Show i Fly Immunity to o DDT Is Debatable Question Some Insects Develop Strain of Resistance Do flies become immune or resistant re to DDT after it has been used for a few years This q que u e s t 11 i o 0 r 0 a arises from the fact that a few fly con f failures ail u res or orf f farms 3 r m s where DDT of raa was e effective f f e c t i v e ir it other years h hl have a V E been h hard a r d to account ac as count for The explanation explanation ex ex- t was thai that the f flies l lie i e s probably had become resistant resistant resist ant to the chemical Uncle Sams Sam's entomologists admit admi that insects can develop resistance to the insecticides used against them as in the case of the apple codling moth against which lead arsenate arsenate ar- ar senate lost its effectiveness Moreover Moreover More More- over Uncle Sams Sam's bug men say they have in the laboratory been able to develop a resistant DDT-resistant strain of oi flies It is not likely that a DDT DDT- resistant strain would develop naturally naturally nat nat- in the short time since DDT was first first- used It is more reasonable to believe that the occasional failure on farms where DDT already has been used with good results is due to carelessness careless ness or inferior product One thing in particular that should accompany the use of DDT is the destruction or removal of fly breeding breeding breed breed- ing places su such h as manure piles weed piles old stack bottoms and wet spots in barnyards One or more such spots may be able to turn out flies flics faster than DDT can kill kiIl them for DDT is not noted for fast action A fly may survive for fOI hours after alighting on a surface coated with DDT |