Title: Timing of eclosion affects diapause development, fat body consumption and longevity in Osmia lignaria, a univoltine, adult-wintering solitary bee Authors
|Bosch, Jordi -|
|Sgolastra, Fabio -|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2010
Publication Date: October 26, 2010
Repository URL: http://hdl.handle.net/10113/45875
Citation: Bosch, J., Sgolastra, F., Kemp, W.P. 2010. Timing of eclosion affects diapause development, fat body consumption and longevity in Osmia lignaria, a univoltine, adult-wintering solitary bee. Journal of Insect Physiology. 56(12):1949-1957. Interpretive Summary: The blue orchard bee, also known as the orchard mason bee, is currently being developed as a commercially viable pollinator for a variety of tree fruit crops, including almonds, cherries, pears, and apples. In artificially-reared populations, variability in developmental rate is high, and the period of adult eclosion – the final molt or step in the development process each year - in a given year spans over a month. We studied whether the timing of adult eclosion in relation to the onset of winter temperature has an effect on fat body depletion, winter survival and post-emergence vigor in blue orchard bee populations reared under natural and artificial conditions. Our results show that pre-wintering duration has important consequences on diapause development, fat body depletion and post-wintering vigor, all of which influence overwintering survival. These results also provided an ecophysiological framework within which to study the potential effect of extended summers on the fitness of this species, in terms of winter mortality and/or reduced post-winter performance. The fitness consequences of developing early were not apparent in this study, but may be strong in years with late winters, which are expected to increase in the current scenario of global climate change. However, observed differences between development times of the blue orchard bee, when compared to a related solitary bee – the alfalfa leafcutting bee, which overwinters as a prepupa - lead us to hypothesize that, in the face of a global temperature increase scenario, the adult-wintering blue orchard bee is more likely to be negatively affected than prepupa-wintering species like the alfalfa leafcutting bee.
Technical Abstract: Most insects from temperate areas enter diapause ahead of winter. Species diapausing in a feeding stage and accumulating metabolic reserves during permissive pre-wintering conditions are expected to enter diapause late in relation to the onset of winter. Instead, species diapausing in a non-feeding stage are expected to lower their metabolism as soon as possible to avoid excessive consumption of metabolic reserves. The solitary bee Osmia lignaria (Hymenoptera: Megachilidae) over-winters as a non-feeding adult within its cocoon, but previous studies show important weight losses and increased winter mortality in populations pre-wintered for extended periods. We measured respiration rates to assess diapause initiation and maintenance during pre-wintering, and tested whether timing of adult eclosion affected fitness by measuring fat body depletion, winter mortality and post-winter vigor. We worked with different cohorts of a population reared under natural conditions, and manipulated pre-wintering duration in a population reared under artificial conditions. In agreement with our expectation, O. lignaria lower their metabolic rates within a few days of adult eclosion, but nonetheless suffer strong weight loss during pre-wintering. Early-developing individuals suffer greater weight loss and fat body depletion, and have lower vigor at emergence. Although, we found no differences in winter mortality among treatments, our results indicate that increased mortality may occur in years with late winter arrivals. We discuss fundamental ecophysiological differences between adult and prepupal diapause within the Megachilidae, and hypothesize that species wintering as adults will be more negatively affected by a situation of extended summers under a scenario of global warming.