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):
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.
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.