Effects of inbreeding on variation in diapause duration and early fecundity in the Kanzawa spider mite

In arthropods, both diapause duration and ability to produce eggs in early adult life (early fecundity) are important life‐history traits for successful settling in a new habitat. In herbivorous spider mites (Acari: Tetranychidae), inbreeding frequently occurs because new colonies are established by only one or a few females. In the present study, we investigated the impact of inbreeding on the phenotypic variance in diapause duration and early fecundity in the Kanzawa spider mite, Tetranychus kanzawai Kishida. Diapause duration was compared between the inbreeding treatment (strongly inbred strains) and the control (strains immediately taken from the stock culture) under winter‐mimicking laboratory conditions. The variance in diapause duration was smaller in the inbreeding treatment than in the control, though the magnitude of decrease of variance was less than expected. On the other hand, early fecundity did not show any reduction of variance. The present results revealed that inbreeding reduces phenotypic variation, as expected in theory.