Insect-microbiome interactions in a changing world

Humans have greatly altered the Earth and its environments through activities such as agriculture, industry, and urbanization. In recent years, the impact of anthropogenic global change on insect populations has become a topic of increasing interest, with much written for both scientists and the public on how insect populations are in decline due to climate change, land-use change, and exposure to chemical pollution. Additionally, many insects host microbial symbionts, which some insect species rely on for a wide range of physiological needs, such as nutrient acquisition, detoxifying dietary substrates, or reproduction. This review summarizes recent experimental and observational studies on the effects of anthropogenic global change on insect microbial symbioses from multiple ecosystems and continents, with a focus on the impacts of climate change, habitat loss, and degradation. Each of these modes of change has been demonstrated to affect the composition of insect microbial communities, with a reduction in species diversity within microbial communities (alpha diversity) as the most common result. Results of an experimental study on heat-stress response in bacterial symbionts suggest that warming temperatures often associated with climate change may have direct impacts on symbiont mortality, as symbionts tend to be more sensitive to thermal stress than free-living bacteria. Habitat loss and degradation impact insect microbial symbionts via the changed microbiomes of host food and environmental substrate. Chemical pollution associated with habitat degradation has altered the microbiomes of insects, though some insects may be able to detoxify chemical pollutants with symbiotic microbial taxa. While early research has shown that human-induced climate change can have negative impacts on insect symbionts, there is still much to learn about how the changing world will impact insect microbiomes and how this, in turn, will impact entire ecosystems at a global scale.