Seasonal Abundance and Natural Mortality of Winthemia manducae (Diptera: Tachinidae) and Degree of Parasitization of Its Host, the Tobacco Hornworm1

Abstract

Adults from the overwintering generation of Winthemia manducae Sabrosky & DeLoach emerged from May 8 to 31, and produced 3 full and a partial 4th generation on Mandnca sexta (Johannsen). Adults were present until the last week in October, and overwintering larvae were produced beginning in late August. Mortalities for stages in the insectary were 3.7% for eggs, 16.9% for larvae before entering the host, 10.8% for larvae within the host, about 1.3% each for full-grown larvae and pupae, and 1.4% for adults before flying; about 64.6% of the eggs produced adults. Mortality in field cages in the soil was about the same except for a mortality of 27.6% as the adults tunneled up to the soil surface. A physiological reaction of the host killed many larvae when only 1, 2, or 3 entered a host. Intraspecific competition among larvae within the host caused a decrease in size and an increase in mortality as the number per host increased. Competitive parasitism on host larvae previously parasitized by Apanteles congregatus (Say) caused a loss to the overwintering generation of W. manducae estimated at 58-74%. W. manducae killed an estimated 7.59% of the population of host pupae in 1962 and 6.61% in 1963.