Hot-Blooded Insects

http://www.sussex.ac.uk/lifesci/goulsonlab/documents/goulson-et-al-animal-behaviour-2002.pdf

Can alloethism in workers of the bumblebee, Bombus terrestris, be explained in terms of foraging efficiency?

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 inhive 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.

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Size variation and foraging rate in bumblebees (Bombus terrestris)

Publisher Summary This chapter discusses the behavioral, ecological, and physiological determinants of the activity patterns of bees. An activity pattern is the change in levels of a particular activity through time. Bees are an excellent taxon within which to investigate both the issues of constraint and currency. Their physiological constraints are better understood than those of almost any other invertebrate, allowing an unparalleled opportunity to integrate physiology into behavioral ecology. Many bees require elevated body temperatures ( T b ) to fly, and hence thermal properties of their environment significantly constrain their activity. However, many species are heterothermic, being able to elevate their T b endothermically when necessary, which gives some degree of escape from the usual thermal constraints on other entirely ectothermic insects. The chapter discusses the factors structuring activity patterns in a wide range of bees. Observed activity patterns are generated by interactions between properties of the bees themselves (intrinsic factors) and properties of their environment (extrinsic factors). Intrinsic factors include physiological differences between species and between the sexes. Extrinsic factors are the fluctuating properties of the environment, and are either abiotic or biotic.

Behavioral, ecological, and physiological determinants of the activity patterns of bees

There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.

/pdf/factors-influencing-site-abandonment-and-site-selection-in-a-2vwmbbjsg3.pdf

Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae

Larvae of Myrmeleon immaculatus in large pits captured both large and samll prey, while larvae in small pits captured only the small prey. Larvae in small pits did not respond to large ants, although they always responded by sand-flinging to small ants. Larvae in medium-sized pits often captured large ants only after prolonged and vigorous sand-flipping. Larvae in large pits usually captured large ants with relatively little sand-flipping. Pit enlargement and pit relocation in the laboratory were not significantly correlated with reduction of rations in the first 3 weeks after a pit was built. However, after a month without food, larvae on the average moved once every 10 days, built successively smaller pits, and moved longer distances before building a new pit. In the field pits were dug primarily in response to microclimatological factors and possibly edge-effects. The presence or absence of suitable prey at a site, per se, had no effect on whether or not a larva would dig a pit there. We conclude that these sit-and-wait predators have a relatively large repertoire of behavior that enhances their foraging success, and we contrast it with previously made optimal foraging models relating to pit locations, pit relocations, pit size and ant lion responses.

The pit-trapping foraging strategy of the ant lion, Myrmeleon immaculatus DeGeer (Neuroptera: Myrmeleontidae)

Bumblebees ranging in mass from 65 mg (the smallest workers of the smallest species) to 830 mg (the largest queens of the largest species examined) maintained similar average thoracic temperatures (TTh) while foraging, even though the passive cooling rates of these bees over this size range varied fourfold. Although the bees regulated TTh between apparent lower and upper set points despite wide ranges of body size (and over wide ranges of ambient temperature), they allowed TTh to fluctuate between the set points. The foraging activity of queens was relatively independent of ambient temperature (Ta), but workers (and particularly the smallest workers) were often excluded at low Ta. Although the size-related rates of passive cooling of drones was similar to that of workers, they did not maintain the same TTh as workers on some kinds of flowers.

Size and Caste in Temperature Regulation by Bumblebees

While foraging from the dense inflorescences of spiraea (Spiraea latifolia) and goldenrods (Solidago sp.), both workers and drones often allowed thoracic temperature ($T_{th}$) to fall below the minimum for flight. The bees were physiologically capable of maintaining a high $T_{th}$, but the periodic decrease in $T_{th}$ was strongly correlated with ambient temperature ($T_{a}$). Decreases of $T_{th}$ were unrelated to fuel reserves carried in the honey stomach. Drones foraging from the inflorescences were more likely to have low $T_{th}$ than workers, even though on the average they carried several times greater fuel reserves in their honey stomach. Within workers, old or parasitized (by conopid flies) individuals were more likely to forage with low $T_{th}$ than young and unparasitized individuals. Workers, unlike drones, showed an increasing tendency to decrease $T_{th}$ with decreasing body mass. Although the decrease in $T_{th}$ while foraging ("torpor"), with its associated sluggishness, appears to ...

Margaret J. E. Heinrich

Papers

The pit-trapping foraging strategy of the ant lion, Myrmeleon immaculatus DeGeer (Neuroptera: Myrmeleontidae)

Size and Caste in Temperature Regulation by Bumblebees

Heterothermia in foraging workers and drones of the bumblebee Bombus terricola