While solar energy accelerates egg development in poikilothermic arthropods via temperature, solar ultraviolet B (UVB) and radiant heat are harmful to mite eggs laid on the upper surfaces of plant leaves. Brevipalpus obovatus, an herbivorous mite, occurs on Viburnum erosum var. punctatum (VEP: a deciduous shrub) only in autumn; one third of the eggs were laid on the upper leaf surfaces. Oviposition on upper leaf surface is beneficial for avoiding phytoseiids, a predator that usually forages on the lower surface. At the same time, it increases the risk of sunlight exposure. Solar UVB intensity reaches the annual maximum in early summer, whereas temperature does in August in Kyoto. We hypothesized such a phase lag is responsible for the autumn-limited occurrence of B. obovatus, and tested egg hatchability under near-ambient and UV-attenuated sunlight conditions from May to October 2012. Hatching success depended on both of the cumulative UVB dose and the mean daily maximum temperature during egg period. A resultant model showed two survivability peaks, which was higher in October (hatchability = 0.55) than that in May (0.35), meaning that temperature (radiant heat) and UVB interactively determine the seasonal existence of B. obovatus on VEP.