کنه قرمز اروپایی red spider mite

6 اردیبهشت 1387 | بازدیدها: 2 116
Adult females are about 0.4 mm long (Plate 1); body oval, strongly convex and dark
red, with long setae arising from light-coloured pinacula. The male is similar to the
female only smaller. Eggs are orange/red and about 0.15 mm long. These hatch into
six legged larvae with an average length of 0.17 mm.
Panonychus ulmi over-winter as diapausing eggs laid on the bark of trees or smaller
branches and spurs (Figure 1). During a heavy infestation, areas of the bark may even
appear red due to the presence of many eggs (Plate 2). In local Bramley orchards,
eggs hatch from mid-April to the end of June depending on climatic conditions
(Cuthbertson, AGS, personal observation). On hatching, juvenile mites move to the
underside of the leaves and begin feeding. They reach maturity in approximately three
weeks after undergoing three moults. The number of generations per year varies
between regions, with up to five being usual for the south of England but the cooler
climate of Northern Ireland is likely to have fewer.
The mites feed on plant sap and unless they are crowded they will mostly be found
alongside the veins on the underside of the leaves. They puncture the plant cells with
their stylets and the contents are exuded due to turgor pressure. The depth reached by
the stylets is approximately 70-120 µm. Depth at which injury occurs is related to
length of the stylet, the feeding time and population density. Continuous feeding leads
to regular spots being formed and when these coalesce characteristic chlorotic areas
develop, often known as the ‘bronzing’ effect.
At high densities P. ulmi reduces the photosynthetic activity of leaves. This damage
can lead to current-year or second-year effects. Current-year damage, depending on
the timing, duration and severity, can reduce levels of foliar nitrogen, cause premature
leaf fall, reduce shoot growth and trunk diameter and most importantly lower fruit
yields. It can also adversely affect fruit quality, for example, size, skin colour, soluble
solids, titratable acids and firmness. Second-year effects of mite damage are reduced
bloom with consequent reductions in numbers of apples and yield.