| Summary: | Wireworms, the larvae of the Elateridae, are among the most
common and widely distributed pests of cultivated crops. They have
undoubtedly caused some losses from the earliest days of agriculture,
since their importance has been recognized from the beginning of economic
entomology. Several species of Elaterids are injurious to crops; scarcely
any plant species being immune; while cereals and vegetables are
most susceptible. the crop in some cases is a total loss, although usually
the damage is moderate, and is often ascribed either to other causes or
overlooked entirely.
Losses caused by wireworms in Western Canada occur yearly in the
same field, since the larvae spend several years in the soil. the direct
loss of plants killed or injured is augmented by weed growth favored by
the thinning of the crop. These increase the cost of production, and
depreciate the value of the land. Thomas (1930) states that the
depreciation in value of Carolina farm land, as a ruslt of wireworm
depredations, has been estimated conservatively at over a Million Dollars.
In Saskatchewan, wireworms reduced the yield of field crops by 1.71%
during the period 1926-1930, and caused an average annual net loss of
$3,274.000 to farmers. (Estimates of Damage 1930, Dom. Ent. Lab.
Saskatoon Tech. report, 1930.)
Observations in this province indicate that wireworms are most
troublesome in older cultivated fields. The wireworm problem is therefore
becoming more important and more accurate information about the
injurious species and their ecological requirements and relationships
must be gathered, if lasting and effective control measures are to be
perfected.
Various recommendations for the control of wireworms have been
made; some being based on field observations, while others are more or
less theoretical and without experimental proof. Poisons and other seed
treatments have proved ineffective; sterilizing the soil and "baits",
too costly for field crops. Hence practical control measures are limited
to modifications of those factors affecting wireworm damage so as to
favor the plant more than the wireworm.
Of the several species of wireworms occurring in cultivated
fields in Saskatchewan, so far as know, only two are of general
economic importance, the others being of more local or of no importance.
Ludiusaereipennis
tinctus.
Leconte; the most injurious species, and Cryptohypnus
nocturnus Eschscholtz,
second in importance, occur widely,
the former causing about four-fifths, the latter one-fifth of the damage
to field crops. (King '28). Although both species are usually found
together, they appear to differ somewhat in their requirements and
activities.
Since the immature stages of C.
nocturnus have never been
described, a study of the external morphology was undertaken and is
presented in the first main division of this report. In spite of the
well known fact that temperature and moisture conditions affect the
activities of soil fauna, as well as plant growth, little, if any, work
has ever been done to determine the influence of these factors on
injury to plants by soil insects. Consequently, a study of some phases
of this problem, chiefly the relation of sil moisture to damage, was
unertaken and is presented in the second section.
The study of the influence of moisture conditions has
proved very interesting and indicates possibilities for much further
work. The work done in the present study is only a small fraction of
what might be accomplished, especially in combination with controlled
temperatures. It is hoped that this phase of the work can be studied in
great detail when better equipment is available.
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