Elicitor-mediated induction of Cajanus cajan defences altered nutritional indices of Maruca Vitrata (Fab.) (Lepidoptera: Crambidae)

Elicitor-induced defences are a new addition in plants’ armour to counter insect herbivory. It is unknown whether exogenously-applied jasmonic acid and salicylic acid (JA & SA) induced defence in pigeonpea (Cajanus cajan) can reduce Maruca vitrata (Fab.) herbivory. We exogenously treated one resistant (AL 1747) and one susceptible (MN 1) pigeon pea genotype with JA (100 µM) and SA (5 mM) at 50% flowering stage (five treatments each). Then, we quantified pigeon pea secondary plant metabolites and M. vitrata nutritional indices. Approximate digestibility, efficiency of conversion of ingested and digested food into body matter, and relative growth rate of M. vitrata larvae were significantly reduced on plants pre-treated with JA and then infested with M. vitrata (PJA + MV); however, consumption index was increased. SA applications also altered the nutritional indices of M. vitrata, but the effects were not as pronounced as JA applications. PJA + MV treatment rapidly increased the level of tannins, total phenols and total protease inhibitors in flowers of both genotypes one day after treatment (DAT); this induction was more noticeable in the resistant genotype. However, only constitutive levels of the aforesaid compounds were detected at 7 DAT. Thus, JA and SA can significantly enhance pigeonpea defences against M. vitrata, providing farmers with an environmentally friendly alternative to synthetic pesticides. Researchers can further explore the use of natural or synthetic elicitors in integrated pest management, potentially combining them with biological control.