common name: predatory gall midge (unofficial common name)
scientific name: Feltiella acarisuga (Vallot) (Insecta: Diptera: Cecidomyiidae)

Introduction - Synonymy - Distribution - Description - Life Cycle - Effectiveness - Commercial Availability and Use - Selected References

Introduction

The predatory gall midge, Feltiella acarisuga (Vallot), is one of the most effective and widespread natural enemies of spider mites (Tetranychidae) (Gagne 1995). It is a particularly important natural enemy of the twospotted spider mite, Tetranychus urticae Koch, in a number of cropping systems (Opit et al. 1997). F. acarisuga could be particularly useful for integrated pest management of spider mites that attack greenhouse crops (Gillespie et al. 1998).

Synonymy

Cecidomyia acarisuga
Mycodiplosis minuta
Therodiplosis persicae
T. beglarovi
Arthrocnodax rutherfordi
Feltiella tetranychi
F. davisi
F. americana
F. ithacae
F. quadrata (Gagne 1995)

Distribution

The genus Feltiella is virtually cosmopolitan and contains eight species: F. acarisuga (worldwide, except for the Neotropical Region), F. pini (Felt) (North and Central America and West Indies), F. curtistylus Gagne (Brazil), F. occidentalis (Felt) (U.S.- California), F. acarivora (Zehnter) (Indonesia- Java), F. insularis (Felt) (eastern U.S., West Indies and Colombia), F. reducta Felt (northeastern U.S. - New York), and F. ligulata Gagne (Cape Verde Is.) (Gagne 1995). F. acarisuga is the most widely distributed species in the genus and is listed from the U.S., Canada, Finland, Germany, U.K., Switzerland, Italy, Morocco, Greece, Israel, India, Sri Lanka, Taiwan, Japan and New Zealand. It is the only species of Feltiella found throughout most of Europe and Asia.

Description

Egg: The shiny, translucent oblong eggs are deposited individually near prey mites on leaves. They are 0.1 x 0.25 mm in size (Koppert 1997). The eggs hatch within two days after oviposition and the larvae immediately begin to feed.

eggs

Larva: The orange-brown larvae vary in length from 0.2 to 2 mm during their four developmental instars (Koppert 1997). They forage for mites on leaves and feed for four to six days, depending on temperature, RH and the abundance of prey mites (Gillespie and Raworth 1999). They feed exclusively on all developmental stages of several species of spider mites. F. acarisuga larvae occur in populations as large as 160 per cm2 of eggplant leaf.

larva

Pupa: The fluffy white, 1 to 1.5 mm long pupa requires four to six days to complete development and produce an adult (Koppert 1997). Pupation occurs mainly on the underside of a leaf next to a vein.

pupa

Adult: The adult F. acarisuga is a delicate pink-brown fly about 2 mm in length with long legs (Koppert 1997). Females have a five day life span and produce about 30 eggs. Males do not live as long as females. The sex ratio is about 1:1. Adult F. acarisuga are not predaceous but drink water and nectar.

adult

Life Cycle

In climates without extremely dry or cold seasons, every stage of F. acarisuga is present year-round. Feltiella spp. apparently develop from egg to egg in 26 to 33 days, averaging around 29 days (Sharaf 1984); however, F. acarisuga requires about 15 days (Gillespie et al. 1998). Reproduction and development occur at 15-25°C. Eggs and larvae do not survive above 30°C or below 30% RH. At least 50% RH is required for a normal rate of development. The optimum temperature and RH combination is about 20°C and 90% RH. However, with an abundance of prey, the level of predation remains constant over the developmental range of temperature and RH (Gillespie et al. 1998). If prey populations are sub-optimal, larvae can survive by pupating at a smaller size. Larvae also can survive for several days without prey.

Effectiveness

Feltiella acarisuga can be used to manage spider mite populations in a variety of greenhouse and field crops, especially when incorporated into a bio-intensive IPM program. In eggplant, for example, F. acarisuga has appeared naturally and reduced spider mite numbers by more than 40% (Sharaf 1984). Each midge larva can consume an average of least 15 adult mites, 30 mixed developmental stages, or 80 eggs per day. Weekly releases of 1000 individuals per ha have been extremely effective for controlling spider mites on tomato, pepper and cucumber (Gillespie et al. 1998). In addition, F. acarisuga (sold as Therodiplosis persicae) is being used to manage spider mites on strawberries and various ornamental crops. It is recommended that 200 to 1000 individuals per ha. be released weekly as a trial rate for growers. The weekly release rate is approximately doubled for heavy infestations, 2,500 adults per ha for six successive weeks (Biobest 1999).

It is highly advised that F. acarisuga be released in combination with the predaceous mite, Phytoseulus persimilis, a well-established natural enemy used to control spider mites. F. acarisuga is more mobile as an adult than is the predatory mite and, once established, eats at least five times as many spider mites (Biobest 1999). However, P. persimilis should not be released where F. acarisuga is becoming established because they are known to eat midge eggs if prey is limited (Gillespie 1998).

Commercial Availability and Use

F. acarisuga pupae are commercially available from several producers and suppliers of natural enemies (http://www.anbp.org/ and http://www.cdpr.ca.gov/docs/ipminov/ben_supp/contents.htm). Pupae are shipped on leaves or an inert substance in various containers, such as 1-liter pots. Pots are placed in the crop on the ground at the beginning of rows and their lids are pierced to release the adult midges. It is best if the midges are released near concentrations of spider mites. To establish, F. acarisuga requires fairly large prey populations (Gillespie and Raworth 1999). The pots should be stored in the dark for no more than two days at 10 to 15°C (Koppert 1997). Adults should be released from containers every 24 hours, late at night or early in the morning because of the cooler and more humid conditions. The RH should be kept above 80%, if possible (Gillespie and Raworth 1999).

It is essential to avoid non-target side effects of chemical pesticides, such as Thiodan, Diazinon, and Kelthane; however, most fungicides are safe to use with F. acarisuga (Gillespie and Raworth 1999). Sulfur products used as dusts or sprays do not cause mortality in larvae but females avoid laying eggs on treated plants. Another concern is parasitization of F. acarisuga larvae by Aphanogmus floridanus, potentially a very abundant parasitoid during warmer months. However, if necessary, releases can be timed to avoid the parasitoid because unlike the parasitoid F. acarisuga does not diapause during the cooler months. F. acarisuga parasitized by A. floridanus have pupal cases with characteristic round emergence holes.

Selected References

Authors: Ryan S. Osborne, Norman C. Leppla and Lance S. Osborne, University of Florida
Photographs: David R. Gillespie, Pacific Agri-food Research Centre (Agassiz), Agriculture and Agri-Food Canada; and Lance S. Osborne, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number EENY-269
Publication Date: June 2002. Latest revision: September 2006.
Copyright 2002-2006 University of Florida

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