Thursday, April 11, 2013

Spring Insect Invaders

Paper Wasps. Paper wasps (Polistes sp.) are long-legged, reddish brown to black insects with slender spindle-shaped abdomens. They may have differing degrees of yellowish or brown striping. Paper wasps can become a problem in the fall as the inseminated queens invade homes in search of overwintering sites. But paper wasps can also become a problem in the spring. As temperatures begin to climb, queens that spent the winter in structures become active and fly about. If they have been resting in an attic, wall void or crawlspace, the wasps may be attracted to light coming through a gap in the baseboard or a wall fixture, or around an AC vent and emerge inside the building. Since there are no nests or young to defend, the only real danger of being stung is from accidentally stepping on or pressing against one.

Figure 1. Use an aerosol insecticide
to destroy a paper wasp nest
(Photo: Patty Alder)
Control. Queens that are found indoors may simply be swatted or vacuumed. If a queen does manage to get outdoors and start a nest, a broom may be all that is needed to knock it down. If a wasp nest has had some time to grow and is considered to be a hazard, they are most easily destroyed in the evening with an aerosol insecticide that is labeled for "hornets or wasps" (see Figure 1). 

Clover Mites. Clover mites are occasional invaders that can become a problem in early spring. They are tiny (1/30-inch long), red to reddish-brown, oval-shaped mites. Clover mites, as do other arachnids, have 8 legs. They hold the front pair of legs straight out in front of the head. Many people actually mistake this pair of legs for antennae. Clover mites do not bite nor do they burrow under the skin. They are strictly plant feeders. Hosts include grasses, clover, and dandelion, to name a few.

Most heavy outbreaks occur in the early spring, especially around heavily fertilized lawns. The mites may invade homes and can leave a reddish-brown stain if crushed.

Control. An 18”-24” grass and weed-free zone around the structure’s perimeter can greatly reduce the number of invading clover mites (Figure 2). In addition, treating a 5-10 foot wide area of ground along the foundation, as well as an 18-24 inch wide vertical band of the foundation wall with an appropriately labeled residual liquid insecticide can help.

Figure 2. Placing gravel around the structure
can help prevent clover mite invasions
(Photo: Mike Waldvogel)
 Many plants are actually unattractive to clover mites, including geranium, marigold, zinnia, salvia, rose, chrysanthemum petunia, juniper, spruce, yew and barberry. Planting these non-attractive plants in the weed-free zone will help reduce the number of clover mites around the structure. You may also contact their county Cooperative Extension Center for advice on proper fertilization of your lawn.

The application of insecticides indoors for clover mites is not warranted. Simply use a vacuum cleaner to collect any mites found indoors. Care should be taken not to crush the mites. The vacuum bag should be sealed in a disposable plastic bag before throwing it away.

Kudzu and Brown Marmorated Sting Bugs. We will most likely start to see an increase in the activity of kudzu bugs and brown marmorated stink bugs as well. The stink bugs have a broad host range and are often found on Paulownia (empress tree), Ailanthus (tree of heaven), and crabapple among others, but at this point in the year (particularly in western NC) those host plants have little foliage and cooler weather has kept the bug activity down. And so, a lot of this current activity is simply a response to the warmer temperature and you'll see the insects on non-host sites, such as house siding, cars, etc. Kudzu bugs will be aggregating on almost anything and so you will see them on wisteria and other plants (even if there isn't much foliage), houses, early-planted beans in people's gardens, etc. But even on plants with foliage the insects will simply be hanging out rather than feeding.

Control. Treating the exterior of buildings with a spray insecticide using products containing pyrethroids (such as bifenthrin) may provide termporary relief, but don’t expect any long term relief. There's a big difference between "killing" individual bugs and "controlling" a population of them when these bugs are essentially a "moving target" in terms of where and when they'll show up. In spring, the situation is different than it is in the fall. In the fall, these insects are searching for a way to get into buildings in order to survive the winter. Now, their attention is focused on heading to the great outdoors in search of food and potential mates. So, spraying aggregations (e.g., clusters on a wisteria plant) will kill a bunch of bugs, but more are likely to show up later.

We have information for residential settings at:

http://insects.ncsu.edu/Urban/kudzubug.htm

Figure 3. Boxelder bug adults and nymphs
(Photo: Whitney Cranshaw)
Boxelder Bugs. Adult boxelder bugs are about 1/2-inch long, black with orange or red markings, including three stripes on the area right behind the head. Their wings lay flat over their bodies, overlapping each other to form an ‘X’ (Figure 3). The immature nymphs are 1/16th-inch long and bright red when they first hatch. As they grow and become larger, they become red and black. You can potentially see all stages at any given time during the summer.

Adult boxelder bugs emerge from their overwintering sites in March and early April and feed for about 2 weeks before mating. These insects prefer sunny areas and, therefore, are found most abundantly on trees in a southern exposure and on sides of buildings facing south. The boxelder bug population increases rapidly from middle July to early September.

Boxelder bugs have unusual feeding preferences. Because these insects feed primarily on boxelder and maple seeds, the insects are found on the ground beneath female trees in the early summer before the seeds start to develop. The bugs move into the trees once seeds begin to form. These insects are cannibalistic, particularly when the victim is molting, and they have been reported to feed on other dead or dying insects.

Control. The most permanent solution to a boxelder bug problem is the removal of female boxelder trees from an area, although in most cases this will not be practical or desirable. Outdoors, a pesticide application around the exterior of structures may help reduce the number of invading boxelder bugs. Preventing boxelder bugs from getting into the structure is key. Caulk or otherwise seal any openings the bugs may be using to get indoors. Bugs that enter the home may simply be vacuumed up.

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