Once we have identified the 'hotspots', 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 Evaluation Plan (IMMEP) 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.

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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

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The Spread of West Nile Virus

Different species of mosquitoes have different life cycles and inhabit different types of waterbodies. Some do not bite humans and are therefore not a serious pest. West Nile Virus (WNV) may be transmitted to humans and/or livestock only by mosquito species that also bite birds. There are thought to be less than 10 species that come into this category in BC (WNV vectors) out of the 50 or so found in British Columbia. It is essential therefore to identify which species of mosquito are found where before making recommendations about WNV control.

During 2003, West Nile Virus has continued to spread from eastern North America into the western provinces of southern Canada. This year numerous reports of infected dead birds were followed by human cases, including recent fatalities in Saskatchewan that have been attributed to the virus. The virus appeared for the first time this year in Alberta. It is almost inevitable that the virus will spread into British Columbia within the coming months and is likely to be a major concern in 2004.

We offer a carefully structured approach to mosquito control based on sound ecological principles and environmental goals. By building on tried-and-tested methodology and sampling protocols as well as using available historical information we are able to create a detailed database that provides a robust platform for responsible decision-making. In response to the likely arrival of West Nile Virus in British Columbia within the coming months, Acroloxus has developed an Integrated Mosquito Management system founded on the premise that natural control methods are preferable to the use of chemical agents. We recognise that short-term measures involving the use of environmentally friendly specific larvicides, such as Bti, are often necessary to avert immediate public nuisance and health concerns. We advise strongly against the use of fogging with adulticides, particularly organophosphates such as Malathion, as we believe this is an ineffective and indiscriminate method of control that may cause long-term damage to the environment.