90 



CIRCULAR 457, U. S. DEPARTMENT OF AGRICULTURE 



nymph is a little larger than the larva and ha? eight legs instead of 

 six. After a longer period of feeding and after undergoing two 

 more molts the nymph becomes an adult mite. At 75 D F. these mites 

 require about 2 weeks to complete their development from egg to 

 adult, while at 55° an average of over 7 weeks is required. 



At rare intervals a migrating stage or condition may occur between 

 two of the nymphal molts, known as the hypopus. In the hypopial 

 stage the mite is flattened, with eight legs, rudimentary mouth parts. 

 and an area of suckers on the ventral side. Not every individual 

 passes through this stage, and the conditions under which it is 

 formed are not well understood. Although unable to feed, the 

 hypopus can survive for a long time under adverse conditions. It 

 will grasp and cling to any moving object with which it comes into 

 contact, and is capable of being carried about by flies and gamasid 

 mites, and on the clothing of workers in the mushroom houses. Flies 

 have been seen that were so covered with mites in the hypopial stage 

 that they were unable to fly. TThen the hypopus drops or is brushed 

 off, it continues its development into an adult mite if it finds condi- 

 tions favorable. 



Prevention of infestation by the mushroom mite is the only certain 

 means of avoiding damage to the crop. It is important that the beds 

 go through a good heat, as the mites are nearly always present in 

 the manure and can be controlled most effectively by killing 1 them at 

 this time. Control by chemicals has been attempted, but in most 

 cases has not been successful, or only partially so. 



When Tyroglyphus mites are numerous on the surface of the beds. 

 flame or hot water will destroy many of them, but will not affect 

 those in the compost. Certain growers report fair control by the 

 use of live steam from a steam atomizer, with a little aniline added. 



THE LONG-LEGGED MITE 



The long-legged mite (Linopodes antennaepes Banks) fig. 9) is 



less abundant than the mushroom mite. It is extremely difficult to 



control. In some places it occurs sporadically, while in others, al- 

 though nearly always present, it is said to do little damage. Since 

 it is native to this country, occurring normally under leaves and 

 boards on the ground out of doors, it may be brought into nearly any 

 mushroom house, and if proper conditions are present it may develop 

 into a serious pest. The body is very minute, yellow to reddish brown, 

 and the legs, especially the front pair, are very long and slender. 



Very little is known of the life history of this mite. The minute 

 round eggs are laid hi groups in the casing soil and hatch in about S 

 or 10 days into very small white larvae. These molt in 6 or S days 

 into nymphs, with longer front legs than hi the preceding stage. These 

 mites have never been observed damaging spawn, and several attempts 

 to rear them beyond the first nymphal stage on spawn have been un- 

 successful, so it is probable that the activities of this species are 

 almost entirely confined to the surface of the mushroom beds. They 

 damage mushrooms by chewing off the feeder roots of the growing 

 mushrooms, causing the sterns to constrict at the base, and injuring 

 or killing the developing mushrooms. 



Sanitation and prevention of infestation are the best methods of 

 avoiding damage by these mites. The mites are easily killed bv heat. 



