Abstract:A population of the predatory miteAmblyseius aberras(Oud.) (Acarina, Phytoseiidae) was reared onVitis viniferavar. Perera plants in the absence of prey. During summer 1993 samples of leaves were collected on 29 different dates. The number of phytoseiids per leaf was positively correlated with the leaf area. The regression coefficient between the variables is significantly different from zero. Nevertheless, when population density is indicated as mites/leaf, the error is too small to affect analysis of data. During the season the growth rate of populations fluctuated between −0.15 and +0.57 mites/mite × day. The ovipositional rate assumed values between 0.005 and 0.17 eggs/female × day. The unit of measurement employed to represent the population density appeared to be relevant in some biological studies. The increase in the number of adults per cm2of leaf surface is correlated with a decrease in the ratios juvenile/adults and eggs/adults suggesting the existence of a self‐regulating mechanism of fecundity or survival inA. abe