © 2020 Society of Chemical Industry.

Resistance Risk Evaluated by Metaflumizone Selection and the Effects on Toxicities Over Other Insecticides in Spodoptera exigua (Lepidoptera: Noctuidae)

Metaflumizone is a novel semicarbazone insecticide. It functions as a sodium channel blocker insecticide (SCBI) with excellent insecticidal activity on most economically important lepidopterous pests. This study assessed the resistance risk of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) to metaflumizone in the laboratory and the effects of metaflumizone selection on toxicities to other insecticides. Spodoptera exigua collected from a field population at Huizhou in 2012 were successively challenged by metaflumizone to evaluate the risk of resistance evolution. Twelve generations of selection increased resistance to metaflumizone by 3.4-fold and threshold trait analysis revealed that the realized heritability (h2) of this resistance was 0.086. When h2 was equal to 0.086 and 90% of individuals were killed at each generation, LC50 to metaflumizone increased by 10-fold after 15 generations. The selection by metaflumizone did not increase the resistance to indoxacarb, chlorantraniliprole, spinosad, methomyl, or endosulfan, suggesting a lack of cross-resistance. However, metaflumizone challenge upheld the recession of resistance to emamectin benzoate, chlorfluazuron, and tebufenozide. The block of resistance drops by metaflumizone exposure implied a possible cross-resistance between metaflumizone and these three insecticides. These results contribute to integrated resistance management of S. exigua.

Characterisation of imidacloprid resistance in the bird cherry-oat aphid, Rhopalosiphum padi, a serious pest on wheat crops

BACKGROUND

Rhopalosiphum padi is a destructive insect pest of wheat worldwide. Studies have shown that R. padi has developed resistance to different insecticides, including imidacloprid. We studied the mechanisms conferring resistance to imidacloprid at the biochemical and molecular levels.

RESULTS

An R. padi imidacloprid-resistant (IM-R) strain and a susceptible (SS) strain were established. Fitness analysis using life-tables showed that the IM-R strain had obvious disadvantages in several parameters, indicating reduced fitness. Profiles of cross-resistance of IM-R and SS to seven insecticides were detected. Both synergistic and enzyme activity data suggested that P450 plays a role in resistance. Furthermore, the mRNA expression levels of cytochrome P450 (CYP) genes CYP6CY3-1 and CYP6CY3-2 were significantly increased in the IM-R strain. No target-site mutation within the nicotinic acetylcholine receptor (nAChR) subunits was detected in the IM-R strain. Interestingly, the expression levels of the nAChR α1, α2, α3, α7-2, and β1 subunit genes were significantly decreased, suggesting that down-regulation of these subunits may be involved in resistance.

CONCLUSION

Multiple mechanisms confer imidacloprid resistance in R. padi. © 2017 Society of Chemical Industry.

Biochemical mechanisms for metaflumizone resistance in beet armyworm, Spodoptera exigua

The metaflumizone, which belongs to the class of voltage-dependent sodium channel blockers, was registered to control Spodoptera exigua on vegetables in China in 2009. The present study revealed S. exigua has developed high resistance to this novel chemistry insecticide shortly after 2-3 years application in Guangdong Province of China. The metabolic mechanisms for metaflumizone resistance in this insect were analysed. The inhibitor of esterases greatly potentiates the toxicity of this chemical against the field resistant populations. The synergism ratio is 5.7 and 3.4-fold for S. exigua collected from Huizhou, Guangdong Province in 2011 and 2012, respectively. The activity of esterases in field populations (HZ12) is also significantly greater than that in the susceptible strain, and further significantly increased by challenge with metaflumizone for 3 generations. However, the inhibitor of P450s or GSTs only has slight synergism on metaflumizone toxicity against resistant populations, and there are no obvious differences in activities of P450s or GSTs between resistant populations and the susceptible strain. These results suggest that esterases might take pivotal role in conferring metabolic resistance to metaflumizone in the field populations of S. exigua, and P450s or GSTs are not involved in this resistance. Moreover, flavin-dependent monooxygenases (FMOs) are discovered to involve in metaflumizone resistance in the field populations of S. exigua. The FMO inhibitor, methimazole, potentiates metaflumizone toxicity in resistant larva of this species substantially. The synergism ratios for methimazole in resistant populations HZ11 and HZ12 were 3.1 and 1.9, respectively. Enzymatic assays also revealed higher FMO activities in resistant populations than in the susceptible strain, and successive selection with metaflumizone further increased the FMO activity in the field resistant population, but not significantly. The higher FMO activities in the older larval stages and in the larval midgut signify the importance of FMO in the detoxification of xenobiotic from food sources. The synergism assay and FMO activity analysis suggest that FMO contributes to metaflumizone detoxification in resistant populations of S. exigua and conferred metaflumizone resistance in S. exigua. A novel mechanism for insecticide resistance by insect was proposed.

Toxicity of insecticides to populations of tomato borer Tuta absoluta (Meyrick) from Greece

BACKGROUND

Tuta absoluta (Meyrick), in only a few years, has become a serious threat to global tomato production. Depending on the cropping system and infestation pressure, T. absoluta control may rely heavily on insecticide applications. By means of a validated IRAC bioassay method, the toxicity of all insecticides registered for T. absoluta control in Greece has been estimated. A non-registered pyrethroid insecticide was also included in this study.

RESULTS

Low heterogeneity was detected in the populations tested with most insecticides. The LC50 ranged from 0.31 to 1.31 mg L(-1) for flubendiamide, from 0.12 to 0.53 mg L(-1) for chlorantraniliprole, from 0.03 to 0.12 mg L(-1) for emamectin benzoate, from 0.08 to 0.26 mg L(-1) for spinosad, from 31.8 to 159.5 mg L(-1) for metaflumizone, from 1.73 to 17.5 mg L(-1) for indoxacarb, from 530 to 2038 mg L(-1) for chlorpyriphos and finally from 475 to 794 mg L(-1) for cypermethrin. The variability of the LC50 values among the tested populations was low (RR under 5×), except for indoxacarb (RR = 10×). In the absence of a reference strain, comparisons with the recommended label rates were performed. Evidence of potential control failures was detected using probit analysis estimates for cypermethrin, chlorpyriphos and metaflumizone.

CONCLUSIONS

For most registered insecticides, a solid set of baseline data has been presented that can be used in future resistance monitoring studies. The interaction of metaflumizone with T. absoluta has been discussed, and for chlorpyriphos it is suspected that the resistance level is underestimated with the present dataset. Finally, it has been demonstrated that the pyrethroid cypermethrin would provide insufficient control of the pest.