A procedure for rearing stable flies (Stomoxys calcitrans) is presented. The procedure uses locally available materials for diet components, equipment and supplies.
Stable flies, Stomoxys calcitrans, are serious pests of livestock, humans, companion animals and wildlife worldwide. During the last 20+ years, changes in agronomic practices resulted in serious outbreaks of stable flies in several countries. These outbreaks disrupted livestock production and human recreation resulting in public demands for increasing research and management efforts for this pest. A simple and inexpensive procedure for rearing stable flies for laboratory studies is presented. The procedure uses locally available diet components, equipment and supplies. The procedure can be adapted for rearing other muscoid flies including face fly (Musca autumnalis), horn fly (Haematobia irritans), and house fly (Musca domestica). The procedure produces stable fly puparia averaging 12.5 mg and ~35% egg to adult survival. Approximately 3000 flies are produced in each pan.
Stable flies, Stomoxys calcitrans (L.), are hematophagous flies whose painful bites disrupt the grazing behavior of livestock, cause pain and suffering to companion animals and disrupt human recreational activities worldwide. Immature stable flies develop in fermenting vegetative matter, often contaminated with animal waste. Changing agronomic practices and crops have produced serious outbreaks of stable flies in crop residues, vegetables in Australia1, sugar cane in Brazil2, and pineapple in Costa Rica3. Although just 14 stable flies per animal are considered to be the economic threshold4, observations of more than 2,000 flies per animal have been made during recent outbreaks5. Such infestation levels reduce host productivity to near zero and can cause mortality6. As a result of agronomically associated outbreaks, stable flies are receiving renewed interest and demand for laboratory colonies has increased dramatically.
As for all holometamorphic insects, stable flies obtain all of the nutrients required for growth during the immature or larval stage. Therefore, an important component of a rearing system is the larval diet or substrate. Stable fly larvae have been observed developing in a broad range of substrates in the field7 and they are dependent upon the microbial community of the substrate8,9. Natural larval substrates are primarily composed of decomposing or fermenting vegetative materials often contaminated with nitrogenous wastes.
For laboratory rearing, stable fly larval substrates are usually composed of a vegetative material and an added nitrogen source. Numerous materials have been used for stable fly larval diets. The first larval diets mimicked natural substrates and included fermenting oat straw and horse or cow manure10,11. Carbohydrate sources include wheat bran12,13,14, alfalfa meal12,13,14 and a commercial formulation developed by Chemical Specialties Manufacturers Association (CSMA, 33% wheat bran, 27% alfalfa meal, 40% brewer's yeast granules)13,14,15,16. Nitrogen sources include yeast suspension12, fish meal and ammonium bicarbonate17. Inert bulking materials are often included in diets including oat hulls12, bagasse13, vermiculite16, wood chips13,18 and pelleted peanut hulls14.
A primary objective of laboratory rearing is to produce a product that is as physiologically similar to "wild type" as possible in order that laboratory experiments will produce results reflecting those of field populations. This requires that in-breeding and selection be minimized to maintain genetic diversity and nutritional resources be comparable to those in the field. Secondary objectives are to minimize labor and expenses. A major component of minimizing expenses is the use of locally available diet components. The stable fly rearing system presented was developed to meet these objectives.
1. Egg Collection (Figure 1)
2. Prepare Larval Rearing Pan
3. Pupal Processing, Larvae Move to The Edge of The Medium 7–9 Days After Oviposition and Pupariate by Days 13 or 14
4. Pupal Shelf, an Alternative Method for Collecting Puparia Is with a Pupal Shelf18
NOTE: The shelf is made from a piece of plastic cut from the end of a 10 L dish pan (10.2 cm tall x 10.2 cm wide x 31.9 cm long).
5. Quality Control
6. Preparing Blood
7. Adult Maintenance
Larvae pupariate 10–14 days and adults emerge 14–16 days after oviposition. Generation time, egg to egg, is ~24 days. Rearing data for May 2013 to January 2017 with three different bulking agents and two colonies are presented in Figure 5. Cottonwood gave the best yield, 3867 ±1442 ( ± standard deviation) pupae weighing 12.5 ±1.6 mg with 74 ±19% eclosion producing 2,872 ±1294 adult flies for the established laboratory colony. Sex ratio was slightly biased towards females 0.97:1 (male:female, 77,141 flies sexed from 1,184 pans). Egg to adult survival is approximately 36%. Unfortunately, cottonwood shavings have become more difficult to obtain forcing us to use pine shavings frequently. Although production with pine is lower, ~1,700 adults per pan, size is slightly larger, 13 mg.
Using the pupal shelf method, about 85% of the larvae migrate onto the shelf, the puparia are cleaner, and most of the medium collected on the shelf is easily remove by flotation. This method can also be used to monitor the rate of larval development when comparing rearing methods. The drawback is that the pans must be monitored daily to assure that sponges remain moist.
The current cost for medium components is $1.17/pan or $0.39/1,000 stable flies produced (Table 1).
Component | Quantity | Cost/Pan |
Wheat bran | 500 g | $0.35 |
Wood shavings | 200 g | $0.06 |
Fishmeal | 115 g | $0.27 |
Water (≈25 °C) | 1600 mL | |
Ammonium Bicarbonate | 50 g | $0.48 |
Table 1: Stable fly larval diet. Combine dry ingredients excluding ammonium bicarbonate and mix thoroughly. Add ammonium bicarbonate to water and mix until dissolved. Add ammonium bicarbonate solution to dry ingredients and mix to ensure no unwetted material. Quantity for one pan.
Figure 1: Materials used for collecting stable fly eggs. Egging cup, squeeze wash bottle and small pan for receiving eggs. Please click here to view a larger version of this figure.
Figure 2: Eggs being applied to prepared medium in pan. Please click here to view a larger version of this figure.
Figure 3: Apparatus used for drying puparia. Please click here to view a larger version of this figure.
Figure 4: Larval rearing pan with pupal shelf. Note the accumulation of puparia on top of and around the cloth. Please click here to view a larger version of this figure.
Figure 5: Summary of rearing data. Mean number of puparia per pan (A), puparia weight (B), and number of adults per pan (C) for stable fly rearing from May 2013 to January 2017 using three bulking agents, cottonwood shavings, pine shavings and vermiculite and two colonies. The Lab colony has been reared continuously in our laboratory for about 10 years. The PL colony was established from wild flies collected at a dairy in Lancaster Co., NE, USA in the fall of 2014. Error bars represent standard deviations. N represents the number of pans upon which the data are based. Please click here to view a larger version of this figure.
Stable flies can be found developing in a broad variety of substrates in nature and can be reared in many types of media in the laboratory. We have used wood shavings and vermiculite as bulking agents. Vermiculite worked well, but made separating puparia from rearing medium difficult and was expensive (~$0.60/pan). Possibly because of the added rigor of separating puparia from the medium, eclosion was also lower with vermiculite, 57% vs. 75% for wood shavings. Cottonwood shavings were comparable to vermiculite, but at times difficult to procure. The most important components appear to be vegetative or cellulosic material to ferment and maintain an "open" or well aerated medium and ammoniacal nitrogen21,22. Stable fly larvae are not found in pure dung, preferring aged dung mixed with vegetable matter. With these thoughts in mind, the rearing procedures outlined here can be adapted to locally available materials to develop inexpensive procedures for rearing stable flies.
Flies reared using these methods are comparable in size to field collected flies. Wing length is correlated with stable fly body weight23. Because the wings of wild flies are frequently frayed, we use the length of the discal-medial cell as an indicator of wing length. Mean length of the discal-medial cell of 249 flies reared with this method was 2.49 ±0.15 mm (range 1.96–2.81) while that of 3,713 flies collected on sticky traps during the summers of 2011 and 2012 near Ithaca, NE was 2.52 ±0.21 mm (range 1.80–3.58) (unpubl. data). Weight of puparia reared with this method is higher than that reported for previous rearing protocols14,24 and survival, egg to adult, is higher than the 5% observed in the field25.
Similar methods can be used for rearing other muscoid flies including face flies, horn flies, and house flies. Face fly and horn fly larvae require a fresh bovine dung medium. House fly medium is made of 470 g calf feed, 500 g wheat bran, and 1,600 mL water (~25 °C). Like stable flies, horn fly adults feed on blood. Face fly and house fly adults can be fed a dry mixture of powdered milk and sugar. Face fly and house fly adults also need a source of water. We use 100 mL plastic bottles with a dental wick passing through the lid.
The authors have nothing to disclose.
We would like to thank Anthony Weinhold and the numerous students who have worked with us over the years for technical support as well as suggestions for improving our insect rearing procedures.
Diamalt | Premier Malt Products, Inc., Saddle Brook, NJ | 2540 | |
CSMA Fly media | Purina Animal Nutrition, Arden Hills, MN | 5S6Z | |
Thin Maxi Pad | The Tranzonic Co., Cleveland, OH, USA | 5001M | |
Calf Manna | MannaPro, Chesterfield, MO, USA | Manna Pro | |
Ammonium Bicarbonate | Spectrum Chemical Manufacturing Corp, Gardena, CA | A1125 | |
Wheat bran, Coarse | Siemer Milling Company, Teutopolis, IL | ||
Wood shavings | Tractor Supply Company, Brentwood, TN | 502770699 | |
Fishmeal | Consumer Supply Distributing, North Sioux City, SD | F1550 | |
Adult cages | All Aluminum Window Company, Lincoln, Ne | Custom | 45 × 45 × 45 cm, 18 × 16 mesh aluminum screen, stockinette access |
9 × 28 cm black cotton cloth | Robert Kaufman Fabrics, Los Angeles, CA | K040-114 | Egging cloth |
10 liter plastic dish pans | Rubbermaid, Saratoga Springs, NY | FG2951ARWHT | Larval pans |
Stockinette, Cotton, 12" X 25 yd roll | Tex-Care Medical Company, Burlington, NC | 91311-225 |