By Dr. Kathy Heinsohn
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Asian lady beetles, Argentine ants, Formosan termites — as their names imply, these insect species aren’t from around here. Once they become established, and we begin to see them year after year, we tend to forget that they were introduced in the first place. They become so much a part of the natural landscape that we lump them in with the other seasonal pest expectations on our general pest control routes.
A recent PCT cover story (October 2012) warned of these invasive species of insects being only a hitch-hiking plane or boat ride away. Once they set tarsi on our shores, they are only a pallet shipment/nursery stock and soil shipment away from arriving at your customers’ doorsteps. A 2004 Cornell University study estimated that more than 4,500 foreign arthropod species reside in the continental U.S. and Hawaii.
Despite its best efforts, the Animal and Plant Health Inspection Service (APHIS) is not able to keep all unwanted pest species out of our national borders. Sometimes our own government introduces the insect as a well-meaning control method for another pest — but then some quirk of biology or behavior in their new home allows the insect to thrive to the point of pest-hood.
What makes a beneficial insect take on the status of pest? In the case of Asian lady beetles, it’s their need to overwinter in structures; our native lady beetles do not do this. Why do invasive or introduced species do so well in their brand new homes? Mostly because the suite of native predators, diseases and pests that would keep their numbers in check is absent in their new environs, and their populations bloom out of control as a result. In addition, pest management professionals may not recognize them as pests until it’s too late — and by then, populations and damage done have already made an impact.
Consider the following invasive urban pest species:
Brown marmorated stink bugs (Halyomorpha halys). This pest is most likely to be familiar to you, as it has been found in the United States for around a decade. It was first (accidentally) introduced on wooden pallets from Asia in Allentown, Pa., during the fall of 1996. Since 2000, populations of the brown marmorated stink bug have been confirmed in multiple mid-Atlantic states, as well as Oregon and California.
These pests now have migrated up and down the east coast and westward. There are no reported predators or pests for these creatures; praying mantis will feed on them, as will robins, although I once saw a robin attempt to eat one before promptly spitting it back out. The stink bug successfully overwinters inside homes and structures, and will destroy orchards, vineyards, crops and backyard tomato patches during the summer. They do not eat the entire fruit; they damage it by causing something called “cat facing,” or a stippling, that makes the fruit ugly and unsellable. It also appears that wines made from stink bug-affected grapes can be tainted. The defensive odor produced when the stink bug is disturbed has been described as cilantro-like, and most people don’t like this smell (or taste) in their homes or in their wine.
Adult stink bugs are 5/8 inch and dark mottled brown. The last two antennal segments have alternating light and dark bands. The exposed edges of the abdomen also have light and dark banding. They emerge from overwintering sites from late March through June, and immediately begin to feed. Females lay clusters of light green, barrel-shaped eggs on the undersides of leaves from June to August. The nymphs are yellowish and mottled with black and red.
Management approaches are similar to other occasional invading pests like lady bird beetles and boxelder bugs. Shore up the cracks and crevices and under parts of siding, especially on the southwest sunny side of the structure before the bugs move in during the early fall. Prevent them from entering a home by sealing cracks with caulk, use weather stripping around doors and windows, remove window air conditioners, secure crawlspace entries. Cap or screen the tops of chimneys. Inspect for and seal foundation cracks. Inside, vacuum up the bugs and place them in an outdoor trash receptacle. A few insecticides are labeled to control stink bugs; read the labels carefully. Research with light traps has shown some promise. USDA also has looked into parasitoid wasp release, but that involves introducing another non-native insect to a new location.
Kudzu bugs (Megacopta cribraria). Kudzu bugs were first detected in Georgia in 2009. They can now be found throughout the southeastern United States. They are more closely related to stink bugs, but are about the size of an adult lady beetle. They are square-shaped, about ¼ inch long and light olive-green in color. Immature bugs look similar, but smaller and “hairy.” Kudzu bug eggs are tan in color, barrel-shaped and found in two rows on plant leaves.
There are two generations of kudzu bugs in the southeastern United States each year. The first population develops on kudzu or wisteria, while the second generation develops on agricultural crops like soybeans. In the fall, kudzu bugs move from plants to sheltered areas to overwinter. They can aggregate in huge numbers. Preferred overwintering sites include leaf litter and crevices on trees or shrubs. But, they also will use cracks, crevices and voids around homes and structures, especially those lighter in color.
During the spring, kudzu bugs become active and move from sheltered areas to search for suitable host plants for feeding and reproduction. For PMPs, managing kudzu bugs requires similar approaches as was discussed for the brown marmorated stink bug.
The Asian needle ant (Pachycondyla chinensis). When one invasive pest species successfully replaces another, kicking it forcibly out of the neighborhood, it’s headline insect pest news! A recent study from North Carolina State University (see page 60 of this issue) reveals that the Asian needle ant has now killed and replaced nearby Argentine ant colonies. PMPs have been fighting Argentine ants for quite a while, but did not realize we’d be assisted by another invasive pest species. Asian needle ants are a dominant species to the exclusion of many beneficial native ants commonly found in similar habitats.
These ants have been in the United States since the 1920s, but their populations have exploded in the past eight years, spreading across the country and establishing themselves in many southeastern states, as well as Connecticut and New York.
It appears that the Asian needle ants are able to tolerate cooler temperatures better than the Argentine ants, according to a recent paper published in the journal PLoS One. These ants come out of winter “hibernation” earlier, allowing them to build nests, find sources of food and start reproducing before the other ants get going. This displaces Argentine ants in urban environments as well as native ants in forested areas. The Asian needle ant also eats other ants, an uncommon behavior.
The species is not aggressive and will flee if disturbed. During the swarming season, chances of being stung increase because females are more likely to land on an individual or to get trapped in clothing. Stung individuals may have allergic reactions, even sometimes anaphylactic shock. Symptoms may last from hours to weeks. Those sensitive to bee or wasp venom are most at risk with Asian needle ant stings.
The female and male swarmers are different in appearance. The winged female is 5.6 millimeters in length, with a black body, brown mouthparts and legs. The smaller winged male is 3.0 millimeters and is light brown in color. The total length of workers is 3.5 millimeters, also with a black body and light brown mouthparts and legs.
The Asian needle ant nests beneath natural and man-made structures; management approaches include limiting structural elements around a property. During swarming season, reduce entry from outdoor habitats into structures with well-fitted screens on doors and windows. If pesticides are used, conduct a direct treatment of nest sites. This will require moving objects that cover and protect the colony to allow insecticide to penetrate the nest. These ants do not form foraging trails, so baiting may be challenging. However, research shows that toxic baits are effective at killing Asian needle ants. More research is needed to understand management of this ant.
Foreign invading pests arrive to the United States in a number of ways, and then become established. A good lesson here may be that next time you travel abroad or to a new location, and are tempted by a beautiful, strange or different insect or plant you see to collect as a prized possession for your own, consider what you might be introducing to your area.
Dr. Kathy Heinsohn, B.C.E., is a technical and training entomologist for American Pest, Fulton, Md. Prior to that position, she was staff entomologist with NPMA and a regional entomologist with Western Pest Services. In all her positions, she has been responsible for developing and delivering training and technical programs for PMPs and their customers. She is currently a member of the Copesan Technical Committee and NPMA’s Technical Committee.