Larvae or Adults

The BLSG Insect Control District operates two different mosquito control programs. The Vermont Agency of Agriculture funds a program to apply bacterial larvicide granules from the air to kill mosquito larvae in standing water. The five towns in the BLSG district fund a program to apply chemical pesticides along roads to kill adult mosquitoes.

The differences between the two methods of controlling mosquitoes are dramatic. Discussions about the effectiveness or safety of BLSG operations should specify which program is being discussed. The table below highlights some of the differences (click for better view).

This is a simplified outline of the two programs and many details are not included. For example, bacterial larvicides are not the only products used to kill mosquito larvae, and bacterial larvicides can be dispersed by hand. Also, spraying of chemical pesticides can be done via a backpack sprayer instead of a truck-mounted ULV machine.

Permanone is in the air

This week the BLSG started roadside spraying of pesticides to kill adult mosquitoes. Pesticide application is now being done under Vermont’s 2017 Pesticide General Permit after the Department of Environmental Conservation approved, on May 15, the BLSG request to continue operation.

We will be announcing, whenever possible, the dates and location of roadside spraying of adulticides in the district. The best way to get advance notice is to follow us on Twitter or Facebook (see the right sidebar).  We might also be able to send alerts by text or email, so let us know if you would be interested in that.

The pesticide being sprayed tonight is Permanone which is a formulation containing about 4% permethrin. Here is the active ingredient list from the label posted by BLSG:

Permethrin………………………………………….. 3.98%
Piperonyl Butoxide* ……………………………. 8.48%
OTHER INGREDIENTS†…………………….. 87.54%
TOTAL: 100.00%
* (butylcarbityl)(6-propylpiperonyl) ether and related compounds.
† Contains petroleum distillate

Piperonyl butoxide is a synergist which works by inhibiting the natural defense mechanisms of the insect. It is not a pesticide, but makes the permethrin more deadly.

Here is what the label says about the environmental hazards of Permanone:

ENVIRONMENTAL HAZARDS This pesticide is extremely toxic to aquatic organisms, including fish and invertebrates. Runoff from treated areas or deposition of spray droplets into a body of water may be hazardous to fish and aquatic invertebrates.

Before making the first application in a season, it is advisable to consult with the state or tribal agency with primary responsibility for pesticide regulation to determine if other regulatory requirements exist.

Do not apply over bodies of water (lakes, rivers, permanent streams, natural ponds, commercial fish ponds, swamps, marshes, or estuaries), except when necessary to target areas where adult mosquitoes are present, and weather conditions will facilitate movement of applied material away from the water in order to minimize incidental deposition into the water body. Do not contaminate bodies of water when disposing of equipment rinsate or washwaters.

This pesticide is highly toxic to bees exposed to direct treatment on blooming crops or weeds. Do not apply this product or allow drift when bees are actively visiting the treatment area, except when applications are made to prevent or control a threat to public and/or animal health determined by a state, tribal, or local health or vector control agency on the basis of documented evidence of disease causing agents in vector mosquitoes, or the occurrence of mosquito-borne disease in animal or human populations, or if specifically approved by the state or tribe during a natural disaster recovery effort. Applications should be timed to provide the maximum possible interval between treatment and the next period of bee activity.

The entire label for Permanone is at the BLSG site.

We hope the guys preparing and driving the spray trucks stay safe.


Methoprene and vernal pools

Thursday’s Rutland Herald article by Will Mathis, Director of Operations of the BLSG Insect Control District, focused on the larvicide program. Although the article was titled “Mosquito spraying program explained,” no mention was made of malathion or permethrin which are sprayed along town roads to kill adult mosquitoes. Instead, the article focused on the program to treat standing water to kill mosquito larvae before they hatch.

The major effort of the larvicide program is spreading bacteria from a helicopter over the Otter Creek floodplain swamps and fields. The two bacteria used (Bacillus thuringiensis israelensis, and Lysinibacillus sphaericus, until recently known as Bacillus sphaericus) contain toxic crystals which are activated by conditions in a mosquito larva’s gut and kill the larvae. These bacteria have shown no toxicity to people or animals other than mosquitoes and a couple of other types of small flies. Well-timed application of these bacteria can dramatically reduce the number of certain species of mosquitoes.

Not all mosquito species breed in floodplain swamps and fields, and helicopter application cannot efficiently target many dispersed small pools. So another type of larvicide, methoprene, is applied by hand to some water bodies. Methoprene is not a bacteria, it is an insect growth regulator. Insect larvae exposed to it never metamorphose into adults. Methoprene is not specific to mosquitoes and interrupts the development of many aquatic insects and other invertebrates. Mosquitoes are very sensitive to methoprene, so if its concentration in water is low, the primary toxicity will be on mosquitoes and some other small invertebrates.

A vernal pool in the Salisbury Town Forest. April 29, 2009

The loss of some harmless non-target creatures might be an acceptable price to pay for controlling mosquitoes, unless those creatures are part of a critical ecosystem. Vernal pools are small temporary ponds that are wet just long enough in the spring to support ephemeral populations including amphibians, fingernail clams, and fairy shrimp. Amphibians hop or crawl away before the pools dry up, but the clams, fairy shrimp, and other invertebrates persist for months until the pools fill up again. There is not much data on how these invertebrates tolerate methoprene, but vernal pool communities are sufficiently valued that it might be wise to avoid the risk of serious disturbance. Some authorities have banned the use methoprene in vernal pools, for example in a California mosquito control district “Because of the effects of methoprene on fairy shrimp and a lack of information on how long the agent remains in the soil, use of the larvicide methoprene within vernal pools or swales at any time, in either wet or dry conditions, is prohibited.”

It will be good to learn more about where methoprene is used in the BLSG district, and how the concentration of methoprene is kept low enough to affect only mosquitoes and other small invertebrates.


Permethrin factsheet

The BLSG Insect Control District sprays pesticides along town roads to kill adult mosquitoes. The most recent public notice from the District identifies the pesticides as “malathion or synthetic pyrethroid insecticides.” Permethrin is the most commonly used synthetic pyrethroid. It is considered to be much less toxic to humans than malathion, and is sometimes less effective for controlling mosquitoes. The equipment used by the BLSG to spray permethrin produces tiny droplets so a very small amount of chemical is needed. Nonetheless, permethrin is toxic to organisms other than mosquitoes. A factsheet on permethrin from the group Beyond Pesticides includes human health precautions about cancer, immune system effects, and effects on reproduction.  Here is a link to the fact sheet which includes citations of the studies on which it is based:…/pe…/factsheets/permethrin.pdf

Pesticide manufacturers and distributors are required to include specific precautions in the labels on their products. This is the label for a product containing permethrin. It states “Avoid breathing vapors or spray mist. … Do not use on humans.”

EPA’s guidance for reducing exposure to malathion

There is a lot of information available about the pesticides used in the BLSG Insect Control District. The most recent public notice from the District identifies the pesticides as “malathion or synthetic pyrethroid insecticides.” On the EPA’s mosquito control website, the page about malathion suggests that “people who are especially concerned may choose to take some of these steps to help reduce exposure”:

1. Stay indoors with the windows closed.
2. If you are outdoors during spraying operations and you can see the spray, avoid contact with it. If you can’t avoid contact, rinse your skin and eyes with water.
3. Wash fruits and vegetables from your garden before storing, cooking or eating.
4. Cover outside items like furniture and grills while the spraying is occurring. Bring pets and items like pet food dishes and children’s toys indoors
5. If you think you have had a reaction to the mosquito spray, talk to your doctor or call the regional Poison Control Center at 1-800-222-1222.

EPA’s information on Malathion is here: