Exposure to males reduces the benefit gained from multiple mating in female Galerucella birmanica Jacoby (Coleoptera: Chrysomelidae)

Abstract

Multiple mating is common in insects and may bring direct and/or indirect benefits to females. Galerucella birmanica Jacoby feeds monophagously on water caltrop Trapa natans L. and is a serious pest in Asia where water caltrop is grown as an aquatic vegetable. It is also used as an effective biological control agent in North America, where water caltrop is a major invasive plant species. In this study, we tested the direct benefits of multiple mating when females were continuously exposed to males and had restricted exposure to males. Under restricted exposure conditions, where females were exposed to males only when mating, multiple mating significantly reduced female longevity but promoted female daily and lifetime reproductive output (LRO) significantly. The average LRO increased from 404 to 674 eggs per female when mating number increased from one to five. Multiple mating also boosted the hatch rate of eggs, especially those produced in the late oviposition stage. Under continuous exposure conditions, females housed with four males died significantly younger than females housed with two or one male, and they also died younger than females subjected to multiple mating but with restricted exposure to males. The LRO decreased significantly with the increase of the number of males that the female was exposed to and was significantly lower for females continuously exposed to males than those with restricted exposure to males. Continuous exposure to males had no significant effect on egg hatch rate throughout the ovipositing period. These results demonstrated that multiple mating is important for female G. birmanica to achieve optimal reproductive output, but male harassment on females caused by exposure to males outweighs this benefit.