The juvenoids fenoxycarb and methoprene were evaluated for morphogenetic activity on last-instar nymphs of the American bird grasshopper, Schistocerca americana (Drury) (Orthoptera: Acrididae). Topical application of fenoxycarb induced supernumerary nymphs, adultoids and adults with curled wings. Methoprene yielded similar morphogenetic effects although at reduced levels of activity. Of particular interest, however, is the discovery that, in addition to its morphogenetic activity, fenoxycarb causes significant mortality in developing fourth-, fifth- and sixth-instar nymphs.

Three aromatic juvenoids were evaluated for morphogenetic activity on Schistocerca americana. Fenoxycarb, the most active insect growth regulator examined, was found to induce a significant mortality in developing fifth stage nymphs and caused severe morphogenetic damage during ecdysis to the adult. Juvenoid treatments were also observed to increase the duration of the last nymphal stage and to induce chromotropic colour changes similar to that observed in the solitary phase of the desert locust, Schistocerca gregaria Forskal.

Changes in the activities of general esterase, L-alanine:2-oxoglutarate aminotransferase (GPT), L-aspartate:2-oxoglutarate aminotransferase (GOT), acid and alkaline phosphatase after allatectomy, brain-cauterization and juvenoid treatment have been studied. It has been shown that allatectomy reduces the GPT, GOT, general esterase and acid phosphatase activity in all tissues from both sexes and alkaline phosphatase activity in all the cases excepting the testis. Treatment with juvenoid in allatectomized insects reverses the effects of allatectomy. Both allatectomy and brain-cauterization cause the drastic decrease of all the enzymes in both sexes. The physiological significance of these findings has been discussed in this paper.