Genetic structure of Hessian files in Tunisia.

The genetic structure of M. destructor and M. hordei was investigated by sa mpling 21 fields of cereals in 14 localities of central and southern Tunisi a. As previously shown, there was no strict association between the cereal species (wheat, barley and oat) and the Mayetiola species. M destructor mal es displayed no heterozygosity at the Pgm3 locus, indicating that they were hemizygous as is the PGM locus in North America. In M. hordei, heterozygou s males were observed at all loci, but strong heterozygote deficits were fo und at two loci (Mdh2 et Hk). Since no such deficit was observed in females , the population structure of M. hordei was studied only in females. Althou gh heterozygosity was two fold higher in M. hordei than in M. destructor, t he two species were similar for other genetic characteristics, including a low (Fst < 0.05) but significant (P < 0.05) genetic differentiation, no iso lation by distance, and similar rates of gene flow (5.7 less than or equal to Nm less than or equal to 9.6). These results are discussed in relation t o their consequences in the event of controlling Tunisian Hessian flies usi ng wheat cultivars that are resistant to a M. destructor biotype.