Fitness cost of spinosad resistance related to vitellogenin in Frankliniella occidentalis (Pergande)

Abstract

Background The western flower thrips Frankliniella occidentalis, a worldwide agricultural pest, has developed resistance to an array of insecticides. Spinosad resistance confers an apparent fitness cost in F. occidentalis. In the present study, we compared the reproductive capacities, ovary development, and the expression of the vitellogenin (Vg) gene in spinosad‐susceptible (Ivf03) and ‐resistant (NIL‐R) near isogenetic lines of F. occidentalis in order to clarify the reason for the fitness cost in spinosad resistance. Results The NIL‐R strain exhibited a 17.9% decrease in fecundity (eggs laid per female) as compared to the Ivf03 strain, and the ovariole was significantly shortened by 2.8% in the NIL‐R strain relative to the Ivf03 strain. Compared to the Ivf03 strain, the expression levels of Vg mRNA and protein were downregulated by 33.7% and 32.9% in the NIL‐R strain, respectively. Moreover, interference with the Vg gene significantly reduced the expression levels of Vg mRNA and protein, and decreased ovariole length, survival rates and the fecundity of both strains. Conclusion The results indicate that the downregulated expression of Vg may contribute to the reduction of ovariole length and consequently to a fitness cost in spinosad‐resistant F. occidentalis. The results not only increase our understanding of the evolution of insecticide resistance, but also could contribute to the formulation of control strategy of F. occidentalis. © 2022 Society of Chemical Industry.

Identification and RNAi‐based function analysis of trehalase family genes in Frankliniella occidentalis (Pergande)

“…Double‐stranded RNA (dsRNA) primers specific for FoTRE1‐1 , FoTRE1‐2 , FoTRE2 , and the control ( EGFP ) (Table S1) were individually designed in gene‐specific regions to avoid potential off‐target effects using the SnapDragon tool (https://www.flyrnai.org/cgi-bin/RNAi_find_primers.pl). RNAi was carried out on insect samples via the feeding method as described by Hua et al 44 . The FoTRE1‐1 , FoTRE1‐2 , FoTRE2 , and EGFP dsRNA primers were synthesized with the T7 Ribomax Express RNAi reagent following the manufacturer's instructions (Promega, Madison, USA).…”

“…At 3 days of feeding, five pairs of thrips were also transferred onto leaf discs (3.5 cm in diameter) obtained from cabbage leaves. Each leaf disc bearing thrips was placed in a separate 3.5‐cm diameter plastic Petri dish containing 3% agar with the adaxial surface facing downward 44 . After 3 days in the dish, the number of eggs on each leaf disc was counted and hatchability was calculated.…”

“…wileyonlinelibrary.com/journal/ps 2.5 RNAi assay Double-stranded RNA (dsRNA) primers specific for FoTRE1-1, FoTRE1-2, FoTRE2, and the control (EGFP) (Table S1) were individually designed in gene-specific regions to avoid potential off-target effects using the SnapDragon tool (https://www.flyrnai.org/cgibin/RNAi_find_primers.pl). RNAi was carried out on insect samples via the feeding method as described by Hua et al 44 The FoTRE1-1, FoTRE1-2, FoTRE2, and EGFP dsRNA primers were synthesized with the T7 Ribomax Express RNAi reagent following the manufacturer's instructions (Promega, Madison, USA). An artificial diet solution was prepared by mixing 0.5 μg • μL −1 of target gene dsRNA in 10% sucrose with 0.2 mL of diet solution and the resulting mixture was referred to as the RNAi solution.…”

“…Each leaf disc bearing thrips was placed in a separate 3.5-cm diameter plastic Petri dish containing 3% agar with the adaxial surface facing downward. 44 After 3 days in the dish, the number of eggs on each leaf disc was counted and hatchability was calculated. Finally, adult thrips were fed on the transgenic pepper plants for 3 days, then transferred to healthy bean pods.…”

Fitness costs of resistance to insecticides in insects

“… Fu et al (2018) , highlights the rapid increase in resistance to spinetoram in Thrips hawaiiensis (Thysanoptera: Thripidae), accompanied by a decline in resistance ratios over generations. Similarly, Hua et al (2023) , demonstrate how spinosad resistance in F. occidentalis (Thysanoptera: Thripidae), incurs fitness costs, affecting fecundity and ovary development. Furthermore, the complexity of resistance in pest management strategies is evident in the study by Chappell et al (2019) , which demonstrates that fitness costs of imidacloprid resistance in Frankliniella fusca (Thysanoptera: Thripidae), may not necessarily impede resistance evolution alone, as consistent insecticide use can offset these costs.…”