38 EXPERIMENT STATION BULLETIN 351 



INSECT CONTROL 



Penetration of Contact Insecticides 



The insect toximeter \\hich was developed in the department of 

 Entomology and described in a previous report was adapted to studies of 

 adult insects capable of flying while a test is in progress. A spherical cage 

 was devised and made available in quantity in order that replications might 

 be run without delav. A cage is maintained on the turntable of the toxi- 

 meter and is slowly revolved while an application of a test material is pro- 

 ceeding. The atomized spray is directed toward the cage from opposite 

 points so that the two cones of spray meet in the cage and fill it with mist. 

 After the caged insects have been subjected to a spray the cage is removed 

 and the insects are transferred to an observation cage. The test cage is 

 then washed in acetone to remove spray residues. 



House fly adults were used for this series of experiments. A room 

 in which temperature and humidity are controlled was equipped for 

 rearing flies in large numbers. A second room, also equipped for control 

 of temperature and humidity, was equipped w ith racks on which a large 

 number of observation cages could be placed. 



Various synthetic organic compounds, dissolved in household spray 

 kerosene, were studied as to toxicity. Among these, three were dis- 

 covered which gave promising performance. These three represented 

 two new groups of synthetic compounds. Each of these was toxic to 

 adult house flies in reasonable concentration. Each of the three gave 

 initial paralysis as well as ultimate death. 



In the present war emergency these studies are especiall\' important 

 because such compounds as these may be able to take the place of im- 

 ported supplies of pyrethrum, gro\\n in Africa and now unavailable ex- 

 cept in limited quantities. Because of the fact that contact sprays such as 

 the ones described are important in control of insects carr)'ing human 

 disease, discovery of materials which can be made in a chemical manu- 

 facturing plant has added significance. 



In the course of these studies a large number of tests have been run 

 and a large amount of data accumulated on the characteristic performance 

 given by various chemicals when utilized as contact insecticides. 



A further study of contact insecticides involved investigations in the 

 performance of materials in the form of dusts. As a part of the necessary 

 equipment an apparatus was built for impregnating inert materials such 

 as talc or pyrophyllite with controlled amounts of a toxic substance in 

 liquid form. Impregnation \\'as accomplished by delivering the inert into 

 a chamber at a controlled rate and by atomizing the liquid into the midst 

 of the dispersed dust as it entered the chamber. 



The usual procedure for preparing impregnated dust is first to pre- 

 pare a so-called "master batch" which is made l)\' adding a measured 

 weight of liquid to a measured weight of inert in a ball mill, or other mix- 

 ing device, the liquid present in much larger percentage than is desired in 

 the final product as actually used. This "master batch" is then diluted by 

 mixing with an inert. In the apparatus constructed in the entomological 

 laboratory the liquid toxicant is atomized into a dispersed inert in the 

 exact proportion in which it is ultimately to be studied. In the case of the 



