52 Experiment Station Bulletin 345 



two groups of chemicals. This program, while still leading toward dis- 

 covery of fundamental facts, has been adapted and modeled to give it a 

 concrete and immediate aspect— a search for new and more effective 

 chemicals with which to control destructive insects. 



The department has exceptional equipment for this purpose. Its 

 research laboratories were designed for its fundamental work in insect 

 toxicology. A new apparatus, built by the department, is developed for 

 the purpose of impregnating inert dusts, such as clays and talcs, with 

 chemicals. Another apparatus has been set up to measure the potency of 

 new chemicals that may serve to kill insects. 



Some of the ingredients that have long been used in the United 

 States for manufacture of sprays are already scarce. Some are imported 

 from regions that are in the heart of the war. The department is search- 

 ing for synthetic compounds that can take the place of materials that are 

 scarce or unobtainable. 



Two synthetic chemicals, which ma}' rival the performance of 

 pyrethrum extract, are under investigation. Pyrethrum extract, made 

 from flowers grown in Kenya Colony, Africa, is becoming more diffi- 

 cult to obtain. In another series of studies a new fumigant has been 

 developed. 



Penetration of Oils into Insect Eggs 



Studies were concluded in which penetration of various types of oils 

 into insect eggs was determined. The petroleum oils employed in this 

 investigation included successive viscosities. In addition, the series in- 

 volved terpenes and a fixed oil. 



It was found that penetration was accelerated as viscosity decreased, 

 up to a certain point. A rise in temperature accelerated penetration, but 

 beyond a fixed point lower temperatures did not result in correspondingly 

 retarded penetration. A correlation was found between age of the insect 

 egg and rate of penetration of an oil. In comparing two types of insect 

 eggs a marked difference was observed in the rate of penetration, owing, 

 no doubt, to the characteristics of the egg itself. (W. C. O'Kane, J. G. 

 Conklin) 



Nature of the Insect Epicuticle 



Since the epicuticle is the uppermost layer of an insect's bodv, the 

 nature of this ultimate covering is important. Presumably, a contact 

 insecticide to reach maximum efficiency must be able to penetrate this 

 layer. 



Studies were carried out intended to shed further light on this prob- 

 lem. Experimental work utilized largely the tomato worm, Protoparce 

 quinquemaculata, which, because of its large size, yields conveniently 

 large pieces of integument. 



The epicuticle of the tomato worm was found to be insoluble in all 

 of a wide variety of solvents tested. This is in agreement with the work 

 of previous investigators. The epicuticle Mas found to be extremely 

 resistant to heat, remaining visibly unchanged after heating to 180° Centi- 

 grade. 



