Rhizoglyphus robini (Claparéde)
Common name: Bulb mite.
Geographical distribution: Cosmopolitan.
Host plants: Onion, garlic and other Allium spp., lily, gladiolus, hyacinth and freesia, grasses such as barley, oats, rice, rye and wheat, as well as potato and carrot.
Morphology: Rhizoglyphus robini is a relatively large, milk-colored mite, whose size (up to 1.1 mm) depends on its diet. The external verticals and the internal scapular setae are very short, some distal setae on tarsi I and II are cone-like, and the gnathosoma and legs are brown.
Life cycle: At 25°C the mite completes a generation in a fortnight, laying 400-700 eggs during six weeks. They mate often, the number of copula being depending on the diets. They feed on many living and dead plants as they are attracted to wounded plant tissues, also devouring live nematodes and various dead invertebrates. The mites are sensitive to low humidities, forming hypopodes as their substrate dries up. The hypopodes, which in and between fields may be disseminated by many soil-borne insects, molt (to third-instar nymphs) when returned to high humidities. Rhizoglyphus robini is a natural soil inhabitant that survives in low numbers in deeper humid soil strata. When stimulated by irrigation and the penetrating roots to move upwards, they feed on the young, weak roots, thus becoming pests.
Economic importance: The bulb mite injures the bulbs, tubers and corms of many plants in storage, and some, including grasses, also in the field. Mites gnawing at young roots of onion and garlic cause the plants to drop and die; entire fields may thus be lost. Potato tubers in storage are sometimes damaged by mites burrowing into their buds (“eyes”). Gladioli corms in storage may be partially injured and fail to produce commercial-rate flowers, with ca 50% or more damage. In other cases young flower leaves shrivel, affecting flower production. Phytopathogenic fungi, such as Fusarium, can add to the damage after gaining entrance to corms and bulbs through mite wounds, and can in turn promote the pest’s development in germinating onions, aggravating overall damage. In Turkey R. robini is the most common and harmful species occurring on bulbs of ornamental plants throughout the growing season and in storage.
Monitoring: Mite presence in soils and the effects of control measures were followed with plastic tubes that were closed by a perforated cap at one end and a wide-mesh metal sieve welded at the other. Pieces of peeled garlic, which attracts the mites, were placed on the mesh. Several such trap-tubes were inserted into the soil to a standard depth (like 5 cm), weekly examined, and provided a monitoring tool and an estimate of mite presence in the soil.
Horticultural method: Avoiding the planting of susceptible ornamentals (like Butcher’s Broom, Ruscus aculeatus Linnaeus) during summer and autumn.
Mechanical method: Hot water baths were used in the past to kill mites within bulbs storage, despite some damage to the plants. Solarisation is an option for control in open spaces in warm climates.
Chemical control: Fumigation with metam sodium is very effective, and various carbamates and organophosphates can also be used. The pest has developed extensive resistance to many chemicals. Onions may be dipped in an organophosphate (like chlorpyrifos).
Biological control: Several Mesostigmata, such as Geolaelaps aculeifer (Laelapidae) suppressed R. robini infesting lilies in room-temperature storage in the Netherlands. The combination of a hot-water treatment (2 hours at 40°C) and biological control may replace acaricide applications to control the pest mite in lilies during the propagation phase.
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Gerson, U., Yathom, S. and Katan, Y. 1981. A demonstration of bulb mite control by solar heating of the soil. Phytoparasitica 9: 153-155.
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Lesna, I., Sabelis, M. & Conijn, C. 1996. Biological control of the bulb mite, Rhizoglyphus robini, by the predatory mite, Hypoasis aculeifer, on lilies: predator-prey interactions at various spatial scales. Journal of Applied Ecology 33: 369-76.
Ofek, T., Gal, S., Inbar, M., Lebiush-Mordechai, S., Tsror, L. and Palevsky, E. 2014. The role of onion-associated fungi in bulb mite infestation and damage to onion seedlings. Experimental and Applied Acarology 62: 437-448.
Xassab, A. S. and Hafez, S. M. 1990. Use of powdered sulfur against the bulb mite, Rhizoglyphus robini, and its effect on nematodes in garlic field soil. Annals of Agricultural Science, University of Ain Shams (Egypt) 35: 533-541.
Websites: https://www.google.co.il/search?q=rhizoglyphus+robini&biw=1280&bih=687&tbm=isch&tbo=u&source=univ&sa=X&ved=0CCIQsARqFQoTCI7B9__W6cgCFQicGgodXnAHfA http://www.nhm.ac.uk/hosted_sites/acarology/saas/saasp/2003/saasp16.pdf