Unwanted Insect Invaders | Hymenopterans

Hymenoptera is the order of insects that includes species that sting humans, particularly, bees, wasps, and certain kinds of ants although, overall, the order is comprised mainly of non-stinging species of many types. Even within the bee and wasp families, non-stinging species far outnumber stinging ones; but it is the stinging species that humans interact with directly.  Ironically, we have magnified the potential for these unpleasant encounters by adding new species to the native American ones. The early introduction of the honeybee from Europe can be judged to be a bright idea.  However, other more recent introductions are hardly a boon as discussed below.

Honeybees, paper wasps, and vespid wasps (hornets and yellow jackets) are all social insects that build colonial nests, raise queens, and defend their nests by attacking trespassers.  Adult honey bees differ from wasps in having hairy bodies and broad wings kept apart when resting. They also have hind legs modified to carry pollen which wasps lack. Wasps have hairless bodies, narrow wings folded when resting, and unlike bees, feed their young animal food. Paper wasps can be distinguished from vespid wasps by their long hind legs that trail behind the abdomen when flying and by their relatively small nests.

AFRICANIZED HONEYBEES

There are no honeybees native to the Americas. The familiar honeybee (Apis mellifera) in our gardens and apiaries, is the European honeybee brought to the New World in the 16th century to take advantage of its effective pollination services and honey production. The European sub-species also occurs naturally in western Asia and in limited areas of North Africa, and there are about 10 additional sub-species of A. mellifera  throughout Africa. One of these is Apis mellifera scutellata from central and southern Africa which, in its adaptation to hot climates, tends to swarm rather than to store honey in winter. “Swarming” refers to bee reproduction at the colony level. The queen leaves the colony with about 60% of the worker bees to form a new colony elsewhere while the remaining colony produces a new queen. Bees of the new colony soon return to the defensive mode that can threaten intruding animals, including incautious humans.

 

Africanized honeybee. Note pollen basket.

The European honeybee performed well in the temperate United States but less so in Central and South America.  Consequently, in the mid-1950s, a Brazilian  scientist  had a “bright” idea. He brought A. mellifera  scutellaria  (AMS)  to Brazil. He hoped through interbreeding with the European honeybee to produce a hybrid that combined the tolerance for tropical climates of the African sub-species (but not its extreme defensiveness) with the honey-producing capacity of the European sub-species. Unfortunately for all but the AMS, his work was interrupted by the escape of the bees via  swarming. Soon the AMS encountered and then interbred with the European-derived strain, producing descendants not subject to the artificial selection that the scientist hoped to impose upon his captive bees.

Descendants of the interbreeding were called “Africanized” because they displayed traits found in their African forebears.  The interbreeding involved AMS drones (males) with queens of the European strain but not vice-versa, for currently unknown reasons. Descendants of the interbreeding spread at a rate of 200 to 300 miles per year, perhaps the fastest spread rate of any introduced species.  By 1990, the hybrids had reached Texas. As of 2006, they had spread to California, New Mexico, Oklahoma, Louisiana, Florida, and states in between. Since then, the spread rate has slowed in the United States probably due to climate. The northern limit appears to have been reached around 34o North Lat., but a warmer climate may change that trend. The Africanized bee appears to be outcompeting the European bee wherever the two meet. All  hives, including commercial ones, may be taken over by the invader unless specific  actions are taken. One of these actions is  annual “re-queening” (i.e., replacing the current queen with a certified  European one). Unfortunately, not all the apiaries manage to regularly do this.

Interestingly but perhaps unfortunately, unless you use a microscope, Africanized and European strains are indistinguishable. Their behavior, of course,  is very different. Unlike the European honeybee, the Africanized bee (AMS) gives only a ½  second warning (essentially none at all) before attacking any approaching human being or other animal. The entire hive, which can contain hundreds or thousands of bees, is mobilized in the attack; and the perceived intruder may be pursued as it flees over distances that may exceed ½ mile from the hive. The comparable data for the European honeybee are a 9-second warning period, an attack party of five to 10 bees and a chase distance of about 300 feet (90 m.). The hybrids are known to react with alarm to ground vibrations from mowing and to attack intruders that are as far as 40 feet away. Many internet sites, such as those of county extension services, the U.S. Department of Agriculture and of states within the hybrids’ range discuss precautions. There aren’t many.  Mainly,  be alert and avoid close approach. Flee if attacked, covering nose and mouth. Get indoors as soon as feasible. Contact qualified pest control specialists to arrange for colony extermination. On a brighter note, Africanized  honeybees have already taken over in South America and are now being selectively bred for docility and greater honey production.

Why might the Africanized bees be more defensive and competitive than the European subspecies? Selection pressure arising from the greater number of  bee and nest predators in Africa than in the temperate zone may be involved. For example, besides the famed honey badger which seems almost immune to bee attacks, there are two families of birds that depend heavily on bees for sustenance in Africa.

The Honeyguide family (Indicatoridae) comprises 11 species of colorful birds, including two in Africa known for guiding honey badgers (and humans) to bees’ nests. Beeswax, adult bees, and their larvae are important food items for honeyguides. The Bee-eater family of the Old World tropics (Meropidae) consists of 24 species for which bees are principal prey items.

Nothing comparable to these bird families exists in the temperate zone habitats of the European sub-species. Although some bird species of the temperate zone will feed opportunistically on honeybees as will bears, more aggressive hive defense by African bees would arguably be under stronger selection pressure than in the European strain. Another advantage of the Africanized bee is that it accepts a wider range of nest sites, including  human structures, which the European honeybee seldom adopts unless assisted by man.

 EUROPEAN GIANT HORNET (Vespa crabro

European Hornet. Photograph by Steve Jacobs of Penn State.

European Hornet. Photograph by Steve Jacobs of Penn State.

The European (or giant hornet), a large, non-native species introduced into the United States in New York in 1854 is  found in the eastern states from New York to Georgia and in Indiana, Illinois, Missouri, Arkansas, and Texas. Like yellowjackets, the invading species builds nests of papery material and covers over the “roof” of the nest cells right after inserting the insect prey. Only the queen overwinters and starts a new colony annually. The native North American yellowjackets, with their yellow-striped abdomens, are in the genus Vespula as are closely related wasps called hornets in North America. The genus of the European giant hornet (Vespa), comprising the true hornets, does not naturally occur in North America.

The European invader ordinarily does not forage around picnic areas and garbage as does the native hornet. It feeds insects to its young but also damages woody plants such as lilac, birch, and willow by removing bark and even living wood from twigs to use in constructing its nest. It will, like the American hornet, aggressively defend its nest and intruders could suffer multiple stings. Like other vespids, only the females (queen and workers) will sting. Adult males can exceed 25 mm and the queen may reach 35 mm (1.4 inches) making them the largest of the social hymenopterans residing in North America.

 GERMAN YELLOW JACKET (Vespula germanica)

German yellowjacket or wasp
German yellowjacket or wasp. Photo by fir002/Flagstaffotos.

Native to Europe, northern Africa, and temperate Asia, this species has become established in the northeastern states and Pacific Northwest of the United States, southern Canada, Argentina, Chile, southern Australia, and New Zealand. Outside of North America, the species is better known as the German or European wasp. It succeeds in both rural and urban areas. In some of its North American haunts, it is outcompeting native yellowjackets. Most nests are built in or near the ground but in North America, usually are found in voids within buildings. Nests can become huge and contain thousands of wasps. A nest reported from an attic in Washington, D.C,. was five feet wide and three feet deep, and another nest excavated in the ground in New Zealand was 14 feet long and five feet wide!

As in other wasps, only the queen survives the winter except in the warmest part of its range where a few colonies survive until next year. Larvae are provisioned with insects (including caterpillars), and the species is considered in this regard to be beneficial. But this is one of the wasp species that is attracted to picnics, trash cans, and open air eating. It is relatively small at 13 mm (ca. ½ inch) in length but more apt to sting, and to sting repeatedly, than are the much larger Vespa crabro and other wasps. This species shares with Africanized honeybees the aggressive habit of chasing after perceived intruders. Given their predilection for buildings, this wasp can become more than just an inconvenience to humans, especially given the size of the colonies that can develop. 

 EUROPEAN PAPER WASP (Polistes dominula)

Eurpapwasp2

This species was first observed in North America in Massachusetts in the 1970s but has already spread to much of the northern United States and British Columbia. It was first identified in Colorado in 2001. There is evidence that its rapid colonization rate adversely affects populations of the native American paper wasp (P. fuscatus). Both species construct nests consisting of cells that are not covered over until the larvae pupate. The invading species, a little smaller than the native Polistes and with more yellow color to the abdomen, provisions its larvae with various kinds of insects. These dietary choices not only suggests a beneficial role from the plant growers’ perspective but also  predatory pressure upon native, desirable insects such as butterflies.

Several attributes of the European paper wasp help explain its competitive advantage over the North American species. Unlike P. fuscatus, the non-native species may reuse its nest. It also nests earlier in the season and typically selects better concealed nest sites. Also, the typical P. dominula colony has more workers and a wider prey base from which to feed its larvae than does P. fuscatus.

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Websites consulted for this article include: edis.ifas.ufl.edu/mg113

 invasivespeciesinfo.gov

ento.psu.edu/extension/factsheets/;

ext.colostate.edu/pubs/insect/05611.html

 whyistheanswer.com/german_yellowjackets

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