Multiorganismal insects: diversity and function of resident microorganisms

Abstract

All insects are colonized by microorganisms on the insect exoskeleton, in the gut and hemocoel, and within insect cells. The insect microbiota is generally different from microorganisms in the external environment, including ingested food. Specifically, certain microbial taxa are favored by the conditions and resources in the insect habitat, by their tolerance of insect immunity, and by specific mechanisms for their transmission. The resident microorganisms can promote insect fitness by contributing to nutrition, especially by providing essential amino acids, B vitamins, and, for fungal partners, sterols. Some microorganisms protect their insect hosts against pathogens, parasitoids, and other parasites by synthesizing specific toxins or modifying the insect immune system. Priorities for future research include elucidation of microbial contributions to detoxification, especially of plant allelochemicals in phytophagous insects, and resistance to pathogens; as well as their role in among-insect communication; and the potential value of manipulation of the microbiota to control insect pests.

Keywords: endosymbiosis; immunity; insect nutrition; microbiota; symbiosis.

Figure 1

Insect habitats for microorganisms. (a) Antennal gland reservoir of the beewolf Philanthinus quattuordecimpunctatus, with “Candidatus Streptomyces philanthi”–specific probe SPT177-Cy3, the general eubacterial probe EUB784-FAM, and DAPI (blue) counterstain. “Ca. S. philanthi” binds both SPT177 and EUB784 probes, generating yellow fluorescence (note red autofluorescence of chitin at right) (micrograph of M. Kaltenpoth). (b) Dissected gut of Drosophila putrida [Py, pylorus; Rv, rectal valve; Car, cardia from a natural population in Rochester, NY, USA (micrograph by V. Martinson)]. (c) Expanded image of ileum in (b) showing bacteria, false color white fluorescence emission from general bacterial probe EUB338-Cy3 (micrograph by V. Martinson). (d) Section through embryo of black bean aphid Aphis fabae, showing Buchnera symbionts with general eubacterial probe EUB338-FITC (green) in bacteriocytes, and DAPI (blue) counterstain (micrograph by S. Chandler).