Abstract
Plants employ an intricate and dynamic defense system that includes physiological, biochemical, and molecular mechanisms to counteract the effects of herbivorous attacks. In addition to their tolerance to phytotoxins, beet armyworm has quickly developed resistance to deltamethrin; a widely used pyrethroid insecticide in cotton fields. The lethal concentration (LC50) required to kill 50% of the population of deltamethrin to gossypol-fed Spodoptera exigua larvae was 2.34-fold higher than the control group, suggesting a reduced sensitivity as a consequence of the gossypol diet. Piperonyl butoxide (PBO) treatment was found to synergize with deltamethrin in gossypol-fed S. exigua larvae. To counteract these defensive plant secondary metabolites, beet armyworm elevates their production of detoxification enzymes, including cytochrome P450 monooxygenases (P450s). Gossypol-fed beet armyworm larvae showed higher 7-ethoxycoumarin-O-deethylase (ECOD) activities and exhibited enhanced tolerance to deltamethrin after 48 and 72 h when compared to the control. Moreover, gossypol pretreated S. exigua larvae showed faster weight gain than the control group after transferring to a deltamethrin-supplemented diet. Meanwhile, gossypol-induced P450s exhibited high divergence in the expression level of two P450 genes: CYP6AB14 and CYP9A98 in the midgut and fat bodies contributed to beet armyworm tolerance to deltamethrin. Knocking down of CYP6AB14 and CYP9A98, via double-stranded RNAs (dsRNA) in a controlled diet, rendered the larvae more sensitive to the insecticide. These data demonstrate that generalist insects can exploit secondary metabolites from host plants to enhance their defense systems against other toxic chemicals. Impairing this defense pathway by RNA interference (RNAi) holds a potential to eliminate the pest’s tolerance to insecticides and, therefore, reduce the required dosages of agrochemicals in pest control.
Highlights
Plants respond to herbivory through an intricate and dynamic defense system that includes physiological, biochemical, and molecular mechanisms to counteract the effects of insect attacks [1,2]
To find out the effect of plant secondary metabolites on insecticide tolerance, we examined the induced effect of gossypol-supplemented diet on the sensitivity of S. exigua larvae to deltamethrin, a widely used pyrethroid insecticide in many crops including cotton
We found that deltamethrin showed lowered toxicity to the S. exigua larvae fed on an artificial diet supplemented with 1% gossypol per gram of diet than it did in the gossypol-free control group
Summary
Plants respond to herbivory through an intricate and dynamic defense system that includes physiological, biochemical, and molecular mechanisms to counteract the effects of insect attacks [1,2]. Gossypol and related sesquiterpene aldehydes are the main secondary metabolites in cotton plants and have been shown to possess insecticidal activities and fungistatic properties [7,8]. Cytochrome P450s (CYPs) are a large gene family of multifunctional enzymes which are involved in both metabolic detoxification of plant secondary metabolites and chemical insecticides in herbivorous insects [10,12]. Cross-resistance of alpha-cypermethrin after ingestion of xanthotoxin in Helicoverpa zea and high expression response of P450s genes (CYP6B2, CYP6B6, CYP6B7, CYP6B8 and CYP321A1) were observed in quercetin fed larvae of H. armigera [11,20] In addition, insecticide resistance was found to be different in populations fed on different host plant species [21], indicating that the host plant and its secondary metabolites may affect insect susceptibility to pesticides. As the main phytotoxin of cotton, gossypol plays an important role in shaping the defensive state of beet armyworm
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
