Impact of environmental temperatures on mortality, sex and caste ratios in Melipona interrupta Latreille (Hymenoptera, Apidae)

Temperature is a major driver of biological phenomena, from metabolism to ecological interactions and rates of evolutionary diversification. However, species vary greatly in their thermal tolerance, as well as the temperature under which they perform best. This study aimed to investigate the effect of experimental manipulation of environmental temperatures on the individual mortality and phenotypic composition of colonies of Melipona interrupta. To fulfill these objectives, 30 colonies in equivalent developmental conditions were artificially subjected to different temperatures. Temperatures were monitored by thermo-hygrometers, and immature mortality and sex and caste ratios were observed in brood combs during 14months. A strong effect of external temperature on immatures was detected on deviations from 28 to 30 degrees C (the natural average temperature inside the colony), causing an increase in mortality. Likewise, a significant effect of temperature on sex ratio was detected, with male:female ratio decreasing at temperatures below and above 28-30 degrees C. Lastly, there was no clear evidence for an effect of temperature on caste ratio, although queens appeared to become relatively more frequent at warmer temperatures. The results of this study allow us to conclude that anthropogenic changes, whose effect can be extrapolated to the similar natural changes, that modify the environmental temperatures to which M. interrupta colonies are exposed are likely to compromise their survival, mainly through individual mortality.