A volatilized pyrethroid insecticide from a mosquito repelling device does not impact honey bee foraging and recruitment.

Because nontarget, beneficials, like insect pollinators, may be exposed unintentionally to insecticides, it is important to evaluate the impact of chemical controls on the behaviors performed by insect pollinators in field trials. Here we examine the impact of a portable mosquito repeller, which emits prallethrin, a pyrethroid insecticide, on honey bee foraging and recruitment using a blinded, randomized, paired, parallel group trial. We found no significant effect of the volatilized insecticide on foraging frequency (our primary outcome), waggle dance propensity, waggle dance frequency, and feeder persistency (our secondary outcomes), even though an additional deposition study confirmed that the treatment device was performing appropriately. These results may be useful to consumers that are interested in repelling mosquitos, but also concerned about potential consequences to beneficial insects, such as honey bees.

Dance-communicated distances support nectar foraging as a supply-driven system.

Much like human consumers, honeybees adjust their behaviours based on resources' supply and demand. For both, interactions occur in fluctuating conditions. Honeybees weigh the cost of flight against the benefit of nectar and pollen, which are nutritionally distinct resources that serve different purposes: bees collect nectar continuously to build large honey stores for overwintering, but they collect pollen intermittently to build modest stores for brood production periods. Therefore, nectar foraging can be considered a supply-driven process, whereas pollen foraging is demand-driven. Here we compared the foraging distances, communicated by waggle dances and serving as a proxy for cost, for nectar and pollen in three ecologically distinct landscapes in Virginia. We found that honeybees foraged for nectar at distances 14% further than for pollen across all three sites (n = 6224 dances, p < 0.001). Specific temporal dynamics reveal that monthly nectar foraging occurs at greater distances compared with pollen foraging 85% of the time. Our results strongly suggest that honeybee foraging cost dynamics are consistent with nectar supply-driven and pollen demand-driven processes.

Honey Bees (Hymenoptera: Apidae) Decrease Foraging But Not Recruitment After Neonicotinoid Exposure.

Honey bees (Linnaeus, Hymenoptera: Apidae) are widely used as commercial pollinators and commonly forage in agricultural and urban landscapes containing neonicotinoid-treated plants. Previous research has demonstrated that honey bees display adverse behavioral and cognitive effects after treatment with sublethal doses of neonicotinoids. In laboratory studies, honey bees simultaneously increase their proportional intake of neonicotinoid-treated solutions and decrease their total solution consumption to some concentrations of certain neonicotinoids. These findings suggest that neonicotinoids might elicit a suboptimal response in honey bees, in which they forage preferentially on foods containing pesticides, effectively increasing their exposure, while also decreasing their total food intake; however, behavioral responses in semifield and field conditions are less understood. Here we conducted a feeder experiment with freely flying bees to determine the effects of a sublethal, field-realistic concentration of imidacloprid (IMD) on the foraging and recruitment behaviors of honey bees visiting either a control feeder containing a sucrose solution or a treatment feeder containing the same sucrose solution with IMD. We report that IMD-treated honey bees foraged less frequently (-28%) and persistently (-66%) than control foragers. Recruitment behaviors (dance frequency and dance propensity) also decreased with IMD, but nonsignificantly. Our results suggest that neonicotinoids inhibit honey bee foraging, which could potentially decrease food intake and adversely affect colony health.

Outcomes of HIV-positive patients lost to follow-up in African treatment programmes.

OBJECTIVE: The retention of patients on antiretroviral therapy (ART) is key to achieving global targets in response to the HIV epidemic. Loss to follow-up (LTFU) can be substantial, with unknown outcomes for patients lost to ART programmes. We examined changes in outcomes of patients LTFU over calendar time, assessed associations with other study and programme characteristics and investigated the relative success of different tracing methods. METHODS: We performed a systematic review and logistic random-effects meta-regression analysis of studies that traced adults or children who started ART and were LTFU in sub-Saharan African treatment programmes. The primary outcome was mortality, and secondary outcomes were undocumented transfer to another programme, treatment interruption and the success of tracing attempts. RESULTS: We included 32 eligible studies from 12 countries in sub-Saharan Africa: 20 365 patients LTFU were traced, and 15 708 patients (77.1%) were found. Compared to telephone calls, tracing that included home visits increased the probability of success: the adjusted odds ratio (aOR) was 9.35 (95% confidence interval [CI] 1.85-47.31). The risk of death declined over calendar time (aOR per 1-year increase 0.86, 95% CI 0.78-0.95), whereas undocumented transfers (aOR 1.13, 95% CI 0.96-1.34) and treatment interruptions (aOR 1.31, 95% CI 1.18-1.45) tended to increase. Mortality was lower in urban than in rural areas (aOR 0.59, 95% CI 0.36-0.98), but there was no difference in mortality between adults and children. The CD4 cell count at the start of ART increased over time. CONCLUSIONS: Mortality among HIV-positive patients who started ART in sub-Saharan Africa, were lost to programmes and were successfully traced has declined substantially during the scale-up of ART, probably driven by less severe immunodeficiency at the start of therapy.

Dancing to her own beat: honey bee foragers communicate via individually calibrated waggle dances.

Communication signals often vary between individuals, even when one expects selection to favour accuracy and precision, such as the honey bee waggle dance, where foragers communicate to nestmates the direction and distance to a resource. Although many studies have examined intra-dance variation, or the variation within a dance, less is known about inter-dance variation, or the variation between dances. This is particularly true for distance communication. Here, we trained individually marked bees from three colonies to forage at feeders of known distances and monitored their dances to determine individual communication variation. We found that each honey bee possesses her own calibration: individual duration-distance calibrations varied significantly in both slopes and intercepts. The variation may incur a cost for communication, such that a dancer and recruit may misunderstand the communicated distance by as much as 50%. Future work is needed to understand better the mechanisms and consequences of individual variation in communication.

Bourgeois behavior and freeloading in the colonial orb web spider Parawixia bistriata (Araneae, Araneidae).

Spiders of the tropical American colonial orb weaver Parawixia bistriata form a communal bivouac in daytime. At sunset, they leave the bivouac and construct individual, defended webs within a large, communally built scaffolding of permanent, thick silk lines between trees and bushes. Once spiders started building a web, they repelled other spiders walking on nearby scaffolding with a "bounce" behavior. In nearly all cases (93%), this resulted in the intruder leaving without a fight, akin to the "bourgeois strategy," in which residents win and intruders retreat without escalated contests. However, a few spiders (6.5%) did not build a web due to lack of available space. Webless spiders were less likely to leave when bounced (only 42% left) and instead attempted to "freeload," awaiting the capture of prey items in nearby webs. Our simple model shows that webless spiders should change their strategy from bourgeois to freeloading satellite as potential web sites become increasingly occupied.

Incorporating variability in honey bee waggle dance decoding improves the mapping of communicated resource locations.

Honey bees communicate to nestmates locations of resources, including food, water, tree resin and nest sites, by making waggle dances. Dances are composed of repeated waggle runs, which encode the distance and direction vector from the hive or swarm to the resource. Distance is encoded in the duration of the waggle run, and direction is encoded in the angle of the dancer's body relative to vertical. Glass-walled observation hives enable researchers to observe or video, and decode waggle runs. However, variation in these signals makes it impossible to determine exact locations advertised. We present a Bayesian duration to distance calibration curve using Markov Chain Monte Carlo simulations that allows us to quantify how accurately distance to a food resource can be predicted from waggle run durations within a single dance. An angular calibration shows that angular precision does not change over distance, resulting in spatial scatter proportional to distance. We demonstrate how to combine distance and direction to produce a spatial probability distribution of the resource location advertised by the dance. Finally, we show how to map honey bee foraging and discuss how our approach can be integrated with Geographic Information Systems to better understand honey bee foraging ecology.

Context affects nestmate recognition errors in honey bees and stingless bees.

Nestmate recognition studies, where a discriminator first recognises and then behaviourally discriminates (accepts/rejects) another individual, have used a variety of methodologies and contexts. This is potentially problematic because recognition errors in discrimination behaviour are predicted to be context-dependent. Here we compare the recognition decisions (accept/reject) of discriminators in two eusocial bees, Apis mellifera and Tetragonisca angustula, under different contexts. These contexts include natural guards at the hive entrance (control); natural guards held in plastic test arenas away from the hive entrance that vary either in the presence or absence of colony odour or the presence or absence of an additional nestmate discriminator; and, for the honey bee, the inside of the nest. For both honey bee and stingless bee guards, total recognition errors of behavioural discrimination made by guards (% nestmates rejected + % non-nestmates accepted) are much lower at the colony entrance (honey bee: 30.9%; stingless bee: 33.3%) than in the test arenas (honey bee: 60-86%; stingless bee: 61-81%; P<0.001 for both). Within the test arenas, the presence of colony odour specifically reduced the total recognition errors in honey bees, although this reduction still fell short of bringing error levels down to what was found at the colony entrance. Lastly, in honey bees, the data show that the in-nest collective behavioural discrimination by ca. 30 workers that contact an intruder is insufficient to achieve error-free recognition and is not as effective as the discrimination by guards at the entrance. Overall, these data demonstrate that context is a significant factor in a discriminators' ability to make appropriate recognition decisions, and should be considered when designing recognition study methodologies.

Working against gravity: horizontal honeybee waggle runs have greater angular scatter than vertical waggle runs.

The presence of noise in a communication system may be adaptive or may reflect unavoidable constraints. One communication system where these alternatives are debated is the honeybee (Apis mellifera) waggle dance. Successful foragers communicate resource locations to nest-mates by a dance comprising repeated units (waggle runs), which repetitively transmit the same distance and direction vector from the nest. Intra-dance waggle run variation occurs and has been hypothesized as a colony-level adaptation to direct recruits over an area rather than a single location. Alternatively, variation may simply be due to constraints on bees' abilities to orient waggle runs. Here, we ask whether the angle at which the bee dances on vertical comb influences waggle run variation. In particular, we determine whether horizontal dances, where gravity is not aligned with the waggle run orientation, are more variable in their directional component. We analysed 198 dances from foragers visiting natural resources and found support for our prediction. More horizontal dances have greater angular variation than dances performed close to vertical. However, there is no effect of waggle run angle on variation in the duration of waggle runs, which communicates distance. Our results weaken the hypothesis that variation is adaptive and provide novel support for the constraint hypothesis.

Row crop fields provide mid-summer forage for honey bees.

Honey bees provide invaluable economic and ecological services while simultaneously facing stressors that may compromise their health. For example, agricultural landscapes, such as a row crop system, are necessary for our food production, but they may cause poor nutrition in bees from a lack of available nectar and pollen. Here, we investigated the foraging dynamics of honey bees in a row crop environment. We decoded, mapped, and analyzed 3459 waggle dances, which communicate the location of where bees collected food, for two full foraging seasons (April-October, 2018-2019). We found that bees recruited nestmates mostly locally (<2 km) throughout the season. The shortest communicated median distances (0.474 and 0.310 km), indicating abundant food availability, occurred in July in both years, which was when our row crops were in full bloom. We determined, by plotting and analyzing the communicated locations, that almost half of the mid-summer recruitment was to row crops, with 37% (2018) and 50% (2019) of honey bee dances indicating these fields. Peanut was the most attractive in July, followed by corn and cotton but not soybean. Overall, row crop fields are indicated by a surprisingly large proportion of recruitment dances, suggesting that similar agricultural landscapes may also provide mid-summer foraging opportunities for honey bees.

Percent lipid is associated with body size but not task in the bumble bee Bombus impatiens.

In some group-living organisms, labor is divided among individuals. This allocation to particular tasks is frequently stable and predicted by individual physiology. Social insects are excellent model organisms in which to investigate the interplay between physiology and individual behavior, as division of labor is an important feature within colonies, and individual physiology varies among the highly related individuals of the colony. Previous studies have investigated what factors are important in determining how likely an individual is, compared to nestmates, to perform certain tasks. One such task is foraging. Corpulence (i.e., percent lipid) has been shown to determine foraging propensity in honey bees and ants, with leaner individuals being more likely to be foragers. Is this a general trend across all social insects? Here we report data analyzing the individual physiology, specifically the percent lipid, of worker bumble bees (Bombus impatiens) from whom we also analyze behavioral task data. Bumble bees are also unusual among the social bees in that workers may vary widely in size. Surprisingly we find that, unlike other social insects, percent lipid is not associated with task propensity. Rather, body size closely predicts individual relative lipid stores, with smaller worker bees being allometrically fatter than larger worker bees.

Correction: Do honey bee (Apis mellifera) foragers recruit their nestmates to native forbs in reconstructed prairie habitats?

[This corrects the article DOI: 10.1371/journal.pone.0228169.].

Brain composition and olfactory learning in honey bees.

Correlations between brain or brain component size and behavioral measures are frequently studied by comparing different animal species, which sometimes introduces variables that complicate interpretation in terms of brain function. Here, we have analyzed the brain composition of honey bees (Apis mellifera) that have been individually tested in an olfactory learning paradigm. We found that the total brain size correlated with the bees' learning performance. Among different brain components, only the mushroom body, a structure known to be involved in learning and memory, showed a positive correlation with learning performance. In contrast, visual neuropils were relatively smaller in bees that performed better in the olfactory learning task, suggesting modality-specific behavioral specialization of individual bees. This idea is also supported by inter-individual differences in brain composition. Some slight yet statistically significant differences in the brain composition of European and Africanized honey bees are reported. Larger bees had larger brains, and by comparing brains of different sizes, we report isometric correlations for all brain components except for a small structure, the central body.

Africanized honeybees are slower learners than their European counterparts.

Does cognitive ability always correlate with a positive fitness consequence? Previous research in both vertebrates and invertebrates provides mixed results. Here, we compare the learning and memory abilities of Africanized honeybees (Apis mellifera scutellata hybrid) and European honeybees (Apis mellifera ligustica). The range of the Africanized honeybee continues to expand, superseding the European honeybee, which led us to hypothesize that they might possess greater cognitive capabilities as revealed by a classical conditioning assay. Surprisingly, we found that fewer Africanized honeybees learn to associate an odor with a reward. Additionally, fewer Africanized honeybees remembered the association a day later. While Africanized honeybees are replacing European honeybees, our results show that they do so despite displaying a relatively poorer performance on an associative learning paradigm.

Alarm pheromones do not mediate rapid shifts in honey bee guard acceptance threshold.

Honey bee (Apis mellifera) guards discriminate nestmates from non-nestmates at the hive entrance. The acceptance threshold of guards is known to change adaptively, for example becoming less permissive when the number of intruder bees from other colonies increases. These adaptive shifts can occur within minutes. What is unknown is the mechanism behind this rapid shift. It was hypothesized that alarm pheromones released by guards may cause the adoption of a less permissive acceptance threshold. Here, we tested this hypothesis on five discriminator hives by using a behavioral assay. We used three amounts each of iso-pentyl acetate (IPA) and 2-heptanone (2H), which are the major components of the pheromones from the sting and the mandibular glands, respectively. Biologically relevant levels of chemicals were delivered to the hive entrance platform via an air pump. We found no effect of either IPA or 2H: there was no change in guard acceptance of either nestmate (on average, 91% accepted) or non-nestmate (on average, 30% accepted) under any of the pheromone treatments compared to the pentane control (98% nestmates accepted and 32% non-nestmates accepted). Therefore, we reject the hypothesis that the presence of IPA or 2H causes a rapid shift of guard acceptance threshold.

Ontogeny of worker body size distribution in bumble bee (Bombus impatiens) colonies.

Bumble bees exhibit worker size polymorphisms; highly related workers within a colony may vary up to 10-fold in body mass. As size variation is an important life history feature in bumble bees, the distribution of body sizes within the colony and how it fluctuates over the colony cycle were analysed.Ten commercially purchased colonies of Bombus impatiens (Cresson) were reared in ad libitum conditions. The size of all workers present and newly emerging workers (callows) was recorded each week.The average size of bumble bee workers did not change with colony age, but variation in body size tended to decrease over time. The average size of callows did not change with population size, but did tend to decrease with colony age. In all measures, there was considerable variation among colonies.Colonies of B. impatiens usually produced workers with normally distributed body sizes throughout the colony life cycle. Unlike most polymorphic ants, there was no increase in worker body size with colony age or colony size. This provides the first, quantitative data on the ontogeny of bumble bee worker size distribution. The potential adaptive significance of this size variation is discussed.

Do honey bee (Apis mellifera) foragers recruit their nestmates to native forbs in reconstructed prairie habitats?

Honey bee (Apis mellifera) colonies are valued for the pollination services that they provide. However, colony mortality has increased to unsustainable levels in some countries, including the United States. Landscape conversion to monocrop agriculture likely plays a role in this increased mortality by decreasing the food sources available to honey bees. Many land owners and organizations in the Upper Midwest region of the United States would like to restore/reconstruct native prairie habitats. With increasing public awareness of high bee mortality, many landowners and beekeepers have wondered whether these restored prairies could significantly improve honey bee colony nutrition. Conveniently, honey bees have a unique communication signal called a waggle dance, which indicates the locations of the flower patches that foragers perceive as highly profitable food sources. We used these communication signals to answer two main questions: First, is there any part of the season in which the foraging force of a honey bee colony will devote a large proportion of its recruitment efforts (waggle dances) to flower patches within prairies? Second, will honey bee foragers advertise specific taxa of native prairie flowers as profitable pollen sources? We decoded 1528 waggle dances in colonies located near two large, reconstructed prairies. We also collected pollen loads from a subset of waggle-dancing bees, which we then analyzed to determine the flower taxon advertised. Most dances advertised flower patches outside of reconstructed prairies, but the proportion of dances advertising nectar sources within prairies increased significantly in the late summer/fall at one site. Honey bees advertised seven native prairie taxa as profitable pollen sources, although the three most commonly advertised pollen taxa were non-native. Our results suggest that including certain native prairie flower taxa in reconstructed prairies may increase the chances that colonies will use those prairies as major food sources during the period of greatest colony growth and honey production.

Location, location, location: larvae position inside the nest is correlated with adult body size in worker bumble-bees (Bombus impatiens).

Social insects display task-related division of labour. In some species, division of labour is related to differences in body size, and worker caste members display morphological adaptations suited for particular tasks. Bumble-bee workers (Bombus spp.) can vary in mass by eight- to tenfold within a single colony, which previous work has linked to division of labour. However, little is known about the proximate mechanism behind the production of this wide range of size variation within the worker caste. Here, we quantify the larval feeding in Bombus impatiens in different nest zones of increasing distance from the centre. There was a significant difference in the number of feedings per larva across zones, with a significant decrease in feeding rates as one moved outwards from the centre of the nest. Likewise, the diameter of the pupae in the peripheral zones was significantly smaller than that of pupae in the centre. Therefore, we conclude that the differential feeding of larvae within a nest, which leads to the size variation within the worker caste, is based on the location of brood clumps. Our work is consistent with the hypothesis that some larvae are 'forgotten', providing a possible first mechanism for the creation of size polymorphism in B. impatiens.

Recognition errors by honey bee (Apis mellifera) guards demonstrate overlapping cues in conspecific recognition.

Honey bee (Apis mellifera) entrance guards discriminate nestmates from intruders. We tested the hypothesis that the recognition cues between nestmate bees and intruder bees overlap by comparing their acceptances with that of worker common wasps, Vespula vulgaris, by entrance guards. If recognition cues of nestmate and non-nestmate bees overlap, we would expect recognition errors. Conversely, we hypothesised that guards would not make errors in recognizing wasps because wasps and bees should have distinct, non-overlapping cues. We found both to be true. There was a negative correlation between errors in recognizing nestmates (error: reject nestmate) and nonnestmates (error: accept non-nestmate) bees such that when guards were likely to reject nestmates, they were less likely to accept a nonnestmate; conversely, when guards were likely to accept a non-nestmate, they were less likely to reject a nestmate. There was, however, no correlation between errors in the recognition of nestmate bees (error: reject nestmate) and wasps (error: accept wasp), demonstrating that guards were able to reject wasps categorically. Our results strongly support that overlapping cue distributions occur, resulting in errors and leading to adaptive shifts in guard acceptance thresholds.

Preemptive defensive self-sacrifice by ant workers.

Worker insects altruistically sacrifice their own reproduction to rear nondescendant kin. This sacrifice reaches its most spectacular level in suicidal colony defense. Suicidal defense, such as when the sting of a honeybee worker embeds in a predator and then breaks off, is normally a facultative response. Here we describe the first example of preemptive self-sacrifice in nest defense. In the Brazilian ant Forelius pusillus, the nest entrance is closed at sunset. One to eight workers finish the job from the outside and, in doing so, sacrifice their lives.