What is supposed to happen? Has it been happening?

Some questions derived from CDC mosquito control guidelines:

1. Where has the County engaged in source reduction, as recommended?

The only source reduction we know of has been undertaken by West Chester Borough to prevent water from standing in storm drains. Does anyone know of other examples?

2. Where has the County engaged in larval mosquito control, as recommended?

They have told us that they do so, but so far have said they do not have records for 2015-17 and do not have time to tell us where for 2018; our Right to Know request on this with the PA Department of Environmental Protection is pending.

3. Has the County maintained a database of aquatic habitats to identify the sources of vector mosquitoes and a record of larval control measures applied to each (last paragraph below)?

From point 2 above, it would seem doubtful; but the public has a right to know, and we will.

Source material: Centers for Disease Control and Prevention, Division of Vector-Borne Diseases, “West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control,” 2016, p. 33. (See the points we have put in boldface below. Download the full publication here).

Integrated Vector Management

Mosquito abatement programs successfully employ integrated pest management (IPM) principles to reduce mosquito abundance, providing important community services to protect quality of life and public health (Rose 2001). Prevention and control of WNV and other zoonotic arboviral diseases is accomplished most effectively through a comprehensive, integrated vector management (IVM) program applying the principles of IPM. IVM is based on an understanding of the underlying biology of the arbovirus transmission system, and utilizes regular monitoring of vector mosquito populations and WNV activity levels to determine if, when, and where interventions are needed to keep mosquito numbers below levels which produce risk of human disease, and to respond appropriately to reduce risk when it exceeds acceptable levels.

Operationally, IVM is anchored by a monitoring program providing data that describe:
• Conditions and habitats that produce vector mosquitoes.
• Abundance of those mosquitoes over the course of a season.
• WNV transmission activity levels expressed as WNV infection rate in mosquito vectors.
• Parameters that influence local mosquito populations and WNV transmission.

These data inform decisions about implementing mosquito control activities appropriate to the situation, such as:
Source reduction through habitat modification.
• Larval mosquito control using the appropriate methods for the habitat.

• Adult mosquito control using pesticides applied from trucks or aircraft when established thresholds have been exceeded.
Community education efforts related to WNV risk levels and intervention activities.

Monitoring also provides quality control for the program, allowing evaluation of:
• Effectiveness of larval control efforts.
• Effectiveness of adult control efforts.
• Causes of control failures (e.g., undetected larval sources, pesticide resistance, equipment failure)….

and p. 34:

Larval Mosquito Surveillance

“Larval surveillance involves identifying and sampling a wide range of aquatic habitats to identify the sources of vector mosquitoes, maintaining a database of these locations, and a record of larval control measures applied to each. This requires trained inspectors to identify larval production sites, collect larval specimens on a regular basis from known larval habitats, and to perform systematic surveillance for new sources. This information is used to determine where and when source reduction or larval control efforts should be implemented….

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What is a Vector Index?

As of 2016, Chester County is using the Vector Index method of using mosquito data to predict the West Nile Virus threat to humans. Here is a summary from “2013 West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control” at the CDC site, p. 18 (boldface added):

The Vector Index (VI) is an estimate of the abundance of infected mosquitoes in an area and incorporates information describing the vector species that are present in the area, relative abundance of those species, and the WNV infection rate in each species into a single index (Gujaral et al. 2007, Bolling et al. 2009, Jones et al. 2011). The VI is calculated by multiplying the average number of mosquitoes collected per trap night by the proportion infected with WNV, and is expressed as the average number of infected mosquitoes collected per trap night in the area during the sampling period. In areas where more than one WNV vector mosquito species is present, a VI is calculated for each of the important vector species and the individual VIs are summed to represent a combined estimate of the infected vector abundance. By summing the VI for the key vector species, the combined VI accommodates the fact that WNV transmission may involve one or more vectors in an area. Increases in VI reflect increases in risk of human disease (Bolling et al. 2009, Jones et al. 2011, Kwan et al. 2012, Colborn et al. 2013 in press) and have demonstrated significantly better predictive ability than estimates of vector abundance or infection rate alone, clearly demonstrating the value of combining information for vector abundance and WNV infection rates to generate a more meaningful risk index (Bolling et al. 2009). As with other surveillance indicators, the accuracy of the Vector Index is dependent upon the number of trap nights used to estimate abundance and the number of specimens tested for virus to estimate infection rate. Instructions for calculating the Vector Index in a system with multiple vector species present are in Appendix 2.

For the actual VI formula and a detailed example, see pp. 64-66 of the above Guidelines.

Zika Surge in Miami Neighborhood Prompts Travel Warning

By PAM BELLUCK, New York Times, AUG. 1, 2016,

This excerpt details why we find reliance on pesticides to solve mosquito problems not only undesirable but potentially unreliable:

…Dr. Thomas R. Frieden, the director of the C.D.C., said that the Aedes aegypti mosquito, which transmits the Zika virus, has proved to be a wily adversary in Wynwood, a crowded, urban neighborhood in north Miami where all the cases were found. The mosquito may be resistant to the insecticides being used or may be able to hide in standing water.

“Aggressive mosquito control measures don’t seem to be working as well as we would like,” he said in a press briefing on Monday.

The authorities had expected additional cases of Zika infection linked to the neighborhood, he said. But officials were particularly concerned by indications over the weekend that “moderately high” numbers of Aedes aegypti mosquitoes and their larvae were still being found in a one-square-mile section in Wynwood, an area of warehouses, art galleries, restaurants, bars, apartments and condominiums….

read the full article at New York Times

Forgo the Fog: Alternatives to Mosquito Fogging

Midwest Pesticide Action Center

Summer is peak mosquito season, complete with annoying bites and fears about West Nile virus. While mosquitoes can be a nuisance, Mosquito Abatement Districts (MADs) do not necessarily have to resort to fogging in order to control mosquito populations.

According to the U.S. Centers for Disease Control and Prevention, and the American Mosquito Control Association, the airborne spraying of pesticides, commonly called mosquito ‘fogging’, to kill adult mosquitoes is the least effective method to control mosquito populations. Fogging usually consists of spraying or fogging pesticides from the back of a truck or plane.

This method is ineffective because the pesticide only kills those mosquitoes flying in the spray; mosquitoes behind buildings or under vegetation are not affected. Airborne pesticides are particularly harmful as they may be easily ingested by humans and wildlife. Pesticide residue can also be left behind on items kept outdoors, such as children’s toys and outdoor furniture, or tracked inside on shoes. Since fogging also kills insects that eat mosquitoes, it can cause future population booms for local mosquitoes….

MPAC recommends three alternatives to fogging…

read more at Midwest Pesticide Action Center