Inter-Specific Relationship of Size and Walking Speed in Predaceous Ladybirds (Insecta: Coleoptera: Coccinellidae)

Abstract

Inter-specific relationships of size and walking speed were examined in five species of predaceous ladybird beetles of aphid prey from different habitats. Lengths of legs, weight and volume of body, and walking speed varied significantly among the five species of different sizes that were reared on their preferred prey food in uniform growth conditions. The species are Menochilus sexmaculata, Coccinella transversalis, Anisolemnia dilatata, Micraspis discolor and Scymnus sp. Lengths of legs and body sizes showed similar growth rates across the five species (isometry), but the giant ladybird species showed significantly higher positive allometry in body volume (allometric coefficient, α = 6.66) and significantly lower negative allometry in walking speed relative to body weight (α = 0.95) when compared to other species (α = 3.54). The unique response by the giant ladybird species in body form and speed may be attributed to its foraging habitat of perennial bamboo forests with large aggregations of non-winged aphid food which seem to favour the evolution of higher body volume and slower speed for giant size when compared to species of smaller sizes which usually forage for short-lived aphid colonies in seasonal and annual habitats of crop plants and weeds. Evidently, size (weight and volume) and speed matter in the evolution of life history attributes of predaceous ladybird beetles.