INSECTICIDES 357 



Japanese beetles. It was found, nevertheless, that Tergitol 7 penetrant 

 can function both as a solvent and as a spreading agent of pyrethrum 

 resins and possesses definite insecticidal properties of its o\\'n.2^ An aqueous 

 solution containing 0.02 per cent total pyrethrins and 0.5 per cent Tergitol 7 

 penetrant gave a satisfactory control of adults (85 to 100 per cent). Of 

 26 species and varieties of plants tested, the foliage of only one (apple) was 

 severely injured, and four species were slightly injured. 



A survey was begun in 1939 to find new wetting agents to improve agri- 

 cultural sprays especially for the control of Japanese beetle. A series of 34 

 wetting agents ^^ were tested in combination A\dth lead arsenate and rote- 

 none sprays for the control of adult Japanese beetles. Ultroil * (a sulpho- 

 nated vegetable oil), when used in combination A\dth lead arsenate, left no 

 visible residue and caused no injury to the foliage of 48 species and varieties 

 of plants tested. This combination appears promising for use on ornamen- 

 tals where a minimum visible residue is desirable. 



Holly leaf miner. Preliminary results ^^ had indicated that a spray con- 

 sisting of two quarts of fish oil, and one quart of nicotine sulphate made 

 up to 100 gallons 'with water and sprayed on the foliage gave a reduction in 

 mines of 91 per cent of the holly leaf miner {Phytomyza ilicicola Loew). 

 Spray applications were made the second and third weeks in May, followed 

 by an application about the middle of June, and a final application around 

 the middle of July. These results were later confirmed by extensive field 

 experiments ^^ made during the season of 1942. It is probable that two ap- 

 plications would be sufficient in a normal year if carefully correlated with 

 the life cycle of the insect, if the first application is made two or three days 

 before the peak, and the second two or three days after the peak of emer- 

 gence of the adults. 



Summary 



The role of surface forces in determining the efficiency of contact insecti- 

 cides has been one of the principal subjects of investigation. 



Spray solutions wet poorly and do not spread over the insect and form 

 a film unless a suitable spreading agent is present. It was also found that 

 spray solutions do not penetrate the tracheal system of insects A\athout a 

 wetting agent. Even with the use of soap as a spreader, the solution did 

 not penetrate the tracheal system of an insect killed -with KCN, indicating 

 that respiratory movements or at least vital activity are necessary for 

 penetration to take place. The angle of contact exhibited by a soap solu- 

 tion with the trachea also indicates that the capillary forces involved can- 

 not account for penetration by this means alone. 



The toxicity of spray solutions containing nicotine and various spreaders 

 follows the same order as the spreading coefficient. 



In the case of pyrethrum it was found that intoxication and death may 



* A product of Hercules Powder Co., Providence, R. I. 



