Laboratory experiments on a change in genetic structure with an increase of population density in the citrus red mite population, Panonychus citri (McGregor) (Acari : Tetranychidae)

A change in genetic structure with an increase of population density in Pan onychus citri was analyzed by laboratory experiments focusing on the inbree ding coefficient (F) and spatial distribution. Genotype frequencies of an e sterase locus, a-Est1, in F-1 females after mating in various population de nsities suggested that P. citri mated randomly. Adult females introduced to small citrus seedlings laid most eggs on the leaves on which they were set . The majority of immature offspring stayed on the leaves where they hatche d. Females with different home genotypes were introduced on leaves at the t op and bottom of seedlings separately. The inbreeding coefficients of the d eveloping populations were kept high for at least a month. A linear relatio nship was observed between mean density of adult females and F. From these results, we concluded that the aggregated egg production by adult females; and low dispersion rate in the immature stages strongly restricts hybridiza tion among breeding patches of this species.