260 



Mite control of 100?; was achieved for 36 days with SD 43775 and 

 BW 21Z on floor-housed hens. Hall et al . (1978) had similar results 

 for 57 days with much lower concentrations of SD 43775- The reason 

 for the extended mite control by synthetic pyrehtrins may be due to 

 their ability to persist on the chickens' feathers (Hall et al., 1978). 



Since the floor litter was not sprayed, the results of the synthetic 

 pyrethroid test were particularly interesting. Mites can exist off the 

 host for 2 to k weeks (Cameron, 1938; Baker et al., 1956; Kirkwood, 1963; 

 Loomis, 1978), and the litter at Chipley, which was compacted and 

 moderately damp beneath the surface, provided conditions necessary for 

 mite survival. After short-term acaricides have broken down, mites 

 hiding in the litter are available to reinfest the birds, but synthetic 

 pyrethroids persist long enough to break this cycle. 



The Effects of Northern Fowl Mites on Egg Production 



When 12 strains of laying hens were treated for control of northern 

 fowl mites, significant differences in production could not be detected 

 when combined production means were compared by treatment. Although 

 investigators have claimed that decreases in egg production were due to 

 northern fowl mites (Cameron, 1938; Metcalf et al., 1962), recent studies 

 have not been able to corroborate these claims (Loomis et al., 1970; 

 Eleazer, 1978; DeVaney, 1979). One author suggested that mites be con- 

 trolled solely to prevent worker discomfort (Bramhall, 1972). 



Comparison of production means of each strain individually revealed 

 a significant increase in production in one strain due to mite removal. 

 Five other strains had nonsignificant improvements in production which 

 compared favorably 10 the results of Combs et al. (1976). 



