Agriculture and Agri-Food Canada Insect Identification Sheet No.
50 March 1981
over 800 species of wireworms in North America, nearly half of
which are found across Canada. While most are harmless,
several species are serious pests of a wide variety of crops including
corn, potatoes, wheat, barley and onions.
Larvae of pest species feed by boring into seeds and underground
portions of plants. Seeds are often hollowed out and seedlings
killed. Later in the season they feed on the small roots of host
plants, stunting the plant's growth or killing them. Disease organisms
often enter plants damaged by wireworms. Tubers such as potatoes
are burrowed into, rendering them unmarketable. As larvae tend
to remain in the field they hatch in, infestation may vary considerably
from field to field.
are known as click beetles because of the distinct clicking sound
they make as they flip into the air after being overturned. Pest
species are usually brown or black, ranging in length from 8
to 1 5 mm. They overwinter both as adults and larvae. Early in
the spring, the beetles become active, mate and lay their eggs
around grass roots. The larvae, hatching in 3 to 10 days, spend
the next 2 to 6 years feeding on
the roots of host species. Larvae of pest species are usually hard,
smooth and dark colored, though some are yellow or white. They
range from 1.2 to 4 cm in length when fully developed. They pupate
late in the summer. Adults overwinter in the ground in the pupal
cell. There are usually wireworms in all states of development
in an infested field as the larval stage takes several years.
on the control of this insect consult your provincial Department
Elaterid larvae (wireworms) require up to five years to mature
in their soil habitat. Damage to tubers and grain roots may subject
the plants to secondary infection by pathogens. Rotation minimizes
THE FOLLOWING (UNTIL OTHERWISE NOTED) IS FROM: GERBER, H.S. 1983.
MAJOR INSECT AND ALLIED PESTS OF VEGETABLES IN BRITISH COLUMBIA.
MINISTRY OF AGRICULTURE AND FOOD.
in the soil for two to five years, attacking a wide range of
plants, including vegetables. Damage is more prevalent in crops
planted in newly broken land following permanent sod. There are
about 150 species in British Columbia, but only seven are of
bean, carrot, cole crops: broccoli, brussels sprouts, cabbage,
cauliflower, kale, kohlrabi, radish, rutabaga, turnip
In the spring,
wireworms bore into seeds or underground stems of seedlings and
transplants, causing the tops to show stunting and abnormal growth
or shriveling. Tops remain attached to their roots. Damage is
distinct from that caused by cutworms, which sever emerging plants
at or below the soil surface. Later in the growing season, wireworms
feed by boring tunnels up to 3 mm in diameter and 4 cm deep in
developing roots, tubers or bulbs. Feeding is most damaging at
this time and reduce yield or makes root, tubers or bulbs unmarketable.
Mid- and late-season damage in root crops cannot be detected until
or beetle is 10 to 16 mm long, hard shelled and flat, black,
tan or dark brown. Beetles fly and feed on the foliage on blossoms
of trees and shrubs. They are called click beetles because of
the clicking sound made when flipping over from their back to
their feet. Eggs are white and round. Newly hatched larvae or
wireworms have three pairs of legs, are white and 1.5 mm long.
Later they become slender, hard-bodied,
shiny yellow-brown and when mature are up to 3 cm long. They move
slowly in the soil and remain motionless when disturbed. Several
developmental stages of one species may be found in the soil at
one time. Pupae are white but are rarely seen.
The life cycle
ranges from three to six years with two to five years as actively
feeding larva-e. Beetles emerge from the soil in early summer
when the soil temperature has warmed to 18ø or 21øC.
Following mating, each female beetle lays 50 to 300 eggs in the
soil 2.5 to 15 cm beneath the surface. Larvae hatch in three
to four weeks and begin feeding. When the surface temperature
reaches about 27øC in mid-summer, wireworms move downward
in the soil until suitable temperature zones are found. When
summer temperatures modulate, they return to the surface and
continue feeding until cooler fall temperatures cause them to
move downward again, where they remain for the winter. In the
spring when surface soil temperatures reach about 10øC,
they again move upward. This cycle is repeated until the wireworms
are mature. Mature worms pupate for three weeks in earthen cells
7 to 20 cm below the soil surface. Beetles emerge in early summer
to repeat the cycle.
directed against the larvae. Recommended insecticides must be
incorporated into the soil to depths of at least 15 cm to be
effective. Fumigants are expensive and reliable only if properly
applied when the surface temperature is over 10øC and
the soil is not excessively wet. Once wireworms have been controlled,
reinfestation to economic levels may not occur for up to 10 years.
Insecticide seed coatings protect direct-seeded crops but only
slightly reduce the wireworm population in the field.
New Ways to Manage European Wireworms:
Ph.D., Agriculture and Agri-Food Canada PARC, Agassiz. V0M 1A0
European wireworms, notably Agriotes
obscurus and Agriotes lineatus,
are gradually spreading in Canada. In the Lower Mainland, these
species are the most important insect pests of many crops in the
Fraser Valley. They cause serious damage to potatoes, corn, ornamental
crops and small fruit, such as strawberries. Since 1990, potato
crops have sustained heavy damage resulting in heavy losses in
some years. For example, the Delta and Surrey areas alone suffered
$500,000 to $800,000 in crop losses in 1994. Wireworm populations
appear to be increasing each year and pose a serious threat to
B.C. farming sustainability.
Wireworms are the larval stage of click beetles. They live in
the soil for 3 to 6 years, depending on the species, where they
feed on plant roots and other organic material (we have even seen
them feeding on dead birds!). Their favourite habitat is grassland
or pasture, where populations can build up to enormous levels over
time. When pasture is replaced with another crop such as potato,
the wireworms left behind in the soil can cause severe damage for
for managing wireworms in plantings of strawberries and potatoes
are non-existent in BC since all previously registered
granular insecticides for wireworm control have been withdrawn
from use. Few new effective insecticides are expected to be registered
for wireworm control, therefore alternative control strategies
must be developed. To address this concern, a research program
was initiated at the Pacific Agri-Food Research Centre, in Agassiz
Potential For Using Trap Crops Several species of wireworms are
known to move through the soil toward pieces of plant roots or
germinating wheat; studies have also found that wireworms could
follow a CO2 gradient for distances up to 20 cm. Since wheat is
a preferred host of the two wireworm species, and CO2 is produced
by germinating wheat, we wanted to find out whether freshly sown
wheat could act as an effective trap crop.
were conducted in a farmer´s field in Agassiz, BC that
had been in pasture for over 10 years. It had been plowed the
previous year and had very high numbers of wireworms (A. obscurus).
First, we studied how wireworms move in the soil, both with and
without a trap crop present. Our studies confirmed that wireworm
populations are near the surface of the soil in April and May,
but move further down later in the summer. In the spring, the majority
of wireworms were actually within the top 8 cm (3 inches) of soil.
This means that we would expect trap crops to be more successful
at attracting wireworms in the spring months than in the summer
We also studied how wireworms move horizontally in the soil using
plots with rows of wheat, seeded 1 meter apart. These were compared
to control plots without any vegetation. The results showed that
the number of wireworms found in the wheat rows was significantly
higher than in the bare soil regions in between the wheat rows
during the first 3 sampling periods in the early spring. We estimated
that on May 23, from 68% to 80% of the resident wireworms in the
soil had moved to the wheat rows. The rest of the population would
have been in between the wheat rows, or further down in the soil.
The number of wireworms in the samples declined steadily after
this date, probably because they were beginning to move deeper
into the soil by this time. The results of these studies showed
that rows of wheat, planted one meter apart, will attract wireworms
from unplanted areas at least half a meter away.
To find out how much wheat seed should be sown in the rows we
also looked at rate of seeding in relation to wireworm attraction.
One week after planting, the number of wireworms aggregated at
the untreated wheat rows increased as the density of the wheat
increased. Doubling the seeding rate about doubled the number of
wireworms caught. Two weeks after seeding, however, there was no
significant difference between rows, probably because most of the
wheat in the untreated rows had been killed by wireworms by that
Our next step was to determine if wireworms aggregating in the
wheat rows could be killed there using wheat seed treated with
insecticide (i.e., Agrox DL plus or Vitavax Dual). In the treated
wheat after 1 week, the number of wireworms aggregated at the wheat
rows also increased with the density of the wheat planted. The
main difference, however, was in the ratio of dead to living wireworms
in these treatments. At the highest seeding rate there were more
dead than living wireworms.
Conclusions from these studies:
- In early Spring, between April and May, the majority of wireworms
in soil are near the surface, and it is at that time that trap
crops would be most effective. Trap crops planted after May and
as winter crops in the fall would likely not be as effective.
- In properly fallowed fields, most wireworms in the spring can
be lured to trap crops such as wheat. The number of wireworms
increases proportionally with increased number of wheat seeds
per foot of row. From the 1996 studies, an optimal seeding
density for a lethal trap crop of wheat will be about 4 treated
inch, with adjacent rows being about one half meter apart.
- Finally, the results indicate that once wireworms have aggregated
to a trap crop, they can be killed by insecticides used as
a seed treatment. It appears as though lethal trap crops
might be a less
expensive and possibly more effective method of reducing
Given the results of the studies described above, we have worked
out how trap crops could be used in agricultural systems. Trap
crops of wheat, for example, could be planted in advance of other
susceptible crops such as strawberries. The earlier planted wheat
rows would theoretically aggregate the wireworms and keep them
away from later planted crops. We have shown this is feasible by
planting wheat 1 week before we set out strawberries between the
rows of wheat. Wireworm populations aggregated at the wheat rows
and did not harm the strawberries. Unprotected strawberries, on
the other hand, sustained severe wireworm damage.
For field crops, such as potatoes, we are in the process of studying
the following procedure to significantly reduce wireworm populations
in a field before planting:
- The field
to be planted should be fallowed overwinter to ensure that
wireworms would not be distracted to other food sources in
- The lethal
wheat crop (i.e., seed treated with insecticide) would be planted
into fallow ground at least 10 days before
were planted. The wheat would then be destroyed. If this
an be done on more than one consecutive occasion prior to planting,
control would likely be improved.
Environmental Impact of Wireworm Pesticides:
Before 1970, the use of organochlorine (OC) insecticides such
as aldrin, heptachlor and chlordane was common. A single applications
of heptachlor to soil could control wireworms for more than 10
years. Unfortunately, many OCs were also quite persistent in the
environment, deleterious to certain wildlife species, and as a
result were eventually withdrawn from use. They were replaced in
the 1970s by other classes of insecticides, such as the carbamates
(i.e. carbofuran; aldicarb) and organophosphates (i.e., phorate,
terbufos and fonofos), which were shorter lived, but more toxic
than the OCs.
In recent years, the use of some of these insecticides has been
linked to mortalities in wild duck and geese populations as well
as eagles and hawks, especially in the Delta region. It is thought
that the problem originates with the use of certain granular materials
in the soil for control of wireworms and other insect pests of
potatoes. It is hypothesized that:
materials become exposed on the soil surface when potato rows
are opened at harvest,
- that ducks
eat the exposed granules later in the autumn when flooding
occurs in the fields,
- that they
become sick and die in the field, and
- that eagles
and other raptors eat the crop contents of the dead birds and
become sick or die.
One OP product,
phorate (Thimet) was associated with several eagle mortalities
in 1993 and 1994, and as a result was withdrawn rom use in B.C.
by the parent company. In a study presently underway by Agriculture
and Agri-Food Canada and the Canadian Wildlife Service, it has
been determined that insecticide residues do, in fact, persist
on the granular carriers of some insecticides long enough in
certain types of soil to pose a threat to wildlife. In another
study in 1996, it was determined that granular insecticides applied
in-furrow at planting can be brought to the surface at harvest
where they would be exposed.
Fatal Attraction" (from http://res2.agr.ca/parc-crapac/english/3electronic_publications/growidea/
giv5a/fatalwireworm.htm) Wireworms (inset), the voracious larvae
of click beetles, are quickly becoming the most troublesome insect
pests of many vegetable and small fruit crops in the Fraser Valley.
Conventional insecticides have not been reliable in controlling
wireworms, and for many crops there are no registered products
available. Recently PARC researchers discovered that wireworm
populations can be lured to migrate en masse through the soil
to rows of wheat
(below), sown as a trap crop between rows of a main crop. The
wireworms are attracted to the CO2 released by wheat at the germination
Once they reach the trap crop, the wireworms indulge their voracious
appetites, but are killed by an insecticide which was applied
to the wheat seed. This method reduces wireworms effectively
a fraction of the pesticide previously required.