Friday, 19 June 2020

Cereal leaf beetle

Cereal leaf beetle (Oulema melanopus) - As of June 14, 2020, cereal leaf beetle (CLB) simulations indicate that oviposition is almost complete with 30% of the population in the egg stage (Table 1).  

Table 1. Predictive model output estimates for O. melanopus development (% of total population for each location) at selected sites across the Canadian prairies (as of June 14, 2020).

Across the prairies, first instar larvae are predicted to be most abundant (prairie average; Fig. 1).  This week, fourth instar larvae may begin to occur.  The following three maps illustrate larval development of first (Fig. 1), second (Fig. 2) and third instar (Fig. 3) stages across the prairies. Based on the simulation, development is greatest across southern Manitoba and southern Saskatchewan.
Figure 2. Predicted percent of cereal leaf beetle (Oulema melanopus) population at first instar stage across the Canadian prairies (as of June 14, 2020).  
Figure 3. Predicted percent of cereal leaf beetle (Oulema melanopus) population at second instar stage across the Canadian prairies (as of June 14, 2020).  

Figure 4. Predicted percent of cereal leaf beetle (Oulema melanopus) population at third instar stage across the Canadian prairies (as of June 14, 2020).  

Manitobans - Dr. John Gavloski is looking for samples of cereal leaf beetle larvae this growing season to determine their range across Manitoba, their population density, and the rate at which larvae are parasitized. Please contact or @JohnTheBugGuy if you observe cereal leaf beetles in your fields. 

Canadians - Dr. Haley Catton is looking for samples of cereal leaf beetle larvae this growing season too!  Help her monitor for the tiny beneficial wasp, Tetrastichus julis, that lives inside the larvae of cereal leaf beetle.  Tracking these biological control agents will help Dr. Catton learn more about their distribution and value in fields.  Please check her Twitter poster for more details or contact her at @HaleyCatton or . Access the recently released Pests & Predators podcast by Real Agriculture which features Dr. Haley Catton and this powerful parasitoid!

Lifecycle and Damage:
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 the males (4.4 to 5 mm). 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. They emerge in the spring once temperature reaches 10-15 ºC and are active for about 6 weeks. They usually begin feeding on grasses, then move into winter cereals and later into spring cereals.  
Figure 3. Adult Oulema melanopus measure 4.4-5.5 mm long (Photo: M. Dolinski).

Egg: Eggs are laid approximately 14 days following the emergence of the adults. Eggs are laid singly or in pairs along the mid vein on the upper side of the leaf and are cylindrical, measuring 0.9 mm by 0.4 mm, and yellowish in colour. Eggs darken to black just before hatching.  

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. 4).  When the larva completes its growth, it drops to the ground and pupates in the soil. 

Figure 4.  Larval stage of Oulema melanopus with characteristic feeding 
damage visible on leaf (Photo: M. Dolinski).

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.

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" available as a free downloadable document in either an English-enhanced or French-enhanced version.