Field release and evaluation of Archytas marmoratus (Diptera: Tachinidae) against larvae of Heliothis zea (Lepidoptera: Noctuidae) in whorl stage corn

Laboratory-reared adults of the tachinid parasitoid, Archytas marmoratus Townsend, were released and evaluated against larvae of Heliothis zea (Boddie) in whorl stage corn during 1986-1988. Resulting rates of parasitism by A. marmoratus on H. zea larvae occurring at 0.3, 0.5, and 1.0 per row-m were 58.3, 44.2, and 52.8%, respectively, when about 340 females/ha were released, and 45.9, 38.2, and 32.1%, respectively, when about 170 females/ha were released. In both studies, no significant differences (P > 0.05) in rates of parasitism were found between host densities. The number of H. zea larvae parasitized by A. marmoratus increased linearly over the range of host densities studied. This suggests that per capita mortality is density-independent and, therefore, should not increase or decrease as host density is varied within the range of early season populations. A. marmoratus females appeared to disperse predominately into the prevailing wind. Rates of A. marmoratus parasitism were significantly higher (P < 0.05) on fourth and fifth instars than on third instars. Approximately 370 and 860 female A. marmoratus/ha would be needed to yield 50 and 80% parasitism of fourth and fifth instars of H. zea, respectively, in 9-14-leaf stage dent corn. Data suggest that A. marmoratus females are highly efficient in finding larvae of H. zea in whorl stage corn, and that rates of parasitism observed in the relatively small release areas are likely far lower than could be expected from sustained releases throughout large corn ecosystems wherein the effects of predominately unilateral movement from release areas would be minimized. With the development of economical methods of mass propagation, A. marmoratus likely could play a major role in the safe, efficient, and selective management of the early season populations of H. zea in whorl stage corn.