December, '09] JOURNAL OP ECONOMIC entomology 399 



are thus parasitized. On some larvfe he observed Tachina fly eggs, 

 and Perilitus limidiatus Cresson was reared from one pupa. Cook 

 found that Glypta simplicipes Walsh was a very effective parasite of 

 the larvae and also reared Microdus laticinctus from one. Snow reared 

 an unknown tachinid from a larva. Lugger mentions the Baltimore 

 Oriole as a particularly effective enemy of the larvae. 



The outbreak observed by us furnished a case of the most complete 

 parasitism we have ever seen. When first observed in late July from 

 one third to one half of the eggs were parasitized by a species of 

 Triclio gramma. Two weeks later it was difficult to find an egg mass 

 in which over 95% of the eggs did not contain the black pupge of the 

 parasite and in most cases 99 to 100% were affected. So effective 

 were the parasites that the control of the outbreak was undoubtedly 

 due to them much more than to any remedial measures. 



Remedial Measures 



Spraying with arsenate of lead was at once advised by us in the 

 greenhouse above mentioned. The owner hesitated to apply it, how- 

 ever, as it would spot the foliage so as to prevent the sale of any pos- 

 sible blooms, and requested that we experiment with fumigation. 



Fumigation. Experiments were, therefore, made at once with 

 hydrocyanic acid gas. For this purpose we had a large box con- 

 structed which fitted just inside a window-frame of the insectary 

 workroom. (Plate 18.) This was fastened tightly to the frame, 

 was covered with sheathing paper, all cracks stopped with putty, and 

 the crack between the window sashes plugged with cotton. Thus the 

 box was fully as tight as the average greenhouse. By raising the 

 window from the outside, potted plants could be placed within to test 

 the effect on them and the box could be quickly ventilated. On the 

 inside, a tightly sliding door was fastened and over the opening to 

 the box a canvas sleeve, which was tapered and constricted by an 

 elastic band at the end. With this arrangement, the plants, insects, 

 and acid could be placed in the box through the window on the outside, 

 everything made tight, and the cyanide then poured in from the in- 

 side with no possible escape of gas. Furthermore, at any time by 

 inserting one's arm in the sleeve, the sliding door could be raised, a 

 tube containing insects removed, the door then shut, and the tube 

 taken out and subsequently returned in the same way, with practically 

 no loss of gas, thus enabling one to accurately observe the effect on 

 the insects after different lengths of time by having several tubes of 

 insects and taking them out at intervals. The first experiment was 

 made with cyanide at the rate of one ounce to 1200 cubic feet, a rate 



