Mosquito Feeding Periodicy in an Isolated, Domesticated Environment. Chris Tarrand

Transcription

1 Mosquito Feeding Periodicy in an Isolated, Domesticated Environment Chris Tarrand Study Abroad Program, Dominica 2014 Dr. Jim Woolley, Dr. Thomas Lacher Department of Entomology Texas A&M University, College Station, TX 77840

2 Abstract During our three week stay on Dominica (located in the Lesser Antilles) at the Springfield Field Research Station, the daily feeding patterns of the mosquitoes were observed and monitored. Using four BG Sentinel traps loaded with pheromone bait, a three hour trapping schedule was implemented to determine a species count at various times during the day. Over 21 days it was determined that three dominant species were present on the station: Aedes buscki, Aedes aegypti, and Culex quinquefasciatus. As shown in our data, cyclical flight activity times was observed for all three of the species with Aedes busckii present during the day and Culex quinquefasciatus predominantly present in the evening and morning. Keywords: BG sentinel trap, Aedes busckii, Aedes aegypti, Culex quinquefasciatus

3 Introduction Dominica, situated in the Lesser Antilles, is a relatively new island with large swathes of rainforest. With a relatively poor economy and unplanned urban development abundant in the larger cities the island has experienced endemic dengue and a recent outbreak of chikungunya. Aedes aegypti is a known vector for various diseases that have a severe impact on human health such as: yellow fever, dengue fever, and chikungunya. Culex quinquefasciatus is a known vector of avian malaria, St. Louis encephalitis virus, Western equine encephalitis virus, and West Nile virus. In an effort to gather information on disease vectoring mosquitoes, four BG Sentinel traps were placed around the Springfield Field Station and checked periodically to determine the peak feeding hours of mosquitoes. One of our principal questions was do mosquitoes have a high enough flexibility in behavior to change their feeding habits according to location? The station had been previously almost cleared of Aedes aegypti. This was completed through rigorous source elimination as many common mosquito pests, such as Aedes aegypti and Culex quinquefasciatus, breed in standing water of artificial containers [Moreira, 2002]. Given that chikungunya is a cause for serious concern for many areas of Dominica, especially urban communities, the original intention was to determine the peak feeding times of Aedes aegypti for more effective vector control. With the near eradication of Aedes aegypti at the Archbold Research Station the focus was widened to include any common mosquitoes from the surrounding area and forest, expecting Culex quinquefasciatus to be at the foremost in all of the trapping efforts.

4 Materials and methods The principal goal was to survey mosquitoes feeding tendencies; four BG sentinel traps were placed at areas of high human activity: near a commonly used trashcan, the boundary to the nearby forest, the kitchens, and the dining tables. Pheromone bait of Octenol and BG-Lure were placed in each trap, and a schedule was devised to check the quantity of mosquitoes every three hours starting at 8A.M. each day and continuing for 24 hours, thus collecting eight data points in a full trapping day. This continued for four non-consecutive days worth of data collection periods. Each data collecting period, the traps were completely emptied and cleaned to prevent additional damage to specimens. This was because many mosquitoes would attempt to fly or move into the catch-bag, often beating off scales in the process. Mosquitoes caught in each batch were identified using the Yale dichotomous key for Dominican mosquitoes [Brown et al, 2007]. In particular, Aedes aegypti was recognized among the Aedes sp. by the silvery-white lyre shaped marking on the scutum and segment 5 of the hind tarsus entirely white with the preceding tarsi banded apically (fig. 1). Aedes busckii, which is a daytime, non-human feeder, indigenous to the Caribbean, was distinguished by golden dorsocentral lines on the scutum and the hind tarsal segments 1-3 with basal white bands (fig. 2). The 4 th and 5 th tarsal segments were also entirely dark (fig. 2). Among the Culex sp. the mosquito Culex quinquefasciatus was identified by the dark hind tarsi and pale, transverse bands on the abdominal tergites of the females (fig 3.).

5 Figure 1. Aedes aegypti Figure 2. Aedes buskii

6 Figure 3. Culex quinquefasciatus Results For a given day there was a repeating cycle of peak mosquito feedings, centering around various points in the day with the exception of 2 A.M., where there was no mosquito activity. The cycle of trends of overall distribution patterns showed that Culex quinquefasciatus had peak feeding hours in the morning before 8A.M. and around 8 P.M. in the evening (fig. 6). Aedes busckii showed that the feeding cycle peaked during the middle of the day often after noon (fig. 6). The two Aedes aegypti caught were both present early in the day, prior to 2 P.M. These different species feeding trends were shown in Figure 6, matching the daily trend lines for each species shown in Figure 4. Figure 5 shows the specimens caught in all traps at each three hour interval for all four days

7 Figure 4. The total specimens caught for each trapping period over the four days of trapping. Figure 5. Peak feedings times by species for all traps over the four days of trapping

8 A B C D Figure 6. A) Trap 1 was placed near the kitchens. B) Trap 2 was placed near a commonly used trashcan at the edge of a veranda. C) Trap 3 was placed near dining tables. D) Trap 4 was placed at the opposite edge of the aforementioned veranda, which is overlooking the nearby forest.

9 Discussion The main goal of determining feeding times for the various species around the field station was a success as shown by the four similar data lines in Figure 4. This was backed by the four individual results from each trap, showing a generalized trend of Aedes busckii appearing in large numbers after noon and a large percentage of them disappearing before sunset. A trend of Culex quinquefasciatus appeared just before 8 A.M. and 5 P.M. This trend did not meet initial predictions since Culex quinquefasciatus is known to primarily be nocturnal, feeding on birds and often laying eggs at night. It was found that this proves insightful into the flexibility of the feeding habits of mosquitoes, indicative of an ability to easily adapt to local environments due to better resources and conditions. Aedes buskii, indigenous to the Caribbean, and possibly exclusively to the Lesser Antilles, behaved as expected for the daytime mosquito. The high numbers of Aedes busckii was theorized to be related to the traps located at the periphery of the station, near the forests. A potential answer to this was suggested that Aedes busckii, while they do not bite humans, might be drawn to certain human pheromones when host-seeking. Only once close to feeding site or landing may they be able to discern humans from intended prey. A result that we cannot account for was the low presence of Aedes aegypti, which have extremely short flight ranges. Given that they spawn in high numbers, it was expected that we would have either no Aedes aegypti or high quantities. Instead several were found sporadically through the trapping period. Unable to locate any Aedes aegypti larvae in the surrounding area, there may be a possibility to an adapted higher flight range of the species, given the lack of conventional Aedes aegypti presence in the area. From our results the vector control methods for an island such as Dominica should be concentrated on hours before and after crepuscular hours to account for the possible changing

10 feeding habits. Not only will this provide a more effective defense against Aedes aegypti and Culex quinquefasciatus, but would be more cost effective to spray repellent or insecticides right before and at peak feeding times. Vector control should be linked with population monitoring to counteract any attempts at behavior adaptation by mosquitoes, and insure a proper level of efficacy. References Moreira, Sidia. Survey of Aedes Mosquitoes in Dominica, W.I Brown, Heidi, Thomas Zavortink, and Durland Fish. "The Mosquitoes of Dominica Acknowledgements I would like to thank Dr. Wooley and Dr. Lacher for the consistent support and advice, and D. Hamer for the direction and enthusiasm given to this project. Lastly I would like to thank Devonda Beach for all the help in editing and data analysis.