April, '21 parrott: dusts for sucking ibsects 213 



while seeking to reduce the cost of insecticides encouragement should 

 also be given to improving machinery which will insure both thorough 

 and economical distribution and thus produce maximum benefits with 

 minimum dosage. I merely wish to emphasize the practical bearing of 

 this phase of the problem. I have not attempted to suggest modifica- 

 tions, but the improvement of machinery to meet the requirements of 

 different crops needs serious attention. 



Chemical Assistance in the Investigation of Dust Mixtures 



In considering materials for dusting to combat such insects as aphids, 

 capsids, etc., it should be noted that there is not a wide range of avail- 

 able substances with desirable insecticidal properties. At present nico- 

 tine sulfate is widely used, and is certainly the most effective constituent 

 of dust mixtures which function as contact insecticides. A serious 

 drawback to its extensive employment for this purpose is its high cost, 

 and besides it has not always been available in sufficient quantities for 

 commercial operations. The situation reveals a great need of more 

 knowledge concerning the insecticidal properties of other substances, 

 as there are doubtless various organic compounds equal to nicotine in 

 value. 



What is true of organic substances holds equally well with inorganic 

 compounds. There is probably a large range of chemical agents which 

 could be prepared in commercial quantities as soon as their properties 

 are known and a need created for them. 



Mention is made of these facts in order to focus attention on the 

 promising field that awaits investigation and to emphasize the great need 

 of cooperation between entomologists and chemists. Entomology is 

 greatly handicapped by a lack of chemical assistance. In plans for the 

 development of efficient dusting preparations it is not sufficient to have 

 expert assistance in the quest for new insecticides only. It is also highly 

 important to have technical knowledge relative to the physical condi- 

 tion of the materials used and of the influence of the physical properties 

 on the effectiveness of the substance as an insecticide, since this is 

 dependent upon factors other than its mere chemical composition. 

 The difficulties that beset the dusting problem, plead loudly for more 

 constructive efforts along these lines and for a sharpening of the weapons 

 of the entomologist. 



Conclusion 



In conclusion, this symposium, attracting as it does workers from the 

 fields of phytopathology and entomology, constitutes a significant step, 

 probably more important than is generally realized. The discussions 

 should bring up new points of view and yield keener analyses of methods 



