Submitted to: Florida Entomologist
Publication Type: Research Notes
Publication Acceptance Date: 12/1/2000
Publication Date: N/A
Interpretive Summary: The cabbage looper and beet armyworm are serious pests of cruciferous vegetables, including cabbage. Issues of pesticide safety, resistance to conventional pesticides, and escalating costs of conventional control methods necessitate development of alternate means to manage these pests. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL, are developing Integrated Pest Management (IPM) programs for vegetable insect pests using a variety of tactics, including biological control. Cotesia marginiventris is a tiny parasitic wasp that occurs naturally and attacks both pest species, but its impact on control of these pests in cabbage is minimal. Cabbage typically is grown in the cool season (fall-winter-spring months) in Florida. Laboratory and field tests were conducted to determine the effects of temperature on the reproductive potential of C. marginiventris in beet armyworm and cabbage looper. When reared outdoors under variable temperature conditions, C. marginiventris reproduced normally suggesting that this species may be present in small numbers in Florida throughout the year. This was supported by parasitism of sentinel host larvae placed in commercial cabbage fields throughout the winter. The decline of C. marginiventris populations in northeast Florida during winter may be caused by a combination of low reproductive rate plus low density of noctuid hosts, lack of flowering plants that provide a nectar food source for adult parasitoids, and dry weather conditions common during winter. The discovery of oviposition at low temperatures and high biotic potential suggest that releases of C. marginiventris might prove to be an effective supplement to an IPM program in cabbage.
Technical Abstract: In the laboratory, temperature was correlated to rate of development of Cotesia marginiventris (Cresson), an important parasitoid of noctuid pests in Florida. Using two different host species with differential growth rates had no effect on the rate of parasitoid development. The oviposition performance of adult females was not correlated with temperatures between 15 degrees C and 25 degrees C, but at temperature below 10 degrees C the wasps' activity ceased. The 24-h fecundity was 85+-3 in fresh females, but declined rapidly in the following days. When reared outdoors in November- December, C. marginiventris reproduced normally which suggests that this species may be present in small numbers in Florida throughout the year. This observation was supported by parasitization of sentinel host larvae (beet armyworm, Spodoptera exigua (Hubner)) placed on cabbage plants in commercial cabbage fields during the same time of the year.