The effect of intrinsic physiological traits on diapause survival and their underlying mechanisms in an annual bee species Bombus impatiens

In the face of insect declines, identifying phases of the life cycle when insects are particularly vulnerable to mortality is critical to conservation efforts. For numerous annual insect groups, diapause is both a key adaptation that allows survival of inhospitable conditions and a physiologically demanding life stage that can result in high rates of mortality. As bees continue to garner attention as a group experiencing high rates of decline, improving our understanding of how annual bees prepare for diapause and identifying factors that reduce survival is imperative. Here, we studied factors affecting diapause survival length and their underlying mechanisms using an economically and ecologically important annual bee species, Bombus impatiens. We examined how age and mass upon diapause onset correlate with diapause survival length, and the mechanistic role of nutrient acquisition and oxidative stress post pupal eclosion in mediating these effects. Our findings show that both age and mass were strong predictors of diapause survival length. Heavier queens or queens in the age range of ∼6-17 days survived longer in diapause. Mass gain was attributed to increases in lipid, protein and glycerol amounts following pupal eclosion, and the ability to deal with oxidative stress was significantly compromised in older pre-diapause queens. Our results demonstrate that age-related shifts in bee physiology and timing of nutrient acquisition may both be critical factors driving diapause survival.