The occurrence of the alfalfa weevil Hypera postica (Gyllenhal) after estivation and optimum time to control adults
2010
Hayashikawa, S., Kagoshima-ken. Inst. for Agricultural Development, Minamisatsuma (Japan) | Takesaki, K. | Nishioka, T.
The alfalfa weevil Hypera postica (Gyllenhal) causes damage for Chinese milk vetch and pastures of Leguminosae. Chinese milk vetch is severely damaged, because its flowering stage is usually coinciding with the larval occurrence. To effectively control eggs and larvae population, we must target the adult weevil. We investigated the optimum timing for such control based on weevil departure from the estivation site, invasion into Chinese milk vetch, and ovary development. Oviposition and ovary development began in late November. The invasion into fields began in mid-November and peaked from late November to early December. The oviposition appeared to begin from late November, because its ovary started to develop just after the invasion. Of the three insecticide applications (in early December, early January, and early February), only the early December application was effective at reducing the number of eggs and larvae. Thus, the optimum time to apply insecticide against alfalfa weevils was early December, coinciding with the peak of invasion and the start of oviposition.
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