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

Abstract

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 strain), were maintained in a sterile insect technique project in Kagoshima Prefecture, Japan. During the first several generations of small-scale rearing of the two strains, selection for increased production efficiency was applied. 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 early-reproduction trait developed in the old strain for 25 generations of large-scale mass rearing; there was no further development of the early-reproduction trait in the new strain. The result obtained with two-way selection 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 strains.