30 



The area on the host most preferred by the northern fowl mite is 

 the vent region (Cameron, 1938), but in severe infestations, mites can 

 be found over the entire body (Anonymous, IS59; Metcalf et al., 1962; 

 Loomis et al., 1970). Cameron (1933) seldom found m.ites on young birds. 

 Kirkwood ( 1 968 ) also found this to be true and suggested that it may be 

 due to lack of contour feathers. He and others (Cameron, 1938; Abasa, 

 1965) stated that roosters have more mites than hens, possibly due to 

 differences in plummage. Males have more contour feathers near the vent, 

 while females have more down near the vent. Feathers are preferred 

 over down by 0. sylvianin (Kirkwood, 1 968) . 



Cameron (1938) described the erratic behavior of mite populations 

 on poultry. Mites transfer from bird to bird and populations rapidly 

 rise and decline, but some birds remain entirely free of mites. This 

 phenomenon has been seen by other authors (Kirkwood, 19&3; Loomis et al., 

 1570), who were also unable to explain its cause. Hall and Gross (1975) 

 found that roosters with high levels of plasma cert icosterone response 

 to social stress that were maintained at high levels of social stress 

 had lower mite populations than when the conditions were reversed, 

 inherited levels of cort icosterone had more effect on mites than did 

 stress alone. it was also found that hens subjected to higher social 

 stress had significantly lower mite populations than unstressed hens 

 (Hall et al., 1378; Turner, 1978). Additional experiments indicated 

 that although hens first coming into production are most susceptible to 

 northern fowl mite infestation, estrogen alone is probably not responsi- 

 ble for the difference in mite susceptibility between hens and roosters 

 (Hall et al., 1978) . 



