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Abstract More than 30% of human food crop yield requires animal pollination. In addition, successful crop production depends on agrochemicals to control pests. However, agrochemicals can have negative consequences on beneficial insect pollinators, such as bees. We investigated the effects of an emerging class of pesticides, sulfoximines, on the common eastern bumblebee, Bombus impatiens. We performed a series of 96-hour toxicity tests on microcolonies of laboratory-reared B. impatiens. Our data showed that sulfoxaflor (SFX) is significantly less toxic to B. impatiens than historically used neonicotinoid pesticides, such as thiamethoxam. Further, for the first time, we found significant differences among castes in sensitivity to SFX; workers and drones were more sensitive than queens. These findings are notable because they reveal both caste and sex-specific differences in bumblebee sensitivity to pesticides. Interestingly, we found no evidence that bumblebees avoid SFX-contaminated sugar syrup. To the contrary, B. impatiens workers had an apparent preference for SFX-contaminated sugar syrup over sugar syrup alone. Overall, our investigation provides novel information on an important pesticide and may help inform regulatory decisions regarding pesticide use. 

Abstract Insects have evolved remarkably complex social systems. Social wasps are particularly noteworthy because they display gradations in social behaviors. Here, we sequence the genomes of two highly diverged Vespula wasps, V. squamosa and V. maculifrons Buysson (Hymenoptera: Vespidae), to gain greater insight into the evolution of sociality. Both V. squamosa and V. maculifrons are social wasps that live in large colonies characterized by distinct queen and worker castes. However, V. squamosa is a facultative social parasite, and V. maculifrons is its frequent host. We found that the genomes of both species were ~200 Mbp in size, similar to the genome sizes of congeneric species. Analyses of gene expression from members of different castes and developmental stages revealed similarities in expression patterns among immature life stages. We also found evidence of DNA methylation within the genome of both species by directly analyzing DNA sequence reads. Moreover, genes that were highly and uniformly expressed were also relatively highly methylated. We further uncovered evidence of differences in patterns of molecular evolution in the two taxa, consistent with V. squamosa exhibiting alterations in evolutionary pressures associated with its facultatively parasitic or polygyne life history. Finally, rates of gene evolution were correlated with variation in gene expression between castes and developmental stages, as expected if more highly expressed genes were subject to stronger levels of selection. Overall, this study expands our understanding of how social behavior relates to genome evolution in insects. 

Many social insects construct nests, which are fundamentally important to the success and survival of the colony. We review recent work on understanding the construction and function of social insect nests and attempt to identify general principles of collective construction and nest architecture in insect societies. We look across taxa, including termites, ants, social bees, and social wasps, specifically focusing on experimental studies that have elucidated the mechanisms by which insect nests are successfully built. We find that selecting materials and nest sites are crucial decisions made by social insects that impact both the resulting nest architecture and colony survival. Social insects utilize cohesive, malleable material to build nests. Often, nests are constructed in a modular manner, allowing social insects to exploit a variety of materials while growing to accommodate population explosions from a few individuals to millions. We note that the regulatory principles that coordinate building behaviors are consistent across taxa. Specifically, encounter rate, positive and negative feedback cycles, stigmergy, and genetic influence all govern the actions of multiple builders and result in a cohesive, functional structure. We further consider empirical studies that demonstrate how nests impact collective behaviors and help insect societies flourish. We find that all social insect nests serve the same key functions: to protect residents and to offer a means of organizing their collective behaviors. Ultimately, we expand our analysis to experiments utilizing robot models of societies, which aim to uncover unifying themes of construction and space use by collectives. Overall, we show that social insect nests represent engineering and construction marvels that provide fundamental insights into how biological collectives succeed in the natural environment, and we suggest that the use of robotic models may provide insight into these fascinating behaviors and structures. 

A diversity of organisms live within underground environments. However, visualizing subterranean behavior is challenging because of the opacity of most substrates. We demonstrate that laser speckle imaging, a non-invasive technique resolving nanometer-scale movements, facilitates quantifying biological activity in a granular medium. We monitored fire ants (Solenopsis invicta) at different developmental stages, burial depths (1–5 cm) and moisture fractions (0 and 0.1 by volume) in a container of 0.7 mm glass particles. Although the speckle pattern from the backscattered light precludes direct imaging of animal kinematics, analysis of integrated image differences revealed that spiking during ant movement increased with the developmental phase. Greater burial depth and saturation resulted in fewer and lower magnitude spikes. We verified that spiking correlated with movement via quasi-2D experiments. This straightforward method, involving a laser and digital camera, can be applied to laboratory and potentially field situations to gain insight into subterranean organism activities. 

Females of many species are polyandrous. However, polyandry can give rise to conflict among individuals within families. We examined the level of polyandry and paternity skew in the common eastern yellowjacket wasp,Vespula maculifrons, in order to gain a greater understanding of conflict in social insects. We collected 10 colonies ofV. maculifronsand genotyped workers and prereproductive queens at highly variable microsatellite markers to assign each to a patriline. Genotypic data revealed evidence of significant paternity skew among patrilines. In addition, we found that patrilines contributed differentially to caste production (worker vs. queen), suggesting an important role for reproductive conflict not previously discovered. We also investigated if patterns of paternity skew and mate number varied over time. However, we found no evidence of changes in levels of polyandry when compared to historical data dating back almost 40 years. Finally, we measured a suite of morphological traits in individuals from the most common and least common patrilines in each colony to test if males that showed highly skewed reproductive success also produced offspring that differed in phenotype. Our data revealed weak correlation between paternity skew and morphological phenotype of offspring sired by different males, suggesting no evidence of evolutionary tradeoffs at the level investigated. Overall, this study is the first to report significant paternity and caste‐associated skew inV. maculifrons, and to investigate the phenotypic consequences of skew in a social wasp. Our results suggest that polyandry can have important consequences on the genetic and social structure of insect societies. 

Ants are millimetres in scale yet collectively create metre-scale nests in diverse substrates. To discover principles by which ant collectives self-organize to excavate crowded, narrow tunnels, we studied incipient excavation in small groups of fire ants in quasi-two-dimensional arenas. Excavation rates displayed three stages: initially excavation occurred at a constant rate, followed by a rapid decay, and finally a slower decay scaling in time as t −1/2 . We used a cellular automata model to understand such scaling and motivate how rate modulation emerges without global control. In the model, ants estimated their collision frequency with other ants, but otherwise did not communicate. To capture early excavation rates, we introduced the concept of ‘agitation’—a tendency of individuals to avoid rest if collisions are frequent. The model reproduced the observed multi-stage excavation dynamics; analysis revealed how parameters affected features of multi-stage progression. Moreover, a scaling argument without ant–ant interactions captures tunnel growth power-law at long times. Our study demonstrates how individual ants may use local collisional cues to achieve functional global self-organization. Such contact-based decisions could be leveraged by other living and non-living collectives to perform tasks in confined and crowded environments.