The Function of Male Dominance in the Eusocial Wasp, Mischocyttarus mastigophorus (Hymenoptera: Vespidae)

Males of a Neotropical eusocial wasp, Mischocyttarus mastigophorus , are dominant over their female nest mates. Mischocyttarus mastigophorus males behave aggressively toward females, while females rarely bite or chase males. Aggressive interactions between the sexes are behaviorally indistinguishable from dominance interactions among females. Males are long-lived as adults, and can reside on nests for periods of at least one month. Furthermore, males comprise a large proportion of post-emergence colony populations throughout much of the colony cycle. Males on the nest perform maintenance tasks at low rates, but contribute little other labor to their colonies. Males do not forage, but consume a disproportionate amount of the food (nectar and insect prey) collected by workers. Males in some colonies direct disproportionate amounts of aggression toward their queens, which may further contribute to males' food procurement. These data suggest that adult males represent a considerable energetic and labor cost to their colonies. I hypothesize that the dominance structure of M. mastigophorus directs food resources to adult males, with the function of increasing their longevity. Increased male longevity may be selectively advantageous in tropical species such as M. mastigophorus that found new colonies throughout much or all of the year. When females initiate new nests over much of the year, individual males' mating opportunities may be temporally distributed, favoring longer adult lifespans. Male dominance is predicted to occur in other populations of independent-founding Neotropical Polistinae with asynchronous colony foundation.     

Males Exhibit Novel Relationships of Dominance with Nest Departure in the Social Paper Wasp Mischocyttarus mastigophorus (Hymenoptera: Vespidae)

In many animal societies, an individual's opportunities to reproduce correspond to their position in a dominance hierarchy. In primitively eusocial paper wasps, female social dominance and direct reproduction are positively associated with taking food from nest mates, but both negatively correlate with foraging flights. Female paper wasps reproduce by laying eggs in their nest, while males reproduce by leaving the nest to copulate. Males of Mischocyttarus mastigophorus are unusual because they reside on their natal nests for prolonged periods, and males direct aggression towards female nestmates. Mischocyttarus mastigophorus males provide an opportunity to further analyse the relationships between dominance, nutrition and nest departure. We found males' rates of social aggression, food taking behaviour, and rates of nest departure were positively correlated. Furthermore, males that initiated aggression at younger ages also began flying earlier, and males engaged in all three behaviours at younger ages than females. Male social aggression may lead to nutrient acquisition, which enable males to depart from the nest. We hypothesise that male nest departure could be adaptive if it increases male mating opportunities. This could account for the positive relationship between dominance and nest departure for males.     

Dual mimicry in the dimorphic eusocial wasp Mischocyttarus mastigophorus Richards (Hymenoptera: Vespidae)

The eusocial vespid wasp Mischocyttarus mastigophorus exhibits two colour morphs, with males and females of each morph co-occurring at Monteverde, Costa Rica. Each morph closely resembles a different sympatric species of swarm-founding wasp in the genus Agelaia. We propose that the Agelaia species are models for a dual mimicry system. The Agelaia species (A. yepocapa , mimicked by the M. mastigophorus pale morph, and A. xanthopus , mimicked by the M. mastigophorus dark morph) are locally abundant wasps with large, aggressively defended colonies. The mimic and models are restricted to high-elevation habitat in the Monteverde area, and the elevational ranges of both Agelaia species partially overlap the elcvational range of M. mastigophorus. Relative frequencies of the M. mastigophorus colour morphs vary with elevation, with the pale morph predominating at lower elevations. Elevational differences in the relative abundances of the Agelaia species suggest that the models act as a selective force maintaining the M. mastigophorus colour polymorphism at Monteverde. Mischocyttarus mastigophorus overlaps only A. xanthopus in the northern part of its range (S. Mexico), and overlaps only A. yepocapa in the southern part of its range (Ecuador). We hypothesize that the M. mastigophorus colour morphs evolved in allopatry and later came into contact in Central America. Appropriate high-elevation habitat for cloud forest species is distributed as discrete patches in Central America and Northern South America. The island-like nature of suitable habitat may favour the isolation and rapid evolutionary diversification of vespid species that are restricted to high elevations in the Neotropics.     

Male Reproductive Behavior of the Social Wasp Polistes fascatus (Hymenoptera: Vespidae)

Populations of male Polistes fuscatus simultaneously exhibit two different mate-locating tactics. Some males defend territories in female nesting and hibernation sites. These males frequently do not occupy the same territory each day, and they drag their gasters over perches, which may function to apply a secretion to the perch. Another segment of the population patrols large overlapping areas in female foraging sites. In contrast to territorial males, patrolling males do not rub their gasters on perches, and males seen on more than one day are tenacious to one area. Males in both sites are aggressive to other males and attempt to copulate with females. A laboratory study indicates that large males have an advantage in male-male competition. The mean size of patrollers is smaller than that of territorial males, indicating that patrollers are competitively inferior males. Yet there is considerable size overlap of males between the two sites, suggesting that there is also overlap in the range of probability of mating success between the two sites.     

Field preferences of the Social Wasp Vespula germanica (Hymenoptera: Vespidae) for Protein-rich Baits

Food preferences displayed by foraging insects are important from a fundamental perspective and in pest control. We studied the preference of an invasive wasp, V. germanica, for protein foods in field conditions. Preferences were evaluated by placing baits in a paired design in different habitats and analyzing wasp visits, using a Bayesian approach to the Thurstone model. V. germanica workers display a clear rating of preferences, but were affected by the presence of competitors at the bait. These results contribute knowledge aimed at toxic baiting protocols for this wasp and suggest that food choice is a complex process subject to the influence of diverse factors. We emphasize the importance of on-site paired comparisons in preference studies to fully understand the drivers of food choice by insects.     

Scraping Sounds Produced by a Social Wasp (Asteloeca ujhelyii, Hymenoptera: Vespidae)

A distinct behavior performed by workers of the social wasp Asteloeca ujhelyii is described: guard waSPS, sitting outside of the nest around the entrance hole, scratch the nest envelope with their forelegs, thereby producing an audible ‘scraping sound’. Field observations revealed a relationship between the occurrence of the scraping behavior and the occurrences of waSPS entering and leaving the nest. The scraping was experimentally reproduced in the laboratory by moving a dissected wasp's leg parallel to the plane of the nest envelope. The resulting substrate‐borne vibrations propagate very well over a distance of a few centimeters. The amplitude of these vibrations depends on the velocity of the scraping movements. The possible role of the scraping behavior in the waSPS’ communication is discussed.     

Age-related changes in the surface pheromones of the wasp Mischocyttarus consimilis (Hymenoptera: Vespidae)

One of the most important attributes that allowed the evolution and maintenance of sociality in insects is their ability to distinguish members of their own colonies. The capacity for individual recognition in social insects is mediated by chemical signals that are acquired soon after the adult emerges, and vary according to the tasks performed by individuals in their colonies. We determined the time when adults of the wasp Mischocyttarus consimilis acquire the chemical signature of their colonies, as well as the variation in the cuticular hydrocarbon profiles of the exoskeleton of individuals, according to their functions in the colony. The method used was Fourier transform infrared photoacoustic spectroscopy directly on the gaster of each individual. Young wasps take three to four days to acquire the colony's chemical signature, with a small change on the fifth day, when the cuticular hydrocarbon profile of the workers is more similar to that of the queens than that of the males, probably because they are of the same sex, but primarily because of the similarity of tasks executed by these two groups of females in the colonies.     

Nutrient Dynamics of a Swarm-founding Social Wasp Species,Polybia occidentalis (Hymenoptera: Vespidae)

The kinds, rates of acquisition, inter-individual transfers, and intra-colonial movements of nutrients were ascertained for the advanced eusocial paper wasp Polybia occidentalis (Olivier). Foraging worker wasps (“foragers”) bring arthropod prey and nutritive liquids (“nectar”) to the nest, and these are usually transferred to nest workers (“receivers”) on the outer nest envelope. Arthropod prey items, which are brought intact to the nest, are malaxated by one or more receivers before being fed to larvae; malaxating adults retain a portion of the hemolymph for their own nourishment. Nectar is usually transferred (via adult-adult torphallaxis) from foragers to receivers on the nest envelope; some nectar is given to larvae, and all adults that imbibe it retain at least some for their own nourishment. Larval saliva of P. occidentalis contains glucose, protein, and free amino acids and so is highly nutritive; the nutrient content of the saliva closely resembles that of the saliva of other social wasp taxa. Adult wasps imbibe larval saliva, but very little is apparently transferred by those adults (via trophallaxis) to nestmates. Brood cannibalism was infrequent during this study. Adult worker and male wasps possess chymotrypsin-like and trypsin-like enzyme in their midguts and so are likely capable of protein digestion. The midgut proteases show an age-correlated variation in concentration. Pulp foragers are significantly smaller and lighter in weight than are receivers.     

Queens of the Paper Wasp Polistes fuscatus (Hymenoptera: Vespidae) Discriminate among Larvae on the Basis of Relatedness

The ability of queens of the paper wasp Polistes fuscatus to recognize larvae on the basis of colony origin was investigated in the laboratory. In a blind, binary choice paradigm, queens discriminated between larvae from their own colony and unrelated larvae, and between larvae from a sister colony and unrelated larvae. However, queens failed to discriminate between larvae from their own colony and larvae from a sister colony, indicating that queens of multiple-foundress colonies may lack the ability to make intracolonial brood discriminations on the basis of relatedness. These results demonstrate that recognition of larvae is mediated by larval-borne, genetically specified odors. Gas chromatograph/mass spectral analysis revealed that adults and larvae have similar cuticular hydrocarbon profiles, suggesting that the cues mediating larval and adult recognition may be the same.     

Molecular Phylogeny and Historical Biogeography of the Neotropical Swarm-Founding Social Wasp Genus Synoeca (Hymenoptera: Vespidae)

The Neotropical Region harbors high biodiversity and many studies on mammals, reptiles, amphibians and avifauna have investigated the causes for this pattern. However, there is a paucity of such studies that focus on Neotropical insect groups. Synoeca de Saussure, 1852 is a Neotropical swarm-founding social wasp genus with five described species that is broadly and conspicuously distributed throughout the Neotropics. Here, we infer the phylogenetic relationships, diversification times, and historical biogeography of Synoeca species. We also investigate samples of the disjoint populations of S. septentrionalis that occur in both northwestern parts of South America through Central American and the Brazilian Atlantic rainforests. Our results showed that the interspecific relationships for Synoeca could be described as follows: (S. chalibea + S. virginea) + (S. cyanea + (S. septentrionalis/S. surinama)). Notably, samples of S. septentrionalis and S. surinama collected in the Atlantic Forest were interrelated and may be the result of incomplete lineage sorting and/or mitochondrial introgression among them. Our Bayesian divergence dating analysis revealed recent Plio-Pleistocene diversification in Synoeca. Moreover, our biogeographical analysis suggested an Amazonian origin of Synoeca, with three main dispersal events subsequently occurring during the Plio-Pleistocene.     

Antennal Drumming,Trophallaxis, and Colony Development in the Social Wasp Polistes fuscatus (Hymenoptera: Vespidae)

Parental care is an important component of social behavior in both vertebrates and invertebrates. Social wasps are a useful system for investigating the interplay between behaviors associated with the feeding of larvae by adults and their role in the evolution and maintenance of sociality. Females of the primitively eusocial wasp genus Polistes perform conspicuous vibratory behaviors closely associated with adult–larva feeding interactions. Prior research strongly indicates that these signals are directed toward the larvae, but their function(s) remain unclear. Existing hypotheses on the function(s) have posited releaser effects on larvae, either stimulating or inhibiting release of larval saliva, a nutrient‐rich glandular secretion attractive to adults. Polistes fuscatus queens perform antennal drumming (AD), a behavior in which they rapidly beat their antennae synchronously on the rims of the nest cells during the feeding of larvae. We used radiolabeled prey to show that adults extract juice from the prey, which they subsequently regurgitate to larvae immediately following each AD burst. We also show that no saliva is imbibed by the queen during the contact. These results are consistent with the inhibition hypothesis on the function of AD, but not the stimulation hypothesis. We further demonstrate that AD is first performed on nests when the oldest larvae reach the third instar, and that the third instar is the first to produce measurable volumes of larval saliva. Removal of third‐, fourth‐, and/or fifth‐instar larvae from single‐foundress, pre‐pupal‐stage colonies did not cause a reduction in the queen’s AD rates compared with controls, suggesting that later‐stage larvae do not maintain AD behavior via an immediate releaser effect. We propose instead that third‐instar larvae, possibly via chemical components of the salivary secretion itself, modulate the physiology of queens so as to indirectly cause the onset and maintenance of AD behavior.     

Genetic relatedness and population structure in the social wasp,Mischocyttarus mexicanus (Hymenoptera: Vespidae)

Summary In primitively eusocial wasps workers often retain the ability to become queens, so their continued performance in the worker role is partly dependent on elevated genetic relatedness between workers and the brood they rear. In colonies of the social wasp,Mischocyttarus mexicanus, workers were related to female pupae by 0.29±0.12, a value that is significantly below the full sister value of 0.75, but not significantly below 0.50, worker relatedness to daughters. Though individuals often build new nests within meters of their natal nest, there was no genetic population structure discernable among four nest clusters, or inbreeding of any kind.     

Reproductive Status of Females in the Eusocial Wasp Polistes ferreri Saussure (Hymenoptera: Vespidae)

In the subfamily Polistinae, caste dimorphism is not pronounced and differences among females are primarily physiological and behavioral. We investigated factors that indicate the reproductive status in females of Polistes ferreri Saussure. We analyzed females from nine colonies and evaluated morphometric parameters, ovarian development, occurrence of insemination, relative age, and cuticular chemical profile. The colony females showed three kinds of ovarian development: type A, filamentous ovarioles; type B, ovarioles containing partially developed oocytes; and type C, long and well-developed ovarioles containing two or more mature oocytes. The stepwise discriminant analysis of the cuticular chemical profile showed that it was possible to distinguish the three groups of females: workers 1, workers 2, and queens. However, the stepwise discriminant analysis of the morphological differences did not show significant differences among these groups. The queens were among the older females in the colony and were always inseminated, while the age of the workers varied according to the stage of colony development.     

Age and Morphological Changes in the Epiponini Wasp Polybia paulista Von Ihering (Hymenoptera: Vespidae)

The division of labor is a central theme in the study of social insects. In bees and wasps, this activity is regulated by age polyethism. Important physiological and morphological changes have been widely studied in the polyethism of honeybee workers. In contrast, this is a relatively unexplored subject in social vespids. Our goal was to determine if there are detectable morphological changes in the body of the Epiponini wasp Polybia paulista Von Ihering or in certain glands in relation to age polyethism. We observed changes in the body weight, the salivary gland, and the mandibular gland that were associated with age, and our results suggest that social relationships and task performance are important to these changes. This contrasts with observations in Polistes and is different from the Apis mellifera Linnaeus age polyethism model.     

Seasonally Variable Eusocially Selected Traits in the Paper Wasp, Mischocyttarus mexicanus

The expression of alternative traits that benefit eusocial individuals but are not directly involved in reproductive differences among those individuals, which I call ‘eusocially selected traits’, may vary in response to environmental changes if this increases an individual's inclusive fitness. In this study, I describe traits that separate individuals within the reproductive division of labor of Mischocyttarus mexicanus, a eusocial paper wasp, and determine whether observed eusocially selected traits vary across seasons. I examined M. mexicanus because females initiate new nests throughout most of the year where they experience different conditions depending on the season. Findings from this study suggest two main conclusions: (1) phenotypic differences among M. mexicanus females are mixed, showing specialized, generalized, and context‐dependent eusocially selected traits and (2) a female's position within the reproductive division of labor may be influenced by its state. The presence of context‐dependent traits, e.g. large females initiated solitary nests in the spring and grouped nests during the summer, suggests that the payoff for pursuing different positions within the reproductive division of labor changes across seasons. The expression of context‐dependent eusocially selected traits also suggests that, roles, instead of castes, may better reflect the reproductive division of labor among individuals of eusocial species like M. mexicanus.     

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.