Several potential insect pests of wheat start making their presence known at this time of year. In last week's issue of the Bulletin (no. 5, April 23, 1999), we discussed armyworms. As you scout for armyworms, you likely will encounter both cereal leaf beetles, particularly in southwestern counties, and aphids. We will focus on cereal leaf beetles this time and save aphids for another issue.|
Adult cereal leaf beetles emerge from overwintering quarters and move to wheat where they feed before they begin laying eggs. An adult cereal leaf beetle is hard shelled, about 3/16 inch long, with metallic blue wing covers and head and red-orange legs and prothorax (the area just behind the head). Newly deposited eggs are elliptical, yellow, and smaller than a pinhead. Just before hatching, they turn almost black. Eggs are deposited singly or in rows of three or four, but never in clusters. They usually are found close to the mid-rib on the upper surface of a leaf. The larva resembles a slug or a small glob of mud. This "glob" is an accumulation of fecal matter carried around by the immature cereal leaf beetle. This behavior probably is a defensive mechanism that discourages some predators and parasitoids from attacking the larval stage of this pest. (This defensive mechanism may discourage scouts, too.) However, at least three parasitic wasps are natural enemies of the larvae. Another small wasp parasitizes cereal leaf beetle eggs, lady beetles prey on the eggs, and one tachinid fly parasitizes the adult.
Adult cereal leaf beetles feed for about 2 weeks before they begin laying eggs. Eggs hatch in approximately 5 days, and larvae usually require 10 days to become full grown. After the larvae finish feeding, they move to the ground, pupate in the soil, and emerge as beetles after 2 to 3 weeks.
The larvae feed on the green epidermal tissue of leaves, causing injured leaves to appear silver. Severely damaged fields look "frosted." The potential for yield loss depends on the stage of growth of wheat plants, location of larvae on the plants, and the density of the pest. Severe damage to the flag leaf can reduce yields by 25 to 30 percent. Larvae feeding on the flag leaf cause more yield loss than larvae feeding on lower leaves of the plant.
We have received no reports of this insect's presence in wheat thus far, but if we do we will offer recommendations for its control. In the meantime, keep scouting.--Kevin Steffey