Lasioglossum malachurum

Physical size is a major distinguishing feature between queens and gynes versus female worker bees. Queens consistently are larger in body size than workers. Queens also tend to have worn wings and worn mandibles as a result of higher activity, in addition to greater ovarian development correlating with the reproductive capacity of queens. Queens also generally have abundant fat stores.[3] This physical dimorphism persists throughout all stages of the lifecycle, from pupae to adult. Rarely, queens can be abnormally small compared to the size of workers, but abnormally large workers have never been observed in the wild.[1]

The sweat bee has a simple nesting architecture consisting of a vertical tunnel into the ground ending in a compartment reserved for brood-rearing.[3] They nest underground, like Lasioglossum zephyrus, but they do not form the same complex structures.[6] Nest entrances are frequently concealed using scattered foliage.[7] For L. malachurum, thousands of nests can be found located within a small region in nesting aggregations, which suggests that the bees likely have some sort of identification mechanism for conspecific nests. In fact, nest entrances and brood cell linings are both impregnated with secretions from the Dufour's gland of the bees, which plays a role in nest orientation.[8] Nests are dug into hard, compact soil and can be sealed from within by the queen using her abdomen. Because nests are dug into hard soil, construction of a nest represents a significant energy expense to a queen, which explains why gynes frequently usurp other nests rather than founding one of their own.[9] L. malachurum is a Western Palaearctic species and nests can be found across Southern England and the Channel Islands, most of continental Europe, and North Africa.[10][11]

L. malachurum colonies are monogynous. Although the queen coordinates the workers within the nest, the workers can exert pressures on the queen, as well. Because queens frequently are replaced through usurpation and queen turnover, the workers within a nest are less related to the queen than expected. As such, the workers are less likely to cooperate with the queen based on maximizing their own fitness. To get the workers to remain with the nest and continue to aid her own offspring, the queen often cedes reproduction to alien workers.[2] These workers can produce males or gynes and have high rates of reproduction. They do not, however, overwinter, nor are they morphologically similar to a queen or gyne.[3] The length of lifespan for the queens may be a factor that leads to more reproductive workers in southern climes that have longer breeding seasons; in northern climes, where the queen is generally alive for production of gynes, workers are less likely to be reproductive. In southern climes, where the queen frequently does not survive to gyne production, workers are more likely to be reproductive.[1]

Communication between males and females of L. malachurum is mediated using pheromones.[2] Virginal queens attract males through a sex hormone that mated queens lack; thus, males are much more attracted to younger queens. The chemical distinctions between the pheromones released by virginal and mated queens are significant in terms of proportions of hydrocarbons and lactones. Whereas isopentenyl esters, unsaturated fatty acids, and hydrocarbons are far more abundant in the chemical makeup of a virginal queen's hormones, the old queen's hormones are more likely to be made up of largely macrocyclic lactones. This chemical distinction between virginal and old females allows males to distinguish between the two, thus enabling male choice in sexual partner. They are also capable of discriminating between familiar and unknown queens, and l generally are more attracted to queens of a foreign colony, which likely arose as an outbreeding mating strategy, which increases genetic diversity of the population and decreases the probability that the next generation would be subject to genetic disease.[8]

Because L. malachurum generally nests in aggregations of thousands of colonies within a small region, the ability of bees to recognize their own nests is crucial. Outside the entrances to the nest, guards are posted. These guards mark the nest entrances with Dufour's gland secretions to create olfactory cues to guide colony specific bees back to the nest. These secretions are largely made up of alkanes and alkenes.[8] Bees of the species L. malachurum also rely on visual cues and landmarks to determine where their nests are, which they establish through orientation flights and continuously update through reorientation flights.[14]

Nestmates are able to identify other nestmates using olfactory cues, as well. Chemical similarities, specifically in nonvolatile alkenes and alkanes, provide this cue. Notably, the component of discrimination is not based on kinship, but on shared nesting site, and individual bees of L. malachurum do not behave differently toward related nestmates and unrelated nestmates. In a given nest, the many different compounds mix together to form a gestalt odor that marks all of the members of the nest. This form of scent blending is found commonly among other members of Hymenoptera including certain bees, wasps, and ants. The gestalt bouquet of odors differs significantly in terms of chemical composition between different nests.[15]

Queens frequently can be usurped by intraspecific gynes, because the creation of a new nest is a significant energy investment for gynes.[9] The probability of a colony usurpation increases steadily as the season progresses, most likely because the probability of a gyne having the time and resources to found a new colony and produce new workers decreases.[2] The increasing risk of usurpation may play a role in the small worker broods, because the queen ceases foraging and seals her nest in mid-May to protect from usurping gynes.[2] Early nest closure has been favored by pressure from usurpation and has developed into an evolutionarily stable strategy.[9] It might also explain why queens are highly aggressive toward other conspecific queens.[2] In confrontations between foundresses and usurping gynes, female size is a significant determinant of outcome because it gives the queen or usurper a significant advantage. Although they have a physical advantage in usurpation, larger queens are more likely to found their own nests rather than usurp another.[9]

The nest aggregation of thousands of colonies that persists throughout the year becomes a lek mating system on warm summer days in the latter half of the breeding season (July through September). The daily operational sex ratio has far more males than females, which is common in a lek mating system and among other bees.[7] The lek mating is a system in which a large group of males clusters at sites visited by females for mating.[16] Males are attracted during mating by a mix of olfactory cues produced in multiple glandular sources from the female. Males seek out unrelated, unmated females; because females are only receptive for a short period following their emergence, males must seek out and find an unmated gyne before the large number of other males.[7] Mating can occur either in the female's nest or on flowers. Queens can be polyandrous, but only rarely do they actually mate with multiple males. Most colonies arise from only one queen and one male.[2]

Aggression is commonly seen between conspecifics of all halictid bees; especially between usurper females, drawn out fights can occur that last for nearly a half-hour and result in damage to or loss of limbs and body parts. Guard bees of the L. malachurum species, which are workers that defend the nest, also demonstrate antagonistic behavior toward non-nestmate conspecifics, by orienting their stingers toward the intruders or blocking the entrance to the nest with their abdomens. They are able to discriminate between non-nestmates and nestmates, which they allow to pass with ease. Foragers, though, are either unable to discriminate between nestmate and non-nestmate conspecifics or are uninterested in pursuing aggression against non-nestmate conspecifics, so exhibit high levels of tolerance toward all conspecifics.[17]