1979 Volume 4 Issue 3 Pages 337-344
The pattern of increase or decrease of dicofol-resistance in the citrus red mite, Panonychus citri (McG.), was different from those obtained with other acaricides. It was often observed under field conditions that dicofol-resistance of P. citri increased gradually by selection with dicofol, but decreased relatively quickly by relaxation of the selection. To analyze such a pattern, the changes of susceptibility of mite populations to dicofol and the genetic basis of resistance were studied.
Natural populations of mite were collected from Tanushimaru, Fukuoka-ken, in August, 1969, and from Yoshii, Fukuoka-ken, in August, 1971, respectively. The initial population was divided into two populations, one population was selected with dicofol and another population was reared without selection. Mites were reared on young citrus trees at 25°C for 2.5-3 years. The dicofol susceptibility of eggs in the selected populations decreased considerably, but its decreasing pattern was complicated. On the other hand, the susceptibility of eggs in the unselected populations increased remarkably after 13 or 23 months (about 33 or 58 generations).
Dicofol-resistant strain selected from Yoshii population, and a susceptible strain of Ogi population collected from Saga-ken, were crossed. The susceptibilities of F1 and B1 adult females were compared with each other by using log concentration-probit mortality lines and curve. No remarkable differences were found between both susceptibilities of reciprocal crosses, but these susceptibilities of hybrid adult females were fairly higher than the average level of both resistant and susceptible parental strains. Thus, it was suggested that dicofol-resistance would be manifested as a recessive character. In the results of backcross series, the observed log concentration-probit mortality curve fitted well with the expected one, based on a hypothesis that one major gene was responsible for the resistance to dicofol.
