Azadirachtin, a Chemical Probe for the Study of Moulting Processes in Rhodnius prolixus

Abstract

The effects of azadirachtin A after injection into timed 4th-instar nymphs of Rhodnius prolixus were studied. A dose-response relationship of Aza A was established using moulting inhibition and mortality as effective parameters. Aza A , if injected 1 to 3 days after blood feeding, inhibited the moulting process. However, if injected during and after the onset of epidermal mitosis, ecdysis was not affected. A single dose of Aza A was able to block the onset of mitosis in the epiderm is, which is associated with the moulting cycle and is triggered by moulting horm one. Ecdysteroid titres, determined by radioimmunoassay, were too low for an induction of ecdysis in the Aza A treated nymphs. During the peak maximum, the predom inant ecdysteroid was 20-hydroxyecdysone. The conjugated ecdysteroids were based on 20-hydroxyecdysone and ecdysone in the same ratio. The significance of these findings in relation to the possibility of Aza A to act either directly on the prothoracic glands or indirectly through releasing sites in the brain or through Corpus allatum is discussed.