THE ALFALFA CATERPILLAR. 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,' 5 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 eurytheme, 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 pupae 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 larvae 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 
