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The bionomics and control of Argyrostagma niobe (Weym.) and Dasychira georgiana Fawc. (Lep., Lymantriidae) On black wattle in kenya
Published online by Cambridge University Press: 10 July 2009
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Argyrostagma niobe (Weym.) suddently appeared as a defoliator of wattle in 1955 in the Turbo area of Eldoret District, Kenya, and spread in this area and outbreaks also developed in two other isolated areas, at Sotik and on the Mimosa-Nandi Border. Study of the life-cycle, of which the various stages are described, revealed a number of causes of mortality of which the initially most promising for control were parasites and a predatory Pentatomid, Glypsus conspicuus (Westw.). None of these, however, increased greatly above their first recorded level of incidence and the population of A. niobe was eventually controlled by a naturally-occurring nuclear polyhedrosis. This disease was found to be transmissible in the laboratory by allowing larvae to feed on foliage sprayed with suspensions of polyhedŕa whilst an indication that this could also be done in the field was obtained in one experiment.
Chamical control presented a number of difficulties, the chief arising from insufficient dispersion of the spray through the canopy of tall trees and the failure of small droplets finally adopted consisted of an application of endrin applied at a rate of 2–4 oz. active ingredient per acre in 2 gall. diesolene. This was satisfactory when applied to yonug trees through a Micron sprayer, and to trees of all heights by aerial boom sprayers. This mathod of control is only suitable where complete elimination of a population is necessary, such as in a new outbreak area, as the costs are too high to permit frequent applications.
Dasychira georgiana Fawc. was recorded in small numbers at about the same time that A. niobe was first recorded, but the population did not build up to serious proportions. Its life cycle, of which the various stages are described, was broadly similar to that of A. niobe but natural agents of control, chiefly the pupal parasite Compsophorus fumosus (Morl.) (Ichneumonidae), were usually effective in keeping the population in check. The reason for the success of this parasite, as compared with those of A. niobe, is not known. The larvae were successfully controlled with the same endrin spray as was used for A. niobe.
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