79 



become a matter of considerable economic import. Doubtless the 

 3^oungest 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 haxe the effect of greatly reducing the insect 

 for future generations, provided the Avork 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 jDole 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 will be reached. — F. H. -C. 



.\.X INSTANCE OF COMPLETE PARASITISM OE THE IMPORTED CABBAGE WORM. 



A number of maturing caterpillars of Pieris rapw were gathered 

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

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

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

 sites of the imported Braconid Afanteles glomeratus Linn., all of 

 which issued in masses of cocoons from their host within tAvo days 

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

 ]3illars all transformed to pupa3 and thereafter to perfect butterflies. 



During the first Aveek of September another lot of these cabbage 

 '• Avorms " Avas obtained from cabbage and other cruciferous plants 

 from our experimental garden, all of the mature indiA^duals that 

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

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

 that not a single larva had surviA^ed. No pupae Avere 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 Avas proA^en. As soon as it Avas noticed that the 

 caterpillars had failed to pupate, both larvae and pupa^ were sought 

 for on the grounds, but Avith negatiA^e results, shoAving that the same 

 condition existed both in rearing jars and in the open. 



The cocoons of Apanteles glomeratus Avere counted and found to 

 A'ary from 30 to 35 to a mass; in other Avords, a full-groAvn cater- 

 pillar usually harbors about this number of parasites. A secondary 

 parasite Avas obserA^ed issuing from a comparatively small proportion 

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

 secondary parasite, a chalcidid, Tetrastichits microgastri Bouche, and 

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

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

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

 but in some cases 3 of the secondary parasites must haA^e issued from 

 a single cocoon. — F. H. C. 



