Pyrethroid knock down resistance in horn fly (Diptera: Muscidae) populations in Brazil Sabatini, G.A.[1]; Ribolla, P.E.M.[2]; Barros, A.T.M.[3]; Guerrero, F.D.[4]; Schmaker, T.T.S1.[1][2][3] [1][1] UniFMU/ USP [2][2] UNESP/ Botucatu [3][3] EMBRAPA CPAP [4] USDA-ARS

1. Introduction Stress and reduction in rate of weight gain (Campbell 1976) efficiency of feed utilization and milk production by the bovine host (Kinzer et al. 1984) Hide damage (Gugliemone et al. 1999) Losses in Brazil: US$ 150 million per year (Grisi et al., 2002)

1. Introduction To minimize losses – insecticides - resistance Few studies on mechanisms of resistance kdr gene mutation (Guerrero et al. 1997) Pyrethroids – sodium channel

1. Introduction Sodium channel structure x pyrethroids: – Drosophila melanogaster (Meigen) (Armichot et al. 1992) – Blattella germanica (L.) (Dong & Scott 1994) – Musca domestica (L.) (Miyasaki et al. 1996) Horn fly - Guerrero et al. (1997) (L1014F and M918T) Spread of pyrethroid resistance - (Barros, 2004) – Mechanism (s)?

2. Material and Methods 2.1. Fly collections 30 populations (+/- 50 flies each/ total of 1454 flies) from all Regions of Brazil - Embrapa/ Barros, ATM - SP; RJ; RO and RS 2.2. Polymerase chain reactions Extraction of Genomic DNA (individual): Aljanabi & Martinez (1997). The kdr gene mutation was detected according to Guerrero et al. (1998) PCR products were visualized on 1% agarose TBE gels coloured by ethidium bromide staining and UV illumination.

3. Results and Discussion

Table 1: Kdr detection in diferent populations of Haematobia irritans irritans from Brazil.

3. Results and Discussion

Control of horn fly in Brazil: 91 products registered

Low frequencies of kdr gene: – Only 3 populations higher than 20% Guglielmone et al., 2002 – Kdr allelic frequency 50% Li et al., 2003 High numbers of SS and SR individuals Resistance to pyrethroids is sex-linked (MacDonald & Schmidt, 1987) Adult males were more susceptible than the females (McDonald & Schmidt, 1990). Li et al., 2003 – Corroborate it in Mexican populations, but not in American. There was no relation between sex and kdr among Brazilian populations. 3. Results and Discussion

Pyrethoroid resistance in the horn fly Metabolic (Lockwood et al., 1985)Behavioural (Sheppard, 1995) KDR (Bull et al., 1988, Sparks et al., 1990) Frequency of kdr gene was quite low Fitness cost (Scott et al., 1997 ) kdr amplification was not observed in all populations found to be resistant in the bioassays. 3. Results and Discussion

These findings indicates that there is at least another mechanism playing an important role in resistance to pyrethroids