Question of the Week
First, I would urge you to contact Neil Miller, who works with the USDA's Agricultural Research Service (ARS) researching fruit fly management. He has been working with many organic growers on the big island to help them manage fruit flies. His contact information is:
Agricultural Science Research Technician (insects)
Phone: (808) 959-4302
Fax: (808) 959-5470
920 Stainback Highway
Hilo, HI 96720
As you are aware, fruit fly control is very difficult, although there are some new products that can be effective. A first step in any pest-management program is to correctly identify the pest, so please collect some adults and have them correctly identified, or collect some infested fruit and rear out the adults to obtain a positive identification. Once this is done, insights into possible management strategies can be gleaned from examining the insect's life cycle. There are dozens of species of fruit flies, each with a range of preferred hosts and a unique set of behaviors. For example, one of the reasons that a new commercial fruit fly bait (GF 120) is effective against the melon fruit fly is the fact that the adult fly overnights and forages away from the host crop in which it lays its eggs. This can be seen as a "weak link" in its behavior that a management strategy can take advantage of. In this case, a border crop can be planted and sprayed with the bait, and if the border is wide enough, the melon fly will feed on the bait and perish before it has a chance to lay eggs on a host crop. Knowing the host plants and crops of the pest will influence management decisions with respect to where a future crop is planted and what types of crop rotations are used. If applied control measures are needed, proper identification is critical; some control measures work well with some species of fruit fly and less well with others.
Life Cycle and Ecology
The description that follows is a generalized life cycle of fruit flies. The adult female will pierce a thin-skinned fruit (a tomato, for example) and lay one to several eggs. Other females may follow suit, depositing eggs in the same hole. A single female generally has the capacity to lay several hundred eggs over the course of her life (1). The eggs hatch in 2 to 20 days (depending on temperature) and the larvae burrow into the fruit to feed for 10 to 40 days. At this time, the larvae will be roughly ¼-inch long and will leave the fruit and pupate in the top 1 to 2 inches of soil. Adult flies will emerge in 10 to 50 days. These times are very temperature-dependent, and the whole life cycle can be completed in two and a half weeks under ideal conditions.
Fruit flies are very mobile as adults and some species are strong fliers (e.g., Bactrocera cucurbitae (Coquillett), the melon fly). Sterile males of the medfly, Ceratitus capitata, have been found 24 miles from their release point.
Likely Species of Fruit Flies
It’s likely that one of three species is attacking your crop. The melon fly, Bactrocera cucurbitae (Coquillett), has more than 80 hosts and is a major pest of beans, bittermelon, Chinese wax gourd, cucumbers, edible gourds, eggplant, green beans, hyotan, luffa, melons, peppers, pumpkins, squashes, togan, tomatoes, watermelon, and zucchini (2). The oriental fruit fly, Bactrocera dorsalis (Hendel), attacks more than 300 cultivated and wild fruits including Annona (cherimoya, atemoya, sugar apple), avocado, banana, bittermelon, citrus, coffee, guava, macadamia, mango, papaya, passion fruit, peppers, persimmon, and tomato (3). This pest will apparently breed in all fleshy fruits. On Oahu it is estimated that 95% of the oriental fruit flies develop on guava, Psidium guajava L. (4). They do not attack cucurbit crops such as cucumber and squash. The last fruit fly suspect is the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). This pest attacks more than 260 different fruits, flowers, vegetables, and nuts, with a preference for thin-skinned, ripe, succulent fruits (5).
Once the female fruit fly has deposited eggs in the fruit, it’s too late for managing the pest. Therefore, focus should be directed at preventing egg-laying, either by mechanical means such as bagging the fruit, or by use of processed kaolin clay (known as particle film barriers), or by removing sources of adult flies (sanitation practices). Use of insecticidal baits to kill the adult female before she deposits her eggs is discussed below, but may not be acceptable under organic production guidelines.
Sanitation is important in the control of any fruit fly. All dropped and prematurely ripe fruit, as well as small fruit suspected of being infested, should be destroyed to prevent the larvae from developing into adult fruit flies. The fruit may be fed to livestock (but must be eaten before any larvae have a chance to emerge), composted in a well-managed compost pile (so the heat will destroy the larvae), or buried 2 feet below the soil surface so that adult flies will not be able to emerge.
Bagging(6): Each fruit is enclosed in an appropriately sized bag tied around the fruit stem. Alternatively, newspaper of an appropriate size can be rolled to enclose the fruit, then tied both around the fruit stem and at the free end.
Bagging should begin when the fruit is small, shortly after the flower parts have fallen. This method of control is more adapted to small plantings (1 to 25 plants) than to large ones (quarter-acre or more). Although bagging the fruit is the most certain method of control it is a laborious process and requires attention at regular intervals (10 to 14 days) to keep the young fruit covered. Also, this procedure will injure some of the fruit unless they are handled carefully.
Particle Film Barrier:Surround® WP is a commercially available formulation of processed kaolin clay. There is some evidence that it can be an effective deterrent to oviposition (egg laying) by some species of fruit flies (Mediterranean fruit fly, Ceratitis capitata, Natal fruit fly, Ceratitis rosa, and marula fruit fly, Ceratitis cosyra, as well as the apple maggot/blueberry maggot, Rhogoletis pomonella) (7). The mode of action is hypothesized to be non-recognition of the host because of changes in the color and texture of the fruit that result from the kaolin clay application (7).
For more information about Surround, contact:
Marketing manager, Crop Protectants
Insecticides:Diatect V is a mixture of silicon dioxide (diatomaceous earth—82.45%) + pyrethrin (.5%) and is acceptable for use in organic production systems. Organic Plus, a similar premix of silicon dioxide (diatomaceous earth—83.2%) + pyrethrin (.2%) + piperonyl butoxide (1.1%), is registered for use on some fruits for control of fruit flies and other pests, but is not likely be acceptable for certified organic production due to the presence of piperonyl butoxide. Pyrellin, a premix of pyrethrin (.6%) + rotenone (.5%), is also registered for use on some fruits for control of fruit flies and other pests (8) but you should check with your certifier to see if its use is acceptable for certified organic production.
There are some new pesticides developed by Dow Ag-Chemicals, based on spinosad, that are approved for use in organic systems. Spinosad is the common name of a mixture of spinosyn A and spinosyn D, two molecules derived naturally from a bacterium through fermentation (9). Entrust is an organically approved formulation of spinosad. There is also a fruit fly bait based on the same pesticide now being marketed under the name GF120. A researcher at Washington State University found that the cherry fruit fly could be effectively controlled using a combination of a wettable powder formulation of Entrust applied at 10-day intervals, combined with use of the GF 120 bait spray. GF-120 bait treatments were applied weekly, and reapplied after rain on some of the sites.
Baits: As noted in the previous paragraph, Dow Ag-Chemicals has developed a fruit fly bait, GF120. This bait, consisting of a small amount of spinosad mixed with sugar and a protein byproduct of corn, is geared toward tropical fruit-fly species. The baits are applied to broadleaf plants that serve as a refuge for fruit-fly adults (5). Its effectiveness on various species of fruit flies is now being researched in Hawaii and other locations. Hawaii is currently involved in a fruit-fly suppression program and is using this bait as one of the tools in the effort. The Hawaiian company that will be distributing this product is United Horticultural Supplies; contact Reginald Hasegawa at 808-935-7191. The bait comes as a concentrate and when diluted according to directions is 80 parts per million (ppm) spinosad (this is equivalent to roughly .01 oz/acre deposition rate of spinosad). This bait is highly toxic to bees (9) and there is some phytotoxicity on cucumber (10). Your organic certifier can tell you whether it is acceptable for certified organic production. For more information on Hawaii’s fruit-fly suppression program, contact: Dr. Roger Vargas Areawide Suppression Program 808-959-4329 Another bait, developed under the name SureDye™, is not yet commercially available, but is reportedly in the EPA registration process (10). SureDye™ is specifically formulated for fruit flies, and is reportedly non-toxic to non-target organisms. The active ingredients are red dye #28 and yellow dye #8. Once ingested, the dyes act as poisons in the presence of light and kill the insect. Unfortunately, SureDye™ is not yet registered for commercial use. Again, your organic certifier can advise you on the acceptability of this product once it becomes available commercially. Parasitic nematodes:Another option is the use of parasitic nematodes to treat the ground around plants where fruit-fly larvae have dropped to pupate. The nematodes will attack the larvae and pupae as they tunnel into the ground. For a listing of retail suppliers of beneficial organisms, see www.cdpr.ca.gov/docs/ipminov/bensup.pdf. A free copy of Suppliers of Beneficial Organisms in North America can be obtained by writing: California Environmental Protection Agency Department of Pesticide Regulation Environmental Monitoring and Pest Management Branch 1020 N. Street, Room 161 Sacramento, CA 95814-5624 References: 1) Metcalf, Flint, and Metcalf. 1962. Destructive and Useful Insects. McGraw-Hill, New York, NY. p. 812-14. 2) Mau, R. F.L, and J. L. M. Kessing. 1991. Melon fly. Accessed April 2002. www.extento.hawaii.edu/Kbase/crop/Type/bactro_c.htm 3) Mau, R. F.L, and J. L. M. Kessing. 1992. Oriental fruit fly. Accessed April 2002. www.extento.hawaii.edu/Kbase/crop/Type/bactro_d.htm 4) Newell, I. M. and F. H. Haramoto. 1968. Biotic Factors Influencing Populations of Dacus dorsalis in Hawaii. Proc. Hawaiian Entomol. Soc. 20(1): 81-139. 5) Mau, R. F.L, and J. L. M. Kessing. 1992. Mediterranean Fruit Fly. Accessed April 2002. www.extento.hawaii.edu/Kbase/crop/Type/ceratiti.htm 6) Pena, J., and F. Johnson. 1998. Website. Insect Management in Papaya. 1999 Insect Management Guide, Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first printed: October 1993. Revised: October 1998. http://edis.ifas.ufl.edu/scripts/htmlgen.exe?DOCUMENT_IG074 7) Mosko, John. 2002. Technical representative for Englehard Corporation. Personal communication. 8) Pena, J and F. Johnson. October 1993. Revised: October 1998. Reviewed: November 2001. Accessed April 2002. Insect Management in Guava. University of Florida Cooperative Extension Service. http://edis.ifas.ufl.edu/IG072 9) Anonymous. 1999. Spinosad: Questions and Answers. USDA Animal, Plant Health Inspection Service (APHIS) Accessed April 2002. www.aphis.usda.gov/publications/plant_health/content/printable_version/faq_phspinosad.pdf 10) McQuate, Grant. 2002 personal communication. USDA ARS Tropical Fruit Research Station 11) Timothy J. Smith, Washington State University Extension, North Central Washington 300 Palouse, Wenatchee, WA 98801 (509) 667-6540; email@example.com www.ncw.wsu.edu/treefruit/documents/2005CFFResultsTJSmithOrganic.pdf Additional reading: Prokopy, R.J., Miller, N.W., Pinero, J., Oride, L.K., Chaney, N.L., Revis, H., Vargas, R.I. 2005. How Effective Is Gf-120 Fruit Fly Bait Spray Applied To Border Area Sorghum Plants For Control Of Melon Flies (Diptera: Tephritidae)?. Florida Entomologist. 87:3. P354-360.
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