Pesticide Biochemistry and Physiology 85 (2006) 161–166 www.elsevier.com/locate/ypest 0048-3575/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.pestbp.2005.11.007 IdentiWcation of mutations in the para sodium channel of Bemisia tabaci from Crete, associated with resistance to pyrethroids Emmanouil Roditakis a , Anastasia Tsagkarakou b , John Vontas c,¤ a Laboratory of Entomology and Agricultural Zoology, Plant Protection Institute of Heraklion, National Agricultural Research Foundation, Heraklion (N.AG.RE.F.), 71003 Heraklio, Greece b Laboratory of Plant Biotechnology, Institute of Horticulture and Floriculture, National Agricultural Research Foundation, Heraklion (N.AG.RE.F.), 71003 Heraklio, Greece c Laboratory of Pesticide Science, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece Received 13 September 2005; accepted 2 November 2005 Available online 6 March 2006 Abstract We investigated the mechanisms of resistance to -cypermethrin in a Q biotype, highly resistant Bemisia tabaci strain (GRMAL-RP) isolated from Crete. Cytochrome P450-dependent monoxygenase activity with the substrate ethoxycoumarin, and carboxylesterase activ- ity with the substrates -naphthyl-acetate, -naphthyl-acetate, and para-nitrophenol acetate were substantially elevated in the GRMAL- RP, compared to the susceptible SUD-S strain, while glutathione-S-transferase activity with the substrate 1-chloro-2,4-dinitrobenzene was not diVerent. The metabolic inhibitors piperonyl butoxide and S,S,S-tributyl phosphorotrithioate synergised cypermethrin toxicity in the GRMAL-RP strain, however, mortality was still lower than that of the susceptible strain, indicating the presence of an additional resistance mechanism. Analysis of the sequence of the IIS4–IIS6 region of the para sodium channel gene of the GRMAL-RP strain revealed two amino acid replacements compared to that of the SUD-S susceptible strain. One is the leucine to isoleucine substitution at position 925 (L925I) previously implicated in B. tabaci pyrethroid resistance and the other is a novel kdr resistant mutation for B. tabaci, a threonine to valine substitution at position 929 (T929V). Genotype analysis showed that the L925I and T929V were present in all GRMAL-RP males tested, at an approximately 1:1 frequency, but never in combination in the same haplotype.  2006 Elsevier Inc. All rights reserved. Keywords: Pyrethroids; Cytochrome P450s; Carboxylesterases; kdr mutations; Genotype; Bemisia 1. Introduction The sweet potato whiteXy Bemisia tabaci (Hemiptera: Aleyrodidae) is one of the most damaging pests of numer- ous crops worldwide, due to its global distribution, wide range of host plants and capability to transmit over 111 virus species [1,2]. The ability of B. tabaci to develop resis- tance to insecticides after only a few applications, in combi- nation with the occurrence of several biotypes with distinct characteristics (host range, developmental rate) makes its control problematic in many areas worldwide [3–7]. Bemisia tabaci has recently become a major pest in Crete (50% of total greenhouse area of Greece) and it is responsi- ble for signiWcant yield losses in protected and Weld crops. After a sudden outbreak in 2000 of Tomato Yellow Leaf Curl Virus (TYLCV) in Crete [8], growers relied on inten- sive use of chemicals for its control, with pyrethroids play- ing a key role due to their eYcacy and low persistence, which favored their extensive use during the harvest period in greenhouse vegetable crops. However pyrethroids, as well as most other registered insecticides, no longer eVec- tively control this pest in certain areas of Crete, due to the development and rapid spread of insecticide resistance. We recently monitored high resistance levels to several insecti- cide classes in Weld B. tabaci populations from Crete, par- ticularly pyrethroids and neonicotinoids [9]. Resistance * Corresponding author. Fax: +302105294514. E-mail address: vontas@aua.gr (J. Vontas).