The reproductive cycles of the sunflower beetle, Zygogramma exclamationis (Coleoptera: Chrysomelidae), in Manitoba

Field and laboratory studies showed that Zygogramma exclamationis (F.) has only one generation per year in Manitoba. New generation adults emerge in August, but do not copulate or develop any eggs before entering the soil to hibernate. They reemerge the following May. Vitellogenesis is initiated either before or shortly after emergence. The first mature oocytes appear 2–4 days after emergence. Oviposition is initiated soon after the first eggs are developed, usually within 1 week of emergence. Copulation is initiated by both males and females within 2 days of emergence and both mate many times during their life. Females lay almost every day during the oviposition period. In the laboratory in 1974, the average number of eggs per female was 1968 (range, 260–3587). In experiments out-of-doors in 1976 and 1977, the females laid 968 (range, 657–1400) and 636 (range, 132–1554) eggs per female, respectively. In these three studies, the average length of the oviposition period ranged between 42.5 days in 1977 and 60.7 days in 1974. In the field in 1975–1977, eggs were found from mid-May to mid-July and the total length of the oviposition period was estimated to be 6–7 weeks. The females normally die a few days after oviposition is completed. A system for classifying the stages of oocyte development is described.