Vespula infernalis is an obligate parasitic wasp, parasitizing the nests of other species in the genus Vespula. Its common host species is V. acadica in North America. It is sometimes called the cuckoo yellowjacket wasp due to its inquiline lifestyle. They differ from other parasitic wasps in their intensely aggressive behaviour during invasion and occupation of the host colony. Several morphological adaptations such as bigger body parts and highly curved stingers are present in these wasps to aid their aggressive parasitic behaviour. Once they occupy a host's nest, V. infernalis are known to engage in mauling and chasing of host workers and forced trophallaxis. Female wasps will also force host workers to feed and take care of their brood .
Taxonomy and phylogeny V. infernalis is a member of the family Vespidae. It is nearly identical in appearance and biology to the Old World species V. austriaca and is considered its sister species. Until recently the Nearctic population was considered to be the same species, and appears in all of the literature before 2012 as V. austriaca, though some sources are not yet updated; see.
Description and identification This wasp is an obligate social parasite. As a result, it possess special morphological adaptations to take over host colonies. These adaptations include larger body parts such as a larger head width than its host V. acadica. As an adaptation to its parasitic lifestyle, V. infernalis has a large, heavily curved stinger; this curving allows the parasitic wasp to puncture through the intersegmental membranes of host colony workers who are defending their nests. The male abdomen is longer with thick lateral black bands while the female abdomen is wider with fewer lateral black bands and black dots. V. infernalis wasps have a characteristic black and yellow colouring throughout their bodies. Irregular margins and narrow yellow marks on the scape are often used to identify Vespula infernalis.
Distribution and habitat Vespula infernalis is found in the Nearctic region, in the Boreal region of North America. The species is not considered rare and is stable throughout its range. These wasps are seen throughout all the provinces and territories of Canada and in certain states in the United States; Alaska, New Jersey, Michigan, Wisconsin, North Dakota, New Mexico, Arizona, and California.
Colony cycle This wasp is known as a social parasite. Their life cycle depends on invading and usurping other wasps' colonies. As an obligate parasite, Vespula infernalis lacks a worker caste and cannot build their own nests or feed their own offspring. V. infernalis females will hibernate longer than their host queens, ensuring that the hosts' nests will be ready when they leave their hibernation spots. After killing the host queen, the female V. infernalis tends to be aggressive towards the host workers who rear her brood. These wasps have very short seasons with flight periods from June to mid July and August to mid September.
Parasitic behaviour V. infernalis parasitises V. acadica. Near the dorsal edge of V. infernalis mandibles, there is a fourth marginal tooth whereas the host, V. acadica has three. When researchers dissected individuals of V. infernalis, they found that they had larger, sturdier mature muscle bundles in abdominal sterna and tergum than the muscles in a queen of V. acadica. As a result, it was more difficult to dissect V. infernalis. Nests of V. acadica were found to be smaller than normal due to the parasitism of V. infernalis.
Invasion
Queen-reared worker stage When a female V. infernalis invades a host's nest such as V. acadica during the queen-reared worker stage, the usurpation can be divided into two phases. The first phase is preusurpation. During this phase, interactions between the intruder and the host queen could be relatively calm and civil or aggressive. The queen may ignore the intruder and refrain from firing an attack first. The workers exhibit the same behavior as their queen. If the intruder attacks first by mauling or attempting to sting a worker, interactions between the queen and intruder become intense. The parasite, if successful, will use its stinger to paralyze the head, thorax, and legs of the host queen. The queen-reared worker stage is when the nest is at its most vulnerable, thus it is when most invasions take place. The nest is more susceptible to invasion at this time because both the queen and workers are less defensive.
Post-emergence colony stage During this stage, the colony is larger. In one experiment, a V. infernalis female was allowed to invade a Vespula atropilosa colony. Different from the queen reared worker stage, the workers in this stage were much more defensive; more aggression was observed in the form of stinging, mauling and chasing. The parasite displays more aggression than the host's queen. During a fight between the parasite and the queen, the parasite will do anything to harm or gain a better position by using her mandibles and stinger. Injuries to the queen include but are not limited to broken antennae and injured fore and hind-leg. The host queen refrained from using her mandibles whereas the workers were quick to use theirs in defense.
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