Olfactometric tests for the determination of repellency action against Spodoptera frugiperda (Lepidoptera: Noctuidae) by leaves and macerated of Azadirachta indica (Neem)

Abstract

Secondary metabolites can be used plants to defend themselves against the attacks of insects. Among these active metabolites, volatile organic compounds (VOCs) are usually found in the essential oils of plants and belong to the family of terpenes. An alternative to the use of synthetic insecticides is the use of aqueous extracts and oils derived from the Azadirachta indica tree (Neem). Neem has been widely used in pest control, since it has several properties such as growth antifeedant, repellent, antiovipositor and sexual communication switch. The active agent is azadirachtin, which has been proven to behave as a natural insecticide; hence, it could be the precursor of a new generation of natural insecticide products. This work provides information on the behavioral responses of fall armyworm Spodoptera frugiperda to the VOCs released by neem fresh leaves in laboratory bioassays. Olfactometry tests were carried out to evaluate the preference of the insect when it was offered the stimulus from two different samples. These tests were carried out with adult females of S. frugiperda and a Y-type olfactometer. A stream of air filtered through activated carbon was supplied to each arm of the olfactometer using an aeration pump. The tests were performed by placing the insect (one at a time and without repeating) against the stimulus from the olfactometer containing the sample and the control corresponding to the absence of test material. Three double-choice bioassays of 30 repetitions each were performed:I) Healthy leaves of Neem vs. control.II) Crushed leaves of Neem vs. control.III) Macerated Neem vs control.Series I and III presented significant differences of choice (p <0.05) being the preference to Neem leaves o macerates lower than that of control. VOC of the healthy Neem leaves and their maceration showed a repellent effect against fall armyworm.