In the past, Chester County has sprayed pyrethrin in an effort to attack mosquitoes. No chemical pesticide is selective; a poison that kills adult mosquitoes will inevitably affect other forms of life. (Biological agents such as larvicides are much more selective.)

Now the County seems to have gone over to another member of the pyrethroid chemical group, DeltaGard, whose active ingredient is deltamethrin.

The information below is mainly about the DeltaGard variant for use in gardens and landscaping, which has the same active ingredient as the DeltaGard insecticide used against mosquitoes. For more on the mosquito spray, see here.

What’s deltamethrin? Of course, the industry doesn’t think it’s dangerous. Some other sources beg to differ. A relatively recent post in Chemicals.News (no friend to the chemical industry) says:

“Deltamethrin — toxicity, side effects, diseases and environmental impacts”

12/05/2017 / By Rita Winters

Deltamethrin is a pyrethroid insecticide that is registered for use in commercial, agricultural, and residential areas. It plays a role in controlling malaria and targets other insects like cockroaches, spiders, ants, fleas, silverfish, bed bugs, bird mites, house flies, and beetles. Deltamethrin products are one of the most popular and widely used pesticides in the world and are very popular with government pest control operations in the country. It is highly toxic to the environment, especially to aquatic life forms like fish and crustaceans. Deltamethrin is also known to be toxic to humans. As a neurotoxin, it attacks the nervous system and causes a variety of negative side effects and fatality. In 2011, a Japanese woman ingested large doses of pesticides that contained deltamethrin, which resulted in motor neuron death.

This chemical compound acts by blocking the closure of the ion gates of sodium channels during repolarization. It then disrupts the transmission of nerve-related impulses causing depolarization of the nerve cell membranes. It is very effective on insects, especially those considered as pests. However, it also affects beneficial insects including honey bees….

read more at Chemicals.News

According to the National Pesticide Information Center: “While children may be especially sensitive to pesticides compared to adults, it is currently unknown whether children have increased sensitivity specifically to deltamethrin….” (Parents will not wish to experiment to find out.)

Also: “When deltamethrin gets in the soil, it has a tendency to bind tightly to soil particles. It has a half-life ranging from 5.7- 209 days. Half-life is the measure of time it takes for half of the applied amount to break down…. Deltamethrin has a half-life of 5.9-17 days on plant surfaces. It is unlikely to be taken up by plants, since it binds to soil particles so tightly….” (So that could be reassuring if you are out for a walk in the street, but not so much if you’d like to consume your own organic produce or turn over your garden knowing that may have pesticide residue in it for up to 7 months.)

“NPIC provides objective, science-based information about pesticides and pesticide-related topics to enable people to make informed decisions. NPIC is a cooperative agreement between Oregon State University and the U.S. Environmental Protection Agency.” Download the pdf of its deltamethrin report here: Deltamethrin General Fact Sheet

See some other sources at these sites:

https://www.ncbi.nlm.nih.gov/m/pubmed/28551743/
https://www.ncbi.nlm.nih.gov/m/pubmed/22079160/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502505/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257607/#!po=76.0417
https://www.ncbi.nlm.nih.gov/m/pubmed/29444244/

The manufacturer’s label (download here: deltagard-5sc-label ornamental) contains an immense list of insects as well as spiders that DeltaGard kills when used on lawns and landscaping. The list includes ants, caterpillars, crickets and grasshoppers, among others that most of us might not see as pests but as important members of the environment; and many of the target species are important food sources for birds, amphibians, and reptiles.

And that is just for the supposed pests. Of course they don’t list the other species than can be killed, such as adult butterflies and dragonflies.

And the label says, not reassuringly for those of us with home gardens:

“DO NOT apply this product to edible crops.”

If you want further non-reassurance, download the manufacturer’s Safety Data Sheet relevant to mosquito spraying here: DeltaGard_Insecticide, including statements such as:

“This product contains material which are Trade Secret and may have Occupational Exposure Limits.”

“Do not allow to get into surface water, drains and ground water.”