But this chemical has been linked to genotoxic and neurological effects in children, and the European Union said recently that no safe exposure level ­can be set for the substance.

Although the chemical is still registered for use by the US Environmental Protection Agency, the Obama administration had planned to ban the its use. But under the Trump administration, that decision has been reversed. Six US states are now pursuing a lawsuit challenging the EPA for continuing to allow what is now believed to be a dangerous toxin to still be sprayed on crops.

McNelly said that over a year ago the MRCU made the decision to move away from the routine use of chlorpyrifos and was using up the last of the stock. He added that most of the unit’s efforts focus on controlling the larval stages of mosquito development, which happen in standing water.

“It is expected that this chemical will be completely depleted within a week or two,” he said, adding that any future use would be contingent on the need to respond to mosquito-borne diseases. “It is used in rotation with other insecticides to control adult, biting mosquito populations. Insecticides like this are always the last tool to be deployed from our toolbox.”

McNelly explained that, as part of its research work, the MRCU had decided to begin incorporating a new product to offset the diminished use of chlorpyrifos. The new product is Merus, an adulticide with natural pyrethrin as the active ingredient.

“This product is Organic Materials Review Institute (OMRI) Listed, meaning it is approved for wide area use in urban or residential areas, as well as in and around organic farms and gardens,” McNelly said. “It is made with imported natural pyrethrins, a botanical insecticide that is naturally occurring in chrysanthemum flowers. The Merus formulation includes no petroleum distillates or chemical synergists, and is highly effective on a wide range of mosquito species.”

McNelly said the formulations used by the unit to control mosquitoes embraces the principles of integrated mosquito management, which includes balancing the goals of public health and public preference.

“As our name implies, an important aspect of our mission is research, and we are always looking at new active ingredients, and new approaches that reflect best practice in using these active ingredients to control mosquitoes and mitigate mosquito-borne disease,” he stated.

Meanwhile, following multiple inquiries from readers about the chemicals currently being used by the MRCU and how they are deployed, McNelly confirmed the list of products it has used over the last month are as follows:

    Mosq Mist II by plane and truck
    Fyfanon by plane
    Vectobac WDG by plane
    Vectobac GS by plane
    VectoPrime by plane
    Natular G30 by plane and hand applications
    Natular G by plane