The microbial dimension in insect nutritional ecology

Summary 1 Many insects derive nutritional advantage from persistent associations with microorganisms that variously synthesize essential nutrients or digest and detoxify ingested food. These persistent relationships are symbioses. 2 There is strong experimental evidence that symbiotic microorganisms provide plant sap-feeding insects with essential amino acids and contribute to the digestion of cellulose in some wood-feeding insects, including lower termites. Basic nutritional information is, however, lacking for many associations, including the relative roles of microbial and intrinsic sources of cellulose degradation in many insects and B-vitamin provisioning by microorganisms in blood-feeding insects. 3 Some nutritional interactions between insects and their symbiotic microorganisms vary among conspecifics and closely related species. This variation can, in principle, contribute to nutritional explanations for variation in the abundance and distribution of insects. For example, the plant utilization traits of phloem-feeding aphids and stinkbugs have been demonstrated to depend on the identity of microbial partners. Evidence that associations can evolve rapidly comes from the demonstration that the impact of the bacterium Wolbachia on natural populations of its insect host can change from deleterious to beneficial within two decades. 4 Developing genomic tools, especially massively parallel sequencing and metagenomic analyses, offer the opportunity to explore the metabolic capabilities of symbiotic microorganisms and their insect hosts, from which defined hypotheses of nutritional function can be constructed. Nutritional ecology provides the appropriate framework to test these hypotheses in the relevant ecological context.