Who says storm drains are a big mosquito problem?

The PA Department of Environmental Protection, that’s who!

We usually call them “storm drains” but others use the term “catch basins” or “inlets.” In any case, that’s where runoff from streets goes through a grill and disappears from our sight. But then were does it go? It should drain by gravity though a pipe system and eventually flow into a stream. That’s a problem for the stream, because street runoff can be polluted, e.g, by car and animal wastes.

But when water is able to remain standing in the storm drain, it provides an ideal habitat for mosquitoes to breed! Then those storm drains need to be “treated” (with a larvicide like Bti) to keep larvae from maturing there into adult mosquitoes. Here’s what PA DEP says (you have to keep refreshing the URL in your browser to find this photo and commentary):

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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….

“Why don’t they just spray and kill all the mosquitoes?”

Yes, people may wonder: “Why don’t they just spray and kill all the mosquitoes?”

First, it’s impossible to kill all the mosquitoes. Any spraying, including from a truck as done by the County, kills only the portion of mosquitoes that happen to be flying around at the time and encounter toxic droplets. We have seen figures of up to an 80% kill rate (yes, this is a serious poison) but no really authoritative figure.

But suppose 20+% of adult mosquitoes survive (and any out of the spray zone, sheltered at the time in thick foliage, or in inaccessible areas like inside bulkheads or hollow trees, will not be affected). The females, at least, will be happily flying around the next day biting people and laying eggs as usual.

The hundreds of eggs that each female lays in stagnant water are affected by spray. Those eggs will become larvae, pupae, and adults, all within a week in hot weather like now.

And current larvae and pupae will not be affected by spray either.

And not all mosquitoes are created equal. Specifications require that spraying occur only in the evening, when honeybees are less active. Disaster for bees ensues if spraying occurs at other times.

Our home-grown mosquitoes, the ones that at least give us an auditory warning hum as they circle us looking for bare skin, tend to be active in the evening; however, the recently established “Asian Tiger” mosquitoes, the silent biters, tend to be active during the day and therefore are not much affected by spraying. Killing off some of the “regular” mosquitoes probably just opens the airways to more Asian Tigers.

Furthermore, anti-mosquito spray actually kills mosquito-eaters like dragonflies and toads, to say nothing of insects that we enjoy seeing or that are important to ecological balance like butterflies.

The County Health Department does not spray for the comfort of people who wish to be outside without the recommended bug repellents, long sleeves, and long pants. People outside need to weigh those nuisances against the nuisance of being bitten. The Health Department is not the Department of Outdoor Living.

Finally, proper public policy is to spray only, in the words of the Chesco Health Department, “after exhausting all other available mosquito control strategies.”

The prime non-toxic mosquito control strategy is larviciding suspect standing water. Individuals can larvicide on their own property but not on public property. We are glad to say that the Borough of West Chester is taking steps for two employees to receive the relatively simple licensing to do that, and we hope other municipalities will do the same.

Currently, the County does the larviciding but obviously needs to be informed where the problem areas are in such a large county. In West Chester, our Adopt A Drain program is clearing drain grills of plastics and other detritus and informing the Borough of drains that need cleaning below grill level or larvicing where they are holding standing water.

Example, as of Aug. 30, 2018: the storm drain at the NE corner of E. Nields and S. Matlack streets. If you check it out, you’ll see a water reflection at the bottom. After the dry last week in August, this drain could already have released swarms of adult mosquitoes to the neighborhood. In dry weather, mosquitoes could also be breeding in stagnant areas of Goose Creek and Plum Run, including water backing up in drainage pipes entering the stream. (Water samples are needed to check it out.)

If residents anywhere are aware of storm drains with standing water, they should inform their municipality. And of course, we should all patrol our own property, even for something as small as a bowl holding water under a potted plant, and put in a helpful word to neighbors who may not be addressing the issue. For some egregious “Case studies in what to avoid,” see here.

A serious case

If you have anything like this on your property, it’s time for immediate action! This photo shows about 100 mosquito larvae. The corresponding video shows them happily snapping their way (that’s how they move) around the shallow water rich in organic organic matter, their ideal habitat.

The good news is that an application of several tablets of the non-toxic larvicide Bti in a surface area of about 100 square feet virtually wiped out the larvae within 2 days.

With a bit of practice, it becomes easy to detect larvae in standing water. Sunlight helps show them, or a good flashlight. They are easily visible, about 3/8″ long, and a slight disruption of the water encourages them to zip around looking for shelter.

Entomologist John Jackson: “Bugs and Weeds Away–the Natural Way”

On May 29, John Jackson (BA in biology, MA in zoology, PhD in entomology) spoke on having a weed-free sidewalk and neutralizing mosquito breeding spots without using harmful chemicals. His talk at Iron Works Church in West Chester was sponsored by Don’t Spray Me! / Sierra Club and the South West Association of Neighbors (SWAN).

Here are some highlights of his talk and the subsequent discussion (with some resorting of topics):

1) Mosquitoes

Mosquitoes are the best-known insects in the world, because of their role in spreading diseases, especially malaria, yellow fever, and dengue. But the ways chemical tools have been overused against them are not in the interest of either people or wildlife. Chemicals may be needed to prevent massive epidemics, especially in the tropics, but when overused become ineffective because insects develop resistance.

There are lots of biting flies beyond mosquitoes. Here, the predominantly evening-biting Culex mosquitoes can carry West Nile Virus but day-biting Aedes (including Asian Tiger, which has been in the US only since 1985) almost never do. People should not view all insects (of which most don’t bite) as enemies.

Culex, the “house mosquito,” overwinters as adults in sheds, porches, tree hollows, and other sheltered areas. The adult mosquitoes we see in May have overwintered; they may have not yet had time to reproduce. Culex mosquitoes love urban environments, where they lay eggs in water where larvae feed on bacteria and organic matter.

West Nile Virus, which came to the US in 1999, depends on birds as a reservoir (unlike Zika, whose reservoir is people, making it easier to contain, as recently in Miami). Some birds, which in the past were often dying of WNV, appear now to be developing immunity. Fortunately, WNV is not transmitted through mosquito eggs, only from a bitten bird to another bitten bird or human. Known human WNV cases have been rare in PA.

Effective non-chemical defenses include tight-fitting screens, fans on ceilings or porches, repellents (notably lemon eucalyptus oil, picaridin, or citronella oil), various odoriferous granules spread in gardens or lawns.

Fogging with pesticides is a bad idea, because it kills many species, including mosquito predators like spiders; drift cannot be controlled; and it kills only adult mosquitoes, whereas many more larvae are just waiting to hatch every day and take over the air space.

The absolutely most important thing is to eliminate standing water, including where we might not think of it: in plastic bottles, the folds of tarps, in the fixed bottoms under some potted plants, even vases in cemeteries.

From mosquito egg to adult probably takes 10-15 days when weather is hot and damp, but 25-30 days with temperatures in the 70’s.

The bacteria-based larvcide Bti is very effective at killing mosquito larvae. The biscuits and granules have slower release than liquid and powder form. The hormonal Methoprene is also not toxic and prevents the metamorphosis to adult.

One of the worst sampling stations is in SE West Chester; it is not clear if that is related to Goose Creek. Trash in suburban streams creates mosquito habitat. And water can stand in old storm sewer lines like the Borough’s.

2) Weeds

Some undesired plants, like dandelions and poison ivy, are best dug up. Weeds are tough, but weakening them by cutting off the leaves a few times makes them more vulnerable to other treatments.

Old-school boiling water works really well; be careful, wear boots and goggles! Ditto butane flame torches. Or: a weak acid breaks down cell walls; vinegar works, but changes the soil chemistry.

He prefers to use 1 cup of borax (another kind of salt) in 1 gallon of warm water to kill weeds. The borax concentration can be doubled if needed. It also, for better or worse, it also kills ants, moss, lichen, and liverwort. Two applications a summer usually suffice, preferably in hot dry weather, since rain washes the borax away.

Regular table salt also kills plants; witness the die-off this past winter along roads and alleys in the Borough, which uses salt and brine to melt snow and ice. Municipalities tend to use twice as much salt as 20 years ago, even though less harmful substances are available. As a result, streams have increased chloride levels; he measured half the salt content of seawater in one stream.


excess salt, edge of alley, West Chester, 12/20/17

The importance of larviciding … including out of sight

In the 4-part mosquito life cycle*, the most vulnerable stage is the larva. Eggs are designed to survive, pupae don’t need to eat and their chief enemy would be rough water preventing them from breathing, and adults are elusive fliers and many survive even the most determined application of toxic chemicals.

But larvae depend on feeding on organic matter in unclean standing water. If they get too hot or cold, don’t find enough food, or can’t breathe regularly at the surface of calm water, they will develop into adults either slowly or not at all. Continue reading

The sump pump danger

Please examine closely:

Potential mosquito breeding ground, right? Nice dirty stagnant water, gathering at the bottom of a bulkhead to be pumped out.

Can mosquitoes fly in? Certainly; no bulkhead is constructed tight enough to keep out a small insect.

Has the homeowner taken the right precautions?

Yes! Note the Bti larvicide tablet floating on the left side. Very good!

Larviciding with Bti

A larvicide (or larvacide) kills larvae.

In a rare too-good-to-be-true moment, the biological agent Bti prevents mosquito larvae from maturing. It’s made from bacteria called Bacillus thuringiensis israelensis, which affects no other forms of life except two other nuisance insects (black flies and midges). It is organic and totally non-toxic.

You can use mosquito dunks in any standing water that you can’t dump out regularly: a small pond or stagnant stretch of stream in your yard, or a built-in plant soaking area that no longer drains, etc.

For a small surface area, just break up the dunks in pieces. In any case, reapply every month or so to be sure the Bti is still actively working.

Dunks usually come in packs of 6 dunks. If you buy more than one at a time at ACE hardware store in East Bradford (720 W Strasburg Rd., just west of West Chester borough, after Daily Local News), ask for a discount.

Just to remind you, we oppose the use of pesticide sprays and SPRAYS HAVE NO EFFECT ON LARVAE (or on eggs, or on pupae, the cocoon-like form that larvae go through before emerging as adults).

For detailed information on Bti, see “Best Natural Mosquito Control: Bti” at mosquitoreviews. Use Bti only on your own property or, with permission, on someone else’s property, but not on public property.

Mosquito dunks