Panonychus ulmi (Koch)

Taxonomic placing: Acari, Prostigmata, Tetranychoidea, Tetranychidae.

Common name: European red mite.

Geographical distribution: Wherever pome and stone fruits, and especially apples are grown.

Morphology: All tarsi carry a claw-like empodium with three pairs of ventrally-directed hairs. The red eggs of the European red mite are onion shaped with a stalk on their tops. The juveniles are green, whereas the adults are red and bear prominent dorsal setae set on whitish tubercles.

Host plants: The pest attacks more than 50 plant species, mostly Rosaceae, but also grape vines, walnut and others, including ornamentals.

Life history: During summer the mite completes a generation in a fortnight at 26°C and each female deposits about 40 summer eggs, mostly on the lower sides of young leaves. The adults, however, are evenly distributed on both sides. This mite is dispersed between trees by ballooning, floating on air streams by holding onto a web thread. Between countries it was probably dispersed on seedlings, root stock or even fruit. Pest populations are most numerous on apples during early summer, before being attacked by their natural enemies. In Israel the pest raises 8-9 annual generations, the populations peaking in late June, declining by August. Reproduction is arrhenotokous. By mid-summer the females begin to lay diapause eggs, covered by a protecting whitish waxy cover (thus different from the summer eggs), deposited on the bark and twigs, near spurs and within buds and the fruit. Shortening autumn days are the main signal that promotes the production of diapause eggs, but deterioration in food quality may also induce diapause eggs. Hgh temperatures can impede the production of diapause eggs. Larval emergence from these eggs in the coming spring depends on the temperatures that have accumulated above the threshold of development. Hatch of all eggs took place after the accumulation of 590 day-degrees. These data are needed to time the pest’s chemical control. Very high humidities during the period of egg hatch reduce the survival rates of the emerging larvae. Agricultural practices that improve tree health and growth, such as pruning and fertilizing, also promote the development of pest population.

Economic importance: The pest, which invaded the Middle East in the 1950’s, infests many deciduous fruit trees in most parts of the world. It is a major pest of apple and sometimes also of pears. The feeding of the mites reduces chlorophyll contents and photosynthetic rates. The resulting silvery spots on the leaves fuse to form wide-spread stippling; the associated foliage russetting (or “bronzing” is due to the mites’ excretions. Heavy infestations result in leaf drop and small, low-quality fruit. When such infestations occur during May to June, fruit size is reduced; if most damage takes place later in the season, the next year’s yield would be affected. Pest effect on apple yield (quantity and quality) depends on the affected cultivar, and is greater when the trees are suffering from water stress. In the Middle East P. ulmi affects mainly apples, whereas in southern Europe it is a major pest of grapes.

Management

Sampling: Similar numbers of females occur on both sides of apple leaves, and there is a good fit between number of females on leaves and the size of the mite population thereon. Thus counting females on the upper side of apple leaves provides a reliable estimate of the size of the population. Samples should be taken from all sides of the trees, because much larger mite populations were found on the southern and eastern aspects of apple trees as compared to the north and west. The mites prefer certain apple cultivars (e.g. Delicious, Orleans) over others (Grand, Golden Delicious),which could affect sampling results.

Plant resistance: Apple cultivars with almost smooth leaves carry fewer mites than setose cultivars, a trait that has served as a basis for selecting pest-resistant trees. However, chemical leaf components may also be involved.

Technical control: Mite eggs on fruit that is being kept in storage or meant for export may be killed by an exposure to atmospheres of enhanced carbon dioxide and reduced oxygen.

Chemical control: The pest’s larvae and young nymphs are quite susceptible to pesticides, thus spraying in the spring, as the diapause eggs are hatching, would give best results. To obtain suitable data twigs may be kept in a covered shed in the field and egg hatching observed until approximately half had emerged, which would be the best time for spraying. It is often recommended that chemical sprayss should not be initiated before the mite has accumulated 150 ACMDs. The pest may be controlled with many acaricides, but has developed much resistance to most pesticides. Avermectins and propargite provided good mite control in Syria. Pyrethroids encourage outbreaks of the European red mite.

Biological control: European red mite is usually maintained below its economic injury level by natural enemies; there is evidence that pest outbreaks often follow the application of indiscriminate pesticides. This suggests that the careful use of selective pesticides, which do not harm the natural enemies, would be the key to European red mite management. Abroad the pest is controlled by various Phytoseiidae. In Israel the mite is often kept below its economic injury threshold by endemic predators, especially Typhlodromus athiasae Porath and Swirski. Species of the coccinellid Stethorus sp. also kill the pest, although this predator often arrives after the pest has already caused much damage. The entomopathogenic fungus Beauveria bassiana (Balsamo) caused over 80% mite mortality in Egypt.

References

Abd El-Wahed, N.M. El-Sayed, K.M. and El-Ghobashy, M.S. 2011. Biological control of the European red mite, Panonychus ulmi (Koch) using the predatory mite, Neoseiulus cucumeris (Oud.) on apple trees. Egyptian Journal of Agricultural Research 89: 951-958.

Afifi, Abd-Allah M., Mabrouk, A.M. and Asran, A.A. 2010. Effect of the entomopathogenic fungus Beauveria bassiana on three acarine pests. Trends in Acarology 439-440

Bond, E.J. and Herne, D.H.C. 1983. The potential of carbon dioxide and low-oxygen atmospheres for control of winter eggs of the European red mite, Panonychus ulmi (Acari: Tetranychidae), on harvested apples. Proceedings of the Entomological Society of Ontario 114: 11-14.

Gerson, U. and Cohen, E. 1989. Resurgences of spider mites (Acari: Tetranychidae) induced by synthetic pyrethroids. Experimental and Applied Acarology 6: 29-46.

Goonewardene, H.F., Williams, E.B., Kwolek, W.F. and Mccabe, L.D. 1976. Resistance to European red mite, Panonychus ulmi (Koch), in apple. Journal of the American Society for Horticultural Science 101: 532-537.

Halloum, M. and Qerhaili, S. 2008. Toxicity of propargite and abamectin to Tetranychus urticae Koch and Panonychus ulmi Koch (Acari: Tetranychidae) and the predatory mite Amblyseius spp. Acari: Phytoseiidae) in Apple orchards. Tishreen University Journal for Research and Scientific Studies - Biological Sciences. Series 30, No. 2.

Jeppson, L.R., Keifer, H. and Baker, E.W. 1975. Mites Injurious to Economic Plants. University of California Press.

Palevsky, E., Oppenheim, D., Reuveny, H. and Gerson, U. 1996. Impact of European red mite on Golden Delicious and Oregon Spur apples in Israel. Experimental and Applied Acarology 20: 343-354.

Shahar, Z. 1985. Studies on the biology and ecology of the European red mite Panonychus ulmi (Koch) (Acari: Tetranychidae) in apple orchards of Upper Galilee. M.Sc. dissertation, Faculty of Agriculture, Hebrew university of Jerusalem, Rehovot, Israel. (In Hebrew, with English Abstract).

Websites: http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=290