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.     

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     

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20°C and maximally 30.6°C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers’ thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.     

Site selection by a social wasp in a nesting association (Hymenoptera: Vespidae)

The tropical social waspMischocyttarus immarginatus is a nesting associate ofPolybia occidentalis in northwestern Costa Rica. We show that an activeP. occidentalis colony is a necessary component of aM. immarginatus nesting site in this part of the latter’s range.M. immarginatus foundresses actively seekP. occidentalis colonies to initiate nests at a modal distance of 8 cm from them. There is an 18-mm lower limit to how closeM. immarginatus can nest in relation toP. occidentalis. At distances of less than this,P. occidentalis workers can reach theM. immarginatus nest while standing on their own nest and robM. immarginatus of its brood when the adults are absent.     

A test of adaptive hypotheses for rapid nest construction in a swarm-founding wasp

Most social insect species enlarge their nests gradually and in close correlation with the growing need for space for brood and/or stored food. In contrast, some species of swarm-founding eusocial wasps construct the nest rapidly to a final size in the first two to three weeks of the founding stage. We considered four hypotheses on the functions of rapid nest construction in the wasp Polybia occidentalis and directly tested two of them. The first hypothesis is that rapid construction maximizes output of the worker force when there are few other work demands; it predicts that construction rate remains high until the first eggs begin to hatch, following which it declines as increasing amounts of worker effort are allocated to the feeding of larvae. The second says that rapid nest construction minimizes the time the adults in the swarm are exposed to predation and the elements; it predicts that nest-construction rate should drop steeply after the nest is large enough to house all the adults in the swarm. We measured pulp-foraging rates for the first 12 days of the founding stage in control colonies and in colonies whose nests we manipulated to prevent housing of the swarm. The treatment and control groups did not differ in construction rate for several days following the housing event, contradicting the adult-protection hypothesis. Late in nest construction, treatment colonies were building at significantly higher rates than were control colonies. If demand for brood care were a major factor in determining construction rate, both groups would have responded to the eclosion of larvae in the same way and shown a parallel decline in construction rate, but this did not happen. Instead, the patterns of nest construction rate we observed provided indirect support for the two remaining hypotheses. The first of these is that rapid construction minimizes exposure of the brood to natural enemies and desiccation. The second is that rapid construction promotes competition among queens by providing empty cells for oviposition, thereby facilitating the selecting out of the less fecund of the multiple reproductive females. Also consistent with this hypothesis is the apparent absence of explosive nest construction in monogynous, eusocial bees. Received 13 October 2007; revised 31 March 2008; accepted 6 April 2008.     

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.     

Nesting behavior and nest site selection in monk parakeets (Myiopsitta monachus) in the Pantanal of Brazil

We examined nesting behavior in monk parakeets (Myiopsitta monachus) in their native habitat in the Brazilian Pantanal. Unique among parrots, monk parakeets build communal nest structures that contain many cavities, each belonging to an individual pair. We studied 41 parakeet colonies that had 104 nest structures. We hypothesized that nest structures would be located in trees providing the greatest support and protection from predators and inclement weather, and that nest sites and nest cavities would differ from random locations with respect to tree characteristics, location of houses, and presence of jabiru stork (Jabiru mycteria) nests, as suggested anecdotally by other authors. Fewer than half of the colonies were close (<350 m) to houses. There was a strong association with jabiru storks; 21 of 23 stork nests had monk parakeet nest cavities attached, accounting for 51% of parakeet colonies. Of the 21 jabiru-associated colonies, 6 had additional parakeet structures and 15 had only the jabiru-attached parakeet structure. Monk parakeet colonies associated with jabiru nests had significantly more nesting cavities than did monospecific monk parakeet colonies, due mainly to those attached directly to the jabiru nest. In jabiru-associated colonies, parakeet nest structures were located higher and in taller trees than in monospecific colonies. There was no difference in trunk diameters of parakeet nesting trees with or without jabirus. Although we tabulated 24 tree species as nest trees, nearest-neighbor trees, or matched-point trees, only 6 species were used for nesting. When compared to matched points, monk parakeet structures were preferentially located in piuva (Tabebuia spp.) and mandovi trees (Sterculia apetela). Parakeet structures were in taller trees with thicker trunk diameters than matched points. Most nest cavities (71%) faced in a northerly direction (northwest to northeast), away from cold southerly winds. Choice of a nest site and orientation appears to reflect structural, weather, and predator constraints. Thick, tall trees with stout branches provided stable sites for their large nest structures, which are known to collapse because of their own weight and strong winds. Nesting with jabirus confers structural advantages (they could attach many nests to the bottom of the jabiru nest, potentially gaining benefits from social facilitation), early warning, and predator defense.     

Observations onApoica pallens,a nocturnal neotropical social wasp (Hymenoptera: Vespidae,Polistinae, Epiponini)

Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos.     

Nest temperature fluctuations in a cavity nester,the southern ground-hornbill

Southern ground-hornbills Bucorvus leadbeateri inhabit savanna and bushveld regions of South Africa. They nest in the austral summer, which coincides with the wet season and hottest daytime temperatures in the region. They are secondary cavity nesters and typically nest in large cavities in trees, cliffs and earth banks, but readily use artificial nest boxes. Southern ground-hornbills are listed as Endangered in South Africa, with reintroductions into suitable areas highlighted as a viable conservation intervention for the species. Nest microclimate, and the possible implications this may have for the breeding biology of southern ground-hornbills, have never been investigated. We used temperature dataloggers to record nest cavity temperature and ambient temperature for one artificial and 11 natural southern ground-hornbill tree cavity nests combined, spanning two breeding seasons. Mean hourly nest temperature, as well as mean minimum and mean maximum nest temperature, differed significantly between southern ground-hornbill nests in both breeding seasons. Mean nest temperature also differed significantly from mean ambient temperature for both seasons. Natural nest cavities provided a buffer against the ambient temperature fluctuations. The artificial nest provided little insulation against temperature extremes, being warmer and cooler than the maximum and minimum local ambient temperatures, respectively. Nest cavity temperature was not found to have an influence on the breeding success of the southern ground-hornbill groups investigated in this study. These results have potentially important implications for southern ground-hornbill conservation and artificial nest design, as they suggest that the birds can tolerate greater nest cavity temperature extremes than previously thought.     

Incubation ability of the functional envelope in paper wasp nests (Hymenopteta, Vespidae, Polistes): I. Field measurements of nest temperature using paper models

Temperature characteristics in paper models of Polistes wasp nests with various numbers (N = 7, 19, 37, or 61 cells) and lengths (L = 10–50 mm) of cells were measured in the field. Temperature distribution in a N61L50 model showed that the central cell provided the best thermal conditions in terms of gained temperature and its fluctuation. The mean temperature excess (difference between cell and ambient temperatures) observed in the diel trial 1 (L50 models with different cell numbers) was 1.5°C in N7 model and 2.3°C in N61, whereas in trial 2 (N37 models with different cell lengths) it was 0.6°C in the L10 model (with 10-mm-long cells) and 2.4°C in L50. In these trials, models with larger numbers of cells or longer cells attained a higher temperature. It seemed that length was more effective in gaining higher maximum temperature than the number of cells. By their heat insulation effect, peripheral cell rings ameliorated the temperature fluctuation in cells at the central part of the comb. Models with more and longer cells maintained temperature slightly higher than the ambient level even during the nighttime. Received: March 10, 2000 / Accepted: December 18, 2000     

Use of terrestrial chemical trails for nest orientation in an open nesting wasp, <Emphasis Type="Italic">Dolichovespula saxonica</Emphasis> F.

Summary The long-cheeked wasp Dolichovespula saxonica typically constructs exposed nests which can be reached by flying. Usually foragers do not walk on substrates in the close vicinity of the nests as cavity breeding wasps do (Steinmetz et al., 2002). Unexpectedly, when forced to walk outside the nest instead of flying in an artificial tunnel system, D. saxonica foragers lay a terrestrial trail and use it for orientation in the nest area in our experiments. 41% of the foragers followed the trail in a direction they were not accustomed to. We suggest that the foragers have employed the same orientation cues normally used for orientation in the close vicinity of the nest when approaching a free-hanging nest by flying, for example nest odour. Nest odour substances may have been transferred to the substrate as a trail as a consequence of foragers walking through the tunnels.Received 23 August 2002; revised 27 January 2003; accepted 30 April 2003.     

Ectoparasites,nest site choice and breeding success in the pied flycatcher

It has recently been suggested that nest box studies might bias the measurement of behavioural and life-history traits, because the removal of old nests may reduce the load of ectoparasites. This experimental artefact may have notable effects on nest site choice and breeding success in cavity-breeding birds. We tested (i) if pied flycatchers Ficedula hypoleuca prefer clean nest boxes and (ii) if old nest material affects the number of parasites and the breeding success of pied flycatchers. In the first experiment we offered birds one cleaned nest box and one nest box with old nest material from the previous year. The two nest boxes were placed in very similar sites near each other. In this experiment all pied flycatchers clearly preferred dirty nest boxes. In the second part of the study we distributed clean nest boxes and dirty ones on the same study area. After breeding was over we counted the number of fleas Ceratophyllus gallinae in the nest material. This flea species was the most abundant and probably the most hazardous parasite in the nests. Surprisingly, we found that there were significantly more fleas in the nest boxes with nests of the current year only than in the boxes with nests of both current and previous year. This might explain the preference for the dirty boxes. However, our results do not indicate that the number of fleas affects breeding success in the pied flycatcher.     

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.     

Plasticity of nest-site selection in the trumpeter finch: A comparison between two different habitats

In habitats with more predators, a species is expected to breed in safer sites and be less successful than in predator-impoverished habitats. We tested this hypothesis by studying nest-habitat selection and nest predation in two populations of Trumpeter finch (Bucanetes githagineus). One breeds in a predator-rich habitat (Tabernas, Iberian Peninsula), and the other is found on an island with fewer predators (La Oliva, Canary Islands). In both localities, we studied the features of nests in two different substrates, on the ground and in cliffs, including visibility and position in the cliff. We measured the habitat characteristics in a series of plots around the ground nests and compared them to random points. We also studied the influence of nest features and habitat selection on predation of both nest types. Trumpeter finches built more nests in cliffs in Tabernas, probably because there are more cliffs available there. In this locality, the patches selected for ground nesting had below-average vegetation cover, lower vegetation height, and were on steeper slopes. In La Oliva, they selected above-average vegetation height and steeper slopes. Cliff nests were less predated than ground nests in La Oliva, but not in Tabernas. The only variable that affected survival rates in Tabernas was the height of vegetation around ground nests, with nests in lower vegetation having higher survival rates. These results suggest that locality-related differences in habitat selection by vegetation height could be related to the different predator assemblages present in any given area, though we cannot rule out confounding influences of other differences between the two sites.     

Manipulation of parasitoid size using the temperature-size rule: fitness consequences

The phenotypic effects of rearing temperature on several fitness components of the koinobiont parasitoid, Aphidius colemani, were examined. Temperatures experienced during development induced a plastic linear response in the dry and fat masses of the immature stage and a non-linear response in the growth rate as well as in the size of adults. We investigated if the phenotypic morphometrical plasticity exhibited by parasitoids reared at different temperatures can induce variations in fitness-related traits in females. We did not find any difference in immature (pupal) mortality in accordance to rearing temperature. However, when examining adult longevity, we found an inverse linear relation with developmental temperature, confirming the usual rule that larger and fatter wasps live longer than smaller ones. The pattern of female fecundity was non-linear; wasps that developed at high and low temperatures were less productive. We suggest that when development is short, the accumulated reserves are not adequate to support both fecundity and survival. By manipulating adult size through changes in the rearing temperature, we showed that the usual shape of the size/fitness function is not always linear as expected. Developmental temperature induced a plasticity in energy reserves which affected the functional constraints between survival and reproduction.     

Comparison of investment in nest construction by the foundresses of consubgenericPolistes wasps,P. (polistes) riparius andP. (P.) chinensis (hymenoptera, vespidae)

Some metric characters of nests built during the founding phase by foundresses were compared between two consubgenericPolistes wasps,P. (Polistes) riparius andP. (P.) chinensis, the former of which inhabit higher latitudes. Volumes and dry weights ofP. riparius nests were strikingly larger than those ofP. chinensis, even when standardized by the foundress weight (2.5 times for volume and 2 times for weight), showing that foundresses ofP. riparius invest much more in the nest construction than those ofP. chinensis. However, percent weights of oral secretion used for nests to total nest weights were smaller inP. riparius than inP. chinensis (52.1% vs. 60.4%). The differences in the investment by foundresses of the two species in the construction and maintenance of nests were discussed in relation to climatic and other environmental factors.     

Effects of nest paper hydrocarbons on nest and nestmate recognition in colonies ofPolistes metricus say

The role of nest paper hydrocarbons in nest and nestmate recognition for the social waspPolistes metricus was examined. Newly emergedP. metricus workers maintained in the laboratory spent four days alone on a fragment of nest paper that was subjected to one of the following tretments: untreated, extracted with hexane to remove surface hydrocarbons, or extracted with extract reapplied. Test wasps were returned to their natal nest with nestmates and observed for 1 h. Time spent on nest by test wasp and its behaviors were recorded. Wasps exposed to untreated and reapplied nest fragments spent an average of 34.13 and 31.75 min on their nests, respectively, while wasps from extracted fragments averaged 17.19 min. Behavior of wasps exposed to extracted paper differed significantly from wasps exposed to paper with hydrocarbons. These results suggest that exposure to nest paper hydrocarbons is important for both nest and nestmate recognition.     

Nest construction by a ground-nesting bird represents a potential trade-off between egg crypticity and thermoregulation

Predation selects against conspicuous colors in bird eggs and nests, while thermoregulatory constraints select for nest-building behavior that regulates incubation temperatures. We present results that suggest a trade-off between nest crypticity and thermoregulation of eggs based on selection of nest materials by piping plovers (Charadrius melodus), a ground-nesting bird that constructs simple, pebble-lined nests highly vulnerable to predators and exposed to temperature extremes. Piping plovers selected pebbles that were whiter and appeared closer in color to eggs than randomly available pebbles, suggesting a crypsis function. However, nests that were more contrasting in color to surrounding substrates were at greater risk of predation, suggesting an alternate strategy driving selection of white rocks. Near-infrared reflectance of nest pebbles was higher than randomly available pebbles, indicating a direct physical mechanism for heat control through pebble selection. Artificial nests constructed of randomly available pebbles heated more quickly and conferred heat to model eggs, causing eggs to heat more rapidly than in nests constructed from piping plover nest pebbles. Thermal models and field data indicated that temperatures inside nests may remain up to 2–6°C cooler than surrounding substrates. Thermal models indicated that nests heat especially rapidly if not incubated, suggesting that nest construction behavior may serve to keep eggs cooler during the unattended laying period. Thus, pebble selection suggests a potential trade-off between maximizing heat reflectance to improve egg microclimate and minimizing conspicuous contrast of nests with the surrounding substrate to conceal eggs from predators. Nest construction behavior that employs light-colored, thermally reflective materials may represent an evolutionary response by birds and other egg-laying organisms to egg predation and heat stress. An erratum to this article can be found at     

Nest thermoregulation in Polybia scutellaris (White) (Hymenoptera: Vespidae)

Polybia scutellaris (White) builds large nests characterized by numerous spiny projections on the surface. In order to determine whether or not the nest temperature is maintained because of homeothermic conditions of the nest individuals or otherwise, we investigated the thermal conditions within the nests built by P. scutellaris. We measured the temperature within active and abandoned nests. The temperature in the active nest was almost stable at 27°C during data collection, whereas the temperature in the abandoned nest varied with changes in ambient temperature. These results suggest that nest temperature was maintained by the thermogenesis of the individuals of the colony. This is the first report of nest incubation caused by thermogenesis of species of Polybia wasps.     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance