Desensitization of fifth instar Spodoptera litura to azadirachtin and neem

Abstract

The deterrence of azadirachtin, in its pure form and as a constituent of neem seed extract, to fifth instar Spodoptera litura (Fab.) larvae, was measured using cabbage, Brassica oleraceae (L.) var. capitata, leaf disc assays. Pairedchoice assays, in which larvae could choose between feeding on a treated (1.3 ng azadirachtin per square cm leaf area) or an untreated leaf disc for 2 h, were conducted at 24 h intervals throughout the fifth instar. In addition, no-choice assays, in which larvae could feed on only one leaf disc (10 ng azadirachtin per square cm leaf area) for 1.5 h, were conducted consecutively over a six hour period at the beginning of the fifth instar. The effects of hunger and habituation on desensitization in our no-choice tests were partitioned. After repeated exposures, larvae became desensitized to pure azadirachtinal in both choice and no-choice tests, but did not desensitize to neem containing the same absolute amount of azadirachtin in choice tests. Hunger was responsible for approximately one third of the desensitization response in the no-choice tests. Sensitivity to azadirachtin was independent of age within the fifth instar.

Toxicity, Feeding Deterrence, and Effect of Activity of 1,8-Cineole from <I>Artemisia annua</I>on Progeny Production of <I>Tribolium castanaeum</I>(Coleoptera: Tenebrionidae)

“…We suggest that strong volatiles, especially in their synergic action, were important for masking the effect of tested solutions on feeding by L. dispar larvae (Chapman 1974). Desensitization to antifeedants in feeding assays has been documented for lepidopteran larvae (Bomford and Isman 1996). However, in our experiment the antifeedant index was maintained at a high level during the observation time for all treatments.…”

Binary mixtures of feeding deterrents mitigate the decrease in feeding deterrent response to antifeedants following prolonged exposure in the cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae)

“…These results corroborate earlier findings with neem and its main constituent azadirachtin (Bomford & Isman 1996), showing that Spodoptera litura developed a rapid decrease in feeding deterrent response to azadirachtin but not to neem containing a mixture of compounds including azadirachtin. Vol.…”

“…When a complex mixture of substances inhibits feeding, however, a decrease in feeding deterrent response may not occur (Jermy 1986;Bomford & Isman 1996).…”

Ecosmart Biorational Insecticides: Alternative Insect Control Strategies

“…Azadirachtin is a common example of a natural plant defense chemical affecting feeding, through chemoreception (primary antifeedancy), that consists in the blockage of the input from receptors that normally respond to phagostimulants, or from stimulation of specific deterrent cells or both (Dethier, 1982) and through a reduction in food intake due to toxic effects if consumed (secondary antifeedancy), where food intake is reduced after application of azadirachtin in ways which bypass the mouth part chemoreceptors (Mordue & Blackwell, 1993). The antifeedant effect is highly variable among pest species, and even those species initially deterred are often capable of rapid desensitization to azadirachtin (Bomford & Isman, 1996). Azadirachtin is a tetranortriterpenoid, structurally similar to insect hormones "ecdysones", its biological activity as ecdysone-blocker thus disturbing insect growth.…”