Passive heat diffusion in nests with downward-facing cells: Implications for early colony development in social wasps

Social insects employ a variety of active and passive mechanisms for nest thermoregulation. Many social wasp species exhibit a particular nest-architecture by building their nests with cells facing downward. By using thermal imaging to characterize the heat diffusion throughout Oriental hornet nests from different angular positions, we show that the heat diffusion along the vertical gradient of nests is more efficient when the cell openings face downward than when facing sideways or upward, demonstrating the efficiency of this specific architecture in increasing the nest temperature. This passive thermoregulation mechanism could be especially important during the initial stage of the colony, when the queen is alone to rear her first brood. Among the social insects that build cells to raise their brood, we suggest that wasps can take advantage of the thermal benefits of this particular architecture of their cells as, unlike bees, they do not usually store food in them.

Nutrient Utilization during Male Maturation and Protein Digestion in the Oriental Hornet

Males of social Hymenoptera spend the first days following eclosion inside the nest before dispersing to find a young queen to mate with. During this period, they must acquire enough nutrients to enable their sexual maturation and store energy to sustain them through their nuptial journey. It was previously argued that adult hornets are unable to process dietary proteins and rely on the larvae to supply them with free amino acids and carbohydrates that they secrete via trophallaxis. Using isotopically enriched diets, we examined nutrient allocation and protein turnover in newly-emerged males of the Oriental hornet during their maturation period and tested the protein digestion capability in the presence and absence of larvae in both males and worker hornets. The results indicated that protein turnover in males occurs during the first days following eclosion, while carbohydrates are incorporated into body tissues at higher rates towards the end of the maturation period. Additionally, we found that males cannot digest protein and depend on larval secretions as a source of nutrition, while workers, in contrast to previous reports, can metabolize protein independently. Our findings demonstrate the contribution of adult male nutrition and larval secretions to colony fitness.