MUSHROOM PESTS AND THEIR CONTROL 



19 



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

 shining white or yellowish, about one-fourth of an inch long when 

 fully matured, 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. Under ordinary con- 

 ditions the time from egg to adult is about 28 days. Unlike the 

 mushroom flies, the manure flies seem to require a period of flight 

 before mating. Attempts to rear them in closed containers have 

 been unsuccessful, although some have 

 been reared in a cage containing about 

 36 cubic feet of space. 



The infestation of mushroom beds 

 by manure flies usually results from 

 the introduction of larvae with com- 

 post that afterwards does not get suf- 

 ficiently 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, ex- 

 cept that since the infestation by 

 these pests occurs early in the develop- 

 ment 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 mushrooms more readily than 

 do the sciarid larvae. The greater 

 part of the damage is done early in 

 the season, usually becoming less no- 

 ticeable 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 is about the same as for mushroom flies, 

 except that dusts must be used more liberally, the manure flies being 

 more resistant to pyrethrum. 



Granular calcium cyanide has been recommended for the control 

 of both mushroom flies and manure flies in dosages of V/ 2 to 2 ounces 

 per 1,000 cubic feet, and has proved successful in some cases, al- 

 though in others severe damage to the mushrooms and a retardation 

 of the spawn has been reported. Experiments have shown that, if care- 

 fully used, calcium cyanide in dosages up to 2*4 ounces per thousand 

 cubic feet of air space does no harm to the mushrooms, and that 

 even when repeated at weekly intervals throughout the crop growth 

 no retardation of spawn results. It is very difficult to so regulate 

 conditions in the average mushroom house that moisture, tempera- 

 ture, and humidity can be exactly duplicated from one fumigation 

 to another. Under commercial conditions this will usually be a 

 matter of guesswork, and will therefore vary greatly. Since 

 moisture and humidity largely govern the rate of generation (evolu- 

 tion) of the gas as well as the rate of absorption, it follows that the 



Figure 7. — An adult manure fly, 

 Megaselia alTjidihalteris, X 18. 

 ( Popenoe. ) 



