40 Experiment Station Bulletin 363 



less sweet. It is recommended that Blue Hubbard squash be canned at 

 about three months of storage after harvesting, in order to get the best 



quality. 



T. Levcowich 



INSECT CONTROL 



Penetration and Toxicity of Contact Insecticides 



Techniques devised for exploring new chemical compounds as in- 

 secticides were continued during the current year. Scores of new com- 

 pounds have been studied as possible toxic agents in a contact spray. In 

 each case a compound is given an initial screening test in which it is in- 

 corporated at 5.0 per cent in a household spray kerosene, and is applied 

 under controlled conditions to five-day-old adult houseflies specially 

 reared for the purpose. If it gives no performance under these conditions 

 it is considered to offer little promise. If it kills 30 per cent or more of 

 the flies, it qualifies for further study. The spraying technique is so set 

 up as to give 50 per cent mortality of flies ^hen using a standard refer- 

 ence material at 5.0 per cent concentration. 



A second technique which is used with more promising materials 

 invokes appHcation to pea aphids under standardized conditions. Here an 

 arbitrary concentration is used which should give 50 per cent or more 

 mortality if a compound is to be given further attention. 



Basing the research program on these techniques, two groups of 

 compounds have been discovered which give promising performance. 

 In each group about 30 related chemicals have been studied. Several in 

 each group stand out encouragingly. In one group a compound was dis- 

 covered in April which appears to be in a class by itself. The exact chem- 

 ical configuration of this compound is not yet known with certainty, al- 

 though its general structure is determined. For the present, therefore, 

 it is designated merely as No. 431, which is its serial number. 



Since a contact insecticide may find its w idest practical use when 

 applied in dust form, attention has been given to this aspect of the sub- 

 ject. If the compound is a solid, it may be well pulverized and diluted 

 with an inert. This was done with No. 431. Since fineness of division 

 of a compound may be critically important in its performance, a mikro- 

 pulverizer was added to the laboratory equipment and is in active use. 

 Where a new compound is in liquid form the department has studied 

 means of incorporating this liquid with an inert. This can be accom- 

 plished in either of two w^ays: first, by incorporating the liquid in a lim- 

 ited amount of inert and then diluting to a satisfactory dusting condition; 

 second, by atomizing a small percentage of the liquid directh- into the 



inert. 



In the studies of new compounds as contact insecticides, several have 

 been discovered which are repellent to insects. Some of these give prom- 

 ise in that direction. 



The department study of aerosols continues. A special room 

 equipped for this purpose serves the exacting needs well. New formulas 

 are under examination. Two or three of the new compounds discovered 



