Sources and Adaptive Consequences of Egg Size Variation in Nezara Viridula (Hemiptera: Pentatomidae)

Abstract

In the southern green stink bug, Nezara viridula, the coefficient of variation for egg size (diameter) is 98% that of female size. Differences in egg size among females account for 57% of the total variation in egg size, with female size accounting for 36% of the variation between females in mean egg size. Male (mate) size also accounts for some of the between-female variation in egg size. Within-female variation in egg size is associated with placement of eggs in the egg mass; eggs in the interior of masses are larger than those on the periphery (explaining 3% of variation). An additional 20% of the within-female variation is explained by egg mass number (e.g. first, fifth, tenth, or fifteenth mass laid); eggs in later masses were larger. Larger eggs were more likely to hatch under adverse conditions (lower humidity), whether located within the egg mass or on its periphery. Within a single egg mass, progeny from larger eggs matured more quickly and attained larger size. Survival rate from egg hatch to adulthood was positively correlated with egg size under harsh (mortality = 41%) but not benign conditions (mortality = 29%). Survival rate was higher for eggs in the interior of masses. Positive correlations between egg size and components of offspring fitness suggest adaptive hypotheses for observed variation in egg size. Laboratory correlation between egg size and population density also suggests that egg size experiences strong selection. Competition for food among offspring, heterogeneity in habitat quality, egg predation, and age-dependent mortality are posited as the selection pressures constraining egg size and variation in egg size. © 1991, Hindawi Publishing Corporation. All rights reserved.