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.