199 



The LCso's of the four synthetic pyrethroid compounds were very 

 closely grouped (Table 55). Ectiban had the lowest LC 5 at 1.8 ppm and 

 SO 43775 had the highest at h.k ppm. The slopes of the synthetic pyre- 

 throid curves were also closely grouped and approaching 1.0 (Table 55, 

 Figure kO) . This indicates that the susceptibility of the mite popu- 

 lations to these compounds was relatively heterogeneous. This may be 

 due to chlorinated hydrocarbon cross-resistance which has been reported 

 for other acari (Nolan et al., 1977). 



The LC 5 o of ma lath ion at 1.7 ppm was only slightly lower than the 

 LC 50 of Ectiban, but the LC 50 of Sevin at O.k ppm was lower than the LC 50 

 of SD 43775 by a factor of 10. The slopes of the malathion and Sevin 

 curves were less than 0.5, thus the curves were flatter than the syn- 

 thetic pyrethroid curves (Table 55, Figure kO) . This indicates that 

 the susceptibility of the mite populations to these two compounds was 

 more heterogeneous than it was for the synthetic pyrethroids, and that 

 the mite populations are in the process of becoming more resistant to 

 Sevin and malathion (Hoskins and Gordon, 1956). Northern fowl mite 

 resistance to malathion was recorded by Hall et al. (1978). 



Although Sevin had the 'lowest LC 50 , it had the highest LC 90 of ali 



compounds tested (Figure kO) . In order to produce mortalities of up to 



100% in the field, the concentration of Sevin would have to be much 



greater than the LC j concentrations of malathion or the synthetic 



pyrethroids. 



Control of Endemic Florida Strains of Northern Fowl Mites with Carbaryl, 

 Malathion, and Ravap 



Data were collected from one hen in each of the first 120 cages on 



the north side of the four California-style houses at the tilling site. 



