Henrique Schanderl

Effect of Temperature and Intraspecific Allometry on Predation by Two Phenotypes of Harmonia axyridis Pallas (Coleoptera: Coccinellidae)

Abstract Harmonia axyridis Pallas is a highly polymorphic coccinellid with a wide geographic distribution. Genetic polymorphism seems to be the strategy adopted for facing different habitats at different times. Many modifications, such as body shape, body size, and elytral patterns, may be adaptive through imparting increased tolerance to adverse conditions. Previous studies evaluating differences in the light-colored aulica and dark colored nigra phenotypes found differences in biological performances at 20°C. However, whether the predatory activity of the different phenotypes changes under different temperatures remains unknown. Relative consumption rate and predation activity of fourth instars and adults of aulica and nigra phenotypes were compared at 10, 15, 20, 25, and 30°C. Our results showed that temperature is a limiting factor to larval and adult relative consumption rate. The thermal optimum of nigra adults was 3.7°C lower than that of aulica. Both larvae and adults of nigra were more stenothermic than aulica. Close to the upper limit of tolerance (30°C), predation activity of nigra adults was more affected than aulica. In larvae body size and shape could explain the differences observed, because aulica is significantly bigger than nigra and thus aulica presumably can better control heat exchange.

Influence of prey quality on the fitness of two phenotypes of Harmonia axyridis adults

The performance of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) adults of the aulica and nigra phenotypes fed on Aphis fabae Scopoli and Myzus persicae (Sulzer) was compared by measuring their voracity, daily biomass consumption, daily weight gain, efficiency of food utilisation, and reproductive capacity. Our results demonstrated differences in the suitability of A. fabae and M. persicae for the two phenotypes of the predator. This suggests that either differences occur in the nutritive requirements of the predators, or in the nutritive value of the two prey species. Both A. fabae and M. persicae supported the growth and oviposition of the aulica and nigra phenotypes. Although nigra females consumed fewer M. persicae, they achieved the same daily weight gain as aulica females. The predator phenotypes consumed the same amount of A. fabae, but the daily weight gain of aulica females was higher than that of nigra. The two predator phenotypes had the same feeding efficiency when consuming M. persicae or A. fabae. The reproductive capacity of nigra females was higher, when this phenotype consumed A. fabae rather than M. persicae.