A Mature Discussion on the Larval Instars of Hymenoptera
Eduardo Gonçalves Paterson Fox, Eduardo Gonçalves Paterson Fox
IBCCF / UFRJ, Brazil; IBCCF / UFRJ, Brazil
Larval biology is a widely neglected topic in Entomology. Excepting Lepidoptera, perhaps Odonata, the larvae of different taxa have remained scarcely studied and vaguely understood. This contrasts with the intensification of the debate around key aspects of social insect biology which ultimately rely on a solid understanding of larval development; e.g. caste-determined ecology & longevity, colony maturation, nutrition. In reality most of such discussions brush over the topic of larvae while proceeding to focus on what is known from adults, if immature life stages are mentioned at all. The present discussion shall focus on the controversial issue of instar determination in wasps, bees, ants. Experience shows there is no universal protocol enabling unquestionable instar diagnosis for most studied species. Commonest protocols of instar analysis are based on larval body length, head capsule width, mandible morphology, or directly observing moults. Each of these present fundamental limitations which are illustrated with examples. Whilst the main results of post-embryonic developmental analysis should include a list of instar-specific traits to empower non-specialists in subsequent studies, this is not frequently done. Moreover larvae are often hard to adequately sample and maintain, frequently introducing artefacts. Finally a number of presumptions are debated, for instance related to intraspecific variation in the number and traits of larval instars, and chaetotaxy. The exposure aims to improve awareness over neglected aspects which are ultimately fundamental to a number of notions around social insect biology.