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European red life-cycle

COLLYER, E. 1974: European red mite, ulmi (Koch), life-cycle. DSIR Information Series No. 105/5 ISSN 0077-9636 Identification be laid in both the calyx and stalk ends of the fruit (see photo), making them unacceptable for All stages of the European red mite are red, dis­ the export market, or the fruit may be somewhat tinguishing it from the ubiquitous two-sl?otte_d undersized and fail to colour up normally. mite, Tetranychus urticae. The adult mite is minute; females are the largest and are only 0.4 mm in diameter, but their bright red colour makes them just visible to the naked eye. It ov~r­ Distribution winters as dormant, onion-shaped, red eggs, which It occurs throughout the country, being most are laid on the under surface of branches and twigs prevalent in the drier areas. of trees. The eggs have a characteristic dorsal spine, are 0.15 mm in diamet7r, and are sm:iller than those of Bryobia rubrioculus (sometimes known as the brown mite) which are laid in similar Life-cycle situations and are spineless. The European red The winter eggs hatch during late September and mite is very similar to the citrus red mite in all October, and a series of overlapping generations stages, but the latter mite occurs only on Citrus follow, summer eggs being laid on the leaf surface, and a few other evergreens and does not have the throughout the summer, until either damage to the dormant winter egg stage of the former, which is leaves or the decreasing day length leads to the adapted to deciduous trees. When a heavy infe_s­ onset of winter egg-laying. There are from five to tation of has occurred in mid to late sum­ seven generations during the summer, each gener­ mer, sufficient winter eggs may be deposited to ation extending over approximately one month, make the branches and twigs appear red on the depending on temperatures. undersides (see photos).

E. COLLYER Host plants This most often inhabits orchard trees of the family Rosaceae; , plum, pear, , and cherry are common hosts. It may also occur on , walnut, currant, gooseberry, raspberry, elm, , and mountain ash, and also on ornamen­ tal trees and shrubs of the genera Prunus, Sorbus, and Ribes.

Damage The main damage to the host results from the feeding behaviour of the mites. All stages feed on the lower surface of the leaves (see photo), by inserting their needle-like stylets [piercing mouth­ parts] through the epidermis [surface layer] , and draining the content from the inner leaf cells, which then collapse and die (see photos). At first the leaves become pale speckled along the mid and lateral veins, then discoloured over the whole sur­ face and eventually brown or bronzed (see photo). The leaves then either remain dried and brittle on the tree, or they may be shed. If drain~ng of chlorophyll from the leaves occurs early m t11:e season, it may have a detrimental effect or;i fnnt bud formation and thus affect the crop m the succeeding year. As the leaves become brown: the mites start to lay winter eggs. Although direct damage to the fruit rarely occurs, winter eggs can

Department of Scientific and Industrial Research, Wellington, New Zealand. 1974. Information Series No. 105/5 EUROPEAN RED MITE (Panonychus ulmi) LIFE-CYCLE

0 EGGS ADULT MITES TREE DAMAGE Printed by N.Z.N. Commercial Printing Division under the authority of A. R. Shearer, Government Printer, Wellington, N.Z.