Biological Activity of Azadirachtin, Component of the Neem Tree1 Inhibiting Molting in the Face Fly, Musca autumnalis De Geer (Diptera: Muscidae)

Abstract

The possible effects of azadirachtin, a component of the neem tree, Azadirachta indica A. Juss, in inhibiting molting in larvae of the face fly, Musca autumnalis DeGeer, were studied. Apart from delayed lethal action, effects on the pupation, adult emergence, and size of pupae or adults have been considered. A baseline exposure for 10 or 20min, ranging from 0.00001 to O.1μg/ml, was used, causing about 20 or 22.5 to 83.5 or 97.6% inhibition (inhibition of adult-concentration-probability lines). Doses required to inhibit the emergence of 50% of the adults (IC₅₀) were found to be very low (0.0024 and 0.000039 μg/ml for the 10- and 20-min exposure times, respectively. The compound is characterized by its inhibition or prevention of formation of adult morphology. The effects on pupae (basedon proportion of undeveloped individuals) and adults (based on incomplete development, attachment to puparia, or inability to fly) were dose-dependent. The development from third larval instar to adult was completely inhibited by exposure to 0.1 μg/ml for 20 min(97.58%). No adults were obtained at doses of 1.10, 10.0, and 100.0 μg/ml. These concentrations caused about 100% mortality of larvae or developed pupae. Results showed a reduction in M. autumnalis size as a function of azadirachtin exposure. There seemed to bea direct relationship between the size of the resulting pupae or adult males and females, since treatment of larvae with 0.00001 to O.1μg/ml azadirachtin caused significant reductions in the pupal weights and dimensions, adult weights, wing dimensions, or interocular distances. Treatments with 0.00001 and 0.001 μg/ml resulted in an insignificant increase(0.8–1.6%) in female wing length/width. Concentrations 0.001, 0.01, and O.1μg/ml also did not significantly affect the wing dimensions of females.