Differential wing strength in Pierella butterflies (Nymphalidae, Satyrinae) supports the deflection hypothesis

The "deflection hypothesis" asserts that conspicuous marginal patches on insect wings function to deflect predator attacks toward such patches and away from more vital body parts. As a result of selection from predator attacks, these marks are predicted to increase the probability of escape by tearing relatively easily. To test if a conspicuous marginal patch is weak relative to a homologous wing area without such a patch, hindwing tear weight was compared among three Pierella species (Satyrinae) differing in the presence of a conspicuous patch in the hindwing tornus. The species with a conspicuous white hindwing patch (P astyoche) had significantly lower tear weights than the two species lacking the patch (P lamia and P lena). Forewing length did not explain variation in wing-tear weight, but wing-tear weight was positively related to insect age in a manner consistent with the deflection hypothesis. Older individuals of P lantia and P lena had higher tear weight, whereas this relationship was absent in P astyoche. These results represent the first direct evidence that deflection marks on butterfly wings are relatively weak and should have an increased tendency to tear when handled by a predator.