Colony Life Cycle Research Articles

Sex ratio variation in the bumblebee Bombus terrestris

Patterns of sex allocation in bumblebees have been enigmatic and difficult to interpret in either a Fisherian context or in a kinselection perspective. We gathered data on several hundred laboratory-reared colonies of the bumblebee Bombus terrestris and analyzed sex allocation as a function of diapause duration and a series of variables describing colony development. Our analyses addressed both sex allocation patterns across different cohorts of laboratory colonies reared at different times and sex allocation patterns across individual colonies within these cohorts. We used path analysis to test a hypothetical model linking a sequence of colony-development variables to the crucial reproductive parameters at the end of the colony life cycle. We show that (1) population-wide patterns of sex allocation show equal investment in the sexes and are thus consistent with queen control, but not with worker control. (2) A significant part of the colony-level and cohort-specific variation in sex allocation is related to the hibernation conditions of founding queens: Queens with longer than average winter diapause produce larger cohorts of first and second brood workers, switch to haploid eggs early, and produce colonies that raise mostly males and few new queens and vice versa. (3) Colony-level sex allocation is significantly related to the time span between the switch point (date of first haploid egg laid by the queen) and the competition point (date of first haploid egg laid by one of the workers): the longer this period, the more male biased the sex ratio. (4) The breeding constraints of an annual life cycle, the short reproductive season, and the presumably high premium on early produced males imply that bumblebee workers have no realistic options to capitalize on their relatedness asymmetry toward the different kinds of reproductive brood by biasing the sex ratio. Key words: Bombus terrestris, bumblebees, colony development, queen control, reproductive strategies, sex allocation. [Behav Ecol 15:71–82 (2004)]

Impacto da queima controlada da cana-de-açúcar na nidificação e estabelecimento de colônias de Atta bisphaerica Forel (Hymenoptera: Formicidae)

Queimadas de baixas intensidades podem promover sensíveis alterações nas propriedades físicas, químicas e microbiológicas do solo, na profundidade onde se estabelecem os sauveiros iniciais de Atta Fabricius. Considerando que o estabelecimento da nova colônia é o período mais crucial da vida da colônia, investigaram-se neste trabalho as implicações pós-fogo de uma queima controlada de palhiço de cana-de-açúcar de intensidade igual a 615 kJ. m-1.s-1 na escolha de locais para escavação dos ninhos e estabelecimento inicial de colônias de Atta bisphaerica Forel. A queima eliminou matéria orgânica superficial da área, o que implicou em aumento significativo de densidade até a profundidade de 15 cm. Da mesma forma, a eliminação da vegetação pelo fogo promoveu maior resistência do solo à penetração. Essas alterações nas propriedades físicas não afetaram significativamente a escavação dos ninhos iniciais por fêmeas de A. bisphaerica e nem tampouco influenciaram a profundidade de construção de suas câmaras iniciais em condições de laboratório. A queima alterou a constituição química do solo e promoveu alterações na atividade microbiológica do mesmo. Em condições de campo, as fêmeas de A. biphaerica apresentaram maior taxa de estabelecimento em locais queimados. Em condições de laboratório, colônias cujas fêmeas estabeleceram-se em solos provenientes de áreas queimadas apresentaram maior mortalidade do que aquelas estabelecidas em solos de áreas não queimadas.

Potential manageable exploitation of social wasps, Vespula spp. (Hymenoptera: Vespidae), as generalist predators of insect pests

A manageable, generalist, predatory insect has to date been considered to be unavailable anywhere for pest insect control. Polistes spp. wasps showed promise, but are limited by small numbers of wasps per nest and short nest life. Social Vespula spp. wasps appear to possess the necessary attributes which will allow their development as manageable, generalist predators of a wide range of pest insects. They have a large number of foragers per nest, a high demand for invertebrate protein, a very wide range of prey, an ability to tolerate low temperatures, a tolerance of nest manipulation, and a colony life cycle that can span at least two summers. High numbers per nest and high nest densities can lead to the consumption of many kilograms of prey per hectare per year. Successful development of characteristics desired of a manageable predator, such as the ability to increase colony numbers by dividing and re-queening, and enhancement of multi-year colony existence, could result in management procedures for Vespula spp. wasps that are similar to those used for honey bees. Farmers could have wasp nests available when and where required and in the numbers desired. Wasps would be especially valuable for growers of some ‘organic’ crops in which conventional pesticides are not permitted.

Nest construction and architecture of the Amazonian bumble bee (Hymenoptera: Apidae)

The Amazonian bumble bee, Bombus transversalis, is mostly restricted to tropical rain forest of the Amazon Basin. Little is known of its biology, in part because its surface nests are cryptic and hard to find. Here we examine nest site characteristics, nest architecture and construction behavior from 16 colonies observed in different regions of Amazonia. We quantify structural features of the nest habitat and external and internal characteristics of the nests. We ascertain that nests are constructed on terra firme, on the surface of the ground and incorporate elements of growing vegetation as physical support. Nests consist of a thatched canopy of tightly woven leaves and rootlets, beneath which lies the brood and food storage pots. To build the nest, workers cut and transport leaves from the surrounding forest floor. Nests are dry inside, despite torrential rainfall and external relative humidity levels near 100%. Nests may be reused although a colony appears to persist for only one season. corbiculate bees / Bombus transversalis / neotropics / leaf-cutting behavior / adaptation / colony life cycle

Effects of selective episodes in the field on life history traits in the bumblebeeBombus terrestris

Natural selection has different fitness consequences when it acts during different life cycle stages of an organism. In social insects, for example, the colony foundation and early colony growth is a critical time period with high probability of failure. Here we used colonies of the bumblebeeBombus terrestrisL. to test whether selective episodes at different life cycle stages result in differences in colony performance and fitness. The timing of a selective episode was varied by field exposure of colonies, either permanently or during a short period at three different colony life cycle stages – early, middle, or late in the cycle. We found that selective episodes at different life cycle stages did not affect maximal size, fitness or survival of colonies, or the time span between colony foundation and reproduction. Instead, the colonies were able to compensate for costs encountered by delaying reproduction. This might have important fitness consequences, since later emerging sexuals might be faced with harsher environmental conditions and increased costs of finding a mate. In addition, an important component of selection might be parasitism and the resulting resource allocation to the immune system. We here measured the generalized immune response (i.e. encapsulation response) of early produced workers as an indicator of a colony's capacity to defend against parasitism. Encapsulation response correlated positively with eventual colony size and fitness, indicating that this measure of “immunocompetence” correlates with important life history traits.

Technique for rearing the European hornet (Vespa crabro) through an entire colony life cycle in captivity

Laboratory rearing of wasps was studied in the European hornet Vespa crabro. Males (N = 10) and gynes (N = 13) were obtained from two field-caught colonies. Mating took place in cages (mean number of 1.31 ± 0.63 matings per gyne) and overwintering in a cool room at 10 °C. Five gynes survived and one queen successfully established a nest that produced sexuals. This is first time that the entire colony life cycle of V. crabro has occurred in captivity. The technique will be useful in vespine research as well as in conservation and breeding programs.

Essential and alternative prey in a ponerine ant: variations according to the colony life cycle

We studied the prey specialization of Plectroctena minor, a ponerine ant known to capture mostly millipedes. We compared the prey spectrum of the hunting workers from large colonies with that of the founding queens. The hunting workers captured all kinds of tested prey, but hunted mostly millipedes. Founding queens, which avoided relatively large prey, including the millipedes tested, captured mostly isopods under experimental conditions. We also verified that the presence of millipedes in the diet of the larvae of large colonies was necessary for the production of winged females and strongly enhanced the production of workers, permitting us to assert that P. minor is a predatory species specialized in the capture of millipedes. In contrast, the presence of millipedes had no impact on the production of males. We thus assert that millipedes constitute the 'essential prey' of P. minor, while other arthropod taxa are therefore 'alternative prey'.

Nest defense and early production of the major workers in the dimorphic ant Colobopsis nipponicus (Wheeler) (Hymenoptera : Formicidae)

Production of the major subcaste and its contribution to nest survival in the dimorphic ant Colobopsis nipponicus was examined in the field. In this species, the first major workers were reared in the second brood, very early in the colony life cycle. A field experiment demonstrated that artificial colonies without major workers could not survive, whereas colonies with at least one major worker per nest entrance could. Because major workers of C. nipponicus defend the nest entrance by head plugging, the lack of nest defenders in the experimental colonies seemed to be a major cause of nest failure. The defensive value of major workers was much higher than that of minor workers. Many artificial colonies without major workers were displaced by competitors for nest sites, especially by those of other conspecific colonies. In addition, more than 90% of field colonies nested with other conspecific colonies on the same tree. The early production of major workers in C. nipponicus seemed to be very important for the survival of incipient colonies.

Thermoregulation in Bumblebee Colonies. II. Behavioral and Demographic Variation throughout the Colony Cycle

Colonies founded by wild-caught queens were reared at either 15 C with or without an insulated nest or at 25 C for the duration of the colony cycle. Brood-maintenance and brood-incubation behaviors, brood (Tbr) and nest-chamber (Tn) temperatures, and the number of bees produced were monitored. The total number of foragers was relatively fixed in young colonies. The occurrence of brood incubation varied inversely with population size and was highest at low ambient temperature (Ta). In contrast, the occurrence of brood maintenance varied directly with population and was highest at high Ta. All colonies had produced their maximum number of workers and started producing reproductives at 9-10 wk after the emergence of the first workers of the colony. The numbers of bees produced per colony at 15 C with insulation and at 25 C were similar. Uninsulated colonies at 15 C produced fewer bees and maintained lower Tbr. These findings suggest that low Ta may limit population growth but has no apparent effect on the timing of events during the colony life cycle.