The relationship between winter egg counts of the European red mite Panonychus ulmi (Acari: Tetranychidae) and its summer abundance in a reduced spray orchard

Abstract

We studied the relationship between counts of Panonychus ulmi (Koch) winter eggs per bud and mite-days per leaf accumulated in early to mid-summer on 92-96 apple trees in an orchard in Quebec, Canada. Stepwise regression was used to compute mite-days in the 4 year (1992-1995) data set using winter egg density, cumulative rainfall (R), cumulative degree-days (D), squared values of R and of D, and the product RD as potential predictors. Degree-days were accumulated above 10.1 degrees C, the minimum threshold of development for P. ulmi in Eastern Canada. The 4-year model that gave the best fit included terms for winter eggs, rainfall, R2, and the product RD, and explained 76% of the variation in mite-days. When the 4-year model was applied to each year's data separately, winter eggs, adjusted for current year rainfall and degree-days, were always highly significant predictors of mite-days. These significant effects of weather indicate that estimation of potential economic loss should take account of rainfall and heat units, as well as the density of winter eggs. Predators, including the stigmaeid, Agistemus fleschneri Summers, and occasional low numbers of phytoseiids, did not have any evident within-season effect on mite-days but their appearance in July-September of 1994 was followed by a ten-fold decrease in the mean density of winter eggs in 1995 compared with the previous spring. This reduction contrasted with increasing densities each successive spring from 1992 to 1994, which followed summers when predators were scarce or absent.

Influence of abiotic factors on diapause termination and temperature requirements for postdiapause development in the European red mite, Panonychus ulmi (Acari: Tetranychidae)

“…These range of values are within the values previously reported for P. ulmi that established the temperature threshold between 5 and 7 ºC (Lees 1953;Cranham, 1971Cranham, , 1972Herbert and McRae 1982). Only Bostanian et al (2007) obtained a temperature threshold of 10.1 ºC using data collected by Herbert (1981); which is a value above the rest of the studies. This may likely be due to differences in methodological approaches as the temperature range for Herbert (1981) was based on data from (15-21 ºC) while in the other studies such that of Herbert and McRae (1982), a broader range was applied (8-20 ºC) allowing for a more precise estimation of the temperature threshold.…”

Studies on Potential Pests of Japanese Quince (Chaenomeles japonica (Thunb.) Lindl. ex Spach) in Latvia

“…ex Spach) in Latvia Jānis Gailis, Inta Jakobija, Edīte Jakobsone, Laura Ozoliņa-Pole, Regīna Rancāne, Ineta Salmane economically important pest of various cultivated plants in many places. Among its host plants are apple trees, plums, cherries, vines, mulberries and others (Bostanian et al, 2007;Dar, Rao & Ramegowda, 2016;Gottwald, 2016;Gravite & Kaufmane, 2013;Kasap & Atlihan, 2021;Mendonça et al, 2011). However, for now, there is reason to believe that Japanese quince may not be a suitable host plant for this mite.…”