Acarid mites

Bulb mites infest the bulbs of many plant species, including Easter lily, onion, daffodil, tulip, and hyacinth.

Damage

Bulb mites feed on the underground portion of bulbs, weakening the plant tissue. Feeding damage also promotes the secondary invasion of plant pathogens such as Fusarium, Pythium, and Rhizoctonia. On Easter lily (Lilium longiflorum), typical symptoms include rosetting, cessation of growth at a height of 3-6 inches, chlorosis, and occasionally death.

Description and life cycle

The slow-moving adult bulb mites are 1/25 inch (1 mm) long and pearly white with short, red legs. Females produce 100-150 eggs, laid singly or in groups on the bulb's surface, near injured or decaying tissue or between bulb scales. A generation can be completed in 10 days at 81°F.

Monitoring

Bulb mites are difficult to observe until their damage becomes apparent. If bulb mites damage your crop one year, plan control efforts the next year based on that experience.

Natural enemies

Bulb mites have few natural enemies, and no known parasites or pathogens control them.

Predators

Hypoaspis aculeifer. This soil-dwelling, laelapid mite is a nonspecialist predator of arthropods, but appears to feed and reproduce best on bulb mites.The light brown adults are less than 1/25 inch (1 mm) long and spend all their time on or in the soil. Adults consume up to 30 bulb mites daily. Females deposit one to three eggs per day.White, nonfeeding, six-legged larvae hatch from the eggs and become eight-legged nymphs in about a day.The nymphal stage lasts 4-5 days. During this phase nymphs consume an average of 15 bulb mites. Both immature and adult predators prefer the larval stage of the bulb mite as prey. Development is faster on larval and egg stages than on adult prey. Adults may live up to 60 days.They are inactive when temperatures are below 57°F.This species is available commercially.

A related species,H. vacua, has similar biology and feeding habits. In small-dish trials in laboratory studies, H. vacua consumed 33 bulb mite nymphs during development, while adult females ate about 13 mite nymphs per day. H.vacua is not available commercially.

Possibilities for effective biological control

Hypoaspis aculeifer or other species may have potential as a biological control agent against bulb mites. In small-scale laboratory experiments H. aculeifer was able to suppress bulb mites to very low levels on lily bulbs.The predators did not leave the bulbs until almost all prey were eaten. In closed plastic bags filled with lily bulb scales and vermiculite (similar to lily bulb propagation conditions), Hypoaspis was also able to suppress the bulb mite to very low numbers. However, no research has been conducted on introducing this predator to greenhouses for bulb mite control.The related species H. miles, sold commercially for fungus gnat control, died out without noticeable impact on the bulb mite population.

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