Quantitative genetics of morphological traits in invasive seven-spotted ladybird beetles, Coccinella septempunctata (Coleoptera: Coccinellidae)

Many insects exhibit wide variation in color patterns and this variation is often thought to be adaptive in nature. The spots on the elytra of seven-spotted ladybird beetles, Coccinella septempunctata, vary in size. Coccinella septempunctata were introduced in the USA from 11 foreign sources as biological control agents to control agricultural pest insects. Previous studies showed that the variation in spot size was correlated with regional precipitation and temperature; however, whether this variation is a function of genetic and/or environmental effects is not known. Differentiating between these hypotheses is critical for understanding how these phenotypes have evolved in both native and introduced populations. We examined whether spot size variation in an introduced population of C. septempunctata was the result of phenotypic plasticity in response to temperature, or additive genetic effects. A total of 207 offspring from 6 pairs collected from New York were reared in either 20°C or 25°C. Phenotypic plasticity in response to temperature was not observed on spot size. Heritability estimates based on mid-parent offspring regressions indicated that more than half of the variation in spot size was a function of additive genetic effects (h²=0.6–0.7). These data suggest that the correlation between temperature and spot size may not be the result of phenotypic plasticity, but may instead be the result of a different selective regime (relationship between fitness and trait value) in native and introduced ranges.