Parasitism and Utilization of Imported Cabbageworm Pupae by Pteromalus puparum (Hymenoptera: Pteromalidae)

Abstract

Pteromalus puparum (L.) parasitized 64.1 and 32.5% of imported cabbageworm, Artogeia rapae (L.), pupae collected from pesticide-free cabbage field plots in 1983 and 1984, respectively, in southwestern Virginia. Parasitism was most pronounced in the latter part of the season. In commercial cabbage fields, 67.2% of overwintering pupae were parasitized. High percentages of parasites successfully emerged as adults, indicating efficient host utilization. Most parasite mortality within the host occurred in the larval stage; mean adult parasite emergence per host for 1983 and 1984 was 52.3, with a 1:1 sex ratio. However, variability of male parasites per host was double that of females. Females weighed twice as much as males, suggesting a compensation of number for size. P. puparum did not parasitize either host sex discriminately, and equal numbers of male and female parasites emerged from both host sexes. Laboratory studies suggest that host/parasite ratios and length of host/parasite exposure time are important considerations for laboratory rearing of P. puparum . Suboptimal conditions result in unparasitized and mutilated hosts.