Mornings are for the bees: How microclimatic factors influence first flight

Flight in insects may be limited by unfavorable environmental conditions that could have downstream effects on reproduction and pollination. Megachile rotundata is a managed solitary bee used across a range of latitudes. Primarily used for alfalfa, M. rotundata can pollinate other crops, but may be limited by unfavorable conditions during peak blooms.  However, little is known about optimal flight conditions for the alfalfa leafcutting bee. Female M. rotundata nest in small cavities with microclimates that may contribute to flight initiation. Temperature and light provide cues that regulate flight. However, the influence of other environmental factors in conjunction with light and temperature is unknown. The purpose of this study was to examine how ambient conditions and nest microclimates stimulate first flight in M. rotundata. To test the hypothesis that multiple environmental factors regulate flight initiation, a weather station was constructed around a polystyrene nesting block and paired with a GoPro programmed to record video of first flight over 34 days during summer 2019. The weather station continuously measured 3 temperature locations, light, wind, humidity, and air pressure throughout the day. Video was recorded from 7-11am of individual bees. At first flight, temperature data showed that even when ambient temperatures are cooler, bees in the nesting cavity and on the face of the nesting block experienced temperatures 5-10°C higher, which may influence flight decisions. Bees also flew when light was greater than 1392 lux, suggesting a lower threshold. Our data shows that multiple measurements are important in determining first flight.