16 



CIRCULAR 457, U. S. DEPT. OF AGRICULTURE 



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

 The time required by the various stages is dependent upon condi- 

 tions 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 

 usual mushroom-house conditions. The larvae, or maggots, are shin- 

 ing white or yellowish, about one-fourth inch long when fully ma- 

 tured, legless, and without head capsules. After feeding for 10 days 

 or more the maggots stop feeding and transform into yellowish 

 pupae, appearing almost like small seeds. From these, after another 

 interval, the adult flies emerge. 



The infestation of mushroom beds by manure flies usually results 

 from the introduction of larvae with compost that afterwards does 

 not get sufficiently heated to kill them, or from eggs laid by adults 



that get into the house immediately 

 after the heating. The damage is 

 done by the larvae and is about the 

 same as that described previously for 

 the sciarid larvae, except that since 

 the infestation by these pests occurs 

 early in the development of the beds, 

 the spawn may be prevented from 

 running out from the spawn pieces, or 

 the pieces themselves destroyed. The 

 larvae also attack the growing mush- 

 rooms more readily than the sciarid 

 larvae. The greater part of the dam- 

 age is done early in the season, usually 

 becoming less noticeable after the beds 

 are producing, although during the 

 warm weather at the end of the spring 

 crop much damage may be done to 

 both spawn and growing mushrooms. 

 Control of manure flies (Phoridae) 

 is about the same as for mushroom 

 flies (Sciaridae), except that dusts 

 must be used more liberally, the 

 phorid flies being more resistant to control measures. 



By light watering and proper temperature, especially in the early 

 flushes, it is possible to force mushroom growth ahead of the devel- 

 opment of the fly maggots, thus producing a crop in spite of the 

 infestation. If dusting to control the adult flies is begun early, all 

 of the eggs will have been laid within a short time, and oviposition 

 reduced to a minimum thereafter. When the maggots in the beds 

 have pupated, the spawn is free to grow without further interference. 



Figure 5. — An adult manure fly. 

 Megaselia albidilialteris, X 18 

 (Popenoe.) 



GALL GNATS 



The adult gall gnats are small, delicate flies, brownish in color 

 with orange abdomen. The species most common at Arlington 

 Experiment Farm, Va., has been determined as Mycophila fungicola 

 Felt, They are very inconspicuous, as they remain flat against the 

 bedboards and usually fly only when disturbed. The larvae are 



