Low temperature stress during pupal development and its effects on adult performance in alfalfa leafcutting bees

Authors: BENNETT, MEGHAN - North Dakota State University; COOK, KEELEY - North Dakota State University; OWINGS, AUSTIN - North Dakota State University; Yocum, George; Rinehart, Joseph - Joe; GREENLEE, KENDRA - North Dakota State University

Submitted to: Annual Meeting of Society of Integrative and Comparative Biology
Publication Type: Abstract Only
Publication Acceptance Date: 9/6/2013
Publication Date: 1/3/2014
Citation: Bennett, M.M., Cook, K.M., Owings, A.A., Yocum, G.D., Rinehart, J.P., Greenlee, K.J. 2014. Low temperature stress during pupal development and its effects on adult performance in alfalfa leafcutting bees [abstract]. Annual Meeting of Society of Integrative and Comparative Biology. January 3-7, 2014. Austin, TX. Abstract Book page 25.

Interpretive Summary: Seventy percent of crops grown for human food production are dependent on pollinators. The value of this pollination service worldwide is estimated to be over 100 billion dollars annually. This value does not include agriculture products that are not directly consumed by humans such as alfalfa that is used as an input for meat and milk production. The alfalfa leafcutting bee Megachile rotundata is the primary pollinator used in the production of alfalfa seed in North America. There is growing interest in M. rotundata for pollination of various specialty crops. These bees may, in the course of normal management, need to be exposed to low temperatures to slow their development in order to match their peak nesting activity to the bloom of the crop. Since low temperature exposure is known to cause developmental abnormalities in other species, we examined the flight physiology of M. rotundata after various temperature treatments to determine if low temperature exposure is detrimental to the bees ability to fly and therefore decreases their ability to pollinate. We found that exposing the bees to 6°C have significant impact on their ability to fly. These studies are clarifying the safe ranges of temperatures that developing M. rotundata can be exposed to and thereby improving pollinator quality to the end-user.

Technical Abstract: Megachile rotundata develop in brood cells constructed in cavities by adult females. Pre-pupal bees diapause over winter and resume development as temperatures (Ta) increase in spring. While many insects are tolerant of suboptimal Ta in their overwintering stages, insects that initiate active development early in the spring due to an increase in the diurnal Ta range may be vulnerable to sudden cold spells, and global climate change is predicted to increase Ta variability, including the risk of spring frost. We tested the hypothesis that pupal bees may be less resistant to low Ta stress and that this stress may result in altered adult phenotypes. Developing pupae were given one of three treatments: 1) normal Ta at 29°C, 2) interrupted with a low Ta stress (6°C for 1 week; STR), or 3) interrupted with low Ta stress plus fluctuating Ta (daily, 1h pulse of 20°C for 1 week; FTR). As an index of adult phenotype, we assessed flight performance and measured flight metabolic rate (MR). Male STR-treated bees had lower flight MR, and 50% of all bees were unable to fly. To determine if the lower MR was due to decreased energy availability, we assessed feeding behavior. STR-treated animals had the lowest feeding activity. To determine if the flight defects were due to structural defects, we measured wing length. STR-treated animals had 3-6% shorter wings, which could impact wing loading. While it is clear that low Ta stress during pupal development negatively affects adult flight performance, resulting in structural and behavioral changes, the underlying mechanism remains unknown. Effects of Ta stress during development may serious consequences for pollinators that rely on flight for reproduction and feeding.