icjio] Pedicidoides Noxious to Man 



37 



the original one. The hght thrown upon the cases of eruption 

 noted by Dr. Harris with reference to Isosoma hordei has ah-eady 

 been explained. The present outbreak of the joint worm in the 

 Ohio Valley probably originated in the upper Shenandoah Valley 

 of Virginia, extending northward and westward throughout West 

 Virginia and eastern Ohio. When investigation of the insect was 

 taken up in 1904, a parasite, Ditropinotus aureoviridis , was 

 also noted in excessive abundance, but for some reason it did 

 not overcome the joint worm. This phenomenon has been noted 

 continually. Since that time it has been a perpetual enigma to me 

 why it was that with such an abundance of its natural enemies 

 the joint worm should continue to spread and increase in destruc- 

 tiveness. Now% however, that we know that this predaceous mite 

 is able to develop through a series of years in such immense num- 

 bers in connection with the joint worm, the matter comes nearer 

 a solution. Ditropinotus, as well as some other parasitic enemies 

 of the joint worm, emerge in early July from eggs that were pre- 

 viously placed in the cells occupied by the joint worm. As soon 

 as these adult parasites emerge they at once oviposit in cells con- 

 taining joint worm larvae of the same generation from which they 

 themselves developed. The puncturing of these cells by the 

 ovipositor of these parasites, particularly Ditropinotus, opens a 

 way for the entrance of this microscopic mite, and, once inside of 

 the cell, it will destroy everything therein, whether it be joint 

 worm or parasite. Thus the predaceous mite has prevented the 

 other parasites from exerting their full influence, because it has 

 continually checked the increase of other parasites, thereby pre- 

 venting them from increasing and exerting the restraining influ- 

 ence upon the joint worm that, but for this mite, they probably 

 would have done. 



In the light of the foregoing, it would appear that the only 

 wa3' to evade this disorder among humans, caused by this mite, 

 lies the prevention of the occurrence of these two destructive 

 grain insects which are responsible for the abundance of the mite 

 itself. There is, therefore, a double incentive for the farmer to 

 use every effort to prevent the occurrence of these pests in his 

 fields. In many fields in Ohio we have found that more than 

 one-half of the straws had been attacked by joint worm, and the 

 damage resulting from their attacks amounted to a considerable 

 percentage of the farmers wheat crop. See Plate V, fig. 2. 

 If, in addition to this, his own family and employees are to suffer 



