Entomology 



House flies Build Up a Resistance 

 to DDT and to Certain Other In- 

 secticides. The toxicity to house- 

 flies of various contact insecticides 

 has been studied for the past several 

 years. In comparing the effect of 

 various materials this year with the 

 results obtained during each of the 

 past three years it was immediately 

 evident that the flies were developing 

 a resistance to the insecticides. With 

 respect to DDT. lethane, and the 



pyrethins the resistance was twice as 

 great this year as it was three years 

 ago. In the case of benzene hexa- 

 chloride, the resistance of the house- 

 flies increased approximately seven 

 times. It is assumed that this in- 

 creased resistance is caused by the 

 continued elimination of the weaker 

 individuals over a period involving 

 many generations. 



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

 R. L. Blickle, and W. J. Morse 



New Pesticides are Effective in 

 Controlling the European Red Mite. 

 Hexaethyl tetraphosphate, DN 111, 

 DND 4, and Xanthone were tested 

 for the control of the red mite on 

 apple trees. The initial reductions 

 in mite population as compared with 

 the untested trees were as follows: 

 Haxaethyl tetraphosphate — 99.3 per 

 cent; DN 111, 97.4 per cent; DND 4, 

 96.7 per cent, and Xanthone, 90.5 

 per cent. Although hexaethyl tetra- 

 phosphate gave the highest initial 

 control the mite population later 

 built up on the plots so that they ex- 

 ceeded those on the check plots. 

 The reason for this is that this chem- 

 ical does not kill the eggs and it also 

 affects the natural parasites of the 

 red mite. If one application only is 

 to be made, hexaethyl tetraphosphate 

 is not recommended. 



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

 R. L. Blickle, and W. J. Morse 



Four Applications of DDT Dust 

 are Needed to Control the European 

 Corn Borer. The marketability of 

 sweet corn in New Hampshire is 

 seriously affected by European Corn 

 Borer damage. Effective and cheap 

 methods of control are highly neces- 

 sary for the successful production of 

 sweet corn. The New Hampshire 

 Agricultural Experiment Station is 

 studying the effectiveness of different 

 methods of control. Although re- 

 search is continuing on this problem 

 we now recommend four applications 

 of a 3 per cent DDT dust. Fair con- 

 trol can be obtained with three ap- 

 plications, but two applications are 

 entirely unsatisfactory. 



Fig. 5 — Doctors Slanetz and Allen 

 examine mastitis cultures. 



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

 R. L. Blickle and W. J. Morse 



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