262 



This time the production rate was not recovered and after 1 week, 

 treated birds were laying at a rate which was less than \% higher than 

 the control birds. If spraying for mites results in a ]% drop in egg 

 production for at least 1 week, but cannot guarantee. a 1% increase over 

 and above the original production level, northern fowl mites should be 

 sprayed, as suggested by Bramhall (1972), only to prevent discomfort to 

 the labor force. 



Long-term compounds like the synthetic pyrethroids could help re- 

 duce the number of times per year that hens must be subjected to the 

 pesticide application stress that occurs when miticides are applied. 

 A well timed application of a long-term miticide when available, could 

 break northern fowl rnite reproductive cycles and prevent unnecessary 

 retreatment of hens. 



Evaluation of the Mite Rating Systems 



The laboratory estimate of northern fowl mite populations was an 

 attempt to correlate field-estimated mite populations with the actual 

 numbers of mites on the hens. However, the data obtained by washing 

 birds are not considered accurate because of the small sample sizes and 

 the high variability within the samples. Since birds were only washed 

 once to remove the mite populations, it is not known if all mites were 

 removed. Also, just one aliquot from each sample was counted. 



Since the laboratory estimate was designed to be used only as a 

 guide, sampling methods that would give statistical confidence were not 

 employed. The devised conversion factor of 8.13 was also used only as 

 a guide. Statistically valid conversion factors would require enough 

 sample numbers to plot a regression line correlating field estimates 

 and mite numbers for actual mite populations. 



