Development and harmfulness of the cabbage moth (Plutella xylostella (L.); Lepidoptera, Plutellidae) on the spring rape crops in Leningrad province

Abstract

Results of the long term research have shown that the cabbage moth causes a serious threat to spring rape plantings in Leningrad Province. During the last decade, there were several cases of mass reproduction of this species when high population density of the insect and heavy injury to the rape leaves and buds were recorded. Mass reproduction of the moth was observed in the early and warm spring, when the plantings were infested by the butter ies earlier and simultaneously, and the caterpillars were feeding on rape plants at the initial stages of their development that strongly reduced the crop yield. The situation was getting worse on rape that was sown late and was also damaged earlier by Phyllotreta ea beetles, and in the hot, dry weather. The crop yield of spring rape was decreased from damage caused by caterpillars according to the data averaged over the entire period of research by 4.7% (0.65 centner∙ha-1), in the years of mass reproduction, by 84%, and in the years of low population, by 2.5%. The harmfulness of cabbage moth caterpillars increased by 2.3 and 4.5 times when leaf area was damaged by 26-50% and more than 50%, respectively, as compared to when damage was low and not exceeding 25%. Application of full dose of mineral fertilizers decreased injury to the leaves and buds by cabbage moth caterpillars and harm caused to spring rape due to a higher plant potential to recover from the damage in icted.