Effect of chemical fogging on immature Aedes mosquitoes in natural field conditions.

INTRODUCTION: Dengue and dengue haemorrhagic fever are common and serious arboviral diseases endemic in a number of countries situated in both the tropical and subtropical belts. METHODS: A prospective study was carried out to examine the environmental factors influencing the ovipositing behaviour of gravid female Aedes mosquitoes in a typical urbanised residential environment in Malaysia. This study reports the effect of the usual ultra-low volume fogging of insecticides carried out by public health officers on the collection of immature Aedes mosquitoes using ovitraps. RESULTS: Throughout the study, no dead immature Aedes mosquitoes was noted in any of the ovitraps set up in all of the fogging and immediate post-fogging periods. The mean number of days of ovitrapping for immediate pre-fogging, fogging and post-fogging periods were 10.3, 10.1 and 10.4 days, respectively. There was no statistically significant difference in the mean duration of ovitrapping cycle among the immediate pre-fogging, fogging and immediate post-fogging periods. The total number of immature Aedes mosquitoes collected in the immediate post-fogging periods was more than the immediate pre-fogging periods, and both were more than the fogging periods. However, there was no statistically significant difference in the total number of immature Aedes mosquitoes collected at various periods. It was not unusual to find dead insects, spiders and even small animals collected in ovitraps or environment in the fogged locality within 48 hours of chemical fogging. CONCLUSION: In this study, the usual chemical fogging in natural environment was ineffective in breaking the reproductive lifecycle by eliminating gravid female Aedes mosquitoes.