Oligonychus perseae Tuttle, Baker and Abbatiello
Common name: Persea mite.
Geographical distribution: The pest, which is of Central-American origin, has spread to the south-western USA and to Israel.
Host plants: In the Israel found only on avocado, but in California also on apricot, bamboo, camphor, carob, grape, peach, persimmon, plum, rose, willow and weeds like Malva sp., Sonchus sp. and others.
Morphology: The body of the ovipositing female is green-yellow with darker spots on the hysteronotum; elder females turn dark green. The striations on the hysteronotum are in an inverted V pattern and the dorsal setae are slender; body length about 0.3-0.4 mm. Immature mites are green- yellow and may also bear dark hysteronotal spots.
Life history: Females place up to 5 eggs in a nest and move to other sites on the leaf to build new nests. A life cycle requires about 2-3 weeks at 25ºC, at which temperature a female lays 40-50 eggs. The calculated female threshold of development is 8ºC and the mite requires 200 day-degrees for its complete development. Populations increase in spring, peak during summer and decline in the fall. Overcrowding leads to dispersal, some mites crawling to find new sites on the same trees, but most migrating to other hosts by ballooning.
Economic importance: This mite is a serious pest of avocado, living and feeding within small webbed nests along the main veins on the underside of leaves. Damage is due to small rounded necrotic spots that coalesce into larger stripes and may cause leaf wilt and drop. Yellow-brown spots also occur on the upper leaf surfaces. Trunks and fruit of defoliated trees become exposed to sunburn risks, leading to reductions in fruit size and yield.
Sampling: A sampling unit consists of the average number of motile mites found in the “half second vein” area of 10 healthy avocado leaves, on their lower surfaces. “Half” because only the left side of the leaf is examined, and “second vein” is the second major vein that runs from the midrib to the leaf edges. The obtained value, multiplied by 12, provides an estimate of the number of mites/leaf. The value of over 100 mites/leaf is considered as the economic injury threshold. Automated image analysis software was developed in California for rapid and reliable mite counting after scanning with a color-defined marking method.
Horticultural methods: The removal of host weeds and of fallen leaves reduces the mites’ population.
Plant resistance: Some avocado cultivars, like “Fuerte” are relatively resistant to the pest, whereas “Haas” is susceptible.
Biological control: In Israel the pest is controlled by the indigenous phytoseiid Euseius scutalis (Athias-Henriot), when provided with sufficient pollen. In California the pest is controlled by other phytoseiids.
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Aponte, O. and McMurtry J.A. 1997. Biology, life table and mating behavior of _Oligonychus perseae _(Acari: Tetranychidae). International Journal of Acarology 23: 199-207.
Hoddle, M.S., Aponte, O., Kerguelen, V. and Heraty, J. 1999. Biological control of Oligonychus perseae (Acari: Tetranychidae) on avocado: I. evaluating release timings, recovery and efficacy of six commercially available phytoseiids. International Journal of Acarology 25: 211-219.
Kerguelen, V. and Hoddle, M.S. 1999. Measuring mite feeding damage on avocado leaves with automated image analysis software. Florida Entomologist 82: 119-122.
Maoz, Y., Gal, S., Zilberstein, M., Izhar, Y., Alchanatis, V., Coll, M. and Palevsky, E. 2011. Determining an economic injury level for the persea mite, Oligonychus perseae, a new pest of avocado in Israel. Entomologia Experimentalis et Applicata 138: 110–116.
Maoz, Y., Shira Gal, S., Argov, Y., Coll, M. and Palevsky, E. 2011. Biocontrol of persea mite, Oligonychus perseae, with an exotic spider mite predator and an indigenous pollen feeder. Biological Control 59: 147–157.
Morse, J.G., Hoddle, M.S. and Urena, A.A. 2000. Persea mite pesticide efficacy trials. California Avocado Society Yearbook 84: 127-137.
Takano-Lee, M. and Hoddle, M.S. 2002. Oligonychus perseae (Acari: Tetranychidae) population responses to cultural control attempts in an avocado orchard. Florida Entomologist 85: 216–226.