Transactions of RHASS Volume 1940 - Page 052
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| Year | 1940 |
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92 INSECT AND OTHER rEsTs on 1939. baits to infested ground have been discovered, but, unfor- tunately, the same cannot be said for VVireworms. Whilst recent research has served to extend our knowledge of their habits, it has to be admitted that there has not yet materialised a direct method of controlling their destructive activities which is at once economical and effective. in recent years, 15. Fig. 3,—7'100 common Click Beet/cs ofyrass [and and cultivated land. A, Athous lizemorrhoidalis; B, Agriotes obscurus. X 6. From nature. both in America and Britain, experiments with baits for attracting and assembling Wireworms previous to their destruction by the application of soil fumigants have been carried out, but inconsistency of results, combined with the high cost of treatment, renders the adoption of the method impractical, except perhaps under the intensive system of cropping in market gardening. INSECT AND OTHER PESTS on 1939. Among insect pests Wirewornis are notable because of the prolongation of the period of theirdevelopment. Altogether they spend about five years in the soil before transformmg to the adult (‘lick Beetle, which returns to grass land or weedy fallow to lay its eggs. Thus infestation of cultivated ground by Wireworms is not attributable to causes immediately connected with the current year’s crop, but harks back to the time when the ground was covered by grass. As one crop succeeds another in the rotation a progressive annual diminution occurs in the density of the wireworm population. This is explained by the fact that the wireworm population of the original grass land is composed of individuals of all ages from less than one up to five years, and each year a certain percentage completes its development and departs as beetles. Nevertheless, the normal density of a wireworm population is such that an infested crop may suffer severe damage any time up to three years after grass land has been broken. With a few exceptions crops of all kinds are liable to attack, and the degree of damage varies roughly with the density of the wireworm population, when it exceeds 200,000 per acre, or about forty per square yard, which is considered by Roebuck 1 the threshold of safety. By the usc'of a refined technique in sampling infested soils, whereby contained insects are floated to the surface of a solution of 25 per cent magnesium sulphate, Ladell 2 obtained counts of as many two to three million VVireworms per acre in patches throughout a field. To make an estimate of the wireworm population of a field, samples of soil six inches square and five to six inches deep are selected at random and carefully examined for Wireworms. Because of the lack of uniformity in their distri- bution the number of VVireworms per sample varies greatly, and thus the accuracy of the estimate will depend on the number of samples of soil examined. Life-history—Thanks to the researches of Bymer Roberts 3 the life—cycle of the species of Wireworms of arable crops is fairly well known. As farmers are aware, VVireworms are the larvae of Click Beetles, which are brown or blackish insects (Fig. 3). Because of their shy retiring habits the beetles are not so commonly encountered as are their larvae, which are often brought to the surface in numbers when infested land is ploughed or otherwise cultivated. The female beetle lays her eggs just beneath the surface of the soil, and in 1 Roebuck, A., 1924. “ Destruction of \Vireworms.” Jour. Min. Agric., V01. XXX., pp. 1047-1051. 2 Ladell, W. R. S., 1938. “ Field Experiments on the Control of VVireWorms.” Ann. App. Biol., Vol. XXV., N0. 2, pp. 341-389. 3 Rymer Roberts, A. \V., 1920-1928. “On the Life History of \Vireworms of the Genus Agriotes, Esch. With some notes on that of Athens hwmorrhoz’dalis F.” Parts I.-IV. Ann. App. Biol., Vols. VI., VIII., IX., XV. |
| Title | Transactions of RHASS Volume 1940 - Page 052 |
