Phyllocoptruta oleivora (Ashmead)
Taxonomic placing: Acari, Prostigmata, Eriophyoidea Eriophyidae
Common name: Citrus rust mite, silver mite.
Geographical distribution: Wherever citrus is grown. CIE Map #78, 1978 (revised).
Host plants: Citrus spp.; Swinglea glutinosa (Blanco) Merr.; Fortunella spp.
Morphology: The citrus rust mite is wedge-shaped, yellowish in color, about 0.15 mm in length, with a pair of very short prodorsal setae. The prodorsum bears a six-sided cell and the opisthosoma is marked by a distinct dorsal furrow. The featherclaws are five-rayed.
Life cycle: This mite develops throughout the year, its entire cycle (egg to egg) requiring about a week in summer, several weeks in winter, and it may raise 30 annual generations. Reproduction is indirect; spermatophores are deposited by males on the leaf substrate and taken up by the females. The species is arrhenotokous, each female depositing about a dozen eggs at 20-32°C and high relative humidities. The threshold of development was calculated to be at 11°C. Populations increase during spring, remain high in summer and decline in autumn. Dispersal between patches is by winds and on infested plant material, such dispersal taking place throughout the year.
Economic importance: The citrus rust mite is a major pest of citrus in many parts of the world. It attacks all citrus varieties, preferring lemons and limes. Damage On these fruits appears as silvery patches, whereas on oranges and grapefruits it is rust-like. As infestations proceed the entire fruit face becomes scaly and blackish, the fruit remaining small with a low juice content. Without control measures 100% of the fruit may be lost. Feeding on the leaves is seen as small dark spots, followed by bronzing.
Monitoring: Orchards, or parts thereof where the pest had occurred in former years, should be monitored early in the season. An examination of four fruits, taken from around the tree (with hand lens of 10X or higher), of 1 cm² per fruit, will provide a reasonable infestation estimate, provided 10 or more mites are present in each sample. A rapid estimate of the population can also be obtained by using standardized visual keys based on estimating infestation rates per 1 cm² of plant surface and comparing them to the keys.
Crop resistance: Lemons, oranges, tangerines and rough lemons are very susceptible to the pest, whereas pummelo and sour orange seem to be resistant.
Chemical control: Due to the pest’s rapid rate of increase, it is recommended to initiate treatments as soon as the mite is recognized, especially at sites where it is known to occur (“hot spots”). A repeat spray may be needed within 4-6 weeks. Fruit intended for processing can tolerate some cosmetic damage and may thus require fewer treatments than fruit for the fresh market. Various Acaricides are in current usage but their efficacy is diminishing, requiring more and more costly annual applications. Overseas demands for pesticide-free citrus fruit leads to fewer (or no) chemical treatments on these fruits.
Biological control: Several predatory mites of the families Phytoseiidae and Stigmaeidae prey on the citrus rust mite in different parts of the world. They may be able to control the pest in pesticide-free orchards, if their diet is supplemented by pollen and if active during early spring. The larvae of two cecidomyiids are efficient predators of the mite in Florida. Three indigenous acaropathogenic fungi were isolated from the citrus rust mite in Israel, but their overall effect is unclear. Another fungus, Hirsutella thompsonii Fisher, periodically controls the citrus rust mite in Florida and has been used for this purpose, but only in very humid environments.
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Maoz, Y. (and 7 co-authors). 2014. Efficacy of indigenous predatory mites (Acari: Phytoseiidae) against the citrus rust mite Phyllocoptruta oleivora (Acari: Eriophyidae): Augmentation and conservation biological control in Israeli citrus orchards. Experimiental and Applied Acarology 63: 295-312.
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