RELATIVE EFFICACY OF ORGANOPHOSPHORUS INSECTICIDES AGAINST SUSCEPTIBLE AND RESISTANT STRAINS OF THE STRIKE BLOWFLY LUCILIA-CUPRINA (CALLIPHORIDAE) IN NEW-ZEALAND SHEEP

Four groups of five Romney lambs were treated by plunge dipping with o ne of four registered organophosphorus flystrike preventatives. Untrea ted lambs acted as controls. The sheep were challenged at weekly inter vals with larval implants of organophosphate-susceptible and -resistan t strains of Lucilia cuprina. All four treatments provided 19-21 weeks protection against susceptible larvae but chlorfenvinphos provided th e longest protection(16-17 weeks), followed by propetamphos(15-16 week s), dichlofenthion (10-13 weeks) and diazinon (9-13 weeks), against th e resistant strain.