Sampling Dormant Apple Twigs to Estimate the Density of Eggs of the European Red Mite

When the overwintering eggs of European red mite, Panonychus ulmi (Koch), were recorded according to their location at or near nodes of randomly collected apple (var. Red Delicious) twigs: (a) the logarithms of the egg counts provided the most useful measurement for studying the infestation; (b) the total number of eggs, i.e., colored plus uncolored, was the most satisfactory unit to use in the log transformation; (c) the ratio of colored to uncolored eggs was 1.27 at the time of sampling; and, (d) the ratio of colored to uncolored eggs varied between Red Delicious twigs (ranging from 1–7 depending on the twig). A formula was developed for comparing the degree of mite, infestation of apple cultivars. The best and most consistent results were obtained when 13 nodes above and 8 nodes below the budscale scar were sampled. Precision can be improved by increasing the number of twigs sampled.