BOARD of PARKS and RECREATION INTER OFFICE
CITY OF VANCOUVER CORRESPONDENCE

PLANNING AND OPERATIONS DIVISION

DATE: June 5, 2003

TO: City Council

FROM: Piet Rutgers, Director of Planning and Operations

COPY TO: Judy Rogers. City Manager

SUBJECT: WEST NILE VIRUS RESPONSE PLAN

Background

Further to questions that were raised by Council members on May 27, 2003, when the original report on this topic was discussed, staff have received further information from other jurisdictions about their response plans and in particular the use of biological and other non-chemical methods. In addition, Dr. Michael Jackson has been invited to share his knowledge with Council on June 12, 2003.

At the Planning and Environment Committee, Council will be asked to approve Recommendation B of the original report:

It is important to note that this program seeks authority for larvicide treatment only, it does not deal with the application of adulticides to adult mosquitos. Two larvicides are recommended to be used: Vectobac (Bti) and Altosid (methopene growth regulator). Bti (Bacillus thuringiensis var israelensis) is a biological agent, which is highly specific to mosquito larvae. Altosid is a chemical insect growth regulator and it would be used in catchbasins only. Since it does havepotential environmental impacts, it cannot be used in those catchbasins discharging directly on fishbearing streams. Both pesticides will be applied in granular form only, no spraying will be undertaken as part of the larvicide program.

As noted below in this memorandum, staff will also incorporate mechanical and other biological means where feasible and possible.

Program Basics

Toronto and New York have dealt with the potential health threat from the West Nile Virus for a number of years. Mosquitoes in these two cities are more prevalent than in Vancouver. Both cities have had the opportunity to use a variety of chemical, biological and other methods.

The basic program components in those cities:
1. Environmental Management, Monitoring and Surveillance, Public Education
2. Larval Mosquito Control
3. Adult Mosquito Control
are consistent with the program presented in the council report dated May 14, 2003. That report seeks authority only for Stages 1 and 2.

Integrated Pest Management

Consistent with existing policy and practices in other jurisdictions, the proposed program is founded on the Integrated Pest Management approach. Under this approach the use of pesticides would be minimized.

Under the WNV response plan, the trigger for larval control would be confirmation of the presence of WNV in the Vancouver Coastal Health Region (Level 2b of the provincial "Arbovirus Response Plan"), with preference given to non-chemical and biological control of the larvae. The criteria for initiating larval control include: Population peaks of mosquitoes of concern; density of mosquito larvae in standing water; optimum timing for larval control; weather conditions; nature of habitat to be treated (e.g. catch basin, versus bodies of water with or without natural vegetation); product application methods/frequency.

Controlling mosquitoes in their larval stage is preferable to using aerial spray pesticides against adult mosquitoes since less toxic pesticides (with far less environmental impact) are available for this purpose and the products can be released in a more controlled fashion. Experience elsewhere shows that an IPM program for mosquito control can reduce or eliminate the need for aerial sprays by using a mix of control methods such as source reduction and mosquito larvicide.

Two Programs - Two Potential Larval Control Methods

In discussions with colleagues in Toronto it has become clear that the larval control programs on public property can best be separated into two categories - one aimed at identification and, if necessary, control of Culex pipiens in catch basins and one aimed at identification and control of mosquito larvae in open bodies of water, both natural and man-made.

Clearly these are two distinct types of treatment environments, the latter more potentially fragile than the former. This year Toronto is focusing their efforts on catch basins, as they have been identified as prime breeding areas for the Culex pipiens mosquito, a known vector for WNV. Based on significant research and the experience of New York City, the Board of Health and City Council has endorsed the Medical Health Officer's proposal to utilize methoprene (an insect growth regulator which prevents the larval stage of mosquitoes from developing into adults) in Toronto's catch basins. Bti, the other larvicide of choice, was not selected for use in catch basins because of the need to re-apply frequently and based on studies that reveal a <40% reduction in larvae in catch basins. Due to the contained nature of catch basins and the absence of other significant fauna in these relatively hostile environments, the use of methoprene has been deemed an appropriate and environmentally sound way of reducing mosquito larvae populations in the 175,000 catch basins in Toronto.

Toronto city staff will be concurrently evaluating other mechanical and non-chemical means of larval reduction, including ultrasonic, electrocution, steam and heat application. Rather than the City of Vancouver duplicating these efforts, City staff will review Toronto's experiences in these areas for possible application.

Toronto will not be conducting a control program against larvae in open bodies of water this year but will be carrying out surveys of stagnant water on public lands to determine the presence of larvae and assess the need for control measures.

Biological Larval and Mosquito Control

Biological control is the effort by humans to control pests through the use of organisms antagonistic to the pest. These biological control agents are often highly specific to the target pest organism. This makes biological controls different from chemical controls which tend to affect a broader range of non-target organisms. Some forms of biological control against some targets can offer permanent control solutions at an excellent cost/benefit ratio. The problem is selecting a biological that will control the pest to a level acceptable to the public. The key to the use of any pest control is the tolerance threshold. Biological controls are used routinely in agriculture and horticulture to maintain pests at an acceptable level to those industries. While 10% losses through pests and disease may be an acceptable level in agriculture, in human health situations such infection levels would be disastrous. Recent experience with SARS, West Nile Virus and Mad Cow Disease indicates that the public tolerance threshold for disease is close to zero.

Both the New York study and a similar study from Toronto, concludes that the most effective method of controlling disease carrying mosquitos is to eliminate, wherever possible, mosquito breeding sites (source reduction). The next most effective control is elimination of mosquito larva through the use of environmentally friendly larvicides. The least effective control method is to spray pesticides to control adult mosquitoes. However, adult spraying was deemed necessary several times in New York in 2002 where source reduction and larvicide methods could not keep pace with growth in WNV carrying mosquitoes.

As part of the New York Comprehensive Mosquito Surveillance and Control Plan, New York reported research on the effectiveness of predatory insects and fish on mosquito larva, and theeffectiveness of birds and mammals on controlling adult mosquitoes in other mosquito control programs, as did the city of Toronto. They concluded that natural predators would be ineffective mosquito larva control in catchbasins.

Dragonfly larva feed on mosquito larva and in lakes and ponds. Where conditions exist to support these insects, they could be introduced or added to augment existing dragonfly populations in natural areas. In the United States, Massachusetts, New Hampshire and Maine, dragonflies have been used with some success in nuisance control programs for mosquitos, however, not for controlling outbreaks of disease. Dragonfly larva are not currently available for sale in Canada and the introduction of non-native species may have unforseen ecological impacts.

Other predatory aquatic insects such as water beetles, hydra, flatworms have been identified as possible controls for mosquitos. Some of these insects have been examined in laboratories for this purpose but there are no commercial sources for the purchase of these insects.

Various species of larvivorous fish have been shown to be effective controls of nuisance mosquito larva in the United States, Africa and the Mediterranean area. New York uses mosquitofish (Gambusia affinis) in the closed water systems of their Water Pollution Control Program to control breeding mosquito populations in the sewers. Vancouver has no similar enclosed storm water system that does not link in part directly to the Fraser River. This non-native species, a voracious feeder, is not used in natural waterbodies due to their potential to replace native fish species. In Napa County California, mosquito fish are released in mosquito breeding sites such as ornamental ponds and swamp areas. Staff have been unable to find documentation on the effectiveness of stickleback fish.

Amphibians such as tadpoles also eat mosquito larva. Tadpoles would be difficult to introduce into the varied mosquito breeding sites and the introduction of large quantities of frogs into the urban environment could have significant impact on the surrounding environment.

Introducing fish, insects, or amphibians to any Vancouver waterbodies, open or closed, would only control a small portion of the mosquito larva populations. Most mosquito breeding sites such as water in containers and temporary storm water retention areas cannot be stocked with such predators. There are concerns about introducing exotic species into the local environment as well as finding a commercial source for most mosquito control species.

Most bats feed on flying insects and can eat large numbers of adult mosquitoes. The New York report raised concerns about introducing this mammal into the city in large numbers to control adult mosquitoes due to the possibility of rabies from bats. Also during the 2001 New York surveillance for WNV, three bats tested positive for WNV. It is unknown whether the bats ingested or were bitten by WNV carrying mosquitoes or whether bats would help prevent or aid the spread of WNV.

Many bird species also eat adult mosquitoes. The New York study reports that in the 2000 United States Geological study, bird to bird transmission of WNV was observed. The report concludes that increasing the bird population would not achieve the goal of protecting public health, given their potential to spread mosquito born diseases and their relative ineffectiveness in reducing adultmosquito populations.

In nature, there are numerous animals such as other insects, fish, birds and bats that feed on mosquito larvae and adults. These predators establish a natural balance controlling some of the mosquito growth in lakes, ponds and wetlands. Within an urban environment, natural predators cannot be relied upon. Mosquitoes breed in phenomenal numbers in standing water such as puddles, discarded tires and catch basins, environments that cannot support most natural aquatic predators. The New York study concludes that some predatory animals are effective at controlling a portion of the nuisance mosquito population in natural environments but are ineffective at controlling disease carrying mosquitoes.

Throughout this program, staff will continue to monitor documentation on the effect of biological controls and integrate them in the program where feasible.

Other Non-Chemical Methods

As noted a number of other non-chemical methods are in various stages of development, application, or evaluation. These methods for catchbasins in particular include ultrasonic, electrocution, steam and heat application. Staff are continuing their investigations into supply, costs, effectiveness, and feasibility of these methods and will use them on a pilot basis, when there is evidence of effectiveness and the resources can be secured.

Conclusions

· City/Park Board staff will implement the mosquito control program consistent with the principles of Integrated Pest Management.

· The larvicide program does not involve spraying, only granular forms of Bti and methoprene will be used.

· There is little evidence that reliance on biological controls would be an effective way of dealing with mosquito population control in their principal breeding grounds, catchbasins and standing (and often temporary) waterbodies.

· Staff will investigate biological control experiences elsewhere and make them part of the program when supported by documentation of effectiveness.

· Various mechanical means are being developed and on a pilot basis staff would include these in the program, when supported by documentation of effectiveness.

· Recommendation B in the Council Report dated May 14, 2003 is a larvicide program only and does not seek authority for an adult mosquito control program.

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Piet Rutgers

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