Seasonal dynamics and spatial distribution pattern of Parapoynx crisonalis (Lepidoptera: Crambidae) on water chestnuts.

Parapoynx crisonalis (Walker, 1859) (Lepidoptera: Crambidae) is a major pest of aquatic vegetables and aquatic landscape plants. It has been responsible for causing considerable economic damage to water chestnut (Trapa natans) plants. In the Changsha vicinity of China, P. crisonalis has five generations a year. Populations of P. crisonalis were relatively low in April and began to rapidly rise at the beginning of May. At the end of July and early August, the population dropped dramatically. A rebound occurred at the end of August and early September, which was referred to as the second population peak. From then, until early November, the P. crisonalis population steadily diminished in preparation for overwintering. The primary factors influencing the seasonal dynamics of P. crisonalis were the climatic conditions, especially the temperature, and secondarily precipitation. Between May and October, the P. crisonalis adults were evenly distributed in the pond. In May and June, the eggs of P. crisonalis were present in an aggregate distribution, due to the effects of environmental heterogeneity. In July and August, however, they were found to be in a uniform distribution.