Apiwat Tawatsin¹
Mir S. Mulla²
Usavadee Thavara¹
Preecha Asavadachanukorn³
Wichai Kong-ngamsuk¹
Jakkrawarn Chompoosri¹

Affiliations :
      ¹ National Institute of Health, Department of Medical Sciences, Ministry of Public Health
88/7 Tiwanon Rd., Nonthaburi 11000, Thailand
      ² Department of Entomology, University of California, Riverside, California 92521, USA
      ³ Department of Statistics, Faculty of Commerce and Accountancy, Chulalongkorn University,
Phayathai Rd., Pathumwan, Bangkok 10330, Thailand

Source:
      14 th European Conference of the Society for Vector Ecology, Bellinzona, Switzerland September 3-6, 2003

Language :
      English

Abstract :
      Dengue haemorrhagic fever (DHF) is considered as one of the mosquito-borne diseases threatening human health especially people in the tropical and subtropical regions whereas Aedes aegypti  (L.) is recognized as the major vector of the disease. As there is no effective vaccine against DHF available now, vector control is therefore one of the main approaches to control this disease. Application of temephos sand granules (Abate 1% SG) at the rate of 1 g/10 L water in water-storage containers (1 ppm AI) has been used to control Ae. aegypti  larvae in large-scale vector control program in Thailand since the early 1970s. Although this larvicide provides good larvicidal effect against Ae. aegypti  larvae for several weeks in the treated containers, it is frequently rejected by many dwellers for application in their water-storage containers because of strong smell and slightly turbidity. Thus, it is needful to develop and/or evaluate new formulations of larvicides for Ae. aegypti  larval control as alternatives or substitutes if the use of conventional larvicide (temephos sand granules) seems to be more unpractical. To achieve these aspects, the study was carried out to evaluate larvicidal efficacy against Ae. aegypti  larvae of two new formulations of microbial larvicides derived from Bacillus thuringiensis israelensis  (Bti): ThaiNIH tablets (1 g/tablet, Bti 12.5%, 750 ITU/mg) and VectoBac tablets (0.37 g/tablet, Bti 5%, 2,700 ITU/mg) and a new formulation of temephos zeolite granules (1%) and their efficacies were then compared with temephos sand granules (1%) in identical glazed clay jars (200 L) under field-simulated conditions. The larvicides were used at the recommended rates (1 tablet/jar for ThaiNIH tablets, 4 tablets/jar for VectoBac tablets, and 20 g/jar for the two temephos formulations). The efficacies of all four larvicide formulations were assessed through two water regimens: full jars and full jars emptied half amount and refilled weekly. Assessment was made through emergence inhibition rate (% EI). Overall, the ThaiNIH tablets provided good control (>90% EI) for at least 2.5 months whereas that of the VectoBac was almost 4 months. As for the two temephos formulations, both zeolite granules and sand granules were equal in efficacy yielding almost 100% EI for more than 6.5 months. It is interesting to note that both Bti formulations and temephos zeolite granules lacked the undesirable odor and turbidity after application in the treated jars. With regard to excellent larvicidal efficacy and lack of unsatisfactory characteristics, the two larvicide formulations: VectoBac and temephos zeolite granules could be served as alternatives or substitutes of the conventional larvicide (temephos sand granules) in large-scale vector control program in Thailand. However, the ThaiNIH formulation, which is locally made can also be an effective alternative larvicide if it is much more developed for longer larvicidal efficacy.