The cereal leaf beetle (CLB) (Oulema melanopus) model predicts that larval development varies across the prairies. The graph predicts development at Lethbridge (Fig. 1). The simulation indicates that populations in southern Alberta should be in the second and third instar. The appearance of pupae is expected to occur by the end of the month across southern Alberta.
Cereal leaf beetle scouting
Give priority to the following factors when selecting monitoring sites:
□ Choose fields and sections of the fields with past or present damage symptoms.
□ Choose fields that are well irrigated (leaves are dark green in color), including young, lush crops. Areas of a field that are under stress and not as lush (yellow) are less likely to support CLB.
□ Monitor fields located along riparian corridors, roads and railroads.
□ Survey field areas that are close to brush cover or weeds, easy to access, or are nearby sheltered areas such as hedge rows, forest edges, fence lines, etc.
Focus site selection on the following host plant priorities:
□ First – winter wheat. If no winter wheat is present then;
□ Second – other cereal crops (barley, wheat, oats, and rye). If no cereal crops are present then;
□ Third – hay crops. If no hay crops or cereal crops are present then;
□ Fourth – ditches and water corridors
Sweep-net Sampling for Adults and Larvae:
● A sweep is defined as a one pass (from left to right, executing a full 180 degrees) through the upper foliage of the crop using a 37.5 cm diameter sweep-net.
● A sample is defined as 100 sweeps taken at a moderate walking pace collected 4-5 meters inside the border of a field.
● At each site, four samples should be collected, totaling 400 sweeps per site. The contents of each sample should be visually inspected for life stages of CLB and all suspect specimens should be retained for identification.
● Because the CLB larvae are covered in a sticky secretion, they are often covered in debris and are very difficult to see within a sweep-net sample.
● To help determine the presence of CLB, place the contents of the sweep net into a large plastic bag for observation.
Visual Inspection: Both the adults and larvae severely damage plants by chewing out long strips of tissue between the veins of leaves (Fig. 1), leaving only a thin membrane. When damage is extensive, leaves turn whitish.
Lifecycle and Damage:
Larva: The larvae hatch in about 5 days and feed for about 3 weeks, passing through 4 growth stages (instars). The head and legs are brownish-black; the body is yellowish. Larvae are usually covered with a secretion of mucus and fecal material, giving them a shiny black, wet appearance (Fig. 2). When the larva completes its growth, it drops to the ground and pupates in the soil.
Pupa: Pupal colour varies from a bright yellow when it is first formed, to the colour of the adult just before emergence. The pupal stage lasts 2 – 3 weeks. Adult beetles emerge and feed for a couple of weeks before seeking overwintering sites. There is one generation per year.
Adult: Adult cereal leaf beetles (CLB) have shiny bluish-black wing-covers (Fig. 3). The thorax and legs are light orange-brown. Females (4.9 to 5.5 mm) are slightly larger than males (4.4 to 5 mm). They emerge in the spring once temperatures reach 10-15 ºC and the adults are active for about 6 weeks. They usually begin feeding on grasses, then move into winter cereals and later into spring cereals. Adult beetles overwinter in and along the margins of grain fields in protected places such as in straw stubble, under crop and leaf litter, and in the crevices of tree bark. They favour sites adjacent to shelter belts, deciduous and conifer forests.
Fact sheets for CLB are published by the province of Alberta and available from the Prairie Pest Monitoring Network. Also, access the Oulema melanopus page from the “Field crop and forage pests and their natural enemies in western Canada – Identification and management field guide” (2018; accessible in either English-enhanced or French-enhanced versions).