Improving Mating Performance of Mass-reared Sterile Mediterranean Fruit Flies (Diptera: Tephritidae) through Changes in Adult Holding Conditions: Demography and Mating Competitiveness

Pablo Liedo, Sergio Salgado, Azucena Oropeza, Jorge Toledo

Abstract


Mass rearing conditions affect the mating behavior of Mediterranean fruit flies (medflies) Ceratitis capitata (Wiedemann). We evaluated the effect of slight changes in the adult holding conditions of adult flies maintained for egg production on their mating performance. Colonization was initiated from wild flies collected as larvae from infested coffee berries (Coffea arabica L.). When pupae were close to adult emergence, they were randomly divided into 3 groups and the emerging adults were reared under the following conditions: (1) Metapa System (MS, control), consisting of 70 × 45 × 15 cm aluminum frame, mesh covered cages, with a density of 2,200 flies per cage and a 1:1 initial sex ratio; (2) Insert System (IS), with the same type of cage, and the same fly density and sex ratio as in the MS treatment, but containing twelve Plexiglas® pieces (23 × 8.5 cm) to provide additional horizontal surface areas inside the cage; and (3) Sex-ratio System (SS), same as IS, but in this case the initial male: female ratio was 4:1. Three d later, newly emerged females were introduced, so the ratio became 3:1 and on the 6th d another group of newly emerged females was added to provide a 2:1 final sex ratio, at which the final density reached 1,675 flies per cage. The eggs collected from each of the 3 treatments were reared independently following standard procedures and the adults were held under the same experimental conditions. This process was repeated for over 10 to 13 generations (1 year). The experiment was repeated 3 times in 3 consecutive years, starting each replicate with a new collection of wild flies. Life tables were constructed for each treatment at the parental, 3rd, 6th, and 9th generations. Standard quality control parameters (pupation at 24 h, pupal weight, adult emergence, and flight ability), were estimated for each treatment every third generation in the third year. For the last generation each year, mating competitiveness was evaluated in field cage tests with wild flies. As colonization progressed, life expectancy and fecundity rates increased in the 3 rearing systems. There was no significant difference in standard quality control parameters among the 3 rearing systems. Wild males always achieved more matings than any of the mass reared males. Mating competitiveness of males from the IS, although surprisingly not from the SS, was significantly greater than that of males from the MS. Our results indicate that these slight changes in the adult holding conditions can significantly reduce the harmful effects of mass rearing on the mating performance of sterile flies.

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