Biorational glycol diesters as dietary toxins versus bioefficacy of sucrose octanoate against lepidopteran larvae

Abstract

A series of biorational glycol diesters were prepared which have similar characteristics as sugar esters. From 62 glycol diesters prepared, 35 compounds were active in the range of 1–10mg/ml concentration in diet that inhibited larval growth of second instars of Spodoptera litura and Helicoverpa armigera. The most inhibitory compounds to growth were ethylene, diethylene and triethylene glycol dialkanoates with EC50 range of 1–5mg/ml for S. litura and 2–6.5mg/ml for H. armigera. Comparatively, sucrose octanoate, the known insecticidal sugar ester, was least active (EC50=10.76 and 9.02mg/ml for S. litura and H. armigera, respectively). Toxicity induced by glycol diesters is not mediated through feeding inhibition as relative consumption rate was never significantly reduced but the relative growth rate was reduced by 25–54% in S. litura and 26–44% in H. armigera. Efficiency of conversion of ingested food (ECI) was also significantly reduced. Obviously, these results do not implicate any absolute antifeedant effect, but a toxicity effect due to a reduced ECI. This was surprisingly opposite to sucrose octanoate action, where a significant effect on consumption and not the ECI was observed after oral administration, which suggests an antifeedant effect. From structure/activity point of view, increasing the chain length of molecules decreased the activity. This is obvious from least activity obtained in molecules like propane, methyl propane and pentane derivatives. Second, the deviation from open chain compounds to cyclohexyl alkanoates also reduced the activity substantially. Therefore, an open chain glycol diester of C-8 carbon length is required for the said activity against lepidopterans.