THE ALP ALFA CATEEPILLAE. 27 



Flora W. Patterson, of the Bureau of Plant Industry, has determined 

 this as a Fusarium. In her letter she says : " The fungus, which bears 

 strong evidence of being parasitic, has quite filled the body cavity and 

 is either a Fusarium or Microcera," and states that the majority of 

 similar fungi are reported upon scale insects. Later she says, " Cul- 

 tures of the above fungus, parasitic upon Eurymus euri/theme, have 

 developed in the most satisfactory manner, and it is probably an 

 undescribed parasitic Fusarium." 



A DISEASE. 



As has been mentioned earlier in this paper^ a disease which is 

 probably bacterial and resembles flacherie of the silkworm is quite 

 common upon larvae and pupa? of Eurymus. At times, evidently 

 during periods of higher humidity accompanied by warm weather, 

 as in July and August, it becomes so widespread as to kill a great 

 majority of a brood and often nearly annihilates it. This disease is 

 by far the greatest natural check against which the alfalfa cater- 

 pillar has to contend and is one of the most important factors look- 

 ing toward its control. 



The dead worms, which are nothing but soft decayed masses found 

 hanging to the alfalfa stalks, are sometimes so numerous as to make 

 sweeping with an insect net impossible, the net in a few sweeps be- 

 coming so foul as to render other insect specimens of little value. 

 The disease has proved a great detriment to the successful carrying 

 on of life-history experiments and the rearing of parasites, owing 

 to the fact that large percentages of larvse taken to the laboratory 

 and confined often die from it. Frequently, where a hay crop is not 

 totally destroyed by a brood of caterpillars before they are killed by 

 this disease, the decayed remains on the hay become so foul as 

 to render the hay quite unpalatable for horses and hence of low 

 value. 



As has been suggested, the development of the diseased condition 

 in either larvae or pupae — for it attacks both — depends largely upon 

 moisture. The disease is present at all times, and a few larvae from 

 each brood are killed, but it is only when a period of high humidity 

 accompanied by warm weather occurs that it becomes so prevalent as 

 to attack the worms in large numbers. It has been found that at 

 certain times these conditions of moisture may be produced arti- 

 ficially by irrigation, and, as is discussed in a later paragraph, the 

 disease, thus fostered, is utilized as a factor in controlling the pest. 

 That the disease does not at all times keep the caterpillar in check 

 is doubtless due to the dry climate of these southwestern countries, 

 and a comparison of the conditions in the Imperial Valley of Cali- 

 fornia with those in the Salt Eiver Valley of Arizona supports this 

 view. The Imperial Valley is unique in location, being below sea 



