No. 5/April 25, 1997
Cereal Leaf Beetles May Appear Soon in Wheat Fields
Scouts may start finding cereal leaf beetles in wheat fields soon as the adults emerge from overwintering quarters and move to wheat, where they feed before they begin laying eggs. An adult cereal leaf beetle is hardshelled, about 3/16-inch long, with metallic blue wing covers and head, and red-orange legs and prothorax (the area just behind the head). Recently 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 midrib 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. 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. Consequently, natural enemies occasionally prevent densities of cereal leaf beetles from exceeding the economic threshold (see below).
Adult cereal leaf beetles feed for about 2 weeks before they being laying eggs. Eggs hatch in about 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 upon the green epidermal tissue of leaves, causing injured leaves to appear silver. Severely damaged fields look "frosted." The potential for yield loss depends upon 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%. An insecticide treatment may be justified when the combination of eggs and larvae averages three or more per stem. Larvae feeding on the flag leaf causes more yield loss than larvae feeding on lower leaves of the plant.
The following insecticides are suggested for control of cereal leaf beetles in wheat: *Furadan 4F at 1/2 pt per acre; Sevin XLR Plus at 2 pt per acre; and *Warrior 1EC at 2.56 to 3.84 oz per acre. Products preceded by an asterisk (*) are restricted for use by certified applicators. Furadan 4F should be applied before heads emerge from the boot.
Kevin Steffey, Extension Entomology, (217)333-6652