Some observations on diapause in winter eggs of Panonychus ulmi (Koch) (Tetranychidae)

Abstract

Some observations are presented on factors influencing winter-egg laying density in autumn, and environmental requirements to break diapause of winter eggs in the European red mite, Panonychus ulmi (Koch), on apple. In our field trial, the presence of phytoseiid mites in the autumn had a decisive influence on the winter-egg density. Deltamethrin treatments eliminated the predatory mite, Amblyseius andersoni (Chant), and as a consequence the number of winter eggs increased. In untreated trees, phytoseiids reduced the winter-egg density in the same period. Chilling requirements to break diapause differ in eggs collected from two localities. In Valencia, the warmer region, only 70 days at 1 °C were needed to break diapause whereas in Lerida it took 90–100 days. The mean incubation time to hatch eggs decreased steadily with time after the cold requirements had been fulfilled. In our trial, the reduction in post-chilling incubation time seems to be independent of mite provenance or temperature (provided that the development threshold of 7°C is not reached). The longer time required to incubate eggs immediately after the completion of the cold treatment seems to be a final phase in the diapause development of this species.