25 



poultry houses. The system provided effective fly control and cost in 

 the range of other fly control systems. 

 Contact residuals and resistance 



The ability of insects to develop resistance was questioned by 

 Melander (191*0. The question was answered when DDT resistance was re- 

 ported from several countries in Western Europe in 1947 (West, 1951). 

 One year later. DDT resistance was reported in the U.S. (h'ansens et al., 

 1 948) . DDT had only recently been advocated for use on poultry farms 

 despite its slow knockdown and kill (Wol fenbarger and Hoffmann, 1944). 

 A survey in Canada showed that house flies were still highly resistant 

 to DDT (Batth and Stalker, 1970). 

 Sequential formation of resistance to contact residuals 



In 1953, Hansens reported that lindane, methoxych 1 or , chlordane, 

 and dieldrin applied as residual sprays failed to give control of house 

 flies. The residual action of diazinon extended 10 weeks against sus- 

 ceptible flies and 4 weeks against resistant flies (Hansens and Bartley, 

 1953). Resistance to diazinon was noted soon afterward (Hansens, 1958) 

 and in Florida it was reported to be S~ to 38-fold (LaBrecque et al., 

 1958). By 1970, diazinon resistance was 8- to 62-foid in New Jersey 

 and a 1 % solution failed to give satisfactory control (Hansens and 

 Anderson, 1970). Flies showing resistance to diazinon also showed re- 

 sistance to stirofos (Fickens et al., 1972), DDT, methoxychlor , chlor- 

 dane, dieldrin. lindane, parathion, malathion, dicapthon, ronnel, 

 trichlorfon, and conmaphos (Hansens, 1958). 



Malathion resistance in Florida was about 4-fold in 1956 (LaBrecque 

 and Wilson, 1961) , 133-fold in 1953 (LaBrecque et al., 1958), and 275- 

 fold in I960 (LaBrecque and Wilson, 1961). 



