Size variation and foraging rate in bumblebees (Bombus terrestris)

Summary: Size polymorphism is an important life history trait in bumblebees with strong impact on individual behavior and colony organization. Within a colony larger workers tend to serve as foragers, while smaller workers fulfill in-hive tasks. It is often assumed that size-dependent division of labor relates to differences in task performance. In this study we examined size-dependent interindividual variability in foraging, i.e. whether foraging behavior and foraging capability of bumblebee workers are affected by their size. We observed two freely foraging Bombus terrestris colonies and measured i) trip number, ii) trip time, iii) proportion of nectar trips, and iv) nectar foraging rate of different sized foragers. In all observation periods large foragers exhibited a significantly higher foraging rate than small foragers. None of the other three foraging parameters was affected by worker size. Thus, large foragers contributed disproportionately more to the current nectar influx of their colony. We provide a detailed discussion of the possible proximate mechanisms underlying the differences in foraging rate.     

Male behaviour in two bumblebees, Bombus nevudensis auricomus and B. griseicollis (Hymenoptera: Apidae)

The mating system of the bumblebees Bombus nevadensis and B. griseicollis involves apparent territorial defence of perch sites near or within visually conspicuous trees. Non–contact chases between perch owners and intruders are rare in B. nevadensis and more common in B. griseicollis. The perches of B. nevadensis are in open areas whereas those of B. griseicoilis are within trees or in sites shaded by trees. The same locations may be occupied on 2 different years. Individual males may return to favoured perches over periods ranging from 2 to 24 days. Males of both species scent–mark spots near their perches early in the morning and then scan visually for passing females for as much as 7–8 h daily. The landmark–based mating system of these bumblebees is similar to that of some other insects and closely resembles the pure dominance (lek) mating system of certain vertebrates. Some hypotheses for the evolution of diversity in male mating tactics among bumblebee species are presented.     

Recognition and avoidance of contaminated flowers by foraging bumblebees (Bombus terrestris)

Bumblebee colonies are founded by a single-mated queen. Due to this life history trait, bumblebees are more susceptible to parasites and diseases than polyandrous and/or polygynous social insects. A greater resistance towards parasites is shown when the genetic variability within a colony is increased. The parasite resistance may be divided into different levels regarding the step of the parasite infection (e.g. parasite uptake, parasite intake, parasite's establishment in the nest, parasite transmission). We investigate the prophylactic behaviour of bumblebees. Bumblebees were observed during their foraging flights on two artificial flowers; one of these was contaminated by Crithidia bombi, a naturally occurring gut parasite of bumblebees (in a control experiment the non-specific pathogen Escherichia coli was used). For C. bombi, bumblebees were preferentially observed feeding on the non-contaminated flower. Whereas for E. coli, the number of visits between flowers was the same, bumblebees spent more time feeding on the non-contaminated flower. These results demonstrate the ability of bumblebees to recognise the contamination of food sources. In addition, bumblebees have a stronger preference for the non-contaminated flower when C. bombi is present in the other flower than with E. coli which might be explained as an adaptive behaviour of bumblebees towards this specific gut parasite. It seems that the more specific the parasite is, the more it reduces the reward of the flower.     

Proboscis length and resource utilization in two Uruguayan bumblebees: Bombus atratus Franklin and Bombus bellicosus Smith (Hymenoptera: Apidae)

Bumblebees (Bombus sp.) are eusocial insects with an annual life cycle whose use as pollinator of crops has gained great importance in modern agriculture. Several authors have found that resource use in Bombus species is usually based on the correlation between the proboscis length of the bumblebees and the corolla depth of the flowers. The aim of this study was to determine proboscis length of Bombus atratus and B. bellicosus, two Uruguayan bumblebees, and verify the resource exploitation testing two cultivated species, the red clover and the bird's foot trefoil. Bumblebee foraging activity was recorded in two culture conditions: in a red clover and bird's foot trefoil mixed meadow, and in contiguous plots of these legumes, and the proboscis length of collected foragers was determined. Both species of bumblebees exploited red clover and bird's foot trefoil although they did it in different proportions in all instances tested. The results indicated that the choice of the resources in B. atratus and B. bellicosus was influenced by their proboscis length. Bombus atratus has a longer proboscis and preferably visited red clover, possibly obtaining nectar easier and faster than B. bellicosus, which has a shorter proboscis. Bombus bellicosus used both resources without any clear preference.     

Effects of clothianidin on Bombus impatiens (Hymenoptera: Apidae) colony health and foraging ability

We conducted laboratory experiments to investigate the lethal and sublethal effects of clothianidin on bumble bee, Bombus impatiens Cresson, colony health and foraging ability. Bumble bee colonies were exposed to 6 ppb clothianidin, representing the highest residue levels found in field studies on pollen, and a higher dose of 36 ppb clothianidin in pollen. Clothianidin did not effect pollen consumption, newly emerged worker weights, amount of brood or the number of workers, males, and queens at either dose. The foraging ability of worker bees tested on an artificial array of complex flowers also did not differ among treatments. These results suggest that clothianidin residues found in seed-treated canola and possibly other crops will not adversely affect the health of bumble bee colonies or the foraging ability of workers.     

Foraging habitats and floral resource use by colonies of long- and short-tongued bumble bee species in an agricultural landscape with kabocha squash fields

Bumble bees pollinate and forage on flowers of crop and wild plants in agricultural landscapes. These interactions may depend on landscape patterns and bumble bee traits. We studied the abundance, colony density, and foraging range in long-tongued Bombus diversus Smith and short-tongued B. hypocrita Pérez, and evaluated their visits to flowers of wild plants and cultivated kabocha squash (Cucurbita maxima Duchesne). In forests in a farmland, B. hypocrita workers were trapped more frequently in the canopy. Full-sibs determined by nuclear microsatellite genotypes among workers collected in the farmland showed higher colony density and a larger foraging radius in B. hypocrita (30.8 km^?2 and 848 m) than in B. diversus (8.3 km^?2 and 723 m), respectively. Regarding wild plants, workers more frequently visited shallow flowers in B. hypocrita and deep flowers in B. diversus. These results suggest that bumble bees with different traits forage on different wild flowers in different habitats. Squash flowers were visited by both bumble bee species at similar frequency in the latter period of colony growth when males and new queens appeared. Composition of full-sib workers visiting squash and wild flowers did not depend on the number of collected workers of individual colonies, indicating that foraging on squash flowers was not associated with colony growth. Thus, growth and reproduction of bumble bee colonies may be supported by various wild plants and cultivated squash, respectively.     

Sex, horizontal transmission, and multiple hosts prevent local adaptation of Crithidia bombi, a parasite of bumblebees (Bombus spp.)

Local adaptation within host-parasite systems can evolve by several non-exclusive drivers (e.g., host species-genetic adaptation; ecological conditions-ecological adaptation, and time-temporal adaptation). Social insects, especially bumblebees, with an annual colony life history not only provide an ideal system to test parasite transmission within and between different host colonies, but also parasite adaptation to specific host species and environments. Here, we study local adaptation in a multiple-host parasite characterized by high levels of horizontal transmission. Crithidia bombi occurs as a gut parasite in several bumblebee species. Parasites were sampled from five different host species in two subsequent years. Population genetic tools were used to test for the several types of adaptation. Although we found no evidence for local adaptation of the parasite toward host species, there was a slight temporal differentiation of the parasite populations, which might have resulted from severe bottlenecks during queen hibernation. Parasite populations were in Hardy-Weinberg equilibrium and showed no signs of linkage disequilibrium suggesting that sexual reproduction is an alternative strategy in this otherwise clonal parasite. Moreover, high levels of multiple infections were found, which might facilitate sexual genetic exchange. The detection of identical clones in different host species suggested that horizontal transmission occurs between host species and underpins the lack of host-specific adaptation.     

Intraspecific aggression, colony identity and foraging distances in Sudanese Microtermes spp. (Isoptera: Termitidae: Macrotermitinae)

Abstract. 1. Intraspecific aggression between termite major workers was used to obtain estimates of foraging distances for three Microtermes species in Sudan.
2. Maximum foraging distance recorded for M. sp. nr albopartitus (Sjöstedt) in Khartoum was 11.3 m, giving an estimated minimum colony area of 100 m². This is probably an underestimate. In the Tokar Delta, individuals from single colonies of M. najdensis Harris were encountered up to 42 m apart, giving a colony area of 1390 m².
3. Intraspecific aggression could not be used reliably to distinguish members of different colonies of M. lepidus Sjöstedt. Soil barrier formation between groups of workers in petri dishes may be of use as a supplementary technique, especially for species showing no clear aggression.
4. Experiments on isolated laboratory colonics of M. sp. Nr lepidus Sjöstedt, established from alates collected in Khartoum, further confirmed the value of inter-colony aggression for indicating colony identity.
5. The complications introduced into estimation of subterranean termite foraging areas by overlap and interdigitation of colonies are discussed.     

Mattesia bombi n. sp. (Neogregarinida: Ophrocystidae), a parasite of Bombus (Hymenoptera: Apidae)

The fat bodies of queen, male, and worker bumble bees were found to harbor a parasite, Mattesia bombi n. sp. (Neogregarinida: Ophrocystidae). The life cycle of this protozoan includes micronuclear and macronuclear schizogonies, gametogony, and sporogony. Sporocysts are predominantly oval in shape and measured 27 × 5.4 μm when mature. The life cycle of the parasite is described and the mode of infection discussed.     

Effects of flowering plant's patch size on species composition of pollinator communities,foraging strategies,and resource partitioning in bumblebees (Hymenoptera: Apidae)

Summary In 4 common Middle-European mainly bumblebee-pollinated plant species (Impatiens glandulifera, Echium vulgare, Aconitum napellus, Symphytum officinale) the influence of patch size on species composition of the pollinator community was studied. Short-tongued species were most dominant in large patches, while small patches were frequented by middle- and long-tongued bumblebees. This phenomenon was extremely obvious in Symphytum officinale and Aconitum napellus, where short-tongued species had bitten a hole in nearly every flower of large patches. Long-tongued species were forced to small patches, where nectarrobbing occurred only exceptionally. In small patches visitationrate (Number of visits per flower per hour) was not lower but either equal or even higher then in large patches. Nectar measurements in Echium vulgare showed, that not only the mean quantity of nectar but also the variance was lower in small patches. As a result, the possible gain can be predicted much more precisely in a small patch than in a large one, and bumblebees have less difficulties in making the right foraging decisions. According to this, foraging strategies depend on patch size. This was confirmed by a computer simulation. The conclusion can be drawn, that many bumblebee species are able to share the same resource by using different patch sizes. Since large flower patches occur mainly in man-made habitats, the dominance of short-tongued species in many bumblebee communities studied by other authors may be unnatural.Supported by the Landesgraduiertenförderung Baden-Württemberg     

Comparison and examination of Bombus occidentalis and Bombus impatiens (Hymenoptera: Apidae) in tomato greenhouses

Experiments were conducted in commercial tomato, Lycopersicon esculentum Miller (Solanaceae), greenhouses to compare the relative foraging effort of two bumble bee species, Bombus occidentalis Greene and Bombus impatiens Cresson, to examine interspecific competition between B. occidentalis and B. impatiens, and to determine whether bumble bee colonies grew to their full population potential in commercial tomato greenhouses. B. impatiens colonies had more brood and workers and made more foraging trips per hour than B. occidentalis colonies. However, B. impatiens returned to the colony without pollen loads and left their colonies without dropping off their pollen loads more frequently than B. occidentalis greenhouse colonies. Our data also suggest that the presence of B. impatiens had a detrimental effect on B. occidentalis populations. Furthermore, B. occidentalis colonies did not grow to their full population potential in tomato greenhouses, with fewer workers in greenhouse colonies than in colonies placed outside in a natural environment, or in colonies that were physically enclosed and protected from external mortality. Together, this study suggests that B. impatiens is a better pollinator than B. occidentalis. It also shows that unknown factors are limiting the size of B. occidentalis colonies in tomato greenhouses.     

Frequency-dependent selection by pollinators: mechanisms and consequences with regard to behaviour of bumblebees Bombus terrestris (L.) (Hymenoptera: Apidae)

Bombus terrestris , a typical pollinating insect species, was offered artificial flowers of two different corolla colours with the same sucrose solution reward in an array. Common colours were significantly preferred, and the strength of the frequency-dependent response increased as a result of learning. There were also frequency-independent biases towards blue flowers, probably because blue flowers appeared more conspicuous to bumblebees than yellow flowers, and the degree of preference for blue was greater when flowers had low nectar rewards. Flower-to-flower movements by individual bumblebees between flowers were non-random, were biased to movements within the same flower colour, and were also dependent on morph frequency. The mechanisms governing flower selection in bumblebees are discussed. Pollinators foraging similarly in a natural situation would induce positive frequency-dependent selection, assortative mating, and directional selection on different corolla colour morphs of the plant population being visited, resulting in stabilizing selection for a single flower colour.     

Brain melatonin content and polyethism in adult workers of Apis mellifera and Apis cerana (Hym., Apidae)

Abstract:  Radioimmunoassay showed that melatonin, N -acetyl-5-methoxytryptamine, was synthesized in the brain of workers of Apis mellifera ligustica Spinola, and related to the polyethism of the workers. Statistically significant differences were found in melatonin levels between workers at different ages and between workers performing different tasks. The level in foragers was higher than that in young nurses. The highest melatonin level was found in 21-day-old adult workers (213.15 pg per worker head) and the lowest level in 1-day-old adult workers (6.08 pg per worker head); and the highest level in pollen-collecting workers (404.13 pg per worker head) and the lowest in nurse workers (13.10 pg per worker head). Apis cerana cerana Fabricius showed a similar pattern, but the nectar foragers had the highest melatonin levels. The melatonin level also showed a daily rhythm. In 30-day-old adult workers there were two peaks, at 7:00 and 19:00 hours, and three troughs at 15:00, 21:00 and 1:00 hours respectively.     

Hazards of insecticides to the bumble bees Bombus impatiens (Hymenoptera: Apidae) foraging on flowering white clover in turf

Insecticides used on turf are sometimes applied to areas with flowering weeds that attract honey bees and native pollinators. We tested residual effects of such treatments on colony vitality and behavior of the bumble bees Bombus impatiens Cresson foraging on turf containingwhite clover, Trifolium repens L. Imidacloprid, a syst emic chloronicotinyl used for preventive control of root-feeding grubs, was applied as granules, followed by irrigation, or sprayed as a wettable powder, with or without irrigation. Hives were confined on the plots in large field cages after residues had dried and colony vitality (i.e., numbers of brood, workers, and honey pots, and weights of queens, workers, and whole colonies with hives) was evaluated after 28-30 d. Workers' foraging activity and defensive response to an aggressive stimulus also were evaluated. In another test, weedy turf was sprayed with chlorpyrifos, carbaryl, or cyfluthrin at labeled rates for surface-feeding pests. Bee colonies were confined on the plots after residues had dried, with effects on colony vitality evaluated after 14 d. Finally, foraging activity of wild bumble bees was monitored on open plots to determine if insecticide-treated areas were avoided. Imidacloprid granules, and imidacloprid sprays applied with posttreatment irrigation, had no effect on colony vitality or workers' behavior, suggesting that such treatments pose little systemic or residual hazard to bumble bees. In contrast, exposure to dry nonirrigated residues of all of the aforementioned insecticides had severe impact on colony vitality. Foraging workers did not avoid insecticide-treated areas. Means by which turf managers can reduce hazards of insecticide applications to pollinators are discussed.     

Foraging behaviour and sequential multisensory orientation in the aphid parasitoid, Pauesia picta (Hym., Aphidiidae) at different spatial scales

Abstract: Foraging females of Pauesia picta, a parasitoid of the conifer aphid Cinara pinea on pine, used a variety of host plant or host-borne cues to find and recognize its aphid hosts. For long-range detection, females rely mainly on secondary plant compounds to locate potential host plants. In the medium-range (i.e. on a given host plant), females detected the presence of hosts by encounters with honeydew-collecting workers of the ant Formica polyctena and by perceiving host-borne cues. For short-range detection, after the discovery of an aphid colony, P. picta females recognize hosts visually. Subsequent antennal tapping, a tactile stimulus, prevents dispersal of aphids and increases the oviposition success of the parasitoid. The final host acceptance is obviously triggered by signals located in the epicuticle of the host. The results demonstrate the importance of sequential multisensory foraging that correspond to a diminishing distance between the parasitoid and the host.