Seasonal Occurrence of Pieris rapae (L.) (Lepidoptera: Pieridae) in Southwest Virginia

Abstract

In Virginia, Pieris rapae (L.) phenology is not well established because earlier studies focused on its occurrence within the growth period of a particular crop. In this study, conducted in 1989 and 1990, we sampled multiple crops in both spring and fall plantings and these data were compared with those from earlier studies to obtain an overall pattern of seasonal occurrence. In 1989, spring crops of broccoli, cabbage, and kale were planted in field plots in Montgomery Co., VA, and sampled weekly for the eggs and larvae of P. rapae. In 1990, both spring and fall crops were planted and sampled. Four P. rapae generations (egg count peaks) were observed in 1989 and 1990, but comparison of data from both years suggested a fifth generation was possible in this region. When these data are compared with egg count data from seven previous years (1981–1988; 1985 not included), evidence indicates a first generation in mid-May, and consistent second and third generations in mid-June and mid-July, respectively. The June and July generations were always well defined by high egg and larva counts per plant. Less predictable are the fourth and fifth generations which may both occur in August or one generation each in August and September. When fourth and fifth generations occur in early and late August, a sixth generation may occur in late September. The regular occurrence and size of the second and third generation can facilitate the planning and implementation of biological or other control measures for P. rapae in this region.