Aggregation, Oviposition and Emergence of Hibiscus Seed Beetles (Althaeus hibisci) at a Central Ohio Marsh

Abstract

Several aspects of the reproductive ecology of the hibiscus seed beetle were investigated during summer 2003 and the succeeding winter and spring. Throughout the flowering period that extended from late Jul. to early Sept., aggregations of adult hibiscus seed beetles (Althaeus hibisci Olivier) were collected from swamp rose mallow (Hibiscus moscheutos L.) flowers at 5 d intervals and counted separately by sex. The occurrence of strongly male-biased sex ratios that decreased progressively during the flowering season, accompanied mid-season by slightly male-biased ratios on incipient fruits, suggests that both the flowers and developing fruits serve as sites frequented by the males to acquire mates. During the apparent peak of beetle activity, a cohort of incipient fruits was examined at 3 d intervals for the presence of beetle eggs. Oviposition began <3 d after corolla abscission and had occurred on nearly 100% of the fruits by day 6. Egg density reached an asymptote at day 12. Adult beetle emergence was monitored from seeds originating from flowers that bloomed during separate dates 5 d apart. The seeds were maintained until spring under weather conditions similar to those at the marsh where they were obtained. From seeds produced by fruits derived from flowers that bloomed early in the season (late Jul.–mid Aug.), beetles emerged in autumn of the same year. However, late-season fruits were colonized by beetles that emerged after mid-winter and thus effectively overwintered in the seed. This corrects previous reports indicating that beetles overwinter exclusively as emerged adults.