32 Experiment Station Bulletin 367 



Insecticidal dusts containing the compound was prepared, and for 

 this purpose a power-driven micropulverizer was installed. Dusts con- 

 taining the equivalent of 0.5 per cent of the gamma isomer were made in 

 ample quantity. Other dusts were produced containing 1.0 per cent. Al- 

 so, a dry spray suspension was prepared containing 2.5 per cent. 



These materials w r ere used on about 40 species of economic insects, 

 including some which are difficult to control bv means hitherto available. 

 Adequate control was secured with nearly all. 



In some instances, control was secured where other means hitherto 

 available have not been satisfactory. Thus, a heavy outbreak of a leaf-tier 

 was treated with a dust containing 0.5 per cent of the gamma isomer. 

 Within an hour the larvae had left their shelters within webbed leaves 

 and were on the ground. They soon died. Adults also were killed. 



The compound supplements DDT in important aspects. For exam- 

 ple, it is toxic against all species of aphids studied in the course of the sea- 

 son, whereas DDT is not equally potent. It is speedily effective against 

 all species of thrips that were available for investigation. 



Evidence was accumulated indicating that the vapor of the com- 

 pound, at temperatures of 70°F or over, is toxic to some insects even 

 though present in minute amounts. In this aspect, the compound is some- 

 what different from DDT which has lower vapor pressure. Also, its 

 action is more rapid than that of DDT. With several important species 

 of insects the toxic effects take place within a few minutes. 



A special study was made of the gamma isomer and its relation to un- 

 pleasant flavor developed in some food products to which the complete 

 compound had been applied. Evidence indicated that the gamma isomer 

 does not in itself cause undesirable flavor. Thus, it is hoped that elimina- 

 tion of other parts of the compound will make it usable on fruits which 

 otherwise would develop an unpleasant taste. This is also true on pota- 

 toes, although in this case either the character of the soil, or the moisture 

 content of the potatoes, or both, appear to be significant, since undesira- 

 ble taste was not developed in potatoes when grown in a sandy soil, and 

 was associated with relatively high moisture content in the tuber itself. 



Experiments in the treatment of pools in which mosquito larvae were 

 breeding indicated that a dust containing 0.5 per cent of the gamma iso- 

 mer, applied at the rate of 10 pounds to the acre, gave complete mortality 

 of larvae, both surface-feeding and those which feed below the surface. 



Intensive investigation of this material is continuing since it is un- 

 doubtedly of genuine importance to the control of destructive insects. 



W. C. O'Kane, J. G. Conklin, W. J. Morse 



Penetration and Toxicity of Ovicides 



A compound applied to the eggs of an insect may not prevent hatch- 

 ing, but may cause death of the insect immediately on emergence from 

 the egg. This is especially true where action of the compound is pro- 

 longed for a number of days, and is probably the mode of action of hexa- 

 chlorcyclohexane with reference to insect eggs, although further studies 

 may indicate that this compound, in a suitable penetrating agent such as 



