Cryptic extended brood care in the facultatively eusocial sweat bee Megalopta genalis

As a result of different brood cell provisioning strategies, nest-making insects may differ in the extent to which adults regularly provide extended parental care to their brood beyond nest defense. Mass-provisioning species cache the entire food supply needed for larval development prior to the oviposition and typically seal the brood cell. It is usually assumed that there is no regular contact between the adult(s) and brood. Here, we show that the bee, Megalopta genalis, expresses a form of cryptic brood care, which would not be observed during normal development. Following experimental injections of different provisioning materials into brood cells, foundresses reopened manipulated cells and the brood were aborted in some cases, implying that the foundresses assessed conditions within the cells. In aborted cells, foundresses sometimes laid a second egg after first removing dead larvae, previously stored pollen and contaminants. Our results show that hygienic brood care can be cryptic and hence may be more widespread than previously believed, lending support to the hypothesis that extended parental care is a preadaptation toward eusociality

Draft Genome Assembly and Population Genetics of an Agricultural Pollinator, the Solitary Alkali Bee (Halictidae: Nomia melanderi).

Alkali bees (Nomia melanderi) are solitary relatives of the halictine bees, which have become an important model for the evolution of social behavior, but for which few solitary comparisons exist. These ground-nesting bees defend their developing offspring against pathogens and predators, and thus exhibit some of the key traits that preceded insect sociality. Alkali bees are also efficient native pollinators of alfalfa seed, which is a crop of major economic value in the United States. We sequenced, assembled, and annotated a high-quality draft genome of 299.6 Mbp for this species. Repetitive content makes up more than one-third of this genome, and previously uncharacterized transposable elements are the most abundant type of repetitive DNA. We predicted 10,847 protein coding genes, and identify 479 of these undergoing positive directional selection with the use of population genetic analysis based on low-coverage whole genome sequencing of 19 individuals. We found evidence of recent population bottlenecks, but no significant evidence of population structure. We also identify 45 genes enriched for protein translation and folding, transcriptional regulation, and triglyceride metabolism evolving slower in alkali bees compared to other halictid bees. These resources will be useful for future studies of bee comparative genomics and pollinator health research

Pre-copulatory courtship behavior in a solitary bee, Nomia triangulifera Vachal (Hymenoptera: Halictidae)

Complex courtship behavior occurs both before and during mating of a solitary bee, Nomia triangulifera. Males begin emerging before females, and patrol over the emergence site, although some males also fly near sunflower plants, the exclusive food source of the females. The sizes of males patrolling at these two locations, and those collected while mating were not significantly different. Courtship behavior involves use of the fore- and mid-legs, the metasoma (abdomen), antennae, and the indirect flight muscles to produce loud, audible buzzes. The hind legs have expanded tibiae which are used for clasping the female. Females rarely mated more than once when held in cages. Receptive females usually lacked sperm in their spermathecae, while unreceptive females often had sperm

Frequency of social nesting in the sweat bee Megalopta genalis (Halictidae) does not vary across a rainfall gradient, despite disparity in brood production and body size

Local environmental conditions can facilitate or preclude the development of eusocial colonies in insects that facultatively express behavioural-caste polyphenism. To explore how environmental variability relates to the expression of social behaviour, we collected 120 nests of the facultatively social sweat bee, Megalopta genalis (Halictidae: Augochlorini), along a nearly twofold rainfall gradient in central Panama. Brood rearing activity of bees in seasonal neotropical forests should track flowering phenologies, which are typically set by rainfall and phylogenetic patterns. Nests were collected at roughly similar times of year from three sites comprising wet, moist and dry lowland tropical forests. There were significant differences in ovarian development, brood production and body size across sites for some comparisons, but no effect on the proportion of social colonies collected at each site. Results show that phenotypes of M. genalis relevant to social behaviour (ovarian development, brood production, body size) may be responsive to variation in local environment over distances of <20 km.S. M. Tierney, C. N. Fischer, S. M. Rehan, K. M. Kapheim, W. T. Wcisl

Nest-mate recognition in Manuelia postica (Apidae: Xylocopinae): an eusocial trait is present in a solitary bee

In eusocial Hymenoptera, females are more tolerant towards nest-mate than towards non-nest-mate females. In solitary Hymenoptera, females are generally aggressive towards any conspecific female. Field observations of the nest biology of Manuelia postica suggested nest-mate recognition. Experiments were performed involving two live interacting females or one live female interacting with a dead female. Live females from different nests were more intolerant to each other than females from the same nest. Females were more intolerant towards non-nest-mate than towards nest-mate dead females. When dead females were washed with pentane, no differences in tolerant and intolerant behaviours were detected between non-nest-mate and nest-mate females. Females were more intolerant towards nest-mate female carcasses coated with the cuticular extract from a non-nest-mate than towards non-nest-mate female carcasses coated with the cuticular extract from a nest-mate. The compositions of the cuticular extracts was more similar between females from the same nest than between females from different nests. The results demonstrate for the first time nest-mate recognition mediated by cuticular chemicals in a largely solitary species of Apidae. The position of Manuelia at the base of the Apidae phylogeny suggests that nest-mate recognition in eusocial species apical to Manuelia represents the retention of a primitive capacity in Apidae