Field attempt to assess the mating competitiveness of sterile males produced by crossing 2 member species of the Anopheles gambiae complex.

In laboratory experiments sterile males produced by crossing member species of the Anopheles gambiae complex competed very successfully with normal males for normal females and the latter when mated with sterile males laid sterile eggs.A field trial was arranged in a small isolated village near Bobo-Dioulasso, Upper Volta; the trial took place at the end of the rainy season against a declining population of species A. Sterile males were produced from the cross between species B males and An. melas females; this cross yielded an F(1) generation mainly composed of sterile males with a sporadic occurrence of a sometimes significant proportion of females which were reproductively normal.The F(1) generation was reared to pupae and these were released into existing breeding places and later from artificial containers.Some 300 000 pupae were so released over a period of 2 months and adult collections were made periodically from inside houses and from outside shelters after releases started. Of the males caught, 75% proved to be sterile while nearly 6% of normal-looking ovipositions failed to hatch. However 2.5% of them proved to be from hybrid females and not from species A females. In control villages, 1.35% of normal-looking ovipositions did not hatch.It was concluded from this field trial that the sterile males were not mating on any significant scale with the natural species A females. This could have been due to a number of factors but the most important is considered to be an ethological one-a mating barrier preventing mating between introduced sterile males and natural females. This is strongly expressed under natural conditions but not operative in the limited confines of a cage. The use of a cross between two species against a third species may well have enhanced this barrier.