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ARS Home » Pacific West Area » Logan, Utah » Pollinating Insect-Biology, Management, Systematics Research » Research » Publications at this Location » Publication #317267
Title: Pre-wintering conditions and post-winter performance in a solitary bee: does diapause impose an energetic cost on reproductive success?

Author
item SGOLASTRA, FABIO - University Of Bologna, Italy
item ARNAN, X - Autonomous University Of Barcelona
item Pitts Singer, Theresa
item MAINI, STEFANO - Federal University Of Pernambuco
item Kemp, William - Bill
item BOSCH, JORDI - Autonomous University Of Barcelona

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2015
Publication Date: 12/22/2015
Citation: Sgolastra, F., Arnan, X., Pitts Singer, T., Maini, S., Kemp, W.P., Bosch, J. 2015. Pre-wintering conditions and post-winter performance in a solitary bee: does diapause impose an energetic cost on reproductive success? Ecological Entomology. doi: 10.1111/een.12292.

Interpretive Summary: Diapause (“hibernation”) is a dynamic process of low metabolic activity that allows insects to survive periods during which conditions are unfavourable for development and reproduction. Furthermore, since diapausing insects do not feed during diapause, the energy spent during this time is not replaced and may affect post-diapause performance. Previous studies on the solitary bee Osmia lignaria have shown that prolonged pre-wintering periods (the time during which individuals have already entered diapause but temperatures are still warm) are associated with elevated lipid consumption, fat body depletion, and body weight loss. In this study, we investigate whether prolonged pre-wintering also affects reproduction, i.e., whether there might be a trade-off between diapause and post-diapause performance in this species. We exposed females to a range of pre-wintering conditions and monitored ovary development and individual post-wintering performance throughout their adult life span. We ask the following questions: Do individuals exposed to prolonged pre-wintering periods take longer to emerge from their cocoons? Do their ovaries take longer to mature? Are they less likely to establish a nest? Do they have shortened lifespans and decreased reproduction? Do they have low rates of making provisions (nectar and pollen masses) resulting in small offspring size and/or mostly male offspring that are smaller than females? We did not find evidence for a trade-off between diapause and post-diapause reproductive success. Expected differences in the timing of nest initiation were not observed because ovary maturation was, surprisingly, not arrested during pre-wintering. Prolonged pre-wintering duration did not result in decreased life span, probably because emerging females could rapidly replenish their energy reserves through feeding. However, we found a very strong effect of the duration of the pre-emergence period (during which individuals experience high weight loss) on the likelihood of starting a nest. Life span appears as the main factor determining reproduction in Osmia.

Technical Abstract: Diapause is a dynamic process of low metabolic activity that allows insects to survive periods during which conditions are unfavourable for development and reproduction. Notwithstanding the lowered metabolism, and since diapausing insects usually have no access to food, diapause has an energetic cost that may affect post-diapause performance. Previous studies on the solitary bee Osmia lignaria have shown that prolonged pre-wintering periods (the time during which individuals have already entered diapause but temperatures are still warm) are associated with elevated lipid consumption, fat body depletion, and body weight loss. In this study, we investigate whether prolonged pre-wintering also affects reproduction, i.e., whether there might be a trade-off between diapause and post-diapause performance in this species. We exposed females to a range of pre-wintering conditions and monitored ovary development and individual post-wintering performance throughout their adult life span. We ask the following questions: Do individuals exposed to prolonged pre-wintering periods take longer to emerge? Do they take longer to mature their ovaries? Are they less likely to establish a nest? Do they exhibit reduced longevity and/or fecundity? Do they have low provisioning rates resulting in low parental investment, small offspring size and/or male-biased progeny? We did not find evidence for a trade-off between diapause and post-diapause reproductive success. Expected differences in the timing of establishment were not observed because ovary maturation was, surprisingly, not arrested during pre-wintering. Prolonged pre-wintering duration did not result in decreased life span, probably because emerging females could rapidly replenish their metabolic reserves through feeding. However, we found a very strong effect of the duration of the pre-emergence period (during which individuals experience high weight loss) on the likelihood of nest establishment. Longevity appears as the main factor determining fecundity in Osmia. Because longevity is subjected to extremely high levels of intrinsic variability (even among females of similar size exposed to identical conditions during development and nesting), the effect of other factors on fecundity may be difficult to detect.