Once we have identified the 'Vectorspots', more detailed work is undertaken to investigate the best course for remedial action in these areas. Each site or group of similar habitats is considered separately with an assessment focusing on the use of natural control methods as the preferred starting point for control.
An Integrated Mosquito Management Plan (IMMP) is created for each area or habitat type based on best available environmentally sensitive practices and offering a variety of alternatives. Control procedures may then be carried out depending on the wishes of the client. Regular monitoring is initiated as part of an adaptive management approach.
Accurate mapping of the breeding habitats of WNv vector mosquitoes provides the opportunity to deliver a targeted control program that fully addresses public concerns. The information collected is designed to form a robust baseline dataset for future monitoring studies, which could be used as a basis for complimentary studies of a wider area.
Sensitive ecosystems where rare species may be at risk will require equally sensitive control methods. In this regard, we believe that our experience in the functional roles of different elements of the aquatic communities will prove extremely helpful to environmentally responsible decision-making.
The Mosquito Life Cycle
Mosquitoes are small flying insects of the family Culicidae. Larval mosquitoes are aquatic and live in standing or relatively slow-flowing shallow water. Adults range in length from 4-10mm and the females may extract blood from animals to provide sufficient nutrient for egg production (Snow 1990). All mosquitoes have a distinctive long proboscis used for feeding, which they use to extract juices from plants as well as blood from animals (Belton 1983; Bates 1949).
Species-specific features can identify most of the mosquitoes that reside in BC in both the larval and adult forms. Body shape, colour patterns, arrangement of hairs, bristles, appendages, wing veins, and wing scales are all distinguishing traits (Belton 1983; Snow 1990).
The life cycle of most species follows a similar pattern (Fig 1) but the timing of different stages varies between species. Mosquitoes lay their eggs on or near standing water bodies or in riparian areas that are subject to ephemeral flooding. Under suitable conditions, the eggs hatch within a few hours into tiny larvae which feed on microscopic suspended organic materials. Most air-breathing larvae typically remain just below the surface with the spiracle at the end of the syphon open to the air, although some species obtain air by boring into the interstitial cavities of emergent plant stems. When disturbed, the larvae usually wriggle downward into the sediments. The larvae undergo four larval stages (instars) averaging ten days in total, depending on the water temperature and the availability of resources (Spielman and D'Antonio 2001). The final instar is usually the longest, lasting several days under normal conditions, after which pupation occurs.
The 'comma-shaped' pupa swims efficiently and breathes air, but unlike the larva, it is unable to feed (Hearle 1929; Bates 1949). After several days, the adult mosquito emerges from the pupal case, but due to differences in tissue and organ development, the male mosquitoes usually develop faster than the females and are able to emerge sooner (P Belton pers. comm.). The emergent adult rests for a short time until blood is pumped into the wings and they are ready for flight (Snow 1990). Mating usually follows soon after the first flight and most females then immediately begin the search for a blood meal (Spielman and D'Antonio 2001).
After ingestion of sufficient protein, the eggs develop in the female and she searches for a suitable egg-laying site. Once the eggs are laid the female may seek additional blood meals to produce more eggs, but this is not always the case (Hearle 1929; Speilman and D'Antonio). Female mosquitoes have a life span of anywhere from two or three weeks to several months and some species do overwinter. Although it is commonly thought that males die soon after mating they too may live for many weeks, although they rarely outlive the females. Birds, amphibians and dragonflies may predate the adults during the day and at night many mosquitoes succumb to bats.
Many mosquito species fulfill the larval stage of their life cycle in a relatively predator-free environment by using ephemeral pools, which predators have trouble in colonising within the time it takes for the adult mosquitoes to emerge (Belton 1983). Deep, permanent water bodies are poor larval habitat because they tend to have resident predator populations. However, the shallow littoral margins of temporary water bodies, where there is abundant emergent vegetation for refuge, may produce extremely high densities (Speilman and D'Antonio 2001; Hearle 1929).
Figure 1 - The life cycle of the mosquito
The Spread of West Nile Virus
West Nile virus (WNv) is a mosquito borne disease that primarily affects birds
but can be spread to humans through the bites of infected
mosquitoes. The virus was first detected in North
America in 1999 when it caused a localized outbreak of human and animal
disease in the New York city area. Since then it has been spreading steadily
across the continent.
In 2003 and 2004, WNv continued to expand westward across the United States and Canada.
Although the virus has not yet been detected in British Columbia, it has been
detected in neighbouring states and provinces and is fully expected to arrive
in BC in 2005.
Mosquito-eating
fish act as natural mosquito control agents
For more information about mosquito
surveillance and control services, please contact:
Culex Environmental Ltd.
Phone: 604-221-9121
Email: info@culex.ca
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