National progress in dengue vector control in Vietnam: Survey for Mesocyclops (Copepoda), Micronecta (Corixidae), and fish as biological control agents

This paper describes the process of expanding a successful dengue control p rogram in 3 provinces in northern Vietnam into a national one and demonstra tes the presence of a rich, low-cost resource that could have similar appli cability to other countries in the region. The cornerstone of the preventiv e strategy is larval control of Aedes aegypti (L.), the major vector, using predators such as copepods, Mesocyclops spp., aided by the corixid bug Mic ronecta quadrishigata Bredd, and fish in large water storage containers. Fr om 1989 to 1998, 9 species of Mesocyclops (M. woutersi Van de Velde, M. asp ericornis (Daday), M. ruttneri Kiefer, M. thermocyclopoides Harada, M. affi nis Van de Velde, M. ogunnus Onabamiro, M. yenae Holynska, M. cf. pehpeiens is Hu, and M. dissimilis Defaye and Kawabata) were found in natural and art ificial habitats in 26 provinces throughout Vietnam. The predatory capaciti es of 6 of these were evaluated in the laboratory. This indicated that dail y consumption/killing averaged between 16 and 41 Ae. aegypti larvae per cop epod. From detailed evaluations in 9 provinces, Mesocyclops spp. were surpr isingly common in 8,413 artificial containers (concrete tanks, wells, ornam ental ponds and in the south, large jars). Because of existing practices fo r washing and water transfer from ponds and lakes in Ha Tay and Ha Bac, Mes ocyclops spp. already occurred in 60-100% of the water storage containers. When the relationship between the presence or absence of Mesocyclops and Ae des larvae in 5,111 containers was analyzed by the chi-square test, their d istributions were significantly related, indicating control (odds ratio = 0 .56). When 3,426 containers that did not contain Mesocyclops or fish were a nalyzed in relation to the distribution of Aedes larvae, those with Microne cta also had significantly less Aedes (odds ratio = 0.43). Therefore, this study demonstrates that there is an abundance of local Mesocyclops spp. in Vietnam that can be incorporated into specifically designed community-based control programs aided by Micronecta and fish.