REPRODUCTIVE CYCLES OF THE RED TURNIP BEETLE, ENTOMOSCELIS AMERICANA BROWN (COLEOPTERA: CHRYSOMELIDAE)

Abstract

AbstractThe reproductive cycles of the red turnip beetle, Entomoscelis americana Brown, were studied in the field in Manitoba from 1974 to 1978. Vitellogenesis is initiated within the first 3 days after emergence from aestivation in early August. Oviposition begins soon after the first eggs are developed, usually within the first 8 days after emergence. The rate of egg laying reaches a peak within 2 weeks after the initiation of oviposition and then declines gradually during the remainder of the oviposition period. Almost all eggs were laid between mid-August and mid-October. The average numbers of eggs laid per mated female in three oviposition studies were as follows: 1 female per cage (1974), 254±74 (±SE) (range, 11–696); 1 female per cage (1976), 273±47 (range, 0–622); and 25 females per cage (1974), 426±3 (range, 392–462). The most eggs were laid at the lowest temperature regime tested (6–20°C; mean, 12°C). Copulation is initiated in males and females during the 1st day after emergence from aestivation and both mate many times. Stimuli associated with copulation and (or) insemination enhance egg output, but are not required for the initiation of vitellogenesis and oviposition. Males transfer sufficient spermatozoa to the females during the first one or more copulations that occur during the first 8 days after emergence to fertilize almost all eggs produced. A system for classifying the stages of oocyte development is described.