Chemosterilization of Oncopeltus fasciatus. 1. Control Experiments1

Abstract

Mortality, mating activity, fecundity, and egg fertility and viability of the large milkweed bag, Oncopeltus fasciatus (Dallas), were measured daily for 40 days in normal adult colonies of the GS strain at 30°C under varying conditions. Median sexually active life span of males varied from 24 to 36 days, of females from 15 to 20 days; most of the females died by day 40. The percentage of males found mating (observed once a day) was relatively constant in any one cage throughout an experiment, except when female mortality caused a large increase in the male:female sex ratio. However, values varied from 20% to nearly 50% in different experiments; this variation might have been caused by variations in sampling from a male population with large individual differences in mating drive. Fecundity (eggs per surviving female per day) was usually 10 or higher during a 20- to 30-day period under optimal conditions, but was depressed at high population density. It was not very sensitive to variations in sex ratio, but it tended to decline as females aged and the cage environment deteriorated. Egg fertilization ranged from 90 to 99% and egg viability (percent of fertile eggs hatching) from 80 to 90% in different experiments; values were somewhat lower in the few instances when mating activity was so low that many females must have remained virgin for a considerable period. Only a small fraction (10%) of the intense mating activity seems to be required to ensure high levels of egg fertilization in this species.