Life-style classification of some Phytoseiidae (Acari: Mesostigmata) species based on gnathosoma morphometrics

Abstract

Life style of phytoseiid species (Acari: Mesostigmata) is an important feature in evaluating their potential as biological control agents. Previous studies suggested that some morphometrics of gnathosoma are related to the feeding habits of phytoseiids. In this study, we showed it is appropriate to estimate feeding habits and/or life styles of phytoseiids based on variations in gnathosoma morphology. Scanning electron microscope pictures of 10 phytoseiid species belonging to four major life styles were taken. For each species, 23 morphometrics of gnathosoma and the length of dorsal shield were measured. Principle Component Analysis (PCA) showed that the 10 species can be divided into three groups based on the first two principle components of these parameters. The 1st group includes one specialized predators of Tetranychus species (Phytoseiulus persimilis) and two selective predators of tetranychid mites (Neoseiulus pseudolongispinosus, Neoseiulus californicus), the 2nd group includes six generalist predators (Amblyseius orientalis, Amblyseius swirskii, Amblyseius tsugawai, Neoseiulus barkeri, Neoseiulus bicaudus, Neoseiulus cucumeris), and the 3rd group includes one specialized pollen feeder (Euseius utilis). This grouping is consistent with the life style division of McMurtry & Croft (1997), except that Type I and II were not separated. However, there is a trend that both Type II species were closer to each other. Overall, species in Group II have larger chelicerae and hypostome than those of Group I and III, while species in Group III have larger lobes and angle of fixed digit than those of the other two groups.