Ecdysones and Plant Growth Regulators Induce Solitarious Characters and Reduce Fertility in the Desert Locust

Abstract

When a zoo‐ecdysone (crustecdysone), a supposed phyto‐ecdysone (from leaves of Podocarpus gracilior), or a plant growth regulator (Alar® 85) were injected into newly ecdysed, gregarious, fourth‐ instar nymphs of the desert locust, Schistocerca gregaria (Forsk.), the morphometric ratios of the resulting adults were intermediate between the two extreme phases. In no case a complete transformation to the solitarious form was obtained. Only the plant growth regulator resulted in the sterility of the adults. The possible importance of non‐neotenic substances in locust control is discussed in relation to neotenic compounds which are structurally more complicated. RÉSUMÉ UNE PHYTO‐ECDYSONE, UNE ZOO‐ECDYSONE ET UNE SUBSTANCE RÉGULATRICE DE CROISSANCE POUR LES VÉGÉTAUX, INDUISENT DES CARACTÈRES DE TYPE “SOLITAIRE” ET RÉDUISENT LA FERTILITÉ CHEZ SCHISTOCERCA GREGARIA Les produits utilisés sont: un extrait brut des feuilles de Podocarpus gracilior, considéré comme renfermant une phyto‐ecdysone (PhE); de la 20 — hydroxyecdysone ou zoo‐ecdysone (ZE); un régulateur de la croissance végétale, le 2,2‐diméthyl‐hydrazide de l'acide succinique (Alar® 85). Chacun de ces produits a été injecté, en une seule fois, à une dose non toxique, à des lots de 30 larves grégaires (♂ et ♀) de Sch. gregaria, larves du 4ème stade venant de muer. En aucun cas on n'a observé une transformation complète de l'adulte vers le type solitaire, mais les indices biométriques montrent une tendance vers les types transiens. Tous les composés chimiques testés diminuent la durée de la vie larvaire et la fertilité des adultes s'est montrée réduite par le composé Alar® 85. L'action des substances testées est discutée par comparaison avec les effets connus de composés chimiques plus complexes à propriétés qualifiées de néoténiques, telle que l'hormone juvénile et ses analogues.

Suppressive Impact of 6-Benzyladenine, A Plant Growth Regulator, on the Adult Performance and Reproductive Potential of Galleria mellonella L. (Lepidoptera: Pyralidae)

“…A similar result was recorded for S. littoralis by the same PGR (Salama and El-Sharaby, 1972). El-Ibrashy et al (1976) injected Alar ® 85 into the newly moulted gregarious 4 th instar nymphs of the desert locust Schistocerca gregaria and recorded complete sterility (zero fertility) in the treated locust. Adding GA3 or ABA to a grass diet of A. elliotti significantly reduced the egg viability (Visscher, 1980).…”

Haemolymph ecdysteroids in the solitary and gregarious larvae ofSchistocerca gregaria

“…Previous experimental findings indicated, however, that differences in the peak concentration may be most significant. It was shown that partial ablation of PG, presumably followed by a reduction of ecdysteroid titre, causes appearance of some gregarious features in the solitary hoppers (Ellis and Carlisle, 1961), and that injection of phytoecdysteroids into gregarious larvae leads to their partial conversion to the solitary phase (El-Ibrashy et al, 1976). Our data do suggest that gregarious phase is associated with a lower ecdysteroid titre than in the solitary phase but additional measurements under various experimental conditions are needed to prove the role of ecdysteroids in the control of locust phase dimorphism.…”

Hormonal Control of the Phase Polyphenism of the Desert Locust: A Review of Current Understanding

“…Moreover, Tawfik et al [158] showed that the titres of ecdysteroid in the haemolymph of the solitary and gregarious penultimate and last instar larvae of S. gregaria; the longer duration of the moult-inducing surge of ecdysteroid; and the frequently higher proportion of highly polar products distinguish the gregarious from solitary larvae of S. gregaria. On the other hand, it was shown that partial ablation of prothoracic (also called ventral) glands (PGs), after which it was presumed that there would be a reduction in the titre of ecdysteroid, causes the appearance of some gregarious features in solitary hoppers [20], and that injection of phytoecdysteroids into gregarious larvae leads to the appearance of some solitary characters [159].…”