How does the biology of the exotic mosquito Culex molestus influence mosquito-borne disease risk in Australia? Nur Faeza Abu Kassim Supervisors: Dr. Cameron E. Webb & Professor Richard C. Russell Department of Medical Entomology, University of Sydney & CIDM, Westmead Hospital
CLIMATE CHANGE & URBAN DEVELOPMENT • Climate change may not directly change Australia’s mosquito-borne disease risks. HOWEVER, human response to a changing climate may have an indirect influence • Water conservation within urban developments may provide new habitats for local and exotic mosquitoes • Water Sensitive Urban Design (WSUD) elements include subterranean storage of rainwater and grey water • Understanding the biology and ecology of mosquitoes associated with these habitats is critical to assessing public health risks
AN EXOTIC MOSQUITO IN OUR MIDST • While Aedes (dengue) and Anopheles (malaria) species are considered key vectors, Culex (West Nile, Japanese encephalitis) species are also important • Culex molestus (Forskal) was introduced into Australia around 1940s with movement of US defence forces into Victoria • Closely associated with subterranean habitats (e.g. septic tanks, stormwater systems, subways) • Concern has been raised as to the potential role this species may play in the transmission of exotic arboviruses such as West Nile virusand locally important arboviruses such as Murray Valley encephalitis and Kunjinviruses
AIMS • To better understand the biology of this species, in particular, the biological factors that predispose this species to be a potentially important urban pest species. • An understanding of the biology and ecology of this species is crucial for the establishment of laboratory colonies, molecular biology works and also further experimentation.
METHODS • A laboratory colony of Culex molestus was established from field collected specimens from Sydney region. • A series of controlled laboratory experiments were conducted to investigate: • Mating • Adult nutritional influence on fecundity • Oviposition (egg-laying) preference • Temperature & nutritional influence on larval development • Blood feeding
RESULTS • All adult mosquitoes successfully mated (as indicated by the detection of viable sperm) in confined spacesindicating Culex molestus is strongly stenogamous. % MATED MOSQUITOES
95% RESULTS • Approximately 95% of all female Culex molestus laid their first batch of eggs without taking a blood meal indicating the species is strongly autogenous. • Females delayedtheir first blood meal until after their autogenous egg raft had been laid, despite the availability of a host. • May reduce the importance of this species as a vector
RESULTS Number of blood feeding adult Culex molestus and number of autogenous egg rafts deposited per day post-emergence when offered a pre-oviposition blood meal .
RESULTS Number of blood feeding adult Culex molestus and number of autogenous egg rafts deposited per day post-emergence when no pre-oviposition blood meal.
120 100 80 Number of eggs per egg raft 60 40 20 0 Autogeny Blood fed RESULTS All females readily took a blood meal prior to developing their second batch of eggs with post-blood feeding egg rafts significantly (P<0.05) larger than autogenous egg rafts.
25 20 15 Number of egg rafts 10 5 0 0% 50% 100% Oviposition water quality (percentage of hay infusion) RESULTS The females did not display a preference for highly organic oviposition water indicating and readily laid eggs in clean water.
MEAN AUTOGENY RATE (% Mosquitoes with eggs without blood meal) RESULTS Larval development rates were reliant on temperature rate but adults emerging from larvae raised at a mean daily temperature of 12.0oC maintained the ability to lay autogenous egg rafts.
CONCLUSIONS & IMPLICATIONS • Culexmolestus has perfectly adapted to urban environments. • This adaptation allows the mosquito to remain active throughout the year and in close contact with humans. • Molecular biology studies to determine the genetic relationship between Culex molestus within Australia and overseas are on going. • Further investigation is required to determine the importance of this species and their habitats to mosquito-borne disease risks.
PUBLICATIONS • Kassim, N.F.A., C.E. Webb, and R.C. Russell. 2011. Culex molestus Forskal (Diptera: Culicidae) in Australia: colonisation, stenogamy, autogeny, oviposition and larval development. Aust. J. Entomol. DOI: 10.1111/j.1440-6055.2011.00834.x (In Press- Published online on June 2011). • Kassim, N.F.A., C.E. Webb, and R.C. Russell. 2011. Is the expression of autogeny by Culex molestus Forskal (Diptera: Culicidae) influenced by larval nutrition or by adult mating, sugar feeding or blood feeding? Journal of Vector Ecology. (Accepted on December 2011).
PRESENTATIONS • Kassim, N.F.A., C.E. Webb, and R.C. Russell. 2011. Understanding the unique biology of an introduced mosquito species: Implications for mosquito-borne disease in Australia. Paper presented as poster in the Hospital Week/ Research Symposium. Westmead, Australia. • Kassim, N.F.A., C.E. Webb, and R.C. Russell. 2011. Culex molestus Forskal (Diptera: Culicidae) in Australia: colonisation, stenogamy, autogeny, oviposition and larval development. Paper presented as Oral Presentation in the 59th Annual Meeting of the Entomological Society of America. Reno, USA. • Kassim, N.F.A., C.E. Webb, and R.C. Russell. 2011. An exotic mosquito exploits cryptic urban habitats in southern Australia: Implications for water conservation strategies and mosquito-borne disease risk. Paper presented as Oral presentation in Symposium Emerging Infectious Diseases & Biosecurity Colloquium. University of Sydney, Australia.
Thank you ACKNOWLEDGEMENTS: Merilyn Geary and Karen Willems of Department Medical Entomology for their advice and assistance on colonisation techniques. Sydney Olympic Park Authority for mosquito collections. Malaysian Government for a national grant for graduate work in Australia.