Developmental and morphogenetic alterations in larvae of Locusta migratoria reared on plant diet with a selectively modified sterol profile
Résumé
Wheat seedlings germinating in the presence of the systemic fungicide fenpropimorph accumulate 9β, 19-cyclopropylsterols (95% of total sterols) in place of Δ5-sterols which are normally produced in these plants. Larvae of the phytophagous insect Locusta migratoria show reduced titres of ecdysteroids and considerably delayed development when reared on fenpropimorph-treated wheat. In addition, a significant number of such larvae exhibit anticipated wing reversal and reach the adult stage after four larval instars in place of the normal number of five. These anticipated morphogenetic events and the reduction of the number of larval instars had been induced in earlier experiments by implantation of supernumerary prothoracic glands into juvenile larvae, but not by injections of ecdysone. The prothoracic glands of experimental larvae reared on fenpropimorph-treated wheat show ultrastructural signs indicative of an intense protein synthesis in the rough-surfaced endoplasmic reticulum, and we hypothesize that proteins secreted by the prothoracic glands are responsible for the morphogenetic changes observed in the experimental larvae.