Cereal Leaf Beetles

By Faith Hillsden, Survey Tech Summer Student and James Tansey PhD, AAg, Provincial Insect and Vertebrate Pest Management Specialist

July 2024

Cereal leaf beetle has been a pest of cereals and grasses in Saskatchewan since it was first reported in 2008. Feeding, both by larvae and adults can significantly reduce yields and quality in a wide variety of cereal crops. Cool, wet conditions in the spring have been associated with increases in populations of this species in the past. Due to the prevalence of these conditions in many regions early in the 2024 season, there is a reason to be on the lookout for this pest.

Overwintering adults emerge from mid-April to May and disperse to host crops to feed, mate and lay eggs. The adult cereal leaf beetle has a brightly coloured orange thorax, yellow or orange legs, and a metallic blue head and wing covers (elytra). Eggs are laid about two weeks later, on the upper surfaces of leaves in singles or clusters of two or three. They start bright yellow and darken to black before hatching. Female beetles will lay between 50 to 275 eggs. Larvae develop through four instars, which takes 10-14 days before they drop to the soil to pupate. The larvae have a yellow body but appear black and slimy, because they are covered in a mixture of mucus and feces. This “fecal shield” prevents desiccation and dissuades predators. New-generation adults emerge three weeks after pupation and will feed for a few weeks on host crops before seeking sites for overwintering.

Cereal leaf beetles have a wide host range consisting of cereals and grasses. This includes oats, barley, wheat, rye, timothy, fescue, grain sorghum and corn. Both adults and larvae feed on plant leaves and strip tissue between leaf veins. However, adult feeding does not typically result in yield loss. All larval instars eat the upper surface of the leaf and leave thin membranes of tissue, giving leaves white or yellow stripes. The damage to the crop occurs through reduced photosynthetic activity. The rate of feeding increases as larvae mature, so most damage is done by fourth instar larvae, particularly when feeding occurs at the flag leaf stage. In severely damaged fields, the tips of the leaves turn white, giving the field a frost-damaged appearance.

Populations of cereal leaf beetle are often reduced below economic thresholds due to the presence of natural predators. Tetrastichus julis is a parasitic wasp used as a biological control to suppress populations of cereal leaf beetle. These wasps lay four to six eggs in cereal leaf beetle larvae and the eggs consume the beetles from the inside out. The parasitized beetle larvae drop into the soil to pupate but will die before it reaches the pupal stage. Parasitism starts in mid-June and continues until larval hosts are no longer available. Tetrastichus julis can cause a 40 to 90 per cent reduction in cereal leaf beetle populations. Other natural enemies of the cereal leaf beetle include several generalist predators including lady beetles and mites.

Monitoring cereals is important for determining population densities and the need for control. Scouting for eggs and larvae should occur at a minimum of five to 10 sites per field, three metres from field margins. Count the numbers of eggs and larvae per plant on a total of 10 plants per site. Biological control, specifically parasitic wasps, has commonly kept populations below thresholds. A nominal economic threshold has been proposed:

• Before the boot stage: 3+ eggs/larvae per plant
• During or after the boot stage: 1+ larvae per flag leaf

For additional information on cereal leaf beetle management, contact the Agriculture Knowledge Centre‑at 1‑866‑457‑2377.