Factors affecting head capsule development in field populations of Altica sylvia (Coleoptera: Chrysomelidae)

Abstract

AbstractTraits such as larval growth rate and head capsule width are often measured in economically important insects to determine their developmental stage. However, these traits have the potential to vary between genotypes or in response to several ecological factors. To determine whether geographic or ecological factors cause variability in the head capsule width of Altica sylvia Malloch (Coleoptera: Chrysomelidae), and to verify whether measures of head capsule width are adequate to identify larval instars in this species, A. sylvia larvae were recovered from 35 fields of Vaccinium angustifolium Aiton (lowbush blueberry; Ericaceae) of eastern New Brunswick, Canada. The distribution of head capsule widths varied in response to accumulated degree-days, A. sylvia larval density, and latitude. An overlap between measures of head capsule width of first-instar and second-instar larvae in fields supporting a high density of A. sylvia larvae suggested that intraspecific competition caused a reduction in larval growth rate that affected head capsule development and may have induced developmental polymorphism. Based on these results, we stress that the sampling protocol of studies conducted to determine head capsule width intervals in a species should include diverse ecological settings as well as several locations within the range of the species.