HortFACT
European Red Mite Life Cycle


COLLYER, E. 1984: European Red Mite, Panonychus ulmi (Koch)

Identification
All life stages of the European red mite are red, distinguishing it from the ubiquitous two-spotted mite, Tetranychus urticae. It overwinters as dormant, onion-shaped, bright red eggs laid in dense clusters on the undersurface of branches and twigs of trees. These hatch into six-legged larvae which develop through two nymphal stages to become adult.
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. Females lay summer eggs on the leaves until autumn. The eggs have a characteristic dorsal spine, are 0.15 mm in diameter, and are slightly smaller and more orange than the winter eggs. They are also smaller than the eggs of Bryobia rubrioculus (sometimes known as the brown mite), which are laid in similar situations and are spineless.
The European red mite is very similar to the citrus red mite all stages, but the latter mite occurs only on Citrus and a few other evergreens and does not have the dormant winter egg stage of the former, which is adapted to deciduous trees. When a heavy infestation of mites has occurred in mid to late summer, sufficient winter eggs may be deposited to make the branches and twigs appear red on the undersides.

Host plants
This species most often inhabits orchard trees of the family Rosaceae; apple, plum, pear, peach, and cherry are common hosts. It may also occur on almond, walnut, currant, gooseberry, raspberry elm, oak, and mountain ash, and also on ornamental trees and shrubs of the genera Prunus, SorbusandRibes.

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 by inserting their needle-like stylets [piercing mouth parts] through the epidermis [surface layer] and draining the contents from the inner leaf cells, which then collapse and die. At first the leaves become pale-speckled along the mid and lateral veins, then discoloured over the whole surface, and eventually brown or bronzed. The leaves then either remain dried and brittle on the tree, or they may be shed. If draining of chlorophyll from the leaves occurs early in the season, it may have a detrimental effect on fruit bud formation and thus affect the crop in 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 be laid in both the calyx and stalk ends of the fruit, making it unacceptable for the export market or the fruit may be somewhat undersized and fail to colour up normally.

Distribution
This mite occurs throughout the country, being most prevalent in the drier areas.

Life cycle

Egg
Immature
Nymphs
Nymphs
Adult
Month
Note: Coloured bars indicate periods of peak activity in each of the life cycle stages

The winter eggs hatch during late September and October, and a series of overlapping generations follow, summer eggs being laid on the leaf surface, throughout the summer, until either damage to the leaves or decreasing day length leads to the onset of winter egg-laying. There are from five to seven generations during the summer, each generation extending over approximately one month, depending on temperatures.

E.COLLYER

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