The use of ovitraps baited with hay infusion as a surveillance tool for Aedes aegypti mosquitoes in Cambodia

This study was conducted to test (a) if a modified version of the CDC-enhanced would attract more gravid female Aedes aegypti mosquitoes than standard ovitraps for more frequent monitoring of oviposition activity, and (b) the placement of ovitraps indoors or outdoors affected their performance. Paired ovitraps were placed in 25 strategically houses in Toul Kouk, a village on the outskirts of Phnom Penh, Cambodia's capital city. Each pair consisted of one ovitrap with 10% hay infusion and the other with plain tap water, one pair placed inside each house and the other outside the same house. Collections were made every other day for four weeks. The number of positive ovitraps was recorded and egg counts made. Thirteen collections made over a 4-week period yielded a total of 7758 eggs, of which 5396 were collected in ovitraps with hay infusion. Ovitraps with hay infusion had a higher positivity (weekly range 15.56-54.55%) than ovitraps with plain water (weekly range 6.67 - 34.88%) (t = 4.92; df 12; p< 0.01) and the mean number of eggs collected was significantly more in the enhanced ovitraps (415.07) than in ovitraps with plain water (181.69) (t = 7.33; df 12; p < 0.001). Indoor and outdoor placement of ovitraps showed no significant differences in positivity or mean number of eggs collected either for infusio-baited traps (t= 0.25; df 12; p > 0.5 and t = 0.06; df 12; p >0.5, respectively) or for plain water traps (t= 1.97; df 12; 0.05 < p < 0.1 and t = 1.03; df 12; 0.2 < p < 0.5, respectively). Overall results indicate that, in the study site (a) hay infusion-baited ovitraps are a more sensitive indicator of the presence and numbers of Aedes aegypti than those with plain water and are suitable for frequent monitoring of Aedes aegypti oviposition activity, and (b) the location of ovitraps, indoors or outdoors, does not influence the performance of the traps.