A morphological study of some of the immature stages of Cryptohypnus nocturnus eschscholtz, and a study of some ecological factors concerning wireworms : a preliminary study
Arnason, Arni Pall
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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.