The Quantitative Genetics of Prescutellar Bristles in Melon Fly, ＂Bactrocera cucurbitae＂ (Coquillett)
摘要
The polymorphism of prescutellar bristles (＂prsc＂) in melon fly, ＂Bactrocera cucurbitae＂ (Coquillett), was investigated by artificial selection of phenotypes and quantitative genetic analysis. In the wild strain, generally more than 95% population have 2 ＂prsc＂ while some may have 4 ＂prsc＂. By selection, however, a group of phenotypes was appeared with the number of ＂prsc＂ reach up to 14 and more. All multiplied bristles were randomly arranged in a region of posterior half of ＂scutum＂ and between the lateral ＂vita＂. The quantitative genetic analysis was conducted by crossing two strains of different phenotypes, one from each strain. In each cross only one virgin male and one virgin female were paired, with a total of 6 pairs in each experiment, and 200-500 offsprings from each experiment were examined for their phenotypes. For each cross, only one 2-＂prsc＂ individuals (the major component of the wild population) and one 12-＂prsc＂ or 14-＂prsc＂ individuals from the selected strains were interbred, and then inbred F_1 for the F_2 progeny. The results showed that for 2-＂prsc＂ × 12-＂prsc＂, the F_1 progeny constituted a group of phenotypes with different ＂prsc＂ numbers, and the mean was 4.7 ± 0.9 which was in-between two parental phenotypes. The mean of ＂prsc＂ in F_2 is 4.7 ± 1.9. The difference between the means of F_1 and F_2 is insignificant in the t-test (P ＞ 0.05). For 2-＂prsc＂ × 14-＂prsc＂, the F_1 progeny constituted a group of phenotypes, with the mean of 5.0 ± 1.0 which was in-between their parental phenotypes. The F_2 offsprings had their mean at 5.1 ± 2.3. The t-test indicated no significant difference between the means of F_1 and F_2 (P ＞ 0.05). Moreover, as the coefficients of variation of F_2 were higher than those of F_1 (40.1% ＞ 19.5% versus 45.9% ＞ 21.7%), it suggests that more variability around the mean of F_2 than that of F_1. The extreme values in ＂prsc＂ for F_2 were extended to the range of their parental values (2-15 ＂prsc＂ and 1-17 ＂prsc＂, respectiv