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Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region
CJAI 05, February 19, 2008
doi: 10.3752/cjai.2008.05

Matthias Buck, Stephen A. Marshall, and David K.B. Cheung

Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1


5. Biology

Solitary wasps | Social wasps

Solitary wasps (Eumeninae and Masarinae)

References. – Hunt 2007, O’Neill 2001, Cowan 1991; Krombein 1979, 1967; Spradbery 1973, Evans and West-Eberhard 1970, Torchio 1970.

The Eumeninae owe the common name ‘potter wasps’ to the fact that some species build more or less free-standing mud nests (e.g., Figs C6.8, C19.5). However, this habit is neither typical nor part of the groundplan for the subfamily. According to Carpenter and Cumming (1985) the primitive, and also the most common, nesting behaviour is ‘renting’, i.e., nesting in existing cavities (Table 1). The most commonly used cavities are borings in decaying wood (e.g., Fig. C51.10), but some species use other structures such as hollow twigs and stems, artificial cavities in man-made structures, empty galls, old mud dauber nests, small cavities in rocks, walls or concrete (e.g., Fig. C51.8), old Polistes nests, and even abandoned ground burrows of other aculeates (especially when located in vertical banks). One species (Ancistrocerus unifasciatus) seems to nest primarily in old mud dauber nests. Several species (in three genera) dig their own ground burrows; of these, two construct a mud tube over the nest entrance. A few species (in five genera) build free-standing mud nests on the surfaces of rocks or vegetation. Some species show a surprising plasticity of nesting habits. The most prominent example of this in our native fauna seems to be Ancistrocerus catskill, which, according to the literature, nests in borings in wood or stems, old mud dauber nests and (probably rarely) in abandoned aculeate burrows. Additionally, we found A. catskill nesting in a small cavity in a rock, which served as a starting point for a series of mud cells, the latter of which were built fully exposed on top of the cavity above the level of the rock surface (Fig. C6.8). This gradation from cells concealed within a cavity to fully exposed, free-standing mud cells involves a series of behavioural steps equivalent to a putative evolutionary sequence leading from ‘renting’ ancestors to species that construct free mud nests. Nests of renters and burrowing species are usually multicellular, though some extralimital burrowing species make unicellular nests only (e.g., Evans 1956). Free-standing mud nests may be unicellular or multicellular (Isely 1914, Clark and Sandhouse 1936). Much of the data on nesting behaviour of Eumeninae was gathered through the very efficient trap nest technique (Krombein 1967), which uses artificial borings and stems. Because this method records renting wasps only, it is likely that the plasticity of the nesting behaviour of certain species has been underestimated. At least some ‘renting’ species are apparently also capable of excavating burrows in soft materials such as the pith in stems or similar artificial substrates like styrofoam (Cooper 1979).
Most Eumeninae provision their nests with caterpillars (usually leaf rollers and tiers). However, four species included in this Atlas exclusively use Coleoptera larvae (Chrysomelidae, Curculionidae, Buprestidae), while three species use both Lepidoptera and Coleoptera larvae. Three species are specialized on leaf miners (either Lepidoptera, or Coleoptera, or both). Records of Eumeninae taking sawfly prey (e.g., Ashmead 1894) are doubtful (Krombein 1967). Each cell within a nest is provisioned with several prey items before the egg hatches (‘mass provisioning’). Cells giving rise to females usually receive a greater amount of food than cells containing males, which usually are smaller.
As in all other Vespidae, the egg is suspended from a thin stalk and deposited before the nest is provisioned. Brood cells of the linear nests of renting wasps are separated from each other by plugs (called cell partitions) of mud or agglutinated sand (reflected in the alternate common name 'mason wasps'). Unlike mud daubers in the families Sphecidae and Crabronidae, Eumeninae usually prepare mud from dry earth and water carried in their crops (but see Fig. C64.5: Symmorphus albomarginatus as an apparent exception). One genus (Leptochilus) uses macerated pith and loose sand for this purpose (Parker 1966). In this case the sand is later incorporated into the cocoon spun by the larva. Sometimes empty intercalary cells are present between provisioned cells. In most species only a small fraction of nests show intercalary cells. A few species, however, seem to include them in the majority of their nests (e.g., Monobia quadridens). The empty cell usually present at the outer end of each nest is called vestibular cell. The outer closure (closing plug) is made of the same material as the cell partitions.
Like many other hymenopterans, Vespidae control the sex of their offspring, which is determined through fertilization of the egg (unfertilized eggs give rise to males, fertilized eggs produce females). The smaller males have a shorter larval/pupal development time than the females. In mixed-sex nests of renting wasps, females develop in the inner cells of the nest and emerge after the males, which develop in the outer cells. Deviations from this pattern have to be considered accidental (e.g., failure of sperm to fertilize egg; nest taken over by another wasp of the same species). Many species (at least in the southern part of their range) produce more than one generation per year. The overwintering stage is in all known cases the fully grown larva.
An interesting detail of eumenine biology is the close relationship between some genera and mites of the family Saproglyphidae (Krombein 1961, Cooper 1954). Each mite-bearing genus (Parancistrocerus, Ancistrocerus, Monobia) is associated with a different genus of mites. Male and female wasps carry hypopi (resting stage of mites) in a specialized area of the body called the acarinarium. In Parancistrocerus and Monobia this mite chamber is formed by the transversely depressed base of tergum 2 which is usually covered by the apical portion of tergum 1. In Ancistrocerus the mite-bearing body parts are only slightly modified (i.e., ventral surface of free apical portion of posterior terga; in A. antilope male and female genital chamber as well as posterior and lateral surfaces of male propodeum). Mites are transferred from males to females during mating. During oviposition up to 20 hypopi transfer from the female wasp into each brood cell. The hypopi develop into adults (through one intermediate stage) within the brood cell while the wasp grows into a fully mature larva. After the cocoon has been completed the adult mites feed heavily on the quiescent wasp larva by piercing its cuticle. Interestingly, the larva does not seem to be adversely affected by this. The mites complete their life cycle (in three stages from egg to hypopus) within the cocoon before the wasp emerges. The new generation of hypopi mounts the adult wasp shortly after eclosion. It is still unclear what benefit the wasps incurs from the association with mites.
In this study new data or inferences on the nesting biology of the following twelve species of Eumeninae are presented (see biology section under each species): Ancistrocerus albophaleratus, A. catskill, A. unifasciatus, Eumenes verticalis*, Euodynerus auranus, E. castigatus*, E. planitarsis*, E. sp. G*, Parancistrocerus leionotus*, Parazumia symmorpha*, Stenodynerus anormis, and S. kennicottianus* (for species marked by asterisks this represents the first published information on nesting biology).
The biology of Masarinae differs from Eumeninae most prominently in that the nests are provisioned with a mixture of pollen and nectar instead of insect larvae. Pollen and nectar destined for nest provisions are temporarily stored in the honey stomach (crop), undergoing very little digestion. The mud nest is attached to inanimate surfaces (rocks, etc.) or vegetation, and consists of one or more cells. After all of the cells of one nest are completed they are usually covered with an additional layer of mud. Pseudomasaris edwardsii, the only species recorded from the study area, uses nectar to moisten soil when preparing mud for nest construction (Torchio 1970).


Social wasps (Polistinae, Vespinae)

References. – Hunt 2007, Ross and Matthews 1991, Turillazzi and West-Eberhard 1996, Akre et al. 1981, Spradbery 1973, West-Eberhard 1969.

With the exception of socially parasitic species that do not have castes, the Vespinae and Polistinae are eusocial insects, with cooperative parental care for offspring, differentiation between reproductive (‘queens’) and sterile castes (‘workers’), and overlapping generations. Eusociality in Vespinae is more advanced than in Polistinae in that castes are more clearly differentiated by size and morphology, and colonies are often much larger. In Polistes, worker size range encompasses the size range of queens (though queens are larger on average). Furthermore, reproductive differentiation between queens and workers is not as firmly entrenched as in Vespinae, with some Polistes workers usually starting to lay eggs in the reproductive phase of the colony cycle, and supersedure of queens by workers taking place much more frequently.
In the geographic area covered by this Atlas the overwintering stage of most species (including all Vespinae) are the new queens, though in some Polistes species (e.g., P. annularis) males overwinter as well, and mating takes place in spring. Under more favourable climates (e.g., in the southern U.S., Central America, and a few countries into which species have been introduced by accident) some species have been reported to develop perennial nests. In Vespinae each colony is founded by a single queen, whereas in Polistes two or more foundresses often cooperate in nest foundation before one of the females gains dominance over the others. This α-female does not leave the nest in order to forage, lays more eggs and participates less in nest construction than subordinate females. After the first workers emerge the auxiliaries are driven away from the nest. In our area, nests of both Vespinae and Polistinae are made of paper carton prepared from masticated plant fibre (weathered or decayed wood, etc.). In Vespinae the combs of the nest are protected by a multi-layered envelope (e.g., Fig. C84.11; often more or less rudimentary when nest is built in smaller cavities). Polistes nests are not protected by such an envelope (e.g., Fig. C78.6). Depending on the species, nests are aerial, built in cavities (hollow logs, etc.) or subterranean (the latter only in Vespinae, and, rarely, in some extralimital species of Polistes). Some species show considerable flexibility in nesting behaviour. During the founding phase the queen performs all the necessary tasks involved in rearing the offspring and nest building. Soon after the first workers emerge the queen stops foraging, and does not leave the nest any more. At first all new offspring reared in the colony are workers but later in the year sexuals (males and queens) are produced. In Vespinae, queens (and some males) are reared in larger cells than workers. Larvae of Polistes are fed mostly with masticated caterpillars (e.g., Fig. C77.14), those of Vespinae are fed with a wide variety of arthropod prey (e.g., Fig. C94.10). Species of the Vespula vulgaris-group also use meat scavenged from carcasses and other sources.
The Vespinae include two species of obligatory social parasites (Dolichovespula adulterina, Vespula austriaca). Females of these species enter nests of their hosts (another species in the same genus) and sooner or later kill the host queen. Invasion takes place either when workers have already emerged (in Vespula austriaca) or before that (in Dolichovespula adulterina). In the latter case the host queen is not immediately killed so that more workers can be reared. Obligatory social parasites lack the worker caste, and all eggs of the inquiline queen give rise to fertile males and females. One species, Vespula squamosa, is a facultative social parasite. Queens either found nests of their own or usurp nests of another yellowjacket species (usually V. maculifrons). Interspecific nest usurpation is otherwise uncommon. Intraspecific nest usurpation on the other hand appears to be very common, both in Vespinae and in Polistes. Whereas in Vespinae the resident queen is killed by the successful intruder, in Polistes she remains at the nest as a subordinate helper.

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