The prey-stage preferences of Amblyseius swirskii Athias-Henriot and Neoseiulus californicus (McGregor) (Mesostigmata: Phytoseiidae), between egg and nymph stages of Tetranychus urticae Koch (Trombidiformes: Tetranychidae)

Tetranychus urticae Koch (Trombidiformes: Tetranychidae), two-spotted spider mite, is a pest mite species that feed on a wide range of plants around the world. Neoseiulus californicus (McGregor) (Mesostigmata: Phytoseiidae) is shown as a predatory mite to be a very efficient biological control agent of T. urticae. Amblyseius swirskii Athias-Henriot (Mesostigmata: Phytoseiidae) is another phytoseiid mite species which can feed and reproduce on a wide range of food sources, including T. urticae. Information about the prey stage preference of a predator is valuable for evaluations of the potential of predatory mites to control of pests. We therefore analyzed the prey-stage preferences of A. swirskii and N. californicus to eggs and nymphs of T. urticae at 15:15, 10:20, and 20:10 egg: nymph ratios under controlled conditions (25±1 °C, 65±5% RH and 16-h light: 8-h dark photoperiod). The experiment was carried out on abaxial surfaces of bean leaf discs with a diameter of 2 cm. Starved (for 24 h), 2-3 days-old gravid females of A. swirskii and N. californicus were used in the experiment. One predatory mite was placed individually on each bean leaf disc infested with 15:15, 10:20 and 20:10 ratios of T. urticae egg: nymph. After 24 h of feeding, the numbers of prey consumed for each prey stage were recorded. From the results, it is clear that while N. californicus showed no preference between egg and nymphs of T. urticae. A. swirskii preferred nymphs to eggs of T. urticae