Maternal effects on offspring development and survival in the alfalfa leafcutting bee, Megachile rotundata

Megachile rotundata, also known as the alfalfa leafcutting bee, is one of the most important and heavily managed pollinators of crops in the United States, following honey bees. Due to their aggregate nesting behavior, alfalfa leafcutting bees (ALCB) can be easily managed by farmers and commercial bee producers. One crucial step in their management is ensuring that bee emergence and crop bloom coincide. This is often achieved by slowing down ALCB development by placing the developing pupa into cool temperatures for an extended period of time. We investigated what effects this prolonged management technique might have on ALCB reproductive females by looking at their reproductive investment and overall offspring survival following cool temperature stalling. We exposed bees to 1, 7 or 14 days of cooler temperatures at 17 days of post diapausing development during the 2018, 2019, and 2020 field seasons. We found no significant differences between these treatment groups as to the amount of nest cells made by reproductive females in early season 2018 and mid season 2019 but saw a decrease in fecundity in late 2019 with significantly fewer nest cells made by females exposed to 14 days of cool stalling. Females that experienced 7 or 14 days of cool stalling provided their offspring with significantly smaller mass provisions in early season 2018 and late season 2019. Photoperiod could be causing maternal effects in addition to cool stalling which we will investigate further by analyzing 2020 data.