Is the carbamate juvenoid W-328 an insect growth regulator for the cockroach Blaberus craniifer Br. (Insecta, Dictyoptera)?

Abstract

Carbamate juvenoids were proposed for their insecticidal potential in various insects, including the cockroach Blattella germanica. Until now, assays were performed using juvenile stages. The aim of the present paper was to investigate the W-328 effects both on vitellogenesis (vitellogenin synthesis by the fat body and uptake by the oocytes) and reproductive behavior in the ovoviviparous cockroach Blaberus craniifer. Imaginal molt decapitated or fed females were used in vivo for this experiment. Vitellogenesis onset and ovarian growth were demonstrated using biometrical, immunocytochemical, ELISA and electrophoretical investigations. In vitro, biosynthesis and secretory capabilities of the fat body were ascertained by antivitellin antibodies. In headless females, the analogue restores the onset of vitellogenesis. An increase in all the ovarian parameters was observed as compared to controls. The ovarian proteinogram in decapitated females resembled that of fed females of the same age. The proteins sequestered by oocytes, which originated from the fat body, were released into the haemolymph. In intact fed females, a significant dose-dependent increase in the ovarian growth was observed by comparison to controls. Up to 50 μg/female, the analogue induced a positive effect on the process, whereas it became inhibitory for higher doses. W-328 induced behavioural disturbances leading to altered mating and oviposition. 10 μg W-328 reduced mating success, and oothecae production. Sterilisation was achieved with 20 μg. These findings showed that the carbamate compound W-328 acts as a juvenile hormone analogue in adult females and causes a physiological disturbance of the reproductive physiology. They suggest that W-328 could be a useful insecticide against adult populations.