E-224 12-04 Using Parasitoids to Control House Flies in Confi ned Animal Facilities Confi ned a lt fl ies emerge once their can use biologica House fl ies’ natural enemies keep house fl ies at les and mites that feed on eggs are part of integrated eral parasitoid wasp species that designed to (1) avoid, pr and (2) minimize environm are unlike most parasitic insects caused by misuse of pesticide y usually kill their hosts. Adult parasitoids pest control alternative. iving; only their immature stages are parasitic, Biological controls use pests’ nat g on or inside their hosts. The most common suppress them, reducing both pest num use fl y parasitoids belong to the family Pteromalidae damage. Using biological controls in CA (Hymenoptera), a large group of benefi cial wasps basic knowledge about the pest’s biology an that will not sting people. Some of these parasitoid enemies in order to evaluate commercially ava species are native to Texas, and many are available biological control agents and select the best one. This commercially for purchase and release. fact sheet will update managers about using biological The female parasitoid wasp seeks out house fl y control practices in their CAFs to combat house fl ies. pupae. Using her ovipositor, she probes the pupa and feeds on it, then deposits one or more eggs inside the House Flies and Their Parasitoid Enemies pupal shell. (An ovipositor is a stinger-like appendage Like all insects, house fl ies, Musca domestica, used to lay eggs.) The female wasp’s probing kills the undergo metamorphosis. Adult fl ies lay eggs on fl y pupa, then a wasp larva emerges from the eggs manure and other substrates such as calf bedding laid in the pupal shell and feeds on the dead fl y inside. materials, wet feed or silage. The eggs hatch, and When fully developed, an adult wasp emerges from maggots emerge to feed for a few days on the the pupal shell to mate and search for new fl y pupae. substrate. Once maggots ingest suffi cient nutrients, The most important parasitoids for biological they transform into pupae protected by reddish- control of house fl ies include several species of Muscidifurax, Nasonia, and Spalangia. These parasitoid attack hosts located as deep as fi ve inches into species have slight but important differences in biology the substrate. Each adult female may produce and host preferences, described as follows: up to 25 viable offspring during her lifetime. • Muscidifurax raptor is the most commonly Little is known about its dispersal from a used parasitoid for biological control of house release point. fl ies. Found naturally throughout the year in • Spalangia endius also is distributed throughout Texas and the rest of the United States, it also the United States; it is one of the parasitoids parasitizes blow fl ies and fl esh fl ies. Female M. preferred for biological control of house fl ies in raptor most actively search for pupae located in North Carolina, where it is active from summer the top two inches of a fl y-breeding substrate; through fall. It attacks house fl ies and other fl y typically they do not attack fl y pupae below species. Searching extends to hosts located up this level. Females deposit one egg per pupa; to fi ve inches below the surface of the soil or each female can lay up to 100 eggs in a lifetime. fl y-breeding substrate. Females deposit one egg Adults are strong fl iers and may disperse from per house fl y pupa, and each female lays an CAFs after release. average of 34 eggs during its lifetime. Little is • Muscidifurax zaraptor is biologically similar to known about its dispersal from a release point. M. raptor. It primarily searches for host pupae • Other species. There are several other house located on surfaces of house fl y-breeding fl y parasitoid species in Texas, including habitats, down to approximately one-inch deep Muscidifurax uniraptor, Pachycrepoideus vindemiae into substrates. Adults may disperse 30 to 70 and Spalangia chontalensis, S. drosophilae, feet from a release point. S. nigra, S. masi and S. nigroaenea. However, • Muscidifurax raptorellus, considered a warm- these species have not received much attention weather wasp, actually may be the species most as biological control agents. commonly produced for sale in the United States. Female M. raptorellus may deposit more Using Parasitoids for Biological Control than one egg per house fl y pupa, laying as Many species of house fl y parasitoids occur many as 150 eggs during a lifetime. The ability naturally in Texas but not in suffi cient numbers or to produce more than one individual per host at the right times to provide desired control levels. pupa accounts for rapid population growth. Native parasitoid populations can be conserved by This species also does not disperse far from using compatible insecticides, such as bait products its release point, so it is more likely to remain containing methomyl and space-treatment products within CAFs after initial release. containing pyrethrin. Purchasing and releasing natural • Nasonia vitripennis, distributed throughout enemies is called “augmentation biological control”; its North America, is easily raised in the intent is suppression of pest populations by increasing laboratory. It parasitizes several fl y species and pest mortality due to these agents. Effective biological can search for pupae located deeper into the control through augmentation requires: fl y-breeding substrate. A single adult female • Selecting parasitoid species adapted to local may produce up to 140 to 200 eggs during her conditions lifetime and may deposit several eggs into • Purchasing high-quality natural enemies a single house fl y pupa. However, Nasonia • Releasing parasitoids at the correct rate, vitripennis is considered generally ineffective frequency and time at suppressing house fl y populations because it cannot locate hosts under fi eld conditions. • Using release methods that ensure parasitoid Consequently, this species is not recommended survival and dispersal for release into CAFs such as dairies. Before purchasing and releasing parasitoids, make • Spalangia cameroni is distributed throughout sure you have answers to these important questions: North America; in southern states like North 1. What species do I have already in my facilities? Carolina, it is active primarily from late Are my natural populations effective at summer through fall. It attacks house fl ies and suppressing house fl ies? other fl y species. Females can discriminate Native populations already may be present in between hosts and prefer un-parasitized hosts your facilities, so inoculation with purchased to previously parasitized ones. Generally, this material might not be necessary. During the species confi nes its searching to the top two summer, collect samples of 10 to 15 house fl y inches of fl y-breeding substrate, but it may pupae from various fl y-breeding sites around your CAF to assess natural control by native Percent emergence can be estimated by counting parasitoids. Collect only old (mature) pupae (dark the number of pupae with wasp emergence brown or black), because they are more likely to holes relative to the total number of pupae in be parasitized then are young pupae (tan or light your sample. Insect diseases may contaminate brown). Place samples in a closed container and insectaries and reduce product quality; it is store them at room temperature. Assess parasitism important to obtain only high-quality, disease-free approximately 2 weeks after sample collection by parasitoids. observing house fl y and parasitoid emergence. 5. Are parasitoid releases cost-effective? Adult house fl ies break off one end of the pupal Sampling methods described above can be used shell upon emergence; adult parasitoids emerge to monitor parasitization rates and house fl y through pinholes. Contact your local county suppression. Compare numbers of fl ies observed Extension agent for help identifying parasitoid in suppression areas to those observed in areas species. without released parasitoids or with previous 2. What parasitoid species should I purchase and infestation records. Monitoring programs also release? help to identify the best release methods to Consider time of year, house fl y-breeding achieve house fl y suppression in particular substrate and infestation levels. Some parasitoids production systems. Prices of parasitoids vary, will attack only those house fl y pupae located averaging about $13.00 per 10,000, plus shipping on substrate surfaces. Muscidifurax raptor and M. and handling costs. Release rates are suggested at zoraptor are more effective at killing house fl ies 200 per cow, which translates into $2.40 to $4.70 than other species. Avoid purchasing N. vitripennis per cow per season. because it is not considered a good biological 6. Where can I purchase parasitoids? control agent. A complete list of suppliers is posted at http:// 3. How many parasitoids should I release? www.cdpr.ca.gov/docs/impinov/ben_supp/fi lthpar.htm. Research in other states has indicated effective 7. How does the company-of-interest compare with weekly release rates of either 200 parasitoids other insectaries? per milking cow or 1,000 parasitoids per calf. Always check the competition and compare However, every situation is different; release rates effectiveness, product quality and per-unit prices. should be adjusted to achieve cost-effectiveness. Check for consistency between shipments, and be 4. What is the quality of the parasitoid product aware of unsupported claims of effectiveness. sold? Parasitoid wasps are sold in the form of Acknowledgements parasitized house fl y pupae. High-quality The authors would like to thank A. Knutson, Texas products will produce high ratios of adult Cooperative Extension, Department of Entomology, wasps to released pupae. Assess product Texas A&M University, and L. Tomberlin for quality frequently by taking a sample of 50 to their helpful comments on earlier versions of this 100 pupae from each shipment and placing it publication.