Immunomodulatory, cyto-genotoxic, and growth regulatory effects of nerolidol on melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

Insects have evolved a robust immune system consisting of humoral and cellular branches and their orchestrated response enables insect to defend against exogenous stressors. Exploration of underlying immune mechanisms of insect pest under allelochemical stress can give us new insights on insect pest management. In this study, nerolidol, a plant sesquiterpene was evaluated for its insecticidal, growth regulatory, immunomodulatory, and cyto-genotoxic effects against melon fruit fly, Zeugodacus cucurbitae (Coquillett). First, second, and third instar larvae of Z. cucurbitae were fed on artificial diet containing different concentrations (5, 25, 125, 625, and 3125 ppm) of nerolidol. Results revealed a significant reduction in pupation and adult emergence as well as prolongation of developmental duration of treated larvae. Decline in growth indices showed remarkable growth inhibitory effects of nerolidol. Pupal weight and nutritional parameters viz. Larval weight gain, food assimilated, and mean relative growth rate declined after treatment. Immunological studies on second instar larvae depicted a drop in total hemocyte count and variations in proportions of plasmatocytes and granulocytes of LC30 and LC50 treated larvae. Phenoloxidase activity in nerolidol treated larvae initially increased but was suppressed after 72 h of treatment. The frequency of viable hemocytes decreased and that of apoptotic and necrotic hemocytes increased with both the lethal concentrations of nerolidol. Comet assay revealed a significant damage to DNA of hemocytes. The findings of the current study indicate that nerolidol exerts its insecticidal action through growth regulation, immunomodulation, and cyto-genotoxicity thus revealing its potential to be used as biopesticide against Z. cucurbitae.