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The cereal leaf beetle (Oulema melanopus L.) is a serious pest of cereal crops and various grasses. The beetle is widely distributed in eastern
North America and has
also been found in most western U.S. states including Washington, Oregon and
Idaho. In British Columbia, it was first detected in 1998 in the
Creston Valley and in 2002 in the east Kootenays. It has more recently been detected in portions of Alberta, Saskatchewan and Manitoba.
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| Cereal leaf beetle adult. Photo courtesy Canadian Food Inspection
Agency |
Cereal leaf beetle larva |
Appearance:
Adult: Adult beetles have shiny bluish-black wing-covers, head,
antenna and abdomen. 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).
Egg: Eggs are cylindrical, measuring 0.9 mm by 0.4 mm, and yellowish
in colour. Eggs darken to black just before hatching.
Larva: The slug-like larva is slightly longer than the adult. The head
and legs are brown-black; the body is yellowish. Larvae are usually covered with
a secretion of mucus and faecal material, giving them a shiny black, wet
appearance.
Pupa: The pupa, when removed from its earthen cell, is enveloped in a
thin, transparent membrane. Its colour varies from a bright yellow when it is
first formed, to the colour of the adult just before emergence.
Hosts:
All cereals (barley, wheat, oats, rye), corn, timothy, brome grass, rye grass,
orchard grass, reed canary grass, quackgrass and other cultivated and wild
grasses.
Damage:
Both the adults and larvae feed on the leaves of host plants by chewing out
long strips of tissue between the veins of leaves. Adults eat right through the
leaf, but larvae eat the upper leaf surface leaving a thin membrane, giving a
window-pane effect. Larvae attack the flag leaf, beginning at the tip and
moving down the leaf. When damage is extensive the leaves turn whitish and the
plant takes on the appearance of frost damage. Young plants may be killed or
the yield may be seriously reduced. Yield reductions of 55% in spring wheat,
23% in winter wheat, 75% in oats and barley, have been recorded.
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Cereal leaf beetle damage to wheat leaf |
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Cereal leaf beetle damage to oat leaf |
Life Cycle:
Adult beetles overwinter in and along the margins of grain fields in
protected places such as in cereal straw stubble, under crop and leaf litter,
and in the crevices of tree bark. They favour sites adjacent to shelterbelts,
deciduous and conifer forests. They emerge in the spring once temperatures
reach 10-15 °C and are active for about 6 weeks. They usually begin feeding on
grasses, then move into winter cereals and later to spring cereals.
Egg laying begins about 14 days after the emergence of the adults. Eggs are
laid singly or in pairs along the mid-vein on the upper side of the leaf. Each
female may lay several hundred eggs.
The larvae hatch in about 5 days and feed for about 3 weeks, passing through
4 growth stages (instars). When the larva completes its growth, it drops to the
ground and pupates in the soil. 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.
Monitoring and Control:
Monitoring: Although crops may appear to be severely attacked,
it is important to assess cereal leaf beetle abundance to ensure the value of
potential crop loss is greater than the cost of chemical control. Action or
economic threshold levels have been determined to economically justify the need
for chemical application. Host crops should be sampled before and after the
boot stage. To determine if the action threshold has been reached, closely
examine 10 tillers (stems) at 10 random sites throughout the crop (not within
2-3 metres of the field margins). Record the number of eggs and larvae per stem
at each location. Control is necessary if an average of 3 eggs or larvae, or
both, per tiller are found before boot stage, and if an average of one
larvae/flag leaf is found after boot.
Chemical Control:
Recommended control products for use on cereal crops (oats,
barley, rye, wheat):
- Several formulations of Malathion are registered for control of cereal leaf beetle. Apply when cereal leaf beetle larvae reach 2 to 3 per stem. May be repeated at 7 to 10 day-intervals, if
necessary. Apply when temperature is above 18°C. Do not treat within 7 days of harvest.
- Sevin XLR (carbaryl) applied for other insects will also control cereal leaf beetle larvae and adults. Do not treat within 14 days of harvest (oats, wheat, rye) or 28 days of harvest (barley).
Usually one application of either product is sufficient to protect the crop
from economic losses.
Biological Control: There are four species of parasitic wasps that
have been introduced into other areas of North America for cereal leaf beetle
control. These biocontrol agents can keep beetle populations below action
(economic) thresholds. The parastic wasp, Tetrastichus julis, was released in the Creston Valley in 2001 and 2003 to provide biological control of the cereal leaf beetle.
Regulatory:
Cereal leaf beetle is no longer a regulated pest in Canada. Previously, cereal leaf beetle was regulated by the Canadian Food Inspection Agency, which resulted in restrictions of movement of hay from infested to non-infested areas, and requirements for hay fumigation. These restrictions are no longer required.
Further Information:
Updated: November 15, 2011 |
