79 



become a matter of considerable economic import. Doubtless the 

 youngest caterpillars of the first generation could be readily reached 

 by means of a spray of Paris green, arsenate of lead, or other arsen- 

 ical, and this would have the effect of greatly reducing the insect 

 for future generations, provided the work is carried on thoroughly. 

 Or the arsenical could be distributed dry, as used against the cot- 

 ton worm, by shaking it from bags fastened to each end of a 

 board or pole and carried by a man mounted on a mule or horse. 

 Later generations of the caterpillars will be apt to be more numerous 

 and more difficult of treatment on account of the difficulty of placing 

 the poison where all of the caterpillars Avill be reached. — F. H. C. 



•VN INSTANCE OF COMPLETE PARASITISM OF THE IMPORTED CABBAGE WORM. 



A number of maturing caterpillars of Pier'ts rapfv were gathered 

 at Washington, August 28, 1904, to ascertain Avliat percentage might 

 be parasitized at this time, as many were obviously injured. kSixty 

 per cent of all that could be found in the last stages developed para- 

 sites of the im2:)orted Braconid Apanteles glomeratus Linn., all of 

 Avhich issued in masses of cocoons from their host within two days 

 after the latter were taken under observation. The remaining cater- 

 pillars all transformed to pupa^ and thereafter to perfect butterflies. 



During the first week of September another lot of these cabbage 

 " worms " Avas obtained from cabbage and other cruciferous plants 

 from our experimental garden, all of the mature individuals that 

 could be secured. These were counted and cared for in the same 

 manner as before, and toward the end of the first week it was noticed 

 that not a single larva had survived. No pupae were formed, and 

 therefore no butterflies issued, and since a mass of Apanteles cocoons 

 was counted for each caterpillar that had been gathered, a case of 

 complete parasitism was proven. As soon as it was noticed that the 

 caterpillars had failed to pupate, both larvae and pupae were sought 

 for on the grounds, but wdth negative results, showing that the same 

 condition existed both in rearing jars and in the open. 



The cocoons of Apanteles glomeratus were counted and found to 

 vary from 30 to 35 to a mass; in other words, a full-grown cater- 

 pillar usually harbors about this number of parasites. A secondary 

 parasite was observed issuing from a comparatively small proportion 

 of the Apanteles cocoons. In one instance the Apanteles and the 

 secondary parasite, a chalcidid, Tetrastichvs mirrogastri Bouche, and 

 an introduced form like the primary parasite and its host, were in 

 equal numbers. In another case the proportions were 13 to 40. The 

 usual number of secondary parasites was 2 to each primary parasite, 

 but in some cases 3 of the secondary parasites must have issued from 

 a single cocoon. — F. H. C. 



