E-542 June 1941 LIBRARY STATE PLANT BOARD CONTROL OF DOG FLY BREEDING IN PEANUT LITTER By W. E. Dove and S. W. Simmons, Division of Insects Affecting Man and Animals Near the coasts of northwestern Florida and in bordering portions of Alabama and Georgia the name "dog fly" is used for the stable fly ( Stomoxys calcitrans (L.)), i a pest of livestock which occurs in all temperate regions of the world. Because this fly is a painful biter of man and other warm- blooded animals and emerges in outbreak numbers during different warm periods of the year from peanut litter left in the fields, it is important to control such breeding places so that outbreaks of the pest may be avoided. In order to control the pest successfully and to determine the degree of control, a good understanding is needed of (1) how dog flies develop, (2) how to recognize favorable breeding places, (3) how to eliminate poten- tial breeding places before they become infested, and (4) how to reduce breeding places if the peanut litter is allowed to become infested. How Dog Flies Develop Dog flies lay elongated, creamy-white eggs, more or less scattered, on moist places of fermenting vegetation. Within 1 to 3 days the eggs hatch, and under the most favorable conditions the larvae become fully developed within about 7 days. The larvae may require 30 days or even longer for development if the food is unfavorable or the temperatures are low. When full-grown, they are about four-fifths of an inch in length, and in fermenting media they move rapidly and can quickly conceal them- selves. When fully developed the larvae become shorter, and the outer surface hardens and gradually assumes a dark-brown color. This is known as the pupa, or resting stage, and it may last from 5 to 20 days or longer before the fly emerges and pushes its way to the surface. The complete development from deposition of the egg to emergence of the fly may take place in a period as short as 14 days, but it usually ranges from 21 to 25 1 Bishopp, F. C. The Stable Fly. Bulletin No. 1097. (Revised October 1939.) S. Dept. Agr. , Farmers - 2 - days and may extend to 76 days. Longer periods undoubtedly occur in un- protected places during the winter months. In laboratory cages the adult flies have been kept alive for 47 days, and often they fed upon blood on two occasions each day. On an average the female flies deposited fertile eggs when they were 11 days old. How to Recognize Favorable Breeding Places When vegetation cured for hay becomes wet from rainfall a mild fermentation sets in which is particularly attractive to dog flies desiring to lay eggs. As the fermentation progresses, the vegetation becomes more suitable as food for development of the larvae, and the moisture assists the pupae in producing adult flies. With these natural food requirements for dog fly development in mind, an investigation was made of an outbreak of flies in northwestern Florida and southern Alabama during the second week of December 1940. In Walton County, Fla. , the livestock were suffering severely from dog fly bites and some young pigs had died from the attacks. An examination of litter in the peanut fields revealed mass infestations of dog fly larvae and pupae in the exact locations where thousands of the flies were emerging. Similarly, in Geneva County, Ala. , where cattle had as many as 300 dog flies per animal and hogs squealed incessantly and stamped their feet because of the biting flies, examinations of peanut litter in the fields again revealed tremendous numbers of dog fly larvae and pupae. Since the outbreak appeared to be of a rather general nature, examinations were made at different places throughout the principal peanut-growing section. It was learned that dog fly breeding was present in every pile of litter examined in 10 counties of northwestern Florida which involved about 70,000 harvested acres, in 9 southern counties of Alabama having about 300,000 harvested acres, and to a limited extent in southwestern Georgia where 33 principal peanut coun- ties having approximately 630,000 harvested acres had received practically no rainfall. From the best data available it appeared that approximately 1,000,000 acres of peanuts were harvested in the principal area and that a considerable number of acres were harvested in other widespread areas of these three States. Allowing 10 acres for each pile of litter in the most important peanut-growing section, it is estimated that there are about 37,000 piles of infested litter in western Florida and southern Alabama and that similar breeding could occur in approximately 63,000 piles of litter located in 33 adjoining counties of southern Georgia. Each breeding place examined in the fields represented the location where peanuts were picked from about 10 harvested acres and where the peanut vines were baled for hay. The piles of litter consisted of leaves, broken stems, and peanuts, u:jually averaged about 25 to 30 feet in diameter, and ranged from 1 inch in depth on the edges to 3 feet or even 4 feet in depth in the center. A screened cage, 6 feet by 6 feet, placed over a portion of - 3 - one of these piles recovered approximately 10,000 newly emerged dog flies within a period of 48 hours. An examination of the wet litter almost com- pletely broken down by decay invariably revealed full-grown larvae and pupae. When portions of piles in early "tages of fermentation were examined, only eggs and active larvae were found. Since about 1 week is required for larvae to develop and pupate, a casual examination of the litter is of assistance in anticipating the stage of development contained in the litter. Portions of piles of litter containing bright, well-cured leaves and stems are capable of developing infestations at some future time. Such material may not become wet until several months after harvest, then promptly undergo fermentation and produce large numbers of flies. In addition to those in peanut litter, dog flies can be found breed- ing in straw mixed with manure, either inside or outside of barns, as well as in any piles of green or cured grasses « and refuse from vegetable packing houses which are allowed to become wet and ferment in the presence of the adult flies. How to Eliminate Potential Breeding Places Before They Become Infested Since infestations of dog fly larvae and pupae may be found through- out piles of wet fermenting peanut litter, with the possible exception of very deep portions, the entire pile should be considered as a potential breeder of dangerous numbers of dog flies, It is recommended: (1) That all peanut litter suitable for feed be baled with the hay or hauled to shelter immediately after harvest and stored so that it will not get wet. (2) That all peanut litter left in the fields be scattered at the location of the piles and plowed under immediately after harvest. (3) That peanut litter, or hay, and manure scattered around feed troughs be hauled to the field each week and thinly scattered so that it will dry completely. (4) Soil erosion on the plowed areas may be avoided by choosing level tracts upon which to scatter the material, or by planting appropriate cover crops, 2 Simmons, S. W., and Dove, W. E. Control of Dog Fly Breeding in Beach Deposits of Marine Grasses. U. S. Dept . Agr. . Bur. Ent . and Plant Quar., E-541 (multigraphed) . June 1941, ,.'^,^.1XI..'?.?'TY OF FLORIDA ._ ^ ^ illllil " iliiilP How to Reduce Breeding if the Peanut Litter Is Allowed to Become Infested It is more satisfactory to scatter the litter thinly immediately after harvest, before it has had an opportunity to become infested with dog fly larvae and pupae than to wait until later. If this is not accom- plished, it is important to reduce breeding to the lowest degree. Remember that any pile of peanut litter remaining in a field without attention can easily produce from 75,000 to 100,000 dog flies. By the time the litter becomes infested it is difficult to scatter the infested portions with a pitch fork because they are partly decayed and do not hold together. At that time much of the infested material may be mixed with soil as a result of "rooting" by hogs and it is absolutely necessary to use a good shovel. All the soil mixed with infested litter should be loaded on a wagon or manure spreader and scattered. If the mate- rial is distributed thinly over the land and allowed to dry, larvae not yet sufficiently developed to transform into flies will be destroyed, and many of the pupae will die from exposure to low temperatures in the winter. Numbers of such pupae will produce fliec when exposed on the surface of the soil, but the emergence will take place during a warm period of winter when there is little opportunity for the flies to survive the colder weather that follows. It is not recommended that the infested material be plowed under immediately, because this would simply delay the emergence of dog flies until later, when the soil has become warm and when the newly emerged adults would easily push through several inches of sandy soil. It is recommended that manure from stables and piles of peanut hay mixed with manure outside of barns be scattered each week of the fly season. This will prevent the development of both dog flies and house flies.