Melia azedarach Extract as an Antifeedant to Bemisia tabaci (Homoptera: Aleyrodidae)

Melia azedarach (L.) is a tree of the family Meliaceae native to India and introduced to Brazil many years ago. The insecticidal property of meliaceous plants has been known for quite a long time (Kraus et al., 1987). Another plant of the same family, the neem tree, Azadirachta indica, is known for its insect antifeedant and/or insect growth regulation activity (Schumuterer, 1990). Tests carried out under screen-house conditions showed that M. azedarach aqueous extract interfered with the transmission of bean golden mosaic virus (BGMV) by Bemisia tabaci (Genn.). The transmission efficiency of this virus by the vector was reduced by 95% in the acquisition or inoculation tests, although the extract had no insecticidal action. The extract interference was also observed under field tests, reducing transmission by 45-60% compared to the control plants (Nardo & Costa, 1990). These results were attributed to a phago-deterrent effect of the plant extract, although a toxic action on the B. tabaci was possible. The purpose of the present study was to verify whether or not M. azedarach extract could affect feeding and colonization on bean plants by B. tabaci. The tests were carried out under screen-house conditions at Campinas, State of Salo Paulo, Brazil. B. tabaci was collected from a colony reared on soybean plants in a screen-house in the same region. Test plant was the common bean, Phaseolus vulgaris L., cv. Carioca, with 2 primary leaves per plant and 2 plants per pot. The extraction procedure was conducted using an aqueous cold infusion of equal parts of leaves and ripe fruits at the rate of 1:5 (w/v). Leaves and fruits were blended with water and maintained in a glass container for 24 h after which the infusion was filtered through a fine cloth and used for spraying. Two experiments were conducted with the extract. The objective of the first experiment was to determine the mortality of B. tabaci caused by M. azedarach extracts. It consisted of 3 treatments with 3 replications at 3 different times. Each experiment consisted of 25 adult B. tabaci of uniform age (1 day) confined in a glass cage (12 x 8 cm) over a pot with 2 bean plants sprayed with M. azedarach aqueous extract (treatment 1); 2 bean plants sprayed with water (treatment 2); and no plants, just soil (treatment 3). The numbers of live insects was counted daily until the last one died. The objective of the second experiment was to evaluate whether or not oviposition of B. tabaci would be affected by treating plants with M. azedarach extract. The experiment consisted of 2 treatments and 3 replicates. Each experimental unit consisted of 10 bean plants sprayed with M. azedarach extract (treatment 1) or water (treatment 2). Potted plants (with 2 primary leaves) were exposed to a dense population (more than 5 x 103) of B. tabaci adults reared on soybean plants. After 72 h the plants were moved to a different screen-house (all adult B. tabaci had been removed from the