18 CIRCULAR 4 5 7, U. S. DEPARTMENT OF AGRICULTURE 



The house should be watched carefully, and as soon as a few flies 

 appear it should be treated with the dust at the rate of 2 or 3 ounces 

 per 1,000 cubic feet of air space. The majority of the growers dust two 

 or three times a week. Before the house is dusted, the temperature 

 should be allowed to reach 60° F. or more, then the dust should 

 be applied, and the house should be left closed overnight. At any 

 lower temperature the flies are less active and the dust is more 

 inert. A good fan-type duster should be used and the dust thor- 

 oughly distributed throughout the house. If a duster is not available 

 a good distribution may be obtained by shaking the dust slowly out 

 of a bag into the air blast from an ordinary electric fan directed 

 toward the ceiling of the house. 



DRENCHES 



Drenches of 2-percent alcoholic extract of pyrethrum used with 

 water at the rate of 1 part to 800, applied to the beds at the rate of 

 about 1 quart to 12 square feet, at weekly intervals, in place of the 

 regular watering, and dichloroethyl ether at the rate of 3 cubic centi- 

 meters (roughly one-seventh of a liquid ounce, or three-fifths of a 

 teaspoonful) per gallon of water, applied to the beds at the same rate, 

 by means of a sprinkling can, have each given an increase in yield of 

 about one-third of a pound per square foot of bed space. Pyrethrum 

 kills few of the insects and mites, but acts as a repellent. It is 

 probable that this is true of the dichloroethyl ether also. 



FUMIGANTS 



Fumigation with granular calcium cyanide at the rate of iy 2 to 2 

 ounces per 1,000 cubic feet of air space has been used with some suc- 

 cess for controlling adult mushroom flies. Its use will be discussed 

 more fully under the following heading (p. 19). 



MANURE FLIES 



At least three species of phorid flies (of the genus (Megaselia) 

 have been reported as doing commercial damage in mushroom plant- 

 ings. These are M. albidihalteris Felt, M. agarici Lintner, and 

 M. iroquoiana Malloch. As in the case of the mushroom flies, these 

 three species of manure flies are so nearly alike in appearance and 

 in their biology that they may be regarded as one species when their 

 control is considered. They are frequently seen in immense numbers 

 on and about the exterior of the houses. The adult flies (fig. 7) are 

 black or blackish and usually slightly smaller than the sciarid flies. 

 They are much more compactly built, the legs are stouter and not 

 so long, and the head is rather small and the thorax large, giving 

 them a humpbacked appearance. They are quite active, moving 

 about constantly in a series of jerky runs. 



The life history of these flies is known only in a general way. 

 The time required by the various stages is dependent on conditions 

 of temperature, humidity, and food, as is the case with the mushroom 

 flies. 



The eggs are very minute, white, and elongate-oval, and are laid 

 in the compost or casing soil. They hatch in about 6 days, under 



