Reproductive compatibility among New World screwworm strains from the Amazon, northeastern and southeastern Brazil

The application of the Sterile Insect Technique (SIT) against the screwworm Cochliomyia hominivorax (Coquerel) has been successfully demonstrated. As a result of a 54-year area-wide program, eradication has been achieved in the USA, Central America, some Caribbean islands and the outbreak in Libya Jamahiriya, North Africa. Before the beginning of new SIT campaigns against this pest in South American countries, a good understanding of the reproductive compatibility of the target populations is of utmost importance for their effectiveness. Two sets of crosses were conducted separately to assess the postzygotic compatibility between a strain from the Brazilian Amazon (the PARÁ strain) and two recurrent strains: one from Northeastern Brazil (the PIAUÍ strain) and another from Southeastern Brazil (the UNICAMP strain). The first set (parental crosses) compared intrastrain and reciprocal interstrain crosses and the second set (F₁ crosses) compared four backcrosses to the recurrent parent (UNICAMP or PIAUÍ strain). The estimated means for the parameters recorded in the hybridization tests were compared by analysis of variance. The biological parameters (egg hatch, larval viability, adult emergence and sex ratio) assessed in the parental crosses were high and did not differ significantly among crosses. In backcrosses, the mean values for egg hatch, larval viability and adult emergence were greater than 70%, sex ratio was about 0.5, and no significant differences were observed among treatments. No evidences of hybrid dysgenesis were found from the interstrain crosses. So far, genetic incompatibility would not be a constraint against new SIT campaigns in Brazil.