oa Journal of the Entomological Society of Southern Africa - The inadequacy of egg counts as indicators of threshold levels for control of Heliothis armigera on cotton
In 1977-78 to 1979-80, eggs of H. armigera (Hï¿½bner) were collected regularly from cotton at two sites in the Transvaal and the percentage that hatched was determined. This varied greatly from week to week (extremes about 30 to 98%), mainly because of changes in parasitism. Other work showed that there was an equally variable incidence of mortality among young larvae. Thus, egg counts are poor indicators of numbers of mature larvae, and threshold levels based on such counts lead to excessive spray applications. It is suggested that counts of mature larvae should be used instead.
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