| Abstract |
The Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae) is a serious pest species which attacks a wide range of fruits and vegetables, and poses one of the most serious threats to agriculture today. Among the methods used to combat it is the Sterile Insect Technique, which involves the release of large numbers of irradiated male flies into the environment, which then mate with wild females, thus reducing the proportion of fertile matings and lowering population sizes. The flies used come from mass cultures of medfly, in which the populations are maintained for many years. The strains used also undergo genetic manipulation designed to facilitate the separation of male and female pupae. Each genetic sexing strain is initiated from one pair of flies. Reproduction in the Mediterranean fruit fly is based on female choice. Females decide whether or not to mate with a particular male on the basis of a male courtship display which consists of pheromone calling, wing vibration, and vigorous head-rocking. Males also have a pair of anterior orbital bristles sprouting from the top of their head, which are long and widen at the tips into a diamond shape - the corresponding bristles on the head of the female are undifferentiated. These bristles have no sensory function and very likely are secondary sex characters which serve to visually stimulate the female during courtship. One of the goals of the present study was to examine the effect of bristle size on male mating success. Studies of Hawaiian Drosophila have shown that the females of derived populations often tend to be less choosy than those of the parental population, and according to Kaneshiro's hypothesis, this is due to the fact that when populations are very small, there is selection for less selective females, since those that are more selective will have a difficult time finding acceptable mates. In this study, comparisons were made between the degree of choosiness of laboratory and wild female fruit flies in mating experiments in which females of each strain were paired with males of the same or the opposite strain. Field and lab experiments conducted with various laboratory strains seem to show that laboratory male medflies are relatively unsuccessful in achieving matings with wild females. This may be due to strain divergence due to the combination of small initial population sizes, reproductive isolation, and adaptation to lab conditions. In addition, the lab strains often have a different geographical origin than the local wild strains and may therefore exhibit geographical differentiation as well. In this study, the morphology of the males of a lab strain originating in Egypt and a local Cretan strain was compared. Morphological measurements included pupal weight, (as a measure of overall size), wing dimensions, and bristle tip area and shape. Differences in morphology, especially of characters that play a part in the courtship display, may affect reproductive isolation among strains. Using Kendall's τ τhe correlation between anterior orbital bristle size and mating success was found to be significant at the 11% level, while the correlations between mating success and pupal weight, and mating success and wing size had p values of 42% and 40% respectively (one-tailed test). The comparisons of wild and lab strain female choosiness showed wild females to be less likely to mate with a particular male, whether wild or lab. Μorphological measurements showed that the two strains had different weight-wing dimension, and weight-bristle area, as well as different wing and bristle shape.
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