ECDYSTEROID-TITER REDUCTION AND DEVELOPMENTAL ARREST OF LAST-INSTAR HELIOTHIS-VIRESCENS LARVAE BY CALYX FLUID FROM THE PARASITOID CAMPOLETIS-SONORENSIS

Fifth-instar Heliothis virescens larvae did not pupate after injections of Campoletis sonorensis calyx fluid in or before the burrow-digging stage of development. Arrested development occurred in 40% of larvae injected at the cell-formation stage. Further experiments showed that the particles in calyx fluid were responsible for developmental arrest. Arrested development due to calyx fluid could be reversed by injecting 10 .mu.g of either ecdysone or 20-hydroxyecdysone, although a second injection of 20-hydroxyecdysone was needed for some larvae 3 days after the first treatment. Ecdysteroid production ceased for up to 10 days in 5th-instar H. virescens after calyx-fluid injection. After 10 days, some experimental larvae began to produce ecdysteroids again but remained developmentally arrested. The head, thorax, or abdomen of larvae were isolated by ligations and calyx fluid injected into the isolated body region. After 24 h, ligatures were relased and the larvae observed for developmental arrest. Only injections into the isolated thorax stopped development. This, along with ecdysteroid data, indicated that C. sonorensis calyx fluid may directly affect the prothoracic glands of 5th-instar H. virescens.