Morphological adaptation in host races of Tephritis conura

The present study investigates morphological differentiation among host races of the fruit fly Tephritis conura Loew (Diptera: Tephritidae) for two fitness‐related traits and whether these traits are host induced or genetically determined. Flies were analyzed from independent sympatric regions, and from one syntopic site where parental host plants [Cirsium heterophyllum (L.) Hill. and Cirsium oleraceum (L.) Scop. (Cardueae)] and hybrid plants (C. heterophyllum×C. oleraceum) co‐occur. As both host races may oviposit on hybrid plants and hybrid plants provide an identical environment for larvae of both host races, flies emerging from C. heterophyllum×C. oleraceum hybrids were used to assess whether host‐race morphological differences are genetically determined or due to phenotypic plasticity. No significant size (wing length) differences were found among host races, whereas flies emerging from C. heterophyllum had on average 8.4% longer ovipositors than flies emerging from C. oleraceum. The mean size‐corrected ovipositor length (i.e., the ratio ovipositor/wing length) was 10.3% longer. These proportions were repeated among host races emerging from hybrid plants. Although flies of the C. heterophyllum host race from hybrid plants were smaller than on parental host plants, the ratio ovipositor/wing length was constant. Hybrid flies (which emerged only on hybrid plants) were intermediate in relative and absolute ovipositor length. Thus, ovipositor‐length differences among T. conura host races most likely have a genetic basis. This suggests that host‐related differences in ovipositor length reflect adaptations to the respective host‐plant species, most likely to the host's flower‐head size, whereas both host races experience similar selection regimes on body size.