Long-term changes in age-specific egg production of two Bactrocera cucurbitae (Diptera : Tephritidae) strains mass-reared under different selection regimes, with different egg collection methods

Two mass-reared strains of the melon fly, Bactrocera cucurbitae (Coquillett ), showed contrasting oviposition patterns throughout a period of long-term culture. The two strains, established in 1980 (old strain) and 1985 (new s train), were maintained in a sterile insect technique project in Kagoshima Prefecture, Japan. During the first several generations of small-scale rear ing of the two strains, selection for increased production efficiency was a pplied. As a result, an early-reproduction trait developed more rapidly in the new strain than in the old strain. After the selection was ceased, an e arly-reproduction trait developed in the old strain for 25 generations of l arge-scale mass rearing; there was no further development of the early-repr oduction trait in the new strain. The result obtained with two-way selectio n for age at reproduction suggested that the new strain had been nearly at the selection limit for early reproduction at the beginning of mass rearing . The following two rearing conditions may be responsible for the observed differences in oviposition patterns of the two strains: differences in the selection regimes during the small-scale rearing and differences in the egg -collection methods used in the subsequent course of mass rearing of the st rains.