Eutetranychus orientalis (Klein)
Taxonomic placing: Acari, Prostigmata, Tetranychoidea, Tetranychidae.
Common name: Oriental spider mite, citrus brown mite.
Geographical distribution: The oriental spider mite occurs in the eastern Mediterranean countries, in Asia from India to China and in most of Africa.
Host plants: The oriental spider mite may develop on over two hundred host plants, mostly dicotyledons.
Morphology: The adult female is about 0.4-0.5 mm in length, brownish, with a oval body and legs that are about as long as the body.
Figure 1: A colony of Eutetranychus orientalis on a citrus leaf
The male is reddish, smaller, its hysteronotum is pointed and the legs are longer than the body. The dorsal setae are short, spatulate and placed on small tubercles. The rounded eggs are pale-brown.
Life history: The mites colonize the upper side of leaves whereon their eggs are deposited along the midrib. The threshold of development is at 10°C and development requires about two weeks at around 25°C. Each female produces 30-40 eggs during two-three weeks. The pest raises about 20 annual, largely overlapping generations. The Oriental spider mite is arrhenotokous, its sex ratio is usually 0.7, female-biased.
Economic importance: The oriental spider mite is an important pest of citrus, especially in drier areas. It is the most persistent citrus pest in Upper Egypt and an occasional serious pest in the south of Israel. The mites colonize the upper side of leaves where they feed, and their damage develops as yellow-grey stippled spots which cause leaf wilting and drop. Heavy infestations can cause fruit drop and the death of upper branches, and next-years’ blossoming may be severely affected. Reduced irrigation increases the damage. Lemon trees are more damaged than other citrus species and varieties, whereas oranges are little affected.
Management
Chemical control: The oriental spider mite has not yet developed resistance to pesticides. Thus it may still be be controlled by commonly-used acaricides like amitraz and dicofol, the organotin fenbutatin oxide and even petroleum oils. However, the pest seems to be less susceptible to some of these chemicals, and continuous monitoring for resistance is thus necessary.
Biological control: The pest is attacked by many indigenous predatory mites of the families Phytoseiidae and Stigmaeidae. The phytoseiid Euseius scutalis appears to regulate this pest in Jordan, but little is known about its specificity and the ability of other predators to reduce pest outbreak populations.
References
Klein, H.Z. 1936. Contributions to the knowledge of the red spiders in Palestine. 1. The Oriental red spider, Anychus orientalis Zacher. Hadar 9: 107-111, 126-132.
Kaspi, R., Drishpoun, Y., Gross, S. and Rotman, N. (Eds) 2017. Citrus Pests and Their Natural Enemies in Israel. Ministry of Agriculture and Rural Development, Extension Service. (In Hebrew).
Kamran, M., Khan, E.M. and Alatawim F.J. 2018. The spider mites of the genus Eutetranychus Banks (Acari, Trombidiformes, Tetranychidae) from Saudi Arabia: two new species, a re-description, and a key to the world species, ZooKeys 799: 47-98.
Khanjani, M., Khanjani, M. and Seeman, O.D. 2017. New spider mites (Acari: Tetranychidae) of the genera Paraplonobia and Eurytetranychus from Iran, and a description of all life stages of Eutetranychus orientalis (Klein). Acarologia 57: 465-491.
Momen, F. and El-Borolossy, M. 1999. Suitability of the citrus brown mite, Eutetranychus orientalis as prey for nine species of phytoseiid mites (Acari: Tetranychidae, Phytoseiidae). Acarologia 40: 19-23.
Osman, M.S. 1997. Petroleum oils as a component of integrated pest management of phytophagous mites. Arab Journal of Scientific Research 15: 125-135.
Tanigoshi, L.K., Bahdousheh, M., Babcock, J.M. and Sawaqed, R. 1990. Euseius scutalis (Athias-Henriot) a predator of Eutetranychus orientalis (Klein) in Jordan: toxicity of some acaricides to E. orientalis. Arab Journal of Plant Protection 8: 114-120.
Zaher, M.A., Wafa, A.K., Maher Ali, M. and Rasmy, A.H. 1970. Survey of mites associated with citrus trees in Egypt and Gaza Strip. Bulletin de la Societe Entomologique d’Egypte 56: 73-79.