Characterization of Insecticide Resistance in Two Colonies of Liriomyza trifolii (Diptera: Agromyzidae) C. B. KEIU AND M. P. PARRELLA2 J. Econ. Entomol. 83(1): 18-26 (1990) ABSTRACT Two populations of Liriomyza trifolii (Burgess),FLA (from celery, Florida) and NP (from chrysanthemum, California), were examined for insecticide resistance by topical application and comparison with a field-collected, susceptible colony APG (from bedding plants, California). Initially, FLA L. trifolii were moderately resistant to meth- amidophos and permethrin. Resistance in this colony declined over three months in the absence of further selection to the level of the susceptible colony at LCoo ' Experiments with synergists indicated that oxidative and hydrolytic metabolism may have contributed to resistance in FLA L. trifolii. NP L. trifolii were resistant to permethrin, methyl parathion, methamidophos, and a mixture of methyl parathion and permethrin. These flieswere also cross-resistantto DDT and cypermethrin. Oxidative metabolism was implicated asa resistance mechanism but could not account for all resistance to permethrin. Anerve insensitivity factor, kdr-Iike, was probably also active in producing permethrin resistance. Methyl parathion effectively synergized permethrin in experiments in which joint action of these compounds was investigated. Developmental time and body size of NP and APG L. trifolii reared on chrysanthemum did not differ. KEY WORDS Insecta, Liriomyza trifolii, insecticide resistance, synergism Liriomyza trifolii (Burgess) is a major ]eafminer pest on a variety of vegetable, floricultural, and ornamental plants, including tomatoes, celery, wa- termelons, and chrysanthemums. The pest status of L. trifolii has been magnified by resistance to a wide spectrum of insecticides. Leibee (1981) re- ported that chlorinated hydrocarbons, organo- phosphates, oxamy], and permethrin were no ]on- ger effective in controlling Liriomyza spp. on F]orida vegetable crops. Kei] et al. (1985) docu- mented that control failures with permethrin di- rected at L. trifolii on chrysanthemums in southern California resulted from resistance. Mason et al. (1987) demonstrated significant differences in to]- erance to permethrin and fenva]erate in different populations of L. trifolii on Oahu, Hawaii. These differences in tolerance were correlated with use patterns of pesticide at the collection sites for the populations. The first step in devising an insecticide resistance management strategy in a situation where resis- tance has already evolved is to understand the re- sistance mechanisms, the extent of cross-resistance, and the stability of resistance. Possible manage- ment strategies and replacement insecticides can be suggested from these data. The wide spectrum of compounds to which L. trifolii is resistant suggested that enhanced metab- olism of insecticides, an altered target site sensitiv- ity, or both, might account for the observed resis- I Address all correspondence to Delaware Agricultural Exper- iment Station, Department of Entomology and Applied Ecology, University of Delaware, Newark, Del. 19717. • Department of Entomology, University of California, Davis, Calif. 95616. tance. In the studies reported here, synergists were used to inhibit two enzyme systems likely to be effective in metabolizing insecticides that are cur- rently used. Restoration of toxicity after synergist treatment would indicate that resistance was linked to metabolism by the inhibited enzyme. We also tested for cross-resistance to DDT and a cyano- pyrethroid to assess the possibility of an altered target site, similar to kdr found in house flies (Mus- ca domestica L.), that may be responsible for re- sistance to permethrin. When confronted with broad-spectrum resis- tance in a pest, growers will frequently apply tank mixes of insecticides with different modes of action such as organophosphates and pyrethroids. In some cases, mixtures of this type have synergistic joint action (All et al. 1977, Kozio] & Witkowski 1982, Robertson & Smith 1984). Simple greenhouse stud- ies demonstrated that such insecticide mixtures may have synergistic action on L. trifolii (Parrella et al. 1982). A detailed evaluation of this possibility with Liriomyza was needed to provide information con- cerning the effectiveness of this technique for con- trolling resistant ]eafminer populations. In many relatively minor crops, improved effectiveness of pesticides that are already registered may be the only available solution to resistance problems be- cause registrations of materials with new modes of action (Parrella et al. 1988) are rare. In the absence of selection, persistance of an allele or set of alleles conferring resistance to a compound depends on the relative disadvantage of resistant, compared with susceptible, individu- alsoThis fitness reduction is manifested in traits not directly involved in resistance to a particular com- 0022-0493/90/0018-0026$02.00/0 © 1990 Entomological Society of America by guest on January 8, 2016 http://jee.oxfordjournals.org/ Downloaded from