Evolution of life-history patterns in the Phytoseiidae

Among mites that inhabit plants, the Phytoseiidae rank as being well studied with respect to their life-history patterns and capacity for population increase. The number of published papers on the Phytoseiidae (between 1950–1991) is not much less than that for economically important phytophagous mites; there are c. 150 papers on Phytoseiidae, compared to c. 200 for the Tetranychidae (phytophagous spider mites). The impetus to study life-history patterns in detail comes from the successful use of the Phytoseiidae as predators to control phytophagous mites on agricultural crops (Helle and Sabelis 1985a, 1985b). Fortunate as this abundance of Phytoseiidae literature may seem to anyone interested in studying life-history patterns, there is a danger that the range of species studied is biased towards phytoseiids that are successful predators of economically important plant mites. This would be a serious problem when research hypotheses merely emerge from comparisons among life-history data, but less so when hypotheses stem from more general considerations about the ecological conditions under which life histories may have evolved. Hence, the approach taken here is to formulate hypotheses independent of the actual life-history data. Support by the data does not mean that the hypotheses hold true, but merely that they are not rejected thus far. The data are only used to falsify hypotheses, and to stimulate thought on more precise hypotheses and more critical tests.