Common Insects

Armyworms can be problematic pests in cereal grains. Armyworms are moth caterpillars that vary in color (gray or green) with a distinct yellow, white, and brown strip along the body. The adult is a yellow-brown moth. Moths emerge in spring months and lay eggs on wheat or barley. Larvae developing from these eggs then feed on wheat from May into the summer.

Aphids can be problematic pests in wheat. There are several species of aphids in wheat fields. These include the English grain aphid and the bird-cherry oat aphid. Different species have different life cycles. Aphids do little direct damage to wheat plants but can be problematic due to transmission of viruses

The cereal leaf beetle can be a problematic pest in cereal. Cereal leaf beetles overwinter and emerge in the spring, where they can move into winter and then spring wheat. Larvae and adults can do significant damage to crops. Biological control has been particularly effective in reducing cereal leaf beetle populations.

Damage caused by Hessian fly in spring wheat is becoming more frequent across parts of eastern Washington.  Crop damage from this pest may include but not limited to: stunted plants, lodging (when plants are attacked after stem-elongation), aborted tillers, and/or whole dead plants

Mites are polyphagous, feeding on numerous different host plants such as oats, barley, spring wheat, winter wheat, corn, and other grasses such as barnyard grass. Because of their small size, mites can be spread by the wind. Fields with heavy infestations typically have a silver or gray coloration. Feeding damage causes reduced photosynthetic potential and reduced yield. The wheat curl mite is the only known vector of Wheat Streak Mosaic Virus (WSMV).

Sawflies are slender wasp-like insects with a shining black abdomen and yellow bands. They range in size from 10mm to 15mm long. Females tend to be larger than males and are easily distinguished by the presence of an serrated ovipositor at the end of their abdomen, which saws into plant stems to lay eggs, thus the name “sawfly”.

The adult wheat midge is about 1/2 the size of a mosquito with an orange body, conspicuous black eyes, three pairs of legs and wings. The females lay eggs on the awns and heads of wheat plants. The eggs hatch into larvae and crawl inside the floret to feed on the developing grain. The larvae are about the same size, shape and color as the anthers of the wheat floret.

Wireworms are the immature larval stage of click beetles, and these beetles can spend several years in this larval stage feeding on germinating seeds and young seedlings, resulting in thin crop stands and lower yields.

Hippodamia convergens, commonly known as the convergent lady beetle is one of the most common lady beetle species in North America. It is found throughout the continent (from southern Canada to South America). Aphids are the main diet for both adults and larvae and thus this species is usually sold by insectaries for aphid control. These predators can be found in wheat, sorghum, alfalfa, vegetables, greenhouse crops, orchard crops, and most crops attacked by aphids.

This lady beetle has been repeatedly introduced to North America from Europe as a biological control agent. It was established in the early 1970s in New Jersey and has been spread naturally throughout North America. Both the adults and the larvae are voracious predators of aphids. C. septempunctata may be a more effective predator than some native lady beetle species, displacing them in some areas. These predator are found in aphid infested crops, including potatoes, legumes, sweet corn, alfalfa, wheat, sorghum, etc.

The most common North American species belong to the genus Collops. Species Collops hirtellus LeConte, 1876 is common in the Pacific Northwest. Most “melyrid” adults and larvae are predaceous. They are generalist predators feeding on aphids, green stink bug eggs, and larvae of the alfalfa weevil. They can be found in wheat, sorghum, alfalfa, grasses, and most crops attacked by aphids.

The Cabbage aphid (Brevicoryne brassicae) is a destructive species of aphid. Canola damaged by aphids in the seedling stage appears stunted and is more susceptible to winterkill. These plants will have curled leaves with shortened nodes. The canola may exhibit a purplish tint associated with plant stress. Aphid populations that develop during early bloom and pod-fill can cause deformed, stunted or completely sterile pods. Black sooty mold is also associated with aphid colonies. Aphids have also been reported to transmit several viruses to canola.

The cabbage seedpod weevil (CSPW), Ceutorhynchus obstrictus (Marsham),  is an introduced insect pest from Europe and causes damage to members of the Brassicaceae or mustard family, including cultivated crops such as canola and brown mustard.

As the winter canola acreage in central and eastern Washington continues to increase, so does the threat of CSPW causing significant damage to yields if left unmanaged.

Diamondback moth, Plutella xylostella (Linnaeus), is not new to our area as it can be commonly found feeding on plants in the mustard family such as canola, oriental or yellow mustards along with weed species. It typically is not a pest of concern; however, in some years like 2023, populations can reach large numbers and cause significant economic damage.

Flea beetles are usually not a problem in winter canola unless 1) the crop is planted very early, 2) plants are stressed, and/or 3) spring canola is in a nearby field and maturing. If young winter canola seedlings are the only green material for flea beetles to feed on, they can quickly move from a neighboring field with a mature crop into a winter canola field and cause damage. The Crucifer flea beetle is the primary species observed in canola in the PNW, although the striped flea beetle is becoming more prevalent in parts of Montana. In spring canola, flea beetles are one of the major pests that can cause economic damage to canola in the PNW.

Grasshoppers are generalist feeders and will attack an array of plants. They may become more abundant in years when conditions are hot and dry.  A reduction in natural vegetation can oftentimes make cultivated crops more appealing, such as canola. Both nymphs and adults can cause significant feeding damage, especially when feeding occurs on the developing or ripening pods. The Two-striped and Migratory grasshoppers (Melanoplus sanguinipes) are the species most often encountered.

The pea weevil, Bruchus pisorum (L.), is considered one of the most widely distributed species in the world and will attack both winter and spring peas. Heavy infestations of this key pest can reduce the pea seed to empty shells, severely impacting yields. A survey in Washington State showed a wide degree of pest numbers with populations reaching 71 weevils in 100 net-sweeps. The Action Threshold for this pest is four weevils in 100 net-sweeps.