Diel changes of temperature in the nests of two Polybia species, P. paulista and P. occidentalis (Hymenoptera, Vespidae) in the subtropical climate

Temperatures in two mature Polybia nests were measured to study the thermal conditions of nests. Temperatures in a Polybia paulista nest were measured when it had adult wasps (trial 1) and after the adult wasps were removed (trial 2), and temperatures in a P. occidentalis nest were measured when inhabited by adult wasps (trial 3). In each trial, C–C thermocouples were set at four points in the nest and at two points outside to discover the ambient and substratum temperatures. In trial 1, nest temperatures basically followed the ambient temperature, but during the day the nest temperatures were lower than the ambient temperature and this relationship was reversed during the night. The temperature fluctuation of the inner substratum points was smaller than that of the outer points. The trend of trial 2 was closely similar to that of trial 1, showing a virtual lack of thermal effects from the presence of adult wasps. In trial 3, the changing pattern in the P. occidentalis nest showed a trend similar to that in the P. paulista nest, but the inside temperatures rose quickly when the nest received direct sunlight in the morning. From these results, thermal characteristics in the Polybia nests are discussed in relation to the nest architecture and their geographical distribution.     

Nest demographics and foraging behavior of <Emphasis Type="Italic">Apterostigma collare</Emphasis> Emery (Hymenoptera,Formicidae) provide evidence of colony independence

Apterostigma collare Emery is a highly derived fungus-growing ant within the Tribe Attini whose small, fungal nests are found in tropical rain forests. This study focuses on determining the colony structure of A. collare, specifically searching for evidence of polydomy or independence. We surveyed and observed nests in the field, and performed foraging bioassays and dissected nests in the laboratory. We determined the size and contents of nests in field populations. Nests found near other nests were not statistically different in size compared to nests found alone. There was also no statistical difference between near and lone nests regarding the presence of a queen in the nest. Most nests contained one queen with brood and workers, regardless of their proximity to other nests. Observations also were made of foraging and trail-marking behaviors. Foraging activity observed in the field revealed that workers left the nest area and followed trails upwards into the canopy, but they did not interact with foragers from other nearby nests. In a laboratory foraging arena, foragers marked a trail to a food source by dragging the gaster. Bioassays showed that A. collare workers preferred their own foraging trails, but not those of other conspecific colonies. All results suggest that each nest represents an independent colony, supporting a previous report that nests found in close proximity do not constitute a polydomous colony. Received 19 July 2006; revised 23 March 2007; accepted 6 June 2007.     

Reconstruction ofRopalidia fasciata nests by progeny females after a typhoon and its significance in the social evolution of wasps

A strong typhoon, Typhoon 13, which swept through Okinawa on 2 and 3 September 1993, knocked down 57 to 61 of 97Ropalidia fasciata nests. Thirty-five colonies soon reconstructed their nests, and these nests produced 54±46 adults per nest during the remaining two and a half months before winter. The number of females involved in nest reconstruction was 21.3±15.7 per nest. The frequency of foraging activity was significantly higher in nests being reconstructed than in normal nests. As only one out of 205 foundresses marked in spring was found in early September, most cases of nest reconstruction were considered to be made exclusively by females that emerged during the spring and summer of 1993 (progeny females). All of the reconstructed nests but one produced adult females. Many females (31%) collected from the two reconstructed nests were inseminated. As all the reconstructed nests became vacant by early January, indicating completion of the colony cycle, and a large number of nests were established in the spring of 1994, females emerging from reconstructed nests in 1993 probably become foundresses in 1994.Ropalidia fasciata is considered to be, at least partially, bivoltine in Okinawa. The significance of these facts for the evolution of multi-queen social systems in the Polistinae is discussed.     

Colony Development and Serial Polygyny in the Primitively Eusocial Wasp Belonogaster juncea juncea (Vespidae: Polistinae)

In Cameroon, the social ropalidiine wasp Belonogaster juncea juncea mostly selects human constructions for nesting, but nests installed in the shelter of large boulders were also noted. Nests were founded throughout the year by one female (25.5%) or by associations of two to eight females. Among the 49 colonies studied from foundation, 24 produced at least one adult, and only 5 produced males among the eight that succeeded in producing sexual individuals. After the first dominant female disappeared (died or abandoned the nest, from 77 to 196 days after foundation) the remaining females fought among themselves, leading to a drastic decrease in the total number of brood. They completely abandoned 22 of 24 surviving nests, over a mean colony cycle lasting about 7 months. Hence the colony and nesting cycles were congruent, illustrating that determinate nesting corresponds to the majority of the cases in this species. In the other two nests, some females remained on the nest and began a new colonial cycle illustrating semi-independence between colony and nesting cycles. Up to four successive cycles were completed in this way in the same nest, thus illustrating the phenomenon of serial polygyny (intermediate between determinate and indeterminate nesting cycles). Serial polygyny in independent founding polistine wasps, previously documented only once, has implications for studies attempting to identify factors involved in regulating the colony and nesting cycles in tropical social wasps.     

Temperature and forager body size affect carbohydrate collection in German yellowjackets, Vespula germanica (Hymenoptera, Vespidae)

The classic formulation of optimal foraging theory predicts that a central-place forager will gather more food if it is required to travel farther from the nest to find that food. We examined the foraging behavior of German yellowjackets (Vespula germanica) to determine whether carbohydrate foragers follow this pattern. We trained foragers to collect 2 M fructose solution at 5 or 50 m from the nest and measured the time spent feeding, load size, and the rate of delivery. We show that as a forager’s crop fills during a foraging bout, the amount of solution ingested per second decreased. However, load size did not change as wasps collected food up to 50 m from the nest. Instead, temperature and body size were better predictors of the volume of fructose a forager carried. Finally, the rate of fructose delivered to the nest was higher at warmer temperatures. Due to the fact that wasps gather more food but feed for shorter periods of time at warmer temperatures, we found an overall negative relationship between feeding time and load size. We conclude that the strong effects temperature had on the behavior of V. germanica foragers imply that feeding time may not always be an accurate predictor of the size of the load an individual carries back to the nest. Results from this study suggest that in yellowjacket colonies, foragers can collect and bring disproportionately more food back to the nest during the warmest days of the summer, a time of year when this pest species reaches peak population size during its annual colony cycle.     

Parasite presence acts as a proximate cue in the nest-site selection process of the solitary digger wasp,Ammophila dysmica (Hymenoptera: Sphecidae)

Nest-site selection by the solitary ground-nesting wasp Ammophila dysmicaMenke was studied during 1982–1986 in California's Sierra Nevada Mountains. Digging females detected and discriminated among members of a complex of insect intruders, including a number of predators and parasites. In response to some natural enemies, wasps sometimes permanently abandoned nests under construction. These selective nest abandonments reduced the mean number of cleptoparasitic chrysidid wasps, Argochrysis armillaBohart, attending the excavation of completed nests. The number of A. armillaattending a nest excavation correlated positively with the probability of nest parasitism by this species. Selective nest abandonment may reduce parasitism rates.     

Colony Wide Behavioral Contexts of Stridulation in Imported Fire Ants (Solenopsis invicta Buren)

Red imported fire ants, Solenopsis invicta, possess stridulatory organs and stridulate in a variety of contexts. We used a stethoscope mounted microphone to study stridulation at the colony level in the context of emigration, disturbance, and excavation. In conjunction with preliminary observations of nest and foraging activities, our results suggest stridulation serves multiple functions in S. invicta. Stridulation was not significantly increased in colonies during responses to disturbance, and only marginally during colony emigration. Colonies involved in excavation, however, exhibited a significant increase in stridulatory activity. Four possible explanations for the function of stridulation in this context are discussed in relation to the stridulatory behavior of individuals, solitary wasps, and published literature on formicid stridulation.     

Founding Swarms in a Tropical Social Wasp: Adult Mortality, Emigration Distance, and Swarm Size

When colonies of swarm-founding wasps lose their nests to predation or accident, the entire adult population escapes, emigrates as an absconding swarm, and renests elsewhere. Such an event causes a reduction in the adult population due to losses during the emigration itself and to adult attrition without replacement during the subsequent preemergence growth period in the new nest. We addressed the first of these sources of mortality for 27 absconding swarms of Polybia occidentalis in Costa Rica. Adult mortality over the day that included swarm emigration averaged 0.044 ± 0.039 (SD) of the original population and was a weak positive function of distance moved, but not of swarm size. A larger data set showed that emigration distance increased with swarm size. This is the first study to measure mortality rates during emigration in a swarm-founding social insect.     

Evaluation of the predatory wasp,Ancistrocerus gazella,for biological control of leafrollers in Otago fruit crops. II. Wasp phenology and seasonal changes in prey composition

The phenology of the predatory wasp, Ancistrocerus gazella (Panzer), colonising artificial nests was studied over 3 years in seven Study Areas in or adjacent to mixed pome and stonefruit orchards in Otago, New Zealand. Each Study Area had three to four nest sites comprising groups of wooden blocks drilled with 6 mm diameter nest tubes 75–150 mm in length. The timing of nest tube colonisation was recorded by observing the presence of nest closures (mud plugs) and their subsequent opening during adult emergence. The nest tubes from some entire nest sites were dissected to determine the stages of development of the wasps and their subsequent emergence, and samples of nest tubes were dissected weekly from a range of nest sites to determine changes in prey composition over the season. A. gazella was found to be primarily bivoltine, but part of each generation entered diapause and a small number of second generation wasps also emerged before winter in warm sites. The adult foraging of each generation was well synchronised with late larval instars of the two generations of three pest leafroller species. However, very low numbers of leafroller larvae were collected because A. gazella was highly polyphagous, predominantly exploiting a sequence of other lepidopterous species. It was concluded that management of A. gazella for leafroller control would be uneconomic but it provides a useful component of the natural enemy complex of pest leafroller species.     

Nest defense behavior against ant attacks in post-emergent colonies of wasp Mischocyttarus cerberus (Hymenoptera, Vespidae)

The primitive eusocial wasp Mischocyttarus cerberus forms colonies of independent foundation, without morphological differentiation among castes. Ants are natural enemies of the social wasps and defending the wasps’ nests involves chemical and active defense strategies. The aims of this work were to verify the kind of defense the wasps use most frequently in post-emergent colonies of M. cerberus. We also observed whether the nest was abandoned during the ant attack and whether any relationship existed between the forms that colony defense took and the number of adults, the number of cells, and the number of immature wasps. The study was carried out on the campus of Universidade Estadual Paulista of Rio Claro, São Paulo, Brazil. The 23 nests under study were mapped weekly, and 68 bioassays were performed by simulating ant attacks against the nests. The results showed that wasps used both active and chemical strategies for nest defense, and the PCA analysis showed that the aggressive behaviors of biting the ant, wings vibrating, gaster hitting, and abdomen pumping were the dominant terms; the PCA correlation values were 2.70, 2.54, 1.64, and 1.63, respectively. The colonies in pre- and post-male substages with few immature wasps and the nests in post-male substage with one adult were more correlated with the nonaggressive behaviors of hiding, staying immobile, and flying; their PCA correlation values were 3.12, 2.56, and 1.77, respectively. These results show that the number of immature wasps is an important factor in the kind and in the intensity of the defense behavior against ant attacks.     

Allocation of Colony‐Level Foraging Effort in Vespula germanica in Response to Food Resource Quantity,Quality, and Associated Olfactory Cues

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher‐quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest‐based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food‐associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour‐long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.     

Nest site selection by a neotropical swarm-founding wasp: seasonal alternation of nest orientation

Nest orientation in social insects has been intensively studied in warmer and cooler climates, particularly in the northern hemisphere. Previous studies have consistently shown that species subjected to these climatic conditions prefer to select mostly southern locations where the nests can gain direct sunlight. However, very little is known on nest orientation in tropical and subtropical social insects. We studied nest orientations initiated by swarms throughout a year in a Brazilian swarm-founding wasp, Polybia paulista von Ihering (Hymenoptera: Polistinae). Swarms selected various orientations as nest sites, but there was a particular trend in that swarms in the winter period (May–August) preferred to build northward-facing nests. This preference is opposite from that of social wasps observed in the northern hemisphere. Colonies of this species can potentially last for many years with continuous nesting, but nesting activities of colonies during the winter are severely limited due to cool temperature and a shortened day length. Northward-facing nests are warmer through the gain of direct solar heat during the winter period; consequently, choosing northward-facing sites may be advantageous for swarms in terms of a shortened brood development and shortened time needed to increase metabolic rates during warm-up for flight.     

The effects of colony characteristics on life span and foraging behavior of individual wasps (Polybia occidentalis,Hymenoptera: Vespidae)

Summary We studied the effects of intrinsic colony characteristics and an imposed contingency on the life span and behavior of foragers in the swarm-founding social waspPolybia occidentalis. Data were collected on marked, known-age workers introduced into four observation colonies.To test the hypothesis that colony demographic features affect worker life span, we examined the relationships of colony age and size with worker life span using survivorship analysis. Colony age and size had positive relationships with life span; marked workers from two larger, older colonies had longer life spans (¯X = 24.7 days) than those from two smaller, younger colonies (¯X = 20.1 days).We quantified the effects of experimentally imposed nest damage on forager behavior, to determine which of three predicted behavioral responses by foragers to this contingency (increased probability of foraging for building material, increased rate of foraging, or decrease in age of onset of foraging) would be employed. Increasing the colony level of need for materials used in nest construction (wood pulp and water) by damaging the nests of two colonies did not cause an increase in either the proportion of marked workers that gathered nest materials or in foraging rates of marked individuals, when compared with introduced workers in two simultaneously observed control colonies. Instead, nest damage caused a decrease in the age at which marked workers first foraged for pulp and water. The response to an increase in the need for building materials was an acceleration of behavioral development in some workers.     

Population consequences of huge nesting aggregations ofRopalidia plebeiana (Hymenoptera: Vespidae)

Nest survival rates and reproductive rates of females of the Australian paper wasp, Ropalidia plebeiana, in nest aggregations under a concrete bridge were studied. The annual colony cycle commenced in August with the reutilization of old nests and by the founding of new nests, mainly by associations of foundresses. Distribution patterns of the number of foundresses per nest was nearly random on new nests while contagious on old nests. About one-third of the increase in number of nest was achieved by dividing large, old nests and two-thirds by founding new nests. Nest survival rates for old nests (August to April) and new nests (November to April) were 89.6% and 88.8% respectively, far higher rates than those of other polistine wasps so far reported. The numbers of nests and reproductive females increased during a colony cycle by 2.30 and 10.98 times, respectively. Thus, huge aggregations of nests are probably beneficial for this species by enabling the realization of high reproductive rates. We could find no density-dependent effect in nest growth rate or production of female reproductives. Ratio of cells parasitized by ichneumonid wasps was low. Nests in the central part of an aggregation were prasitized at significantly lower rates than nests on the periphery or scattered nests outside a dense aggregation, suggesting a selfish herd effect.     

Hunting behaviour,prey capture and ant avoidance in the tropical social waspPolybia sevicea (Hymenoptera: Vespidae)

Summary Polybia sericea (Hymenoptera: Vespidae) prey foraging was studied by following individual foragers as they hunted in the field, by observing how wasps handled prey once they had captured it, and by observing wasps as they returned to the nest with prey. Wasps were most likely to forage for prey between 0700 and 1300 hours and between 1600 and 1700 hours. The prey foraging sequence consisted of the behaviours high flight, search, touch, land, groom, walk, bite and malaxate. Captured small prey were malaxated and carried to the nest. Wasps removed the gut from large prey and dragged the meat up a twig or grass stem. A load of the meat was then bitten off and malaxated; the remainder was cached while the wasp made an orientation flight and returned to the nest. The forager returned within minutes for the remainder of the prey. Experiments demonstrated that caching the prey remains above the ground rather than close to the ground, where the prey are generally captured, reduces the chance that the prey will be found and expropriated by ants.     

Aerial prey caching by solitary ground-nesting wasps: A test of the predator defense hypothesis

Many solitary ground-nesting wasps in the families Pompilidae and Sphecidae excavate nests after capturing prey for provisions. These wasps generally cache their immobilized prey temporarily during nest excavation, frequently by suspending the prey in a plant (aerial caching). Here I test the hypothesis that aerial caching by Ammophila spp. wasps (Sphecidae) functions to reduce prey theft by generalist predators, Formica spp. ants. Foraging ants removed baits placed on the ground more rapidly than baits suspended in plants; mean half-lives for ground and aerial baits were 14.5 and 145.7 min, respectively (mean values for experiments 1–3). Ant foraging activity decreased during the midday. Ant interference with nesting activities of Ammophila spp. also decreased during the midday, paralleling observed fluctuations in ant foraging activity.     

Larval feeding experience influences adult predator acceptance of chemically defended prey

Generalist predatory paper wasps, Polistes dominulus, experience plant secondary defensive compounds as developing larvae through their herbivorous lepidopteran caterpillar prey and as adults through attacking caterpillars while foraging. We evaluated the role that larval and early adult experience with unpalatable prey plays in subsequent foraging choices by adult wasps. For periods of two or four weeks, caged wasps were raised exclusively on caterpillars of either unpalatable Buckeye, Junonia coenia, that sequester substantial levels of iridoid glycosides (IG) or on Painted Lady, Vanessa cardui, that contain very low levels of IG. Wasps were then allowed to forage on both caterpillar species simultaneously. Patterns of prey capture differed significantly based on previous prey experience. Regardless of previous feeding experience, adult wasps overwhelmingly preferred to take Vanessa. Yet Junonia-experienced wasps continued to attack and take back to the nest over 50% more Junonia than did Vanessa-experienced wasps. The longer the wasps' larval experience with Junonia, the more likely they were to capture Junonia caterpillars. However, the life stage at which the wasps experienced Junonia was also influential as young adult experience with the unpalatable prey was more of a deterrent than was experience strictly as larvae for Junonia-experienced wasps. The results demonstrate that, in these predators, previous experience with deterrent chemicals during their larval development alters patterns of prey acceptability to the adult insects.     

Nest recognition in neighboring colonies: a comparison of two European species of Polistes wasps (P. dominulus and P. nimphus, Hymenoptera: Vespidae)

The ability of two species of Polistes wasps to distinguish their own from nearby nests was tested, following the procedure used by Espelie et al. Our experiments demonstrated that, in the laboratory, females of Polistes dominulus and Polistes nimphus preferentially selected their own nests rather than nearby nests. We also evaluated the role of odor cues in nest recognition by washing nests in hexane to remove the apolar solvent-soluble components of nest odor. Although P. nimphus females continued to discriminate nests even after washing, P. dominulus individuals failed to discriminate between their own and a foreign neighboring nest. In both species, wasps were able to recognize their own nests when nest extracts were subsequently reapplied to the nest surface. These results indicate that P. dominulus wasps recognize their nests through perception of nest odor. The ability of P. nimphus wasps to distinguish their own nests even after presumed removal of the nest odor is discussed. Received: January 27, 2000 / Accepted: May 22, 2000     

Both cooperation and nest position improve larval survival in the sweat bee, <Emphasis Type="Italic">Lasioglossum</Emphasis> (<Emphasis Type="Italic">Evylaeus</Emphasis>) <Emphasis Type="Italic">baleicum</Emphasis>

Nesting by multiple females in sweat bees raises the question of the benefits associated with grouping. Adult numbers of the sweat bee, Lasioglossum (Evylaeus) baleicum, exhibited variation within a nest population. The effects of adult number and nest position on larval survival were analyzed in a nest aggregation. Both variables independently affected larval survival, with the presence of multiple adults in a nest markedly improving survival rate. Nests located near the periphery of the aggregation of nests suffered high larval mortalities. Increased frequency of cell-inspection in multiple-female nests seems to be associated with a concomitant increase in larval cell protection from external predation. Such predation pressure was assumed, given the existence of an underground ant colony that employs a recruitment system while foraging in the study area.     

Raiding and Foraging Behavior of the Blood-Red Ant,Formica sanguinea Latr. (Hymenoptera,Formicidae)

In this paper we report the results of a detailed study on the behavioral ecology of slave raiding and foraging activity in the European blood-red ant, Formica sanguinea Latr. The field study was conducted over an unbroken period of 78 days, during which the activity of two dulotic colonies of this facultative slave-maker was observed for 10 h each day. It was possible to observe 26 raids distributed over 23 days, among which 18 were followed by the sacking of nests belonging to the species F. cunicularia, F. fusca, and Lasius emarginatus, whereas 8 failed. Simple, continuous, and simultaneous raids occurred. We recorded the timing, frequency, distance, and direction of slave raids, including the number of participants and the type of booty. Particular attention was devoted to the scouting behavior and raiding organization. Moreover, every day, we observed foraging and predatory behavior, during which adult insects (mainly ants), seeds, and berries were retrieved to the dulotic colonies. On the basis of our observations F. sanguinea seems to be a very efficient slave-maker and predatory species of the Raptiformica subgenus. Moreover, its dulotic behavior may be regarded as a continuation and an expansion of its foraging and predatory behavior, as predicted by Darwin's hypothesis for the origin and evolution of slavery in ants.