Insect Diagnostic Laboratory -

Week of August 21: Mimosa Webworm

Sat, 19 Aug 2006 00:00:00 -0500

Mimosa Webworm Damage

Mimosa webworm is a Southern insect that only occurs occasionally on honey locust trees in Iowa. Mild winters over the past few years seem to have lead to increased incidence of this caterpillar pest.

Damage occurs when the caterpillars tie honey locust leaflets together and feed on the foliage inside the tightly compressed, protective webs. Affected foliage gradually turns brown. There are two generations of caterpillars per year. Extensive damage is most obvious following the second generation in August.

Damage from the mimosa webworm is seldom serious to otherwise healthy, well-established trees. The webs and browned foliage are unsightly and caterpillar silk hanging from the trees may be annoying. The damage is more aesthetic than serious.

Chemical control for mimosa webworm is rarely warranted. A treatment after foliage has turned brown is ineffective and a waste of time. Such late treatments may do more harm than good by destroying the natural enemies of the pest rather than the pest itself. Sprays must be applied at the start of the caterpillar period and before webbing is apparent to be effective (mid-June and again in early August). Insecticides available to homeowners include (e.g., Dipel), Sevin, permethrin, bifenthrin, cyfluthrin, deltamethrin, fluvalinate, lambda-cyhalothrin and spinosad. Read and follow directions on the insecticide label.

Week of August 14: Fall Webworm

Fri, 18 Aug 2006 00:00:00 -0500

Fall Webworm

From mid-July through the end of the summer fall webworm caterpillars construct loose, gray, silken webs on the ends of the branches on walnut and other hardwood trees. We always have a few fall webworms, but reports and observations indicate there will be more than usual this year.

Fall webworm tents start small, but the yellow, hairy caterpillars enlarge the web every few days as they grow and consume the leaves within the tent. By the end of the summer webs may be 2 to 3 feet long and enclose the entire end of a branch. The old gray webs hang on the trees most of the winter.

Although the fall webworm has been recorded feeding on more than 200 species of deciduous trees and shrubs, the favored host in Iowa is the black walnut tree. Tents are particularly common on walnut trees growing in the open or on trees at the edge of the woodland.

Damage caused by the fall webworm is not significant to well-established, otherwise healthy trees. Damage is more unsightly than serious because of the limited amount of foliage consumed and the time of the year. Trees are not killed by this pest and control is not essential. Applications of insecticide are of little or no benefit and should be avoided in order to preserve predators, parasites and other biological control organisms. To be effective sprays must be applied early in the season and with sufficient pressure to penetrate the silk web and reach the leaves within.

The only practical control is to cut off webs when they are first noticed. Prune and discard the webs you can reach and ignore the rest. Because caterpillars remain in the tent, time of day is not important.

Week of August 7: Bagworm

Thu, 17 Aug 2006 00:00:00 -0500

Bagworm

The bagworm has historically been an occasional pest on evergreen and deciduous trees and shrubs in southern Iowa. Infestations have been increasing in number and severity during the past few years, possibly because this Southern pest has benefited from our recent mild winters. Bagworms are still rare north of Interstate Highway 80.

The most noticeable sign of a bagworm infestation is the presence of tough silken bags on the branches or foliage. Each caterpillar produces an individual protective silken bag or case around its body. With its head and legs free, it is able to move about the plant as it feeds on the foliage. As the larva grows it increases the size of its bag and incorporates into it bits of twigs and leaves for strength and camouflage protection. The larva will spend its entire life within its bag. Larvae first appear about mid-June and are full grown by mid-August. Bags of mature larvae are approximately 2 inches long.

Large larvae are difficult to control with insecticide sprays and late sprays after the beginning of August do little to protect the foliage on the tree. Evaluate carefully if larvae are still feeding before deciding to spray. Insecticides that can be used against the bagworm include Bt (Bacillus thuringiensis), Sevin, permethrin, Orthene, or malathion. Apply according to label directions.

Week of July 17: Tomato Hornworm

Sat, 05 Aug 2006 00:00:00 -0500

Tobacco Hornworm on Tomato

The tomato hornworm is one of our best known garden pests. It’s almost as big around as your thumb and can be 4 to 5 inches long. It’s bright green and has a hornlike hook at one end that can be either red or green depending on which of the two species you have on your plant. After feeding, hornworms move to the soil where they pupate and spend the winter. The following summer the pupae transform into five-spotted hawk moths and start the cycle over.

Tomato hornworms feed on the leaves and fruit of tomatoes and other vegetables including eggplant, potatoes and peppers. They can quickly defoliate portions of the plant, reduce its productivity, and heavily scar the fruit. Toward the end of the summer when the caterpillars are fully grown, it seems they can eat about a leaf an hour!

The first control option is to pick the caterpillars off your plant by hand. They won’t hurt you but the challenge is that they are well camouflaged. They are the same color as the foliage so it will take some hunting to find them when they are small. When they are big, they will be easier to find but then that means they will have grown and developed by feeding on your tomato foliage already!

Another control option is to use a biological insecticide known as Bacillus Thuringiensis or Bt or a synthetic home garden insecticide available in local garden centers. Be sure to follow label directions.

Week of July 10: Cicada Killer Wasp

Sat, 15 Jul 2006 00:00:00 -0500

Cicada Killer Wasp

The cicada killer wasp is the largest wasp found in Iowa. They may be up to 2 inches long and are black with yellow markings on the thorax and abdomen and they have rusty colored wings.

The cicada killer wasp and other digger wasps are solitary wasps; that is, they live independently rather than in colonies and do not depend on other members of a colony to share in the raising of young or the maintaining of a nest.

The female cicada killer wasps capture annual cicadas in July and August and place them in cells located at the ends of tunnels they have dug in the ground. Each tunnel is about the size of a quarter and extends 24 inches or more into the ground. One or two paralyzed cicadas are placed in each cell, and a single egg deposited before the cell is closed by the female, who flies away, never to return. The wasp grubs feed on the cicadas and develop into wasps that emerge the following summer.

The cicada killer, like other solitary wasps, has the capability to sting, but won't unless handled or threatened. Only female wasps have the ability to sting. Stings inflicted by solitary wasps are usually not severe but reaction varies with each individual.

Wasps are generally beneficial and a nest in an out of the way location where it is not likely to be disturbed should be left alone. If, however, a nest is located where problems could arise, such as under a deck or near an often used door, removal is justified. Ground nests of cicada killers and other digger wasps can be destroyed by placing an outdoor use insecticide dust into the nest entrance during the night. The dust particles will adhere to the wasps as they come and go from the nest. Cover the nest opening with a shovelful of soil after all activity has stopped.

Week of July 3: Japanese Beetle

Thu, 29 Jun 2006 00:00:00 -0500

Japanese Beetle

The Japanese beetle is considered the worst pest of turfgrass and landscapes in the United States because they attack so many different types of plants. The adult beetles eat the foliage, fruits and flowers of over 300 different plants. The larvae are white grubs in the soil from August until June where they feed on plant roots (especially turfgrass) and organic matter.

Adult beetles are about 3/8 inch long and 1/4 inch wide. The head and thorax are shiny metallic green, and the wing covers are coppery red. The row of five tufts of white hairs on each side of the abdomen is a distinguishing feature.

Control of adult beetles is difficult because they emerge every day for a period of several weeks, beginning in late June. Handpicking or screening or high-value plants may be of benefit in isolated situations with limited numbers of beetles. Spot spraying infested foliage of high value plants with carbaryl (Sevin), permethrin (Eight) or cyfluthrin (Tempo) may reduce damage for several days, but multiple applications are required to maintain control. Spraying the adult stage is not an effective strategy for prevention of white grubs.

JB has been reported from 19 different counties in Iowa since 1994, predominantly in the east-central region of the state. Please let us know if you find JB in a county where they have not already been reported: Black Hawk, Boone, Clayton, Clinton, Dallas, Dubuque, Floyd, Jackson, Johnson, Lee, Linn, Madison, Marshall, Muscatine, Page, Polk, Scott, Story, Woodbury.

Week of June 26: Imported Longhorned Weevil

Tue, 27 Jun 2006 00:00:00 -0500

Imported Longhorned Weevils

The imported longhorned weevil and the strawberry root weevil are common "accidental invaders" that crawl into houses and buildings from outdoors by mistake during late June and July. The weevils are harmless; they do not damage the house or furnishings; they can not bite or sting people or pets. They are merely a nuisance by their presence.

The larvae of these weevils live in the soil and feed on the small roots of many different plants, including aster, clover and turfgrass. They do not cause apparent damage to the plants and control of the larvae in the soil is not practical nor necessary.

Some of the invasion by longhorned weevils can be prevented by exclusion techniques that close their routes of entry. Look for and seal cracks and gaps through which the adults can crawl into the building. Spraying a residual insecticide labeled for beetle control outdoors on and along the foundation and in outdoor areas of weevil abundance may be of some benefit. Fro more information on insecticides please see "Insecticides in the Home Landscape and Garden."

Adults already inside need only be vacuumed or swept up and discarded. Household aerosol insecticides are not very effective for controlling these weevils.

Week of June 19: Soldier Beetles

Tue, 13 Jun 2006 00:00:00 -0500

Soldier Beetle

The soldier beetle is a common outdoor insect found throughout Iowa. They usually go un-noticed except when they are exceedingly abundant on flowers where they feed on nectar and pollen. They are especially common on the blossoms of linden trees and Japanese tree lilacs in June and on goldenrod in September.

Soldier beetles are elongate-narrow, soft-bodied and about ½ to ¾ inch in length. One very common species is orangish-tan with darker color at the wing tips. They are nicknamed leatherwings because of their soft, flexible "leathery" texture wing covers. Soldier beetles resemble lightningbugs but do not have light-producing organs.

Soldier beetle adults and larvae are predacious and feed on other insects. They are beneficial and harmless. It is unnecessary to control them.

Week of June 12: Boxelder Bug Nymphs

Sun, 11 Jun 2006 00:00:00 -0500

We have had numerous calls and messages all this month about boxelder bug nymphs. Boxelder bugs have a simple life cycle of three stages: egg, nymph and adult. The adults are well-known; the nymphs look very similar but are smaller and bright red because they don't yet have the black wings to cover their abdomen. The picture above is of an older nymph with the black wing buds showing. Younger and smaller nymphs are more red with little if any discernable black markings where the wings will someday be.

These bright red, soft insects are very abundant and present in unlikely places, and not just on trees like we expect.

It is not essential to control boxelder bug nymphs this early in the summer. These are not the same bugs that will invade the house in the fall. The nymphs present in June will mature into adults that will reproduce in July. It is this second generation of the summer that produces the accidental invader adults in October. The number that will be present in October is dependant on the upcoming weather, and killing some nymphs now will not make as much difference as will the weather in July.

Week of June 5: Seedcorn Maggot Flies

Tue, 30 May 2006 00:00:00 -0500

Small dead flies on shrubs, vines, flowers and vegetable plants is a common sight in some springs. The small gray flies resemble small house flies (slightly less than ¼ inch long). They may be noticed everywhere and anywhere, but always dead.

These small flies are the adult stage of a moderately important pest called the seedcorn maggot. As the name implies, the larvae (or maggots) attack and damage seed corn (and seeds of other crops such as soybeans, vegetables, etc.) planted in damp, high organic matter soil. Populations are highest in cool springs when seeds are slow to germinate.

The adult flies are harmless. They cannot bite, sting or carry diseases. They cannot feed on plants. No control is necessary.

Part of the reason seedcorn maggot flies attract attention is their method of death. A large portion of the flies dies as a result of a fungus that invades their bodies. Many of the infected flies die after landing and attaching to the foliage of ornamental plants. The dead flies, stuck to the plants, are obvious to homeowners and landscapers inspecting plants for signs of trouble and they are improperly blamed for any and all symptoms on the plants. However, the flies did not feed on the plants or cause any of the holes, spots or discolorations that may be present. To repeat, no treatment is warranted. They are dead, for gosh sakes!

Seedcorn Maggot Fly

Week of Dec 12: Soldier Fly Larvae

Fri, 09 Dec 2005 00:00:00 -0600

This week we got an interesting sample of brown maggots. Our fly expert, Dr Ken Holscher, was able to correctly identify them as maggots of the soldier fly. Soldier fly maggots occur in decaying organic matter. They are often found in manure or garbage. When found indoors they may be coming from garbage, a broken septic tank, or possibly a bee nest in the wall. Soldier flies are harmless, and the best control is to locate and eliminate the organic matter they are breeding in.

Week of Nov 7: Woolly Bear Caterpillars

Tue, 08 Nov 2005 00:00:00 -0600

As you drive in the country during the fall, you are probably noticing many caterpillars crossing the road. These are woolly bear caterpillars and there are 8 or more species in the U.S. The best-known woolly bear is called the banded woolly bear. It is black at both ends and reddish-brown in the middle. The adult is called the Isabella moth. The second generation is the one noticed in late fall when the woolly bears are crossing the roads, usually in great haste as if they have someplace special to go. In fact they are only scurrying to find a sheltered location under dead plant debris, etc. where they will spend the winter as a larva. In the spring they will feed briefly before changing into a cocoon and eventually a moth. Eggs laid by the female moths start the cycle over again.

The banded woolly bear is the species mentioned in winter-prediction folklore that claims longer the black at the ends of the body, the more severe will be the coming winter. As you might expect, science has debunked this legend by showing the amount of black varies with the age of the caterpillar and the moisture levels in the area where it developed.

Banded woolly bear caterpillar.

Week of Oct 17: Larger Yellow Ants

Mon, 17 Oct 2005 00:00:00 -0500

The past couple of weeks many Iowans have been encountering the one of my favorite ants, the larger yellow ant. In the late summer and fall mixed colonies of winged swarmers and wingless worker ants move toward buildings and try to enter through cracks or gaps in the foundation. During the summer the workers feed almost exclusively on honeydew gathered from aphids or mealybugs and they are active at night. In the winter the ants commonly gather near foundations and enter houses to spend the winter. The temporary indoor, winter nest is usually somewhere in the basement under a loose brick or board or in a crack in the wall or floor. The ants do not forage for food through the house and apparently cause very little damage except to create piles of dirt at the entrance to the nest. Reportedly, these ants try to return to the outdoors sometime in the early spring if left undisturbed. Control of larger yellow ants is not critical, since they cause little damage other than the annoyance of their presence.

Week of Oct 3: Minute pirate bugs

Fri, 07 Oct 2005 00:00:00 -0500

During the late summer, small, black and white insect known as the minute pirate bug makes its presence known in a very convincing manner by biting with an impact that is out of proportion with its size.

Minute pirate bugs are present all summer in fields, woodlands, gardens and landscapes where the feed on small insects and insect eggs.. They quietly go about their business without anyone taking notice until late in the summer when they migrate from fields and woodlands and begin the disagreeable behavior of biting humans. Their bite is surprisingly painful for such a small insect as they probe their short blunt beak into the skin. They do not feed on blood or inject a venom or saliva. People differ in their response to pirate bug bites. Bites on some swell up like a mosquito bite, some turn red and for others there is no reaction at all.

Wearing dark clothing on very warm days when pirate bugs are abundant may help reduce your attractiveness to the bugs. Repellents are generally not effective though you may want to try them to see for yourself if they work or not for you.

Week of Sept: 19: Giant Water Bug

Thu, 22 Sep 2005 00:00:00 -0500

The giant water bug is one of the largest insects commonly encountered in Iowa. These moderately common aquatic insects live in lakes, ponds and quiet streams. They are strong fliers, they are attracted to lights, and consequently, often are found a considerable distance from water. They may be found in the yard or street under a street lamp, or they may have crawled by accident into the house or other building.

Giant water bugs are 2 1/2 inches long and brown in color. The body is flat and elongate oval in shape but pointed at both ends. The front legs are enlarged and pincer-like with a resemblance to praying mantis front legs. A short beak is visible on the front of the underside of the head. The legs and beak combine to make the giant water bug an effective predator. They feed on other aquatic insects, snails, tadpoles and even small fish.

Giant water bugs are in no way related to, or connected with the household cockroaches that are nicknamed 'waterbugs.' The giant water bugs are harmless and interesting. They do no harm to crops, structures, people or pets and they will not reproduce or establish indoors. The worst that can happen is a painful bite if they are handled carelessly.

Special controls for giant water bugs are not necessary. Most of them die quickly if they can not get back to water.