Extreme heat exposure of host plants indirectly reduces solitary bee fecundity and survival

Abstract

Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry ( Vaccinium corymbosum ), phacelia ( Phacelia tanacetifolia ) and white clover ( Trifolium repens ) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.

Bee microbiomes in a changing climate: investigating the effects of temperature on solitary bee life history and health

“…Thus, Arsenophonus -mediated lipid consumption may be affected by environmental temperatures. Alternatively, heat-stress may affect the nutritional quality of pollen: although provision mass was comparable between treatments , O. lignaria larvae consuming provisions with pollen collected from plants that experienced a heatwave had lower survivorship than immature bees fed pollen from non-stressed plants [88]. Regardless of the mechanism, reductions in total fat content of O. lignaria larvae reared on microbe-rich provisions, as found in this study, is concerning, as lipids obtained early in bee development are converted into fat reserves used during diapause.…”