Southern Cutgrass, Leersia hexandra Swartz, Allows Rice Water Weevils to Avoid Summer Diapause
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The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is an important insect pest of rice, Oryza sativa L., in the United States and Asian countries. Previous reports indicated that most first-generation adults (summer weevils) entered reproductive diapause with only a few of the population reproducing to form a second generation. However, the environmental factors responsible for diapause induction have not been thoroughly studied. Southern cutgrass, Leersia hexandra Swartz, is a widely distributed perennial grass in the rice ecosystem of regions where rice water weevil occurs. After feeding on cutgrass for 30 days, summer weevils initiated oviposition rapidly after being transferred to young rice plants, and the percentage of ovipositing weevils was 80-100% after 2 weeks. Summer weevils feeding on southern cutgrass did not enter diapause but developed into a reproductive state, suggesting the grass might allow rice water weevils to avoid summer diapause. Such "diapause-avoiding" weevils laid an average of 7-21 eggs within 30 days feeding on rice plants, which was substantially less than that of nondiapausing weevils (overwintered weevils, 45 eggs), suggesting great plasticity of the insect during summer diapause. Our data suggested many weed hosts, such as southern cutgrass, affect the population dynamics of summer rice water weevils and their offspring.
