[Show abstract][Hide abstract] ABSTRACT: Animal communication signals generally evolve to become increasingly conspicuous for intended receivers . However, such conspicuous signals are also more susceptible to eavesdropping: exploitation by unintended receivers . It is typically thought that eavesdroppers harm signalers and select against conspicuous signals . But, if signal conspicuousness deters eavesdroppers by indicating a cost, all receivers benefit. This may occur when eavesdroppers exploit food recruitment signals but need to fight for food access . Using eusocial insects, stingless bees, we show that conspicuous signals can indicate competitive costs and enable signalers to escape eavesdropper-imposed costs. The dominant eavesdropper, Trigona hyalinata, avoided higher levels of T. spinipes pheromone that indicate a food source difficult to win, and showed attraction to lower pheromone levels that indicate a relatively undefended resource. Our decision analysis model reveals that eavesdropping individuals who assess takeover costs can benefit their colony by recruiting to weakly defended resources and avoiding costly takeover attempts.
[Show abstract][Hide abstract] ABSTRACT: Parasitic Tropilaelaps (Delfinado and Baker) mites are a damaging pest of European honey bees (Apis mellifera L.) in Asia. These mites represent a significant threat if introduced to other regions of the world, warranting implementation of Tropilaelaps mite surveillance in uninfested regions. Current Tropilaelaps mite-detection methods are unsuitable for efficient large scale screening. We developed and tested a new bump technique that consists of firmly rapping a honey bee brood frame over a collecting pan. Our method was easier to implement than current detection tests, reduced time spent in each apiary, and minimized brood destruction. This feasibility increase overcomes the test's decreased rate of detecting infested colonies (sensitivity; 36.3% for the bump test, 54.2% and 56.7% for the two most sensitive methods currently used in Asia). Considering this sensitivity, we suggest that screening programs sample seven colonies per apiary (independent of apiary size) and 312 randomly selected apiaries in a region to be 95% sure of detecting an incipient Tropilaelaps mite invasion. Further analyses counter the currently held view that Tropilaelaps mites prefer drone bee brood cells. Tropilaelaps mite infestation rate was 3.5 +/- 0.9% in drone brood and 5.7 +/- 0.6% in worker brood. We propose the bump test as a standard tool for monitoring of Tropilaelaps mite presence in regions thought to be free from infestation. However, regulators may favor the sensitivity of the Drop test (collecting mites that fall to the bottom of a hive on sticky boards) over the less time-intensive Bump test.
Full-text · Article · Aug 2013 · Journal of Economic Entomology
[Show abstract][Hide abstract] ABSTRACT: Recent declines in honey bee populations and increasing demand for insect-pollinated crops raise concerns about pollinator shortages. Pesticide exposure and pathogens may interact to have strong negative effects on managed honey bee colonies. Such findings are of great concern given the large numbers and high levels of pesticides found in honey bee colonies. Thus it is crucial to determine how field-relevant combinations and loads of pesticides affect bee health. We collected pollen from bee hives in seven major crops to determine 1) what types of pesticides bees are exposed to when rented for pollination of various crops and 2) how field-relevant pesticide blends affect bees' susceptibility to the gut parasite Nosema ceranae. Our samples represent pollen collected by foragers for use by the colony, and do not necessarily indicate foragers' roles as pollinators. In blueberry, cranberry, cucumber, pumpkin and watermelon bees collected pollen almost exclusively from weeds and wildflowers during our sampling. Thus more attention must be paid to how honey bees are exposed to pesticides outside of the field in which they are placed. We detected 35 different pesticides in the sampled pollen, and found high fungicide loads. The insecticides esfenvalerate and phosmet were at a concentration higher than their median lethal dose in at least one pollen sample. While fungicides are typically seen as fairly safe for honey bees, we found an increased probability of Nosema infection in bees that consumed pollen with a higher fungicide load. Our results highlight a need for research on sub-lethal effects of fungicides and other chemicals that bees placed in an agricultural setting are exposed to.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods Chemical information can mediate indirect interactions between competitors in plant-animal mutualistic networks. Eavesdropping, exploiting evolved signals aimed at others, has the potential to strongly affect dynamics within a foraging guild. Stingless bees (Hymenoptera: Apidae, Meliponini), critical tropical pollinators, provide a good system to study eavesdropping with a trophic level. Several genera recruit nestmates to rich food sources with pheromone trails. Stingless bees frequently live in close proximity to multiple related species with similar diets, thus exploiting non-nestmate trails should increase search efficiency and ultimately colony fitness. Here we investigated rules underlying heterospecific eavesdropping by stingless bees. Using preference tests, we determined how the dominant Trigona hyalinata responds to various concentrations of the subordinate T. spinipes' trail pheromone. We then quantified the T. spinipes recruitment process to determine whether pheromone concentrations correlate with the effort required for successful resource takeover by eavesdroppers. Finally, we implemented a decision analysis model to test if eavesdropping decisions that are sensitive to both reduced search effort and potentially high costs of gaining access can maximize colony fitness.
Results/Conclusions Eavesdropping T. hyalinata showed a non-linear response across the T. spinipes pheromone concentration gradient. They were attracted to low concentrations, but avoided the higher concentrations left by an actively foraging T. spinipes colony. Their behavior matched the T. spinipes activity level indicated by pheromone concentration. Model results matched empirical eavesdropping behavior of three stingless bee species, and confirmed that assessing takeover effort maximizes net benefit to the focal colony. Additional model analyses predict how environmental factors and bee traits affect eavesdropping behavior. This research significantly improves understanding of interspecific dynamics and decision-making within a trophic level. Eavesdropping may be a key mechanisms increasing patch switching by foragers, and thus increasing plant outcrossing potential.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Interactions between competitors can be indirect, such as foraging decisions based on "social information" gained from monitoring others' interactions with the environment. Eavesdropping, or exploitation of evolved signals aimed at others, in particular, has the potential to strongly affect dynamics within a foraging guild. Despite its ecological implications, little is known about eavesdropping within a trophic level. To investigate rules underlying such behavior, we tested heterospecific eavesdropping on food recruitment pheromone by stingless bees (Hymenoptera: Apidae, Meliponini). Anecdotes and previous eavesdropping studies suggested that the dominant Trigona hyalinata would be attracted to the pheromone of T. spinipes. Dominant species should eavesdrop on subordinate species to facilitate discovery of high-quality resources that they can take over. We used preference tests with free-foraging bees to test this hypothesis. We then developed a decision-analysis model to test the fitness effects of the eavesdropping strategy documented in our experiments.
Trigona hyalinata foragers showed a concentration-dependent response to T. hyalinata food recruitment pheromone. They were attracted to low concentrations, but avoided the higher concentrations maintained by an actively-foraging T. spinipes colony. Empirical results suggested that dominant eavesdroppers will avoid heterospecific food location signals when the conflict costs indicated by those signals are too high. These costs are incurred not only during physical interactions, but also during "access time" when the dominant species is displacing subordinates. Modeling results confirm that matching eavesdropping behavior to non-physical costs maximizes net benefit to the focal colony, and should thus increase the colony's fitness. Our work significantly improves understanding of eavesdropping within a trophic level. It indicates that eavesdroppers respond to perceived costs, and highlights the importance of indirect conflict costs such as access time.
[Show abstract][Hide abstract] ABSTRACT: Foragers can improve search efficiency, and ultimately fitness, by using social information: cues and signals produced by other animals that indicate food location or quality. Social information use has been well studied in predator–prey systems, but its functioning within a trophic level remains poorly understood. Eavesdropping, use of signals by unintended recipients, is of particular interest because eavesdroppers may exert selective pressure on signaling systems. We provide the most complete study to date of eavesdropping between two competing social insect species by determining the glandular source and composition of a recruitment pheromone, and by examining reciprocal heterospecific responses to this signal. We tested eavesdropping between Trigona hyalinata and Trigona spinipes, two stingless bee species that compete for floral resources, exhibit a clear dominance hierarchy and recruit nestmates to high-quality food sources via pheromone trails. Gas chromatography–mass spectrometry of T. hyalinata recruitment pheromone revealed six carboxylic esters, the most common of which is octyl octanoate, the major component of T. spinipes recruitment pheromone. We demonstrate heterospecific detection of recruitment pheromones, which can influence heterospecific and conspecific scout orientation. Unexpectedly, the dominant T. hyalinata avoided T. spinipes pheromone in preference tests, while the subordinate T. spinipes showed neither attraction to nor avoidance of T. hyalinata pheromone. We suggest that stingless bees may seek to avoid conflict through their eavesdropping behavior, incorporating expected costs associated with a choice into the decision-making process.
Electronic supplementary material
The online version of this article (doi:10.1007/s00265-010-1080-3) contains supplementary material, which is available to authorized users.
[Show abstract][Hide abstract] ABSTRACT: Competition for floral resources is a key force shaping pollinator communities, particularly among social bees. The ability of social bees to recruit nestmates for group foraging is hypothesized to be a major factor in their ability to dominate rich resources such as mass-flowering trees. We tested the role of group foraging in attaining dominance by stingless bees, eusocial tropical pollinators that exhibit high diversity in foraging strategies. We provide the first experimental evidence that meliponine group foraging strategies, large colony sizes and aggressive behavior form a suite of traits that enable colonies to improve dominance of rich resources. Using a diverse assemblage of Brazilian stingless bee species and an array of artificial "flowers" that provided a sucrose reward, we compared species' dominance and visitation under unrestricted foraging conditions and with experimental removal of group-foraging species. Dominance does not vary with individual body size, but rather with foraging group size. Species that recruit larger numbers of nestmates (Scaptotrigona aff. depilis, Trigona hyalinata, Trigona spinipes) dominated both numerically (high local abundance) and behaviorally (controlling feeders). Removal of group-foraging species increased feeding opportunities for solitary foragers (Frieseomelitta varia, Melipona quadrifasciata and Nannotrigona testaceicornis). Trigona hyalinata always dominated under unrestricted conditions. When this species was removed, T. spinipes or S. aff. depilis controlled feeders and limited visitation by solitary-foraging species. Because bee foraging patterns determine plant pollination success, understanding the forces that shape these patterns is crucial to ensuring pollination of both crops and natural areas in the face of current pollinator declines.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Social animals are predicted to increase dominance of a resource by foraging in groups. Group foraging strategies may be particularly important for the eusocial stingless bees (Hymenoptera, Apidae, Meliponini), tropical pollinators that experience high levels of competition for floral resources. We tested the role of group foraging in attaining dominance using six Brazilian stingless bee species that span a broad range of foraging strategies, colony sizes, body sizes, and aggression levels. Simulating mass-flowering trees with an array of artificial “flowers”, we compared species’ dominance and visitation under unrestricted foraging conditions and with removal of group-foraging species. For each species we calculated numerical dominance (local abundance), behavioral dominance (a colony’s ability to control feeders), displacement success (individuals’ ability to win fights) and attack probability. We hypothesized that removal would increase feeding opportunities for all species, with solitary foragers benefiting manly after removal of all group-foraging species.
Species that recruit large numbers of nestmates — Scaptotrigona aff. depilis, Trigona hyalinata, T. spinipes — dominated both numerically and behaviorally. They also had high displacement success and attack probability. Removal of group foragers increased feeding opportunities for the solitary foragers: Frieseomelitta varia, Melipona quadrifasciata, Nannotrigona testaceicornis. Individual body size, which is also hypothesized to predict dominance, did not correlate with dominance. Our results show that group foraging, in conjunction with large colony sizes and aggressive behavior, enables stingless bee colonies to improve dominance of rich resources. Because bee foraging patterns determine plant pollination success, understanding the forces that shape these patterns in the natural context of diverse, interacting communities is crucial to ensuring pollination of both crops and natural areas in the face of current pollinator declines.
[Show abstract][Hide abstract] ABSTRACT: Stingless bees deposit target-only odor marks and odor trails that help nestmates locate high-reward floral resources. Because such marks exist in the public domain, they are susceptible to eavesdropping by competitors. Dominant species, which displace other species from food sources, should benefit by eavesdropping on odor trails of subordinate species, because dominant species can be relatively poor at locating new food sources (the dominance-discovery trade-off). We show that dominant species can detect odor marks deposited by subordinate species, but that their response to these marks is context-dependent. One dominant species is attracted to odor marks of a subordinate species only when scouting for new food sources, while another appears to switch from attraction to avoidance depending on odor mark concentration. These results suggest dominant stingless bee species follow a cost-minimizing strategy when eavesdropping on odor marks of subordinate species. Subordinate species, however, show variability in the degree to which their eavesdropping behavior appears risky. Some species play it safe and avoid odor marks of dominant species, while others seem unaffected by these marks, responding the same as when no odor marks are present, and forage in a manner that may put them at high risk of attack. Our results indicate that how stingless bees respond to heterospecific odor marks is a complex behavior varying with dominance, strength of odor marks and location; complex behavior rules resulting from interactions between these factors are of interest for future research.