Development Times Under Long- and Short-Day Conditions in the Kanzawa Spider Mite Tetranychus kanzawai (Acari: Tetranychidae)

Abstract

In a theoretical framework, the development time of arthropods is closely associated with population growth, so that strong selection pressure may be imposed on development patterns. In this context, selection towards shorter development times may act on female mites in the season when population size is growing. In contrast, such selective pressure may be weaker just before hibernation, because the stage adjustment may be more important than population growth in such seasons. Thus, selection to shorten development times may act more strongly in long daylength conditions, so that different developmental responses among the seasons (reaction norm) may evolve. I predicted that the development time is shorter under the long-day conditions of population-growing seasons than under the short-day conditions of hibernating seasons, and that genetic variation at the long-day is smaller than that at the short-day. In order to test this prediction, the egg-to-adult development time of a population of Tetranychus kanzawai (Acari: Tetranychidae) was investigated under short (9L:15D) and long (15L:9D) daylength conditions at 18 degrees C. In addition, genetic variation in female development times under these conditions was estimated by using half-sib design. The development time of females at short day was 1 day longer than at long day under the experimental conditions. Male development times follow the pattern of females with <1 day delay. However, heritabilities under these two treatments were quite low and neither was significant. Thus, only the first prediction was supported by the results. In addition, maternal and/or non-additive effects in the female development time were highly significant under both daylength conditions examined.

Effect of photoperiod on immature development and diapause induction in the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)

“…In TSSMs, Suzuki and Takeda (2009) reported that the developmental period for the deutonymphal stage seemed to be influenced by metabolic suppression related to diapause induction. Ito (2005) reported that the developmental period for immature stages of KSMs was shorter during seasons of population growth (i.e. long light period) than during the hibernation season (i.e.…”

“…The delay was probably due to metabolic suppression related to diapause-inducing stimuli. Ito (2005) reported that the developmental period for the total immature stages of KSM was affected by photoperiod. However, the developmental periods for larval, protonymphal and deutonymphal stages of KSMs has not been examined under various combinations of light and dark periods.…”

Does artificial selection on diapause incidence cause correlational changes in other life‐history traits? Case study in a spider mite population

“…This might be due to differences in life cycles between spider mites and other arthropods. The spider mite generally may be under strong directional selection for short development time (r‐selected species; Saito, 1985; Sabelis, 1985), as supported by the absence of significant genetic variation in development time in this population (Ito, 2005). On the other hand, diapause induction may be under stabilizing selection for initiating diapause at an appropriate seasonal time.…”