How environmental conditions affect the acquisition, establishment, and persistence of microbial endosymbiosis in insects

Long-term interactions between insect hosts and their internal microbial symbionts are ubiquitous. As these interactions support many aspects of the insect host biology, restrictions to their establishment and maintenance could have important consequences to the survival of insects and functioning of ecosystems. The current literature provides extensive evidence that rapidly changing environmental conditions can challenge the four steps to the successful establishment of novel symbioses — namely (i) the horizontal transfer of the microbe between hosts, (ii) the internalization of the microbe within the naive host, (iii) the persistence of the symbiosis over generations in the host lineage, and (iv) the spread of the symbiont across the host population. We provide here a timely synthesis of this field and show that despite the richness of case studies conducted over the last decades, the majority of these studies test, under laboratory conditions, the effects of variation in temperatures on symbiotic partnerships between bacteria and Hemiptera. These studies cover a small fraction of taxa in which, and environmental conditions under which, endosymbiosis occur. We discuss biotic and abiotic uncertainties in the acquisition, the establishment, and the persistence of symbioses in insects under changing environmental conditions.