CROSS-RESISTANCE PATTERNS AMONG LUCILIA-CUPRINA (DIPTERA, CALLIPHORIDAE) RESISTANT TO ORGANOPHOSPHORUS INSECTICIDES

Strains of Lucilia cuprina (Wiedemann) have been characterized as havi ng low, intermediate, or high levels of esterase-mediated hydrolysis O f the organophosphorus insecticide, chlorfenvinphos. These levels corr elate respectively with susceptibility to organophosphorus insecticide s, malathion resistance, or diazinon resistance. Diazinon and chlorfen vinphos are diethyl organophosphorus insecticides having 2 ethoxy grou ps attached to their central phosphorus atom, whereas malathion is a d imethyl organophosphorus insecticide having 2 methoxy groups attached to its phosphorus atom, and, unusually, malathion also has 2 carboxyle ster bonds in addition to the phosphoester bonds that define organopho sphorus compounds. We tested larvae for resistance to diazinon and als o assessed representative malathion-resistant and diazinon-resistant L . cuprina strains at the adult stage for resistance to 12 organophosph orus insecticides, including analog pairs differing only in respect to their dimethyl-diethyl status. Two malathion-resistant strains have l ow-level cross-resistance to diazinon (3 to 4-fold), 4 diazinon-resist ant strains have high-level diazinon resistance (11 to 16-fold), and 2 strains with a combined (malathion plus diazinon) resistance type als o have high-level diazinon resistance (17 to 18-fold) relative to 3 or ganophosphorus insecticide-susceptible strains. One of the diazinon-re sistant strains showed approximate to 2 times greater resistance facto rs toward diethyl organophosphorus insecticides than their dimethyl an alogs while (leaving aside malathion to consider only the majority whi ch have no carboxylester groups) a malathion-resistant strain showed 2 -5 times greater resistance factors toward the dimethyl organophosphor us insectides than their diethyl analogs. The diazinon-resistant strai n showed no resistance to 2 di-isopropyl organophosphorus compounds or to 2 organophosphorus insecticides which are asymmetric about the pho sphorus atom (optically active). The malathion-resistant strain showed only slight resistance (<3-fold) to either the di-isopropyl or optica lly active organophosphorus insecticides, including the di-isobropyl a nalog of malathion. These cross-resistance patterns parallel those of certain organophosphorus insecticide-resistant strains of Musca domest ica L., in which diazinon and malathion resistances also are proposed to be esterase mediated, reinforcing other biochemical data suggesting a general mechanism among the higher Diptera.