モモアカアブラムシの色彩2型の発生消長と殺虫剤感受性について

Abstract

The winter population of Myzus persicae in a Chinese mustard field in Shiga contained a large proportion of red (R) aphids, whereas the proportion of yellow green (YG) aphids began to increase in spring. When R aphids were reared at 25°C, some YG progenies appeared at F2 generation and all aphids were found to be YG ones after 2 months. Very few YG progenies were produced in R colonies and no R progenies were produced in YG colonies when both the colonies were continuously reared at 15°C. A short period (4 to 8 days) of chilling treatment of YG aphids at 5°C was effective in producing R aphids in their F1 progenies reared at 25°C. The stage most sensitive to the chilling treatment was the fourth (final) instar. Adults and third instar nymphs were also sensitive, but younger nymphs died during the chilling treatment. The number of aphids per colony was greater in colonies from R parents than in those from YG ones in the winter field, but this tendency was reversed late in march. The growth of experimental populations was faster in clones from YG parents than in those from R ones under the high temperature of 25°C.When exposed to the low temperature of 5°C, most of YG adults died during the first 8 days, whereas most of R ones survived for more than 16 days. These facts suggest that the occurrence of two colour types in M. persicae is a kind of dimorphism adaptive to seasonal changes of the environment. When tested at 25°C, R aphids were 2 to 8 times as susceptible to 5 insecticides tested as YG aphids, though two insecticides, 2-(N, N-dimethylcarbamoyl)-4-isoxazolin-3-one and O, O-diethyl-S-(4-chloro-5-methyl-3-oxo-4-isoxazolin-2-ylmethyl) dithiophosphate, were quite effective against YG aphids.