Contagious Diseases of Insects. 295 



the worms and selecting others as a check on those treated, but 

 the appearance in this field, at about this time, of the common 

 flacherie of the cabbage worm, and the death, from this cause, of 

 several of both lots of larvae interrupted the experiment. The 

 general outbreak, also, of the same spontaneous affection of the 

 Pieris larvae elsewhere in the vicinity, precluded all attempts 

 at a repetition of these field experiments. 



THE YELLOW -NECKED APPLE CATERPILLAR. 



(Datana ministra, Drury.) 



On this species my first studies of the bacterial diseases of 

 caterpillars were made in the autumn of 1883. The affection 

 which attracted my attention broke out in our breeding room 

 shortly after the larvae were collected, but was not seen among 

 the species anywhere in the field. It probably was not differ- 

 ent from the disease well known to entomologists who rear 

 caterpillars to the imago, especially liable to appear in close and 

 sultry .weather, and when the breeding cages are insufficiently 

 ventilated. 



A lot of the larvae, two or three hundred in number, 

 obtained July 23, was reported to me, August 1, to have been 

 mysteriously dying for several days at the rate of two or three 

 a day. The small room in which they were kept was open to 

 the south by a large window, and breeding cages of ample size 

 were used, so placed as to be well ventilated. The larvae were 

 fed and the cages cleaned daily. 



DESCRIPTION OF THE DISEASE. 



Except that no change of color was usually perceptible, the 

 symptoms of this disease were not especially different from 

 those which have been already given for the silkworm and 

 cabbage worm. Sluggishness and evident weakness and loss of 

 appetite were the first noticeable phenomena. A larva while 

 resting upon a vertical surface would often partly lose its hold, 

 and hang only by a few of the legs, this occurring long before 

 the power of active locomotion was lost. As a very common 

 thing a discharge of a brownish fluid from the vent occurred 

 early in the disease, but occasionally this symptom was not 



