Seasonal trends in the condition of nesting females of a solitary bee: wing wear, lipid content, and oocyte size

Abstract

During the nesting season, adult females of the solitary bee Megachile rotundata (F.) face considerable physical and energy demands that could include increasing wear and tear on their bodies and decreasing lipid reserves. Consequently, their reproductive performance may be affected not only by extrinsic factors (e.g., weather and floral resource availability), but intrinsic changes in their own bodies. Because of the potential fitness effects of seasonal changes in body condition, our objectives were to determine how wing wear, lipid reserves, and oocyte sizes vary during nesting seasons, beginning when females emerge as adults. As nesting progressed, females in two populations experienced a steady increase in wing wear, which is known to reduce foraging efficiency and increase risk of mortality in other bees. Soon after emergence, females exhibited sharp declines in lipid content which remained low for the remainder of the season. Newly-emerged females ingested pollen, an activity known to be correlated with the initiation of egg maturation in this species. Additionally, the early summer drop in lipid stores was correlated with an increase in the size of the oocytes carried. However, by ∼6 weeks after emergence, oocytes began to decrease in length and volume, perhaps due to nutrient deficiencies related to loss of stored lipids. Our results suggest management of M. rotundata should include rearing bees at temperatures that maximize stored lipid reserves in adults and timing bee release so that significant pollen resources are available for both adults and offspring.

Solitary Bee Life History Traits and Sex Mediate Responses to Manipulated Seasonal Temperatures and Season Length

“…If pre-emergence weight loss is indicative of storedenergy consumption, the amount of energy available to Osmia spp. for fitness-related activities, such as gamete production, mating, nest construction, and offspring provisioning (Hahn and Denlinger, 2007;O'Neill et al, 2015) may be affected by climate change (Bosch et al, 2010). Although we cannot draw a causative link between increased pre-emergence weight loss and post-emergence fitness in this study, structural equation analyses revealed a significant negative correlation between preemergence weight loss and post-emergence lifespan without feeding in both Osmia spp.…”

Specialization on pollen or nectar in bumblebee foragers is not associated with ovary size, lipid reserves or sensory tuning

“…The vials were left open in a drying oven to evaporate the ethanol and then weighed. The bees were then soaked in ether, dried, and re-weighed (Ellers, 1995; Brown, Loosli & Schmid-Hempel, 2000; Strohm, 2000; O’Neill et al, 2011; O’Neill, Delphia & Pitts-Singer, 2015; Graystock et al, 2016). The difference between the two dry weights represents the amount of lipids present in each bee ( n  = 132, 80, 216, 85, for colonies 4, 6, 8, 9, respectively) and is reported as a percentage of total body weight to standardize for intra-individual size variation.…”

Effects of nutritional deprivation on development and behavior in the subsocial beeCeratina calcarata(Hymenoptera: Xylocopinae)

“…To quantify body lipids from lab-reared adult bees raised on manipulated pollen quantities, we followed methods previously published for honey bees (Toth and Robinson, 2005) and solitary bees (Richards and Packer, 1994;O'Neill et al, 2015). Briefly, bees previously frozen at −80°C (see 'Behavioral assays', below) were placed in a homogenizer tube and ground with a glass rod.…”