Differential Mortality in Immatures between Two Different Spatial Distributions of the Phytophagous Lady Beetle, Epilachna vigintioctomaculata, with Reference to Arthropod Predation

We investigated the effect of spatial distribution pattern on the immature of Epilachna vigintioctomaculata (Ev), on mortality employing two different clumped distributions (one large clump and several small clumps). We also examined the role of predators on the mortality of Ev immature stages with an experiment in which cages were used to eliminate natural enemies in the field. Mortality was higher in the small clumped distribution as compared to the large clumped one in 1994 and 1995. A certain degree of clumped distribution was maintained throughout the immature life of Ev. Overall mortality of Ev immature stages was significantly higher in uncaged areas than in caged areas in both distribution patterns, and the mortality due to predation (mainly by spiders and ants) was ca. 40% for each stage up to the 3rd stadium. The spatial distribution of predators was frequently close to random or slightly clumped in each of the experimental fields in both years. The cause of the differential mortality rates between the two different spatial distributions is discussed.