24 other and the human population density is high, environ- mental conditions are more suitable for Ae. aegypti. Parks and gardens in developing countries may enhance the breeding of Ae. albopictus even in urban areas. Water storage behavior at times of drought may produce more breeding sites for dengue vectors. The difference in water storage customs among localities may modify the infesta- tion of Ae. aegypti and Ae. albopictus because habitat preference differs between the two species. Furthermore, the expansion of Ae. albopictus by the trade in tires may continue in the future. The impact of human activities on vector mosquitoes is considered to be larger for Ae. aegypti than for Ae. albopictus in view of the ecology and biology of the two species. However, the increasing abundance of Ae. albopictus in urban areas should be of particular concern. There are many reports showing that Ae. aegypti populations in the U. S. are being replaced by Ae. albopictus populations newly introduced by the trade in used tires [3]. Ae. albopictus has a wider range of activity than Ae. aegypti, feeds on wild animals as well as humans, and therefore is more adaptive to a variety of environments. Increased contact between humans and wild animals because of deforestation may enhance human-Ae. albopictus contact as well, and the role of Ae. albopictus in arbovirus transmission may become more crucial than ever. It has already been reported that Ae. albopictus contributes largely to chikungunya transmission both in tropical countries where dengue epidemic occurs and in Europe. This implies that the co-occurrence of dengue and chikungunya epidemics is highly possible. In such a situation, vector-borne disease control will be ever complicated, because the vector mosquitoes targeted will be both Ae. aegypti and Ae. albopictus with equivalent priority. 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