Voltinism, seasonal reproduction, and diapause in the squash bug (Heteroptera: Coreidae) in Kansas

Abstract

The squash bug (SB),Anasa tristis DeGeer, completes 1.5 generations per yr in northeastern Kansas. Overwintered adults mate and oviposit on cucurbitaceous host plants from early June to mid-August. Most eggs are deposited from June to early July when female survivorship is highest, but some oviposition occurs through mid-August. First-generation adults begin to emerge between the 1st and 3rd wk of July. Oviposition commences 7-10 d after emergence. Females that emerge before late July avoid diapause and produce a second generation. Thereafter the incidence of diapause increases progressively, reaching 100% in first- and second-generation females that emerge in early September. Diapausing females do not mate or reproduce until the following spring. SB males also appear to undergo diapause but, unlike females, they overwinter with mature reproductive organs. The primary expression of male diapause is suppressed reproductive behavior. Reproductive periods of overwintered and first summer-generation adults overlap. The extent of this overlap depends in part on spring temperature conditions that influence field entry by overwintered adults; the oviposition schedule; and development of first-generation progeny. During cool springs, a large proportion of first-generation SB emerge late in the season and enter diapause. In these years, smaller, less-damaging, populations occur.