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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOCHEMISTRY OF PEST AND BENEFICIAL INSECTS AND INTERACTIONS WITH HOST PLANTS AND NATURAL ENEMIES

Location: Insect Genetics and Biochemistry Research

Title: The long summer: Pre-wintering temperatures affect metabolic expenditure and winter survival in a solitary bee

Authors
item Sgolastra, Fabio -
item Kemp, William
item Buckner, James
item Pitts Singer, Theresa
item Maini, Stefano -
item Bosch, Jordi -

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 2011
Publication Date: December 1, 2011
Citation: Sgolastra, F., Kemp, W.P., Buckner, J.S., Pitts Singer, T., Maini, S., Bosch, J. 2011. The long summer: Pre-wintering temperatures affect metabolic expenditure and winter survival in a solitary bee. Journal of Insect Physiology. 57(12):1651-1659.

Interpretive Summary: Insects are generally recognized as excellent models for studying the potential impacts of climate change on biological systems. Under a scenario of global warming, species currently under cold-induced stress are expected to attain higher survival rates and expand their distribution area, while others appear to be compensating for delayed winter arrivals – longer summers - through altered responses to seasonal shifts in day length which normally signal that winter will be soon arriving. The solitary bee Osmia lignaria has biological traits that make it a priori highly sensitive to global warming, and thus a useful indicator for monitoring for potential impacts of climate change. This species has a single generation each year and does not depend on shifts in day length to begin preparations for wintering. Because O. lignaria winters as an adult and requires a long period of cold temperatures for the completion of its internal wintering program, individuals exposed to warm or extended pre-wintering conditions – long summers - lose weight rapidly compared to chilled adults. To better understand the potential effects of longer summers on O. lignaria, we exposed individuals to three treatments simulating early, mid and late winter arrivals, and measured respiration rates, weight loss, fat body depletion, lipid levels and winter mortality. The early-winter treatment disrupted the insect’s normal preparations for winter, but had no apparent negative effects on fitness. In contrast, bees exposed to a late winter scenario suffered increased weight and lipid loss, fat body depletion, and a 20 % increase in mortality. We also monitored when bees became adults and the subsequent arrival of winter temperatures under natural conditions in four years and found a positive correlation between heat accumulation during pre-wintering (a measure of asynchrony between the timing of the adult molt and winter’s arrival) and winter mortality at the population level. At the individual level, bees experiencing greater heat accumulations – longer summers - exhibited reduced post-winter longevity. The timing of the arrival of the adult stage in O. lignaria is highly dependent on the duration of the summer (prepupal) diapause - a period of temporarily suspended development - which is longer in populations from southerly latitudes. In a global warming scenario, we expect extended summer diapause phenotypes to replace short summer diapause phenotypes, effectively maintaining short pre-wintering periods in spite of delayed winter arrivals.

Technical Abstract: Impact of global warming on insect populations is highly dependent on specific life cycle traits and physiological adaptations. Species currently under cold-induced stress are expected to attain higher survival rates and expand their distribution area. Other species appear to be compensating for delayed winter arrivals through altered photoperiodic responses for diapause induction or the production of an extra generation. The solitary bee Osmia lignaria exhibits biological traits that make it a priori highly vulnerable to global warming. This species is univoltine and diapause induction does not depend on photoperiod. It winters as an adult, and requires a long period of cold temperatures for diapause completion. Adults exposed to warm pre-wintering conditions loose weight rapidly compared to chilled adults. To understand the potential effects of longer summers on Osmia lignaria, we exposed individuals to three treatments simulating early, mid and late winter arrivals, and measured respiration rates, weight loss, fat body depletion, lipid levels and winter mortality. The early-winter treatment disrupted diapause development, but had no apparent negative effects on fitness. In contrast, late-winter bees suffered increased weight and lipid loss, fat body depletion, and a 20% increase in mortality. We also monitored adult eclosion and arrival of winter temperatures under natural conditions in four years. We found a positive correlation between degree-day accumulation during pre-wintering (a measure of asynchrony between adult eclosion and winter arrival) and winter mortality at the population level. At the individual level, bees experiencing greater degree-day accumulations exhibited reduced post-winter longevity. Timing of adult eclosion in O. lignaria is highly dependent on the duration of the summer (prepupal) diapause, which is longer in populations from southerly latitudes. In a global warming scenario, we expect extended summer diapause phenotypes to replace short summer diapause phenotypes, effectively maintaining short pre-wintering periods in spite of delayed winter arrivals.

Last Modified: 8/29/2014