Fly Breeding in Livestock Manure

Jerome A. Hogsette
USDA-ARS, Gainesville, FL

Probably one of the most overlooked aspects of manure management and utilization is the ability of nuisance flies, particularly the house fly, Musca domestica, to exploit these nutrient-rich media and produce tremendous volumes of offspring that can result in litigation and closure of farming operations (Thomas and Skoda 1993). The potential for problem situations has increased with the continued development of high-intensity confinement livestock facilities and urban encroachment into what were formerly agricultural areas. The large size of the average confinement farm plus increased regulation of manure disposal by state and federal agencies have forced producers to remove manures from farms more often, and seek environmentally friendly methods for disposal of their animal manures.

Land application of manures has been the method of choice for many producers, although in many states there are no local data on nutrient loading rates. Manure can be removed from housing, transported to the desired locations, and spread on land with no further processing. Organic farming has increased the demand for pesticide-free animal manures and enabled producers to view manures as a resource instead of a waste. There is now a trend by producers to store manure until the market price is high. Also, many producers with lagoon systems are interested in making the change to dry systems to be able to produce a saleable manure product. With this emphasis on manures and manure production, there has to be an increased emphasis on flies and fly production.

When substrate temperatures are between 80 and 90° F, houseflies can complete the cycle from egg to adult in 6-7 days (Larsen and Thomsen 1940). Females can produce 600-800 eggs, which they lay in cluches of 150-250 eggs. House fly larvae can survive burial at depths of 4 ft, and temperatures approaching 120° F

(Mellor 1919). Adults are strong fliers, and the recorded flight range of 20 miles (Bishopp and Laake 1921) is far short of their ability. The flight range of the stable fly, Stomoxys calcitrans, a sister species that is similar in size, is at least 135 miles (Hogsette and Ruff 1983). With these capabilities, it is not surprising that houseflies can locate desireable breeding sites and develop large populations in a relatively short period.

An important but widely unrecognized problem is the control of flies in manure deposition (dairy or beef feedlots) or application (cropland, pastures, etc.) sites. In these cases, manure may be mixed with soil or other substrates and fly breeding may occur from 1 to >12 inches below the surface (Hogsette 1996). Sites near Perth, Australia, have been inundated with flies for several years because litter (chicken manure plus wood or paper products like wood shavings) from broiler houses is being used for crop production. Similar but less serious situations occur in the Middle East and South America (J.A.H., personal observation).

House fly development sites in manure-laden soil have been defined on dairy (Meyer & Shultz 1990) and beef cattle confinement facilities (Skoda et al. 1993). However, no studies had been done to quantify the amount of manure needed in the soil for fly development to occur. Larvae of Hydrotaea irritans (Fallen) have been found only in pastures in soil substrates (Robinson & Luff 1976), but no subsequent studies have been performed to further define the habitat. Therefore, this study was performed to quantify the amount of manure solids required for house fly development in sand under varying moisture levels.

Treatments were formulated in coarse (30-65 mesh) builders sand because it simulates closely the sand used in confinement lots on many feedlot dairies in Florida. Treatments were based on levels of moisture originating from water alone, manure moisture alone, or from a combination of the two. Within each moisture level, water/manure moisture combinations were as follows:

1. 100% moisture from water.
2. 75% moisture from water and 25% moisture from manure.
3. 50% moisture from water and 50% moisture from manure.
4. 25% moisture from water and 75% moisture from manure.
5. 100% moisture from manure.

Moisture levels ranged from 10 to 130 ml. At each moisture level, moisture (amount, not percentage) was held constant and the accompanying manure solids (nutrients) increased from zero in water/manure moisture combination 1 to a maximum in water/manure moisture combination 5.

Manure used in these studies was < 12 h old and field-collected from a feedlot dairy milking herd. A portion of the manure was dried to determine moisture content (81.3%), and the remainder was placed in air-tight containers and frozen (20?F) until needed. Treatments were replicated four times at each level, and each replicate was formulated by mixing 200 cc (?272.2 g) of sand with a predetermined amount of manure, water, or both manure and water. Each formulated replicate was then loosely packed into a 240-ml (10-cm high) clear plastic specimen cup. Newly hatched house fly larvae (50) were added to each treatment cup.

To compare laboratory results with what might be found in the field, 10 soil samples (250-cm² cores, 15 cm in depth) were collected from a confinement dairy. Lots were prepared with sand similar to builders sand < 3 wk before samples were collected. Some samples were collected near manure pats, but collection of visible amounts of raw manure was avoided.

Houseflies developed in sand containing just 1 ml (0.47%) of dairy manure solids and 10 ml (4.74%) of moisture. At these levels, development was slow (21.5 d from 1st-instar larva to adult), adult survival was low (7.5%), but successful development did occur. At higher manure and moisture levels, rates of development and survival were similar to those reported in the literature

Moisture content of field-collected samples from the confinement dairy was similar to laboratory moisture levels 10-40. However, manure solids in field-collected samples exceeded all levels tested in the laboratory. The highest proportion of manure solids tested in the laboratory was 7.3%, but the lowest proportion of manure solids found in the field-collected samples was 47.7%. Accordingly, the percentage sand in all of the field-collected samples was lower than that of the laboratory samples.

In Nebraska feedlots, fly larvae were most numerous in habitats that were not routinely trod upon by cattle (Meyer & Petersen 1983, Skoda et al. 1993). Soil substrates apparently pack tightly enough under the weight of the cattle to kill fly larvae developing within. Enabling feedlot cattle to walk on manure-laden soil containing fly larvae has been recommended as a fly control technique (McNeal & Campbell 1981). However, Skoda et al. (1993) consistently found small numbers of house fly larvae in general lot areas used daily by cattle.

Large concentrations of fly larvae on California dairies were found in moist areas near water troughs and in stacked manure (Meyer & Schultz 1990). But, moderate numbers of fly larvae were also recovered from lots occupied by animals.

The potential problems for fly control are dependent on how much fly development actually occurs in manure-soil substrates in pastures and confinement lots. More studies are needed to learn how fly larvae use nutrient rich soil substrates in conjunction with associated physical and microclimatic variables - e.g., soil compaction, moisture, and temperature. Until we can map the areas of larval fly development on pasture and confinement cattle facilities and predict the contribution that these areas make to the facilities' total adult fly populations, fly management will remain an elusive proposition.

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