Australia’s Dengue Risk: Human Adaptation to Climate Change - Recent Advances and Issues in Environmental Science - page 143

increased use of domestic water storage in tanks could deliver stable primary larval
sites into urban neighborhoods. In Queensland's capital city, Brisbane--which is cur-
rently Ae. aegypti free--severe water shortages resulted in escalating water restric-
tions with an eventual prohibition on the use of all outside reticulated water outlets
(November, 2007-July, 2008) and 75,000 domestic water tanks being installed by late
2007. This number of tanks represents approximately 21% of households with reticu-
lated water in the Brisbane area (F. Chandler, Brisbane City Council, pers. comm.).
Additionally, ad hoc uncontrolled water tanks are now also commonly being used to
store rainwater, adding to the potential surfeit of stable breeding sites around Australia
that are likely to facilitate the expansion risk of Ae. aegypti into urban areas. It is
unlikely that any of these water storage tanks--government approved or not--will be
maintained suffi ciently to prevent mosquito access in the long term.
The fl ight range for Ae. aegypti is understood to be generally small: mark-release
recapture experiments show them to have a fl ight range of only hundreds of meters
[42-44]. However, these estimates are limited in time and space, being derived from
a snapshot of one or a few gonotrophic cycles which take place in the context of an
abundance of ovipositing sites. Longer distance fl ight range dispersal may be more
common, especially when ovipositing sites are rare, but this is diffi cult to quantify
[45, 46]. Human mediated long distance dispersal events are mostly responsible for
Ae. aegypti movement: their highly domestic nature and desiccation-resistant eggs fa-
cilitate successful movement via human transport routes. Surveys in Queensland in the
1990s [17] and 1990-2005 (P. Mottram, unpublished) reveal Ae. aegypti collections
from over 70 townships and this number is likely an underestimate. As the numbers of
individuals and populations of Ae. aegypti increase in Queensland towns, the incursion
risk beyond these regions via human-induced long distance dispersal events also in-
creases, and with the presence of new stable oviposition sites growing, the expansion
of this dengue vector must now be expected.
Operations to remove Ae. aegypti incursions are resource-heavy, often requiring
both government legislation and widespread community cooperation to reduce adult
mosquito populations. A recent example from a 2004 incursion of Ae. aegypti into the
small Northern Territory town of Tennant Creek (pop 3,200) from Queensland resulted
in a 2-year eradication campaign that required 11 personnel and cost approximately
$1.5 million and was achieved in 2006 [8].
CONCLUSION
Determining the potential distribution of Ae. aegypti in Australia using climatic param-
eters can be problematic and in this case produced results that neither fully match the
known distribution, nor reveal cold climate limits in Australia. Reasons for this may
exist in the difficulty of relating the point occurrence data of a species' distribution that
is closely tied to humans--unlike native mosquito species in Australia where GARP
models appear more representative of known distributions [26, 47]. We must also con-
sider the limited climatic parameters available through the OzClim climate scenario
generator that reduced the GARP modeling to a subset of environmental parameters
that may have little influence on the organism. Because the GARP models showed no