Vertical stratification of adult mosquitoes (Diptera: Culicidae) within a tropical rainforest in Sabah, Malaysia.

BACKGROUND: Malaria cases caused by Plasmodium knowlesi, a simian parasite naturally found in long-tailed and pig-tailed macaques, are increasing rapidly in Sabah, Malaysia. One hypothesis is that this increase is associated with changes in land use. A study was carried out to identify the anopheline vectors present in different forest types and to observe the human landing behaviour of mosquitoes. METHODS: Mosquito collections were carried out using human landing catches at ground and canopy levels in the Tawau Division of Sabah. Collections were conducted along an anthropogenic disturbance gradient (primary forest, lightly logged virgin jungle reserve and salvage logged forest) between 18:00 and 22:00 h. RESULTS: Anopheles balabacensis, a vector of P. knowlesi, was the predominant species in all collection areas, accounting for 70 % of the total catch, with a peak landing time of 18:30-20:00 h. Anopheles balabacensis had a preference for landing on humans at ground level compared to the canopy (p < 0.0001). A greater abundance of mosquitoes were landing in the logged forest compared to the primary forest (p < 0.0001). There was no difference between mosquito abundance in the logged forest and lightly logged forest (p = 0.554). A higher evening temperature (p < 0.0001) and rainfall (p < 0.0001) significantly decreased mosquito abundance during collection nights. CONCLUSIONS: This study demonstrates the potential ability of An. balabacensis to transmit P. knowlesi between canopy-dwelling simian hosts and ground-dwelling humans, and that forest disturbance increases the abundance of this disease vector. These results, in combination with regional patterns of land use change, may partly explain the rapid rise in P. knowlesi cases in Sabah. This study provides essential data on anthropophily for the principal vector of P. knowlesi which is important for the planning of vector control strategies.

Effects of marking methods and fluorescent dusts on Aedes aegypti survival.

BACKGROUND: Tracking the movement of mosquitoes and understanding dispersal dynamics is essential for the control and prevention of vector-borne diseases. A variety of marking techniques have been used, including dusts and dyes. METHODS: In this study, Aedes aegypti were marked using fluorescent dusts ('DayGlo': A-19 Horizon Blue & A-13-N Rocket Red; 'Brian Clegg': pink, blue & red), fluorescent paints ('Brian Clegg': blue, red & yellow) and metallic gold dust ('Brian Clegg'). Dusting methods were those previously used in mark-release-recapture experiments, including application with a bulb duster, creation of a dust storm or shaking in a bag. RESULTS: Results showed marking mosquitoes using a dust storm allowed relatively high survival, compared to unmarked controls (Males: χ² = 3.24, df = 4, p = 0.07; Females: χ² = 3.24, df = 4, p = 0.04), and high marking efficiency. Using a bulb duster showed high survival in male mosquitoes (χ² = 12.59, df = 4, p < 0.000), but low survival in female mosquitoes during the first 15 days of the study (χ² = 5.17, df = 4, p < 0.05). The bulb duster also had the lowest marking efficiency compared to other dry marking techniques. The bag method showed low survival in males during the first 15 days of the study (χ² = 5.77, df = 4, p < 0.05). Applying paints had an overall negative impact on survival for males (χ² = 5.03, df = 3, p < 0.05), but not for females (χ² = 0.19, df = 3, p = 0.661). Males dusted with DayGlo Horizon Blue dust, and females dusted with DayGlo Rocket Red dust, had the most significant reduction in survivorship in comparison to the control (Males: χ² = 15.70, df = 6, p < 0.000; Females: χ² = 24.47, df = 6, p < 0.000). Mosquitoes marked with Brian Clegg gold dust showed mortality rates similar to controls within male mosquitoes (χ² = 0.18, df = 6, p = 0.674), but significantly lower in females (χ² = 16.59, df = 6, p < 0.000). CONCLUSIONS: This study showed that marking technique and colour can have a significant impact on the survival and marking coverage of a mosquito.