The effects of putrescine on diapause incidence in the alfalfa leafcutting bee, Megachile rotundata

Diapause is a halt in development in insects to avoid undesirable environmental conditions. It is unknown what is responsible for controlling diapause in many species. In the solitary bee widely reared for use in alfalfa crop production, Megachile rotundata, maternal effects are thought to play a role. In diapausing M. rotundata, the amine, putrescine was found to be highly upregulated when compared to non-diapausing individuals. Putrescine is a biogenic amine in the spermine pathway that is found in all organisms. The aim of this study is to determine the role of putrescine in M. rotundata diapause. We hypothesize that higher putrescine levels in larval M. rotundata provisions cause a hormonal cascade resulting in higher diapause incidence. We will test this using in vitro rearing and adding putrescine to the larval diet, as well as measuring putrescine content of natural larval provisions. The treatment groups will be as follows: unchanged homogenized diet (0.0% putrescine added to diet), low putrescine (0.01% putrescine solution added to diet), and high putrescine (1% putrescine solution added to diet). It is predicted that putrescine presence in larval diet will increase diapause incidence in first cohort M. rotundata. Putrescine levels in provisions will also be measured throughout the season. We predict that putrescine levels in provisions will increase throughout the summer. Determining mechanisms influencing diapause may lead to ways of controlling diapause incidence, which could be helpful for farmers to increase yields and decrease bee losses.