Effect of teflubenzuron on ultrastructure and components of the integument in Schistocerca gregaria (Forskal) 5th instar nymphs

Abstract

Newly ecdysed 5th instar Schistocerca gregaria nymphs were orally treated with LC75 of the chitin synthesis inhibitor teflubenzuron (135ppm) for 24h; subsequently they were offered an untreated diet for the duration of this instar. Ultrastructural observation of the cuticle in 7 day old untreated 5th instar desert locust nymphs showed that the moulting events had already began. Meanwhile, in treated nymphs of the same age, the ultrastructure of the integument showed that the moulting process was delayed, as no new chitin lamellae of 5th instar were formed and lamellae of the previous instar were still evident. Furthermore, a protein matrix was observed as a homogenous layer with the lack of chitin and occurrence of vacuoles and abundance of mitochondria. The cuticle dry weight in treated 8day old nymphs was significantly less than that of the control, (i.e. 8.5 and 15mg/nymph, respectively). Furthermore, in 8day old treated 5th instar nymphs, chitin and total soluble protein content were 4.5 and 4.85mg/ nymph, respectively. These weights were also highly significantly less than their equivalent control being 8.5 and 7.85mg/nymph for chitin and total soluble protein, respectively. Inhibition in chitin and protein synthesis was calculated to be 88.9% and 61.85%, respectively, in 8day old 5th instar nymphs following their treatment with LC75 concentration of teflubenzuron.