Understanding the chemical ecology of Brassicaceae specialist herbivore P.xylostella and its predators

Abstract

Plant infochemistry plays crucial role in governing the tritrophic interactions. Biological pest control is an environmental friendly approach that uses the natural enemies to control the pest population. To establish a potential biocontrol agent it’s crucial to understand the natural enemy’s response to the plant-produced as well as herbivore-metabolized chemicals. Here we tried to investigate the effect of glucoraphanin and its metabolized forms produced by the diamondback moth larvae on plant-herbivore-natural enemy interactions to reveal the ecological significance of plant’s defense and herbivore’s phytotoxin detoxification mechanisms in the tritrophic interactions. Native Indian biological control agents for the diamondback moth were collected and identified based on the available keys. Plant-mediated RNA interference (PMRi) was used to silence the detoxification gene in Plutella xylostella. PMRi led to the accumulation of toxic isothiocyanates in gut, hemolymph and frass of P. xylostella larvae. These toxic isothiocyanates showed detrimental effects on growth of the herbivore. Three predatory spider species- Hasarius adansoni, Plexippus paykulli and Wadicosa fidelis were used to evaluate the effect of gene silencing on the behaviour and choice of the predators. Spiders showed uniform behavior to the changes in metabolite composition of their prey. Frass analysis of these spiders revealed that the spiders were able to detoxify the toxic isothiocyanates via mercapturic pathway. Thus, this case study demonstrates the ecological significance and metabolism of glucosinolates in plant-herbivore-natural enemy interaction. This study contributes valuable inputs towards devising integrated pest management strategies against the pest P. xylostella.