Bionomics of the sunflower beetle, Zygogramma exclamationis (F.) (Coleoptera: Chrysomelidae), and its parasites in Manitoba

Abstract

The sunflower beetle, Zygogramma exclamationis (F.), has one generation per year in Manitoba. The beetle overwinters as a sexually immature adult in soil, usually at a depth of 15 cm or less, in fields in which it completed larval development. Mating and egg-laying do not take place prior to hibernation. The mean date of first emergence of beetles, over a four-year period, was May 20, the range being May 11 to 27. In one year, overwintering beetles emerged over a period of 24 days with peak emergence on day 13... The mid-point in the development of the second-instar was determined as the optimal time for control of larvae since at the time most eggs had hatched and little foilage damage had occurred. Methods of accurately predicting this point, based on field observations and TU accumulations were developed. Following completion of the fourth instar, larvae entered the soil to pupate... The total developmental time from egg to adult was 44.6 days at 20*C. Upon emergence from pupation, prehibernation adults fed for one to three weeks prior to entry into the soil to overwinter... A number of different predators attacked the different life stages of the sunflower beetle... Four species of parasites were reared from different stages in the life cycle of the sunflower beetle... Control of host larvae with insecticides would effectively eliminate the parasite in any treated area because D. macella initiates larviposition very soon after first emergence of host larvae... Parasites and predators are important natural control agents of the sunflower beetle in Manitoba, and aid in suppressing pest populations in most years.