MOSQUITO LARVICIDAL TRAP ( MLT ) AS SURVEILLANCE AND CONTROL TOOL FOR AEDES MOSQUITOES

The larvicidal potential and ovipositional effect of an insect growth regulator, 2% Novaluron (Mosquiron), in an oviposition trap or ovitrap on dengue mosquito vectors were determined under field condition. The set-up is hereafter referred to as Mosquito Larvicidal Trap (MLT). This MLT is a modification of an ovitrap utilized by De Las Llagas et al (2002, 2007, 2012) in all dengue mosquito surveillance and control studies in the Philippines. Variation entails mixing 40 parts per million (ppm) of an insect growth regulator (2% Novaluron), proven to have an attractant effect in an ovitrap clean water. The study was conducted from July 2012 to June 2013 in Barangay Batong Malake and Barangay San Antonio in Los Baños, Laguna, both places known as endemic sites for dengue transmission. The MLTs were installed and serviced every three weeks inside each household. Two hundred twenty households per study site were installed with MLT. Efficacy of MLT as a surveillance tool was measured against the conventional inspection of containers with water and the classical ovitrap. The Breteau Index (BI), Ovitrap Index (OI), and MLT positive for immatures of mosquito were determined. Breteau and ovitrap indices are known entomological indicators depicting the level of household mosquito infestation. The MLT as an autocidal/larvicidal trap was gauged in terms of its relative attractiveness to ovipositing mosquitoes compared to other containers and the classical ovitrap. Results showed that MLT was more attractive to Aedes for egg deposition than ovitrap or other containers inside the house. The mean MLT found positive with mosquito was 70.5% in Batong Malake while the OI was 53.5%. In San Antonio, the MLT was 56.6% compared to 50.4% OI. The added Novaluron increased the attractiveness to female mosquitoes to lay their eggs and has killing effect on the larvae. The findings indicate that MLT is more attractive than containers or ovitraps as oviposition medium. It is also lethal to the deposited eggs. Moreover, MLT prevented pupal development, indicating its autocidal activity to larvae. Thus, MLT prevents adult emergence by preventing pupal development. In conclusion, the use of MLT as an integral component of dengue vector control program will enhance reduction in density of mosquitoes at SoutheaSt aSian J trop Med public health 702 Vol 47 No. 4 July 2016 INTRODUCTION Aedes aegypti and Aedes albopictus mosquitoes are known vectors of dengue, chikungunya, and yellow fever (Gaedner and Ryman, 2010; Guzman et al, 2010). Presently, dengue is the most important among the arboviruses transmitted by mosquitoes throughout the world. It has become a public health problem in all of the continents, except Europe (Nogueira et al, 2001; Fontoura et al, 2012). Researchers from the University of Oxford and the Wellcome Trust reported that around 390 million infections occur annually, of which 96 million are severe cases and approximately 300 million are mild or asymptomatic episodes (Hirschler, 2013). The data compares with the World Health Organization’s (WHO) most recent estimate for overall infections of 50-100 million a year (WHO, 2007) and approximately 2.5 billion people live in areas where dengue can be transmitted (Gubler, 1998). Dengue has spread rapidly along with urbanization and globalization because it thrives in tropical mega-cities. Half of the world’s population is now exposed to the disease and it occurs mostly in the developing countries (Hirschler, 2013). In the Philippines alone, the reported dengue cases were 42,207 with 193 deaths in 2013. Although there was almost 50% reduction of cases to 23,867 in January to May 31, 2014 (Herriman, 2014), the disease is still a major medical and public health problem. In the absence of vaccines or anti-drugs, prevention of dengue fever and its more severe forms is of primary importance. Rapid responses to dengue outbreaks are needed in order to control the spread of the virus and to manage the high number of cases (Pilger et al, 2010). Currently, vector control remains the key strategy in dengue prevention and control (Ng, 2011), as it reduces or interrupts the dengue virus transmission. It also plays a critical role in the prevention and containment of epidemics. One of the strategies in vector control is mosquito surveillance (NEA, 2006). Regis et al (2008) indicated that the implementation of preventive measures targeting critical locations at specific times requires efficient vector surveillance tools and methods sensitive enough to predict or detect in real time a sudden mosquito population growth. Several tools and methods have been designed for vector surveillance to establish the minimum threshold of vectorial density (eg, vector indices). The use of oviposition traps or ovitraps (Fay and Eliason, 1966) is a possibility to indirectly estimate the female mosquito population. An ovitrap is a device which consists of a black cylinder with a piece of hardboard (Cheng et al, 1982; Wan Norafikah et al, 2011), cloth (Lenhart et al, 2005) or wood pallet (Focks, 2003; Regis et al, 2008). It is a technique recognized by the WHO, which can attract Aedes females to oviposit (WHO-WPRO, 1995). The ovitrap was first used for the immature stages thus lessening dependency on adulticiding efforts. With the threat of vertical and transstadial dengue transmission in nature, managing the vector at its youngest developmental stage must be done.