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Cereal Leaf Beetle
The cereal leaf beetle is a pest of cereal crops and various grasses and has
the potential to cause significant losses. The beetle is widely distributed in eastern
North America and has
also been found in most western US 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. The cereal leaf beetle is
regulated by the Canadian Food Inspection Agency to prevent introduction of the
pest into non-infested areas such as the prairie provinces.
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Cereal leaf beetle adult. Photo courtesy Canadian Food Inspection
Agency
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Cereal leaf beetle larva
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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 in 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:
Chemical control: 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.
Recommended control products and rates for use on cereal crops (oats,
barley, rye, wheat) are:
- Malathion 50% EC at 2.2 L /ha (890 L/ac) at 7 to 10 day-intervals
necessary. Do not treat within 7 days of harvest. Kills larvae and adults.
Apply when temperature is above 20ºC.
- Sevin XLR Plus at 2.7 L/ha (1.1 L/acre) at 7 to 10 day-intervals as
necessary. Do not treat within 14 days of harvest. Kills larvae and
adults.
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. Efforts are underway by the BCMAFF to introduce
parasitic wasps into BC.
Movement within Canada:
The Canadian Food Inspection Agency requires hay from the Creston Valley, the
east Kootenays and cereal leaf beetle infested areas of the US to be fumigated
before allowing movement into uninfested areas of British Columbia. From
October 1 to March 31, hay from infested areas can be moved into uninfested
areas of BC (excluding the Peace River Region) without fumigation. A domestic
movement certificate (for BC- sourced hay) or an import permit (for US-sourced
hay) must accompany the hay shipments. The Directive
02-09 Hay and Straw -
Import and Domestic Movement Requirements to Prevent the Introduction and
Spread of Cereal Leaf Beetle (Oulema melanopus) outlines the regulation
of host material.
Further Information:
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