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Smidge Midge Muscles Out Spider Mites

Bank on Biocontrol for Clean Tomato Crops

The Tomato Magazine
October 2004

There's a minute, highly mobile winged predator particularly suited to patrolling tomatoes and other greenhouse vegetables searching for spider mites on which to feed. Known for its keen searching ability, this flying midge will promptly jet to spider mite outbreaks, even remote ones. "Whenever I place a spider mite-infested plant outside the greenhouse one of the first things to colonize it is Feltiella," says Lance Osborne, professor of entomology with the University of Florida's Mid-Florida Research and Education Center. Tomato growers who use this biocontrol agent -- and know how to maximize its effectiveness - witness extreme spider mite control.

Feltiella acarisuga is a tiny (2mm long) predatory midge that boasts a robust list of qualities and characteristics to recommend it over other greenhouse biocontrol agents. "For high density spider mite infestations the strongest predator around is Feltiella - it only feeds on spider mites," says Osborne.

Learn Which Pest and Assess the Degree of Infestation
"Before you select any natural enemy," Osborne says, "you must accurately identify the pest at issue." The degree to which biocontrol will be effective depends on this. Osborne, who heads up research on integrated pest management and biocontrol in protected culture, uses biocontrols in his greenhouses "For example, if you've got Tetranychus evansi -- which will devastate a plant quickly -- you're wasting your time with anything other than Feltiella. The predatory mites just don't cut it," he adds. (Note: T. evansi is orangy-red in color and can be found balled up at the end of a plant.)

"For low density populations we recommend Californicus because it can feed on alternative food sources," says Osborne. Since Feltiella feeds only on spider mites, it is particularly suited to heavy cleanups. "Feltiella is more capable in responding to high density populations than Californicus because -- although Californicus gets around -- Feltiella can fly. It is exceptional at searching out and locating infested areas. If spider mite populations are high Feltiella can also co-exist with Phytoseiulus persimilis. When used together biocontrols can provide even more effective broad-based spider mite control."

How Feltiella Operates
Feltiella locates a spider mite outbreak and deposits its eggs inside spider mite colonies. Females lay about 30-100 eggs each. 2-7 days later (depending on conditions) the eggs hatch into tiny larvae which prey on all stages of spider mites immediately after hatching. Larvae can consume up to 30 spider mite adults or 80 eggs a day. After a week of feeding mature maggots begin to pupate by spinning tiny white fluffy cocoons on the underside of leaves. An adult emerges in about a week.

Keeping Feltiella Around
"Feltiella isn't cheap," says Osborne, "but its effectiveness makes it worth having around. To cultivate our supply we use banker plants, which are an integral part of Feltiella management." Banker plants attract and support many greenhouse beneficials. In environments suited to their needs beneficials gain ground and grow in number. The grower can "bank" the beneficial's favorite food supply and in turn preserves or "banks" his investment in spider mite biocontrol - the beneficials meet, mate and multiply. The grower's initial investment multiplies as well. "One of the largest growers we know produces their own mite banker plants," adds Osborne, "but he always buys his predators. [With the banker system] he can release a shipment of 1,000 predators and in a week or two be up to 10,000."

Using a banker plant system, Osborne is assured that Feltiella will promptly find food and a mate to ensure hearty reproduction rates. Feltiella is famous for promptly getting down to the business of biocontrolling spider mites but sometimes this is at the cost of finding reproduction: its rapid dispersal makes finding mates a challenge. When the grower gets involved, releasing incoming Feltiella on banker plants, the beneficials feed and mate before they disperse, which helps them get better established.

How the banker plant system works

Osborne has been able to build a huge population of Feltiella because of his banker plant system. His banker plant is corn on which he banks grass mites (which do not attack tomatoes). When his Feltiella shipment arrives he releases them on these banker plants which are kept in the corner of the greenhouse. When the Feltiella emerge they have an immediate and convenient food source. This encourages them to pause before dispersing throughout the greenhouse at large. They mate and then take off, embarking on a seek-and-destroy mission in search of spider mites.

"We use banker plants for mites and whitefly," says Osborne. According to him banker plants are great because they:
1) provide a source of honeydew,
2) provide a ready source of food,
3) are an economical way to ensure that your investment in biocontrols will grow,
4) provide a concentrated site for easy management. You can further manage reproduction rates by inoculating banker plants with egg production stimulants.

The Outcome of Biocontrol Management
According to Osborne they have not had to treat for spider mites on either their banker or tomato plants using this system. And "even if, due to the precarious nature of shipping live insects, only a few beneficials survived after transit the banker system helps those who survived recover, reproduce and multiply," Osborne adds.

When asked to sum up his recommendations to tomato growers using biocontrol Osborne says:
1) When Feltiella first arrives concentrate them where there is food - either on banker plants on near spider mite populations
2) Give them some attention and assistance as they begin to multiply because once they're in place the greenhouse gains a hearty and mobile natural enemy.

References and Resources for Tomato Growers
· For more information on Feltiella visit: www.creatures.ifas.ufl.edu/beneficial/f_acarisuga.htm
· For more information on the banker plant system visit: www.mrec.ifas.ufl.edu/lso/
· For a convenient, easy-to-follow fact sheet on biocontrol for the tomato grower contact IPM Laboratories, Inc. at 315-497-2063
· For advice on the biocontrol of two-spotted spider mite in the greenhouse you may contact Carol Glenister, entomologist, at 315-497-2063 or e-mail her at carolg@ipmlabs.com.

8 ways in which Feltiella acarisuga outperforms predatory mites:
1. It can tolerate lower temperatures.
2. It can tolerate lower humidity.
3. It eats 5 times more.
4. It does not have day-length sensitivity and remains active year-round, as long as its prey is available.
5. It works best on crops with hairy leaves or glandular trichomes (Phytoseiulus can get trapped in the sticky hairs of tomato or cucumber plants).
6. It can fly. Its keen searching ability enables it to promptly located spider mite outbreaks from a distance -- even isolated ones.
7. It feeds on all species of spider mite.
It maintains a positive functional response to spider mite populations: its numbers grow as spider mite numbers increase.

Other Tips on Feltiella Management
· Avoid using broad-spectrum insecticides while Feltiella is getting established
· Avoid using sulphur which kills Feltiella larvae and interferes with its ability to locate infested plants
· Use banker plants as a release site. When Feltiella arrives release on bankers to encourage eating and mating before dispersal
· Treat banker plants with egg production stimulants.

© 2004 Columbia Publishing

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