115 



not having had very encouragmg results owing to lack of concerted 

 action and natural difficulties. The mustard aphis caused considerable 

 damage, but was controlled in a small area by spraying with crude oil 

 emulsion. Jute was attacked by Diacrisia obliqua and Cosmophila 

 {Anomis) sahulifera, measures against which were only partially 

 successful. In one district borers in sugar-cane are being effectively 

 controlled and several new borers in citrus trees have been sent to 

 Pusa for identification. 



Moore (W.). Observations on the Mode of Action of Contact In- 

 secticides. -J/. Econ. Entom., Concord, N.H., xi, no. 6, December 

 1918, pp. 443-446. 



In a recent paper on the physical properties governing the efficacy 

 of contact insecticides [see this Review, Ser. A, vi, p. 397] it was 

 shown that fat solvents, oils and soaps were able to penetrate the 

 tracheae of insects by capillarity. It was also noticed that heavy, 

 practically non-volatile and non-toxic oils that had thus penetrated 

 the tracheae caused the death of the insects, but that the tissues of 

 such insects were not stained by trypanblue until ten, twenty or more 

 hours had elapsed. The question then arose as to whether the insects 

 did not die from lack of oxygen resulting from the closing of the 

 tracheae. 



Experiments with contact insecticides containing oil or soap, 

 ■which are detailed in this paper, show that such an insecticide may 

 penetrate the tracheae of the insect, thus preventing normal oxida- 

 tions from taking place in the insect's body, with the result that the 

 insect dies from their mechanical action alone. It is necessary, if 

 death is to be insured, that all the tracheae be filled with the spray.; 

 The vapour of the insecticide, such as nicotine, may produce 

 death by chemical action without materially influencing the intake 

 of oxygen. For small insects, such as Aphids, an insecticide killing 

 in a mechanical way alone will give good results, since all or nearly 

 all the trachea will be filled. For larger insects, such as Lygus- 

 prafensis, L. (tarnished plant bug), it is not likely that all the tracheae 

 would be filled and therefore it would be necessary to add to the spray 

 an insecticide capable of killing in a chemical manner in order to ensure 

 death even if only one trachea were filled. The efficacy of free 

 nicotine sprays is found to be increased, sometimes by 50 per cent., 

 by the addition of soap. 



In studying the effect of laundry processes upon the active stages 

 of Pediculus humanus {corporis) (clothes louse), it was found that 

 this insect is able to close its tracheae quickly enough to keep out 

 soap solutions, lubricating oils, oxylene, and frequently even ether. 

 Haematopinus suis (hog louse) and H. piliferus (dog louse) have the 

 same power in a less degree. Cteyiocephalus cams {Pidex serraticeps) 

 (dog flea), Pseudococcus (mealy bug), Coccus (soft scale), Musca domes- 

 tica (house-fly), larvae and adults of Sitotroga cereaJella (Angoumois 

 grain moth), larvae of Hemerocampa {Notolophus) leucosligma (tussock- 

 moth) and Aeyrthosiphon {Macrosiphum) pisi, Kalt. (pea aphis) were 

 all found to be unable to prevent the penetration of ether, but it 

 does not follow that some of these might not be able to shut out 

 heavy oils or soap solutions. If parasitic lice, ticks, etc. should be 



