Molecular characterization and expression profiles of nicotinic acetylcholine receptors in Bradysia odoriphaga

Impacts of Non-Lethal High-Temperature Stress on the Development and Reproductive Organs of Bradysia odoriphaga

Simple Summary

Bradysia odoriphaga is a soil-dwelling insect native to China, and its preferred host is Chinese chives. In this study, non-lethal high-temperature as an important limiting factor to affect the population and development of B. odoriphaga was assessed. Meanwhile, the physiological mechanism on non-lethal high-temperature to reduce the population was also identified. These would lay a key theoretical foundation for the future development of high-temperature products for environment friendly pest control strategies.

Abstract

Bradysia odoriphaga is an agricultural pest in China’s vegetable industry. In this study, pupae and adults were exposed to various non-lethal high-temperatures. The results demonstrated a decreased rate of eclosion once the pupae were exposed to temperatures exceeding 37 °C for 1 h. No effect on the lifespan of unmated female adults was observed after exposure to temperature stress, while unmated male adult lifespan decreased (>37 °C for 2 h). The size of the testis and ovaries for unmated male and female adults decreased, as did the fecundity and egg hatching rate for mated females. Compared with the control group (25 °C), the testis size of unmated male adults decreased after high-temperature stress followed by recovery at 25 °C for 1 h, though the size of the ovaries of female adults did not change. Additionally, the size of the testis and ovaries for unmated male and female adults decreased following high-temperature stress and 24 h of recovery at 25 °C. High temperatures affected males more than females; 37 °C is the critical temperature to control the population of B. odoriphaga. These results lay the foundation for the future development of environmentally friendly high-temperature prevention and pest-control strategies.

Geographic Monitoring of Insecticide Resistance Mutations in Native and Invasive Populations of the Fall Armyworm

Simple Summary

The moth fall armyworm (Spodoptera frugiperda) is a major agricultural pest insect damaging a wide range of crops, especially corn. Field evolved resistance against Bacillus thuringiensis (Bt) toxins and synthetic insecticides has been repeatedly reported. While the fall armyworm is native to the Americas, its biological invasion was first reported from West Africa in 2016. Since then, this pest has been detected across sub-Saharan and North Africa, Asia, and Oceania. Here, we examine the geographical distribution of mutations causing resistance against Bt or synthetic insecticides to test if the invasion was accompanied by the spread of resistance mutations using 177 individuals collected from 12 geographic populations including North and South America, West and East Africa, India, and China. We observed that Bt resistance mutations generated in Puerto Rico or Brazil were found only from their native populations, while invasive populations had higher copy numbers of cytochrome P450 genes and higher proportions of resistance mutations at AChE, which are known to cause resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and the resistance against synthetic insecticides in invasive Chinese populations. This information will be helpful in investigating the cause and consequence associated with insecticide resistance.

Abstract

Field evolved resistance to insecticides is one of the main challenges in pest control. The fall armyworm (FAW) is a lepidopteran pest species causing severe crop losses, especially corn. While native to the Americas, the presence of FAW was confirmed in West Africa in 2016. Since then, the FAW has been detected in over 70 countries covering sub-Saharan Africa, the Middle East, North Africa, South Asia, Southeast Asia, and Oceania. In this study, we tested whether this invasion was accompanied by the spread of resistance mutations from native to invasive areas. We observed that mutations causing Bt resistance at ABCC2 genes were observed only in native populations where the mutations were initially reported. Invasive populations were found to have higher gene numbers of cytochrome P450 genes than native populations and a higher proportion of multiple resistance mutations at acetylcholinesterase genes, supporting strong selective pressure for resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and resistance to various synthetic insecticides in Chinese populations. These results highlight the necessity of regular and standardized monitoring of insecticide resistance in invasive populations using both genomic approaches and bioassay experiments.

Low expression levels of nicotinic acetylcholine receptor subunits Boα1 and Boβ1 are associated with imidacloprid resistance in Bradysia odoriphaga

BACKGROUND

Neonicotinoid insecticide imidacloprid acts on insect nicotinic acetylcholine receptors (nAChRs). The mechanisms of insect resistance to imidacloprid include target-site alteration and increased detoxification metabolism. In Bradysia odoriphaga, cytochrome P450 monooxygenase has been found involved in metabolic resistance to imidacloprid. However, the situation of target-site related resistance to imidacloprid in B. odoriphaga is still unknown.

RESULTS

Nine field-collected B. odoriphaga populations showed various sensitivities to imidacloprid compared with the susceptible (SS) strain, including susceptibility, decreased susceptibility, low resistance, moderate resistance and high resistance. Seven nAChR subunit genes including α1, α2, α3, α7, α8, β1 and β3, were examined for site mutation and changes in transcription levels in field populations. No nAChR polymorphism potentially related to the resistant phenotypes was found. However, differential expression of nAChR subunit genes was found in imidacloprid resistant field population. In high imidacloprid resistant population LC-2 (93.14-fold resistance), the transcription levels of α1, α2 and β1 subunits were significantly down-regulated, while the transcription levels of α3 and α8 subunits were significantly up-regulated, compared with that in SS strain. In addition, imidacloprid acute exposure induced differential expression of nAChR subunit genes in B. odoriphaga. Furthermore, RNA interference (RNAi) suppressed the transcriptional expression of Boα1 and Boβ1, and decreased mortality of B. odoriphaga by 23.03% and 18.69%, respectively, when treated with imidacloprid.

CONCLUSION

These results indicated that, although no target-site mutation was found in imidacloprid resistant B. odoriphaga population, the reduced expression of α1 and β1 subunits contributed to B. odoriphaga resistance to imidacloprid. © 2020 Society of Chemical Industry.