December, ’18] 
MOORE: ACTION CONTACT INSECTICIDES 
445 
Exp. 12. One injected larva dipped in light lubricating oil so as to fill treachese of 
cephalic portion and another dipped to fill tracheae of caudal end. Removed, heart 
beating and larvae did not lose its blue color. Placed in water until stupefied and 
heart had ceased to beat. Larvae now colorless were removed to the air and dried, 
when the portion with oil filled tracheae remained colorless while the other half of the 
larvae assumed a bright blue color. Later the larvae revived, the heart started beating 
and the whole larvae became blue. 
Exp. 18. Injected larva placed in soap solution becoming colorless. Removed, 
carefully washed in distilled water and rolled on filter paper to remove as much as 
possible of the soap solution from the tracheae. Within an hour, a bluish color devel¬ 
oped in the vicinity of each spiracle, until after ten hours, the larva was irregularly 
blue over the entire body. 
These experiments show that a contact insecticide containing oil or 
soap may penetrate the tracheae of the insect; thus preventing normal 
oxidations from taking place in the insect’s body with the result that 
the insect dies from their mechanical action alone. In order to insure 
death in this manner, it is necessary that all the tracheae be filled with 
the spray. The vapor of the insecticide such as nicotine may produce 
death by chemical action without materially influencing the intake of 
oxygen. For small insects such as plant lice, an insecticide killing in 
a mechanical way alone will give good results, since all or nearly all 
the tracheae will be filled. For larger insects, such as the tarnished 
plant bug ( Lygus pratensis L.) filling all of the tracheae becomes un¬ 
likely, hence it would be necessary to add to the spray an insecticide 
capable of killing in a chemical manner, thus insuring death, even if 
only one trachea is filled. Field experiments with sprays containing 
free nicotine have shown that the efficacy of such sprays is sometimes 
increased 50 per cent, by the addition of soap. These experiments 
were conducted during the past summer by S. A. Graham and will be 
reported by him elsewhere. 
A further point, however, which has a decided bearing upon this 
question, arose in the study of the effect of laundering processes upon 
the destruction of active stages of the clothes louse ( Pedicuius corporis ). 
In these experiments it was shown that the clothes louse was able to 
close its tracheae quickly enough to keep out soap solutions, lubricating 
oils, xylene, and in seven cases out of twelve, even ether was prevented 
from entering. A few experiments have shown that the hog louse 
(.Hcematopinus suis) and the dog louse ( Hcematopinus piliferus ) possess 
a similar power of keeping ether out of their tracheae, but are not as 
successful in general as the clothes louse. The dog flea ( Pulex serra- 
ticeps), mealy bugs ( Pseudococcus sp.), soft scale ( Coccus sp.), house¬ 
flies ( Musca domestica), angumois grain moth, larvae and adults ( Sito - 
troga cerealella), tussock moth larvae ( Notolophus leucostigma) and pea 
aphis ( Macrosiplum pisi Kalt) were all unable to prevent the penetra- 
