Comparative studies on the biology and filarial susceptibility of selected blood-feeding and autogenous Aedes togoi sub-colonies

Abstract

Ae. togoi subcolony was an efficient laboratory vector in study of filariasis. Key words: Aedes togoi -blood feeding -autogeny -biology -filarial susceptibility -Brugia malayi -Dirofilaria immitisLymphatic filariasis, due to Brugia malayi and Wuchereria bancrofti, is still an important mosquito-borne human disease in many countries of Asia, particularly in India, Indonesia, Malaysia, the Philippines, Sri Lanka and Thailand (WHO 2001).In order to carry out a variety of research and development concerning lymphatic filariasis, e.g., physiology, biochemistry, pharmacology, pathology, immunology and molecular biology, it is necessary to use infective larvae as a starting point of investigations. This has led to a search for a reliable laboratory vector. Consequently, Aedes togoi (Taiwan strain) has been selected and used widely for more than three decades as an efficient laboratory vector in the mass-production of infective larvae. It is easily bred and maintained in an insectarium, is a good bloodfeeder and highly susceptible to a wide range of genera and species of filariae, i.e., periodic B. malayi, subperiodic B. malayi, B. pahangi, rural strain of W. bancrofti, Dirofilaria immitis, Breinlia sp. and Setaria sp. (Ramachandran et al. 1963). An additional strain of Ae. togoi (Thailand strain) was subsequently affirmed (Choochote et al. 1983(Choochote et al. , 1987, since it was highly susceptible to the nocturnally periodic (urban strain) and subperiodic (rural strain) W. togoi is the regular live bloodmeals necessary for routine maintenance. However, the Ae. togoi (Thailand strain) exhibited autogenous behavior (Choochote et al. 1987), and to take advantage of this, a selected autogenous subcolony was established and subsequent generations prove to be an efficient laboratory vector of filariae. This was because the 8th and 17th generations of the selected sub-colony yielded similar susceptibilities (to B. malayi and D. immitis) to the stock colony (mixed blood-feeding and autogeny) (Riyong et al. 2000). As an addition to the previous study, we report herein, the comparative biology and filarial susceptibility of the 11th and 13th generations of selected blood-feeding, and the 38th and 40th generations of selected autogenous Ae. togoi sub-colonies. MATERIALS AND METHODSMosquitoes -The stock colony of Ae. togoi was obtained originally from Koh Nom Sao, Chanthaburi province, Southeast Thailand. The colony was established in the insectarium of the Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand in 1981. Since 1983, it has been maintained continuously for several generations in the insectarium of the Department of Parasitology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.Establishment of blood-feeding and autogenous subcolonies -As declared by Choochote et al. (1987) and Riyong et al. (2000) and, this stock colony-strain of Ae. togoi exhibited both blood-feeding and autogenous behavior simultaneously within the colony, thus, the selec-

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