Life history traits and nucleotide sequences of mt-DNA of thelytokous and arrhenotokous races of Thrips nigropilosus Uzel
Nakao S1, Muraji M2
1Lab. of Landscape Entomology, Faculty of Systems Engineering, Wakayama University, Sakaedani, Wakayama 640-8510, Japan.
2Lab. of Insect Molecular Evolution, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan
Correspondence: nakao@sys.wakayama-u.ac.jp
Thrips nigropilosus is a pest of chrysanthemum in Japan, and the females exhibit wing polymorphism. It is known that mode of reproduction and critical daylengths for induction of reproductive diapause and brachypter production in females show geographical variations (Nakao S et al. 1997. Environmental Systems Research 25: 665每669; Nakao S, Yabu S. 1998. Japanese Journal of Entomology 1: 9每19). Prevalent mode of reproduction of the wild populations of T. nigropilosus was examined in Wakkanai city, Hokkaido Island, Japan. Furthermore, photothermal responses, reproductive schedule, fecundity, and partial nucleotide sequences of mitochondrial DNA were compared between thelytokous and arrhenotokous races. Percentages of thelytokous thrips were 0.8每4.0% in the wild population. Significant differences between thelytokous and arrhenotokous races were not observed in the duration of pre-ovarial maturation and oviposition periods at 18C and 15L-9D condition. The mean numbers of eggs deposited by thelytokous and arrhenotokous females were ca.63 and ca.142 at the same condition, respectively, and the hatchabilites were not different from each other. At 18C, the critical daylength for the production of the brachypters and the induction of the reproductive diapause of thelytokous females was 14每14.5h, and that of arrhenotokous ones was 13每14h. Even under short-daylength, the higher temperatures inhibited the development of the brachypters and the induction of the diapause in thelytokous and arrhenotokous females. The molecular phylogenetic tree of the CO I nucleotide sequences revealed that T. nigropilosus are divided into two clusters which consist with the thelytokous race and the arrhenotokous ones. This result was consistent with their esterase zymograms (Nakao S, Yabu S. 1998. Japanese Journal of Applied Entomology and Zoology 42: 77每83). A previous study (Nakao S, Yabu S. 1998. Japanese Journal of Entomology 1: 9每19) had revealed that the arrhenotokous population of Wakkanai city has a dominant short-wing gene inducing brachypters in females irrespective of day length and temperature. Thus, the thelytokous race seems to be derived from an arrhenotokous female lacking the dominant gene, in the colder climatic periods or at a little north from the northern edge of Hokkaido Island.
