Tropical Entomology - Persea Mite
Oligonychus perseae (Acari: Tetranychiidae)
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Description
Persea miteThe persea mite, Oligonychus perseae Tuttle, Baker and Abbatiello (previously miss identified as Oligonychus peruvianus [McGregor]) is native to Mexico and invaded Costa Rica (in 1974), California (1990), Israel (2001), Spain (2004) and Florida (2007). Persea mites are found in avocado orchards year round and avocado varieties vary significantly in their susceptibility to infestation (Kerguelen and Hoddle, 2000). Mites prefer to live on mature leaves, and in California, populations begin to build in April-June, peak in July-August, and crash in September-October (Kerguelen and Hoddle 1999a,b; Hoddle et al., 2000). In Israel, the mite was found for the first time in October 2001 (Swirski et al. 2002) and has since become a serious pest of avocado there. In Israel an additional peak of infestation appeared in October-November (Maoz et al. 2011). In Florida the mite was detected in 2007 with few additional detections thereafter. However, so far no economically damaging populations have been observed.
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Damage
Part of plant damaged: Leaves
Mites live, feed, and breed on the undersides of avocado leaves in small colonies within the protection of circular silken nests (Aponte and McMurtry 1997a). Characteristic circular necrotic spots result from feeding (see Hoddle 2010a for color photos of O. perseae, its natural enemies, and damage). Once necrotic feeding damage on the undersides of leaves approaches ~10% (or around 100 mites per leaf), trees begin to drop leaves (Kerguelen and Hoddle, 1999; Hoddle et al. 2000).
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Management
Monitoring and Action Levels
Maoz et al.(2011) recommended that scouts adopt an action threshold of 50-100 mites per leaf in Israel, but cautioned that more research is needed to refine the action threshold. Hernandez et al. (2000) suggested the removal of fallen foliage infested with mites from the ground below infested trees as a cultural control method. However, this tactic is not efficacious (Takano-Lee and Hoddle, 2002). According to Hernandez et al. (2000) no known prey-specific predators of the persea mite have been reported in Mexico. Consequently, research into the management of the persea mite has focused along three major avenues: (1) biocontrol with commercially-available predatory mites, (2) enhancement of naturally-occurring predator populations via resource subsidies, and (3) pesticides.
Biological Control
Field tests screening of six species of predatory mite species (Hoddle et al. 1999) indicated Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) could provide control equivalent to pesticide applications (Hoddle et al., 1999; Kerguelen and Hoddle, 1999). However, the cost was 13-14 times more expensive than pesticides (Hoddle et al. 2000a). A modified mist blower was shown to be very effective at delivering predators to avocado trees (Takano-Lee and Hoddle 2001) but this application technology was not sufficiently efficient to reduce costs associated with predator introductions. Generalist predator populations do build in response to increasing O. perseae populations, but control is often inadequate (Yee et al. 2001a).
In Spain, an omnivorous phytoseiid mite, Eusieus stipulatus (Athias-Henriot) can be enhanced in avocado orchards via the artificial provision of pollen from deliberately planted maize plants. Increased populations of E. stipulatus were correlated with lower persea mite populations (González-Fernández et al., 2009). Additionally, airborne pollen from surrounding olive groves was also correlated with increased populations of E. stipulatus in avocado orchards. Subsequent laboratory experiments indicated olive pollen was suitable for E. stipulatus development (González-Fernández et al., 2009). In Israel, Euseius scutalis (Athias-Henriot) previously described as Euseius rubini (Swirski and Amitai) demonstrated was effective reducing mite populations. Eusieus scutalis will respond positively to resource subsidization via windblown pollen from patches of Rhodes grass or artificial application with an electrostatic sprayer, with the former being more beneficial for predator mite population growth (Maoz et al., 2009).Field surveys concluded that pollen subsidization generally promoted higher predator populations which were correlated with lower pest densities but this was not significantly different from control treatments that did not receive pollen (Maoz et al., 2009). Signficant practical and economic challenges confront the use of pollen for enhancing predator populations in avocado orchards.
Chemical Control
In California, the standard industry control practice for the persea mite is the application of abamectin combined with a horticultural oil in summer. This product is also used against avocado thrips, Scirtothrips perseae Nakahara, in the spring to control populations of this pest. Consequently, pest populations in avocado orchards can be exposed to two abamectin applications per year. Abamectin applications have a very long period of activity against targeted avocado pests, ~10-12 weeks (Morse et al., 2000) and resistance development is a concern (Humeres and Morse, 2005). To combat this potential problem in California, pesticide rotation programs to manage resistance development are encouraged. In Mexico, use of hot-pepper extracts failed to provide significant mite control (Reyes et al., 1995), and the best chemical control was obtained with organophosphates and poorest control was observed with sulfur applications (Andrade, 1988). Martinez (1989) has suggested that the persea mite has developed resistance to organophosphates in the states of Morelos, and Michoacan in Mexico.