Polistes annularis

Appearance

Unlike other North American ''Polistes'' species, ''P. annularis'' shows little sexual dimorphism in coloration. This species differs from ''Polistes metricus'' in terms of the coloration of the antennae and thorax. There is geographical variation in coloration between northern and southern populations. In the north, the thorax of ''P. annularis'' has ferruginous markings on a predominantly black background, while in the south, the thorax is mostly ferruginous, with black markings. The legs also vary from black to ferruginous. In terms of size, the forewings are 18.5–23.5 mm long in females, and 17.5–19.5 mm long in males.

Distribution

''P. annularis'' is found across the eastern United States from New York to Florida, and west to a line from South Dakota to Texas. This range is similar to that of ''Polistes exclamans''.

''P. annularis'' forms its nests on the branches of trees and shrubs as well as in sheltered parts of some buildings. The nests differ markedly from those of other species in the genus ''Polistes''. They are much larger, with around 500 cells, and are wide, rather than the slender, elongate nests seen in some other species.

''P. annularis'' preys on caterpillars from a large number of lepidopteran families, including Arctiidae, Saturniidae, Geometridae, Limacodidae, Lymantriidae, Notodontidae, Nymphalidae, Sphingidae, Erebidae, Noctuidae, Amphisbatidae and Elachistidae.

Behavior

In the absence of a queen, dominance conflicts will arise between foundresses on the nest. Wasps will routinely attack each other over a several week period, and certain wasps will eventually remit, leaving room for a new queen. Subordinates may then be chased from the nest. During the competitions, cell construction has been observed to stop, as well as oviposition. The new queen will lay more eggs than her co-foundresses, and dominate them as explained above. In so doing, she will cause the ovaries of other workers to decrease in size, to the point that they will be eliminated following the hatching of new workers. The queen will lay eggs, while the other females are constrained to laying eggs solely at the beginning of the association of the group. The queen may lay up to 55% of eggs, while her direct subordinates, named beta subordinates, will lay most of the remaining eggs. Should the queen disappear, the previous beta subordinate will take over as the new queen, leading to increased aggression. This aggression may result from the competition to lay eggs. When a foundress succeeds as the new queen, no additional aggression is observed, but if a worker becomes queen, aggression rises, likely because the dominance hierarchy is not as well established on these nests. Often when the queen dies, the oldest foundress will succeed her, due to her size and dominance in the nest. Despite aggression after the removal of a queen, brood care does not decrease.Despite morphological similarities, queens and workers exhibit different behavior over the winter months. Queens will overwinter, whereas workers will not. Researchers have theorized that this difference in behavior is a direct consequence of the dominance hierarchy. Experimental treatment of wasps to cold conditions resulted in increased trehalose in both sexes, though females also increased levels of glucose and fructose, while males maintained or decreased these levels. Wasps at normal foraging temperature showed significantly lower carbohydrate levels than wasps treated at colder temperatures. In addition, exposing ''P. annularis'' to low temperatures over a two week period caused many workers, but no foundresses and few males, to die. Foundresses appear to have greater glycogen storage capability than workers, helping them survive low temperatures. Males often have higher glucose, fructose, and trehalose levels higher than those of queens, indicating that mating may continue into autumn or winter. ''P. annularis'' cannot tolerate frost, though it has been shown to be able to survive at temperatures below the minimum temperature in the area in which it resides.

Habitat

''P. annularis'' is found across the eastern United States from New York to Florida, and west to a line from South Dakota to Texas. This range is similar to that of ''Polistes exclamans''.

''P. annularis'' forms its nests on the branches of trees and shrubs as well as in sheltered parts of some buildings. The nests differ markedly from those of other species in the genus ''Polistes''. They are much larger, with around 500 cells, and are wide, rather than the slender, elongate nests seen in some other species.

''P. annularis'' preys on caterpillars from a large number of lepidopteran families, including Arctiidae, Saturniidae, Geometridae, Limacodidae, Lymantriidae, Notodontidae, Nymphalidae, Sphingidae, Erebidae, Noctuidae, Amphisbatidae and Elachistidae.

Food

Due to the dominance hierarchy, the queen leaves the nest as little as possible, and has the other wasps forage on her behalf. In small groups of wasps , the queen may be forced to forage. As workers emerge, they take over the role of foraging. ''P. annularis'' preys on moths, butterflies, flies, and other insects. Unlike other organisms in the genus, ''P. annularis'' generally takes its food from wooded areas, and not from fields. However, prey represents only 20% of food resources; the other 80% is liquid.

Predators

Multiple foundresses may create a nest; some studies have shown that an average of four to five foundresses may inhabit a ''P. annularis'' nest. However, selective pressure tends to eliminate any additional foundresses once workers emerge. This is due to multiple factors. First, given the scarcity of space and resources, the foundresses will compete with each other to raise the best offspring. In addition, workers can perform all the same functions as foundresses with minimal competition. Lastly, the relatedness between workers and their eggs versus those of the foundress; workers would be more related to their sisters than their own offspring. These factors may combine to result in the expulsion of the subordinate foundresses. Such behavior was first seen in another polistine wasp, ''Polistes gallicus''. Subordinate foundress mortality has been found to significantly increase following worker emergence when compared to mortality rates prior to worker emergence. This pattern is also observed in ''P. exclamans'' and ''P. carolinus'', but not ''P. bellicosus''. In some of these species, including ''P. annularis'', subordinates decrease foraging rate following worker emergence. Unlike other polistine wasps, ''P. annularis'' tends to more severe consequences after worker emergence, despite this change in behavior. This puzzle is currently unsolved, though it may deal with senescence. Decreased foraging also accompanies decreased aggression. Comparing across polistine wasps, foundress eviction is generally independent of rate of usurpation; ''P. annularis'' has a usurpation rate of about nine percent. When all foundresses are evicted, colony failure rate is high: in nests where multiple foundresses are evicted, around 19% of nests fail, but when only one foundress was originally present, almost 80% of nests will fail. When pupae appear, queens are less aggressive towards their subordinates, as compared to the times at which only larvae are present. Some other social insects, such as ants, evict queens, while others, such as termites, seem to permit multiple queens.

Defense

As new nests are established by ''P. annularis'', many behavioral characteristics from the prior nest are taken to the new one. Notably, related siblings tend to aggregate together and go to the same nest, where possible. However, unlike in other Hymenoptera , the wasps tend to act as independent agents; while the queen is at the top of the dominance hierarchy, the other wasps may lay eggs and forage for themselves as they see fit. As queens or foundresses evict other females, the aggregations will begin to dissolve.