How air temperature and solar radiation impact life history traits in a wild insect
Ectotherms are essential components of all ecosystems and rely on external heat to regulate their body temperature. For most terrestrial ectotherms the primary sources of heat are ambient temperature and solar radiation. Many insects can use movement to respond to changes in temperature and solar radiation in order to manage their body temperature and optimise life history traits. However, we lack the understanding of the relative importance of temperature and shade that we need to predict how the combined effects of changes in air temperature and cloud cover will impact terrestrial insect populations. We reared developing nymphs of the field cricket (Gryllus campestris) at high and low air temperature sites with partially shaded and unshaded treatments at each site. Given the broad altitudinal range of this species, we tested the possibility of local adaptation to these climate variables by rearing nymphs from high and low altitude genetic lineages in all treatment combinations. We found that development time was strongly affected by air temperature, but not by a substantial increase in shade. This suggests that developing crickets can compensate for an increase in shade, presumably because in unshaded conditions they forgo some opportunities to gain energy from the sun. We found that mass at adulthood was affected by an interaction between availability of sun (shading treatment) and air temperature. This indicates that changes in cloud cover will impact insects differently in warmer and cooler areas. We found no evidence for local adaptation in these traits. Our findings underscore the need to consider both ambient temperature and solar radiation in predicting the impacts of climate change on insect populations, as shifts in temperature and cloud cover may have complex and region-specific effects on these vital ecosystem components.