WELLFLEET — Along Duck Harbor Road, a long-sleeved 100-percent cotton shirt didn’t cut it — much less, a pair of leggings. Mosquitos latched onto my clothes and plunged their proboscises right through the fabric. Everything prickled as I followed a team from the Cape Cod Mosquito Control Project into the Herring River basin. The professionals were clad in thicker apparel treated with insecticide.
“Stop for 30 seconds, and you’ll get chewed up,” warned Bart Morris, the project’s assistant superintendent. The group pressed on, ducking under fallen branches, wincing through a thorny briar patch — all while swatting, fruitlessly, as mosquitos descended.
This tangle of vegetation has prevented crews from reaching bodies of stagnant water and treating mosquito habitats with larvicide, hampering Mosquito Control’s counteroffensive against this summer’s nightmarish mosquito boom here. But after lengthy discussions, a special use permit was granted by the Cape Cod National Seashore on Monday, and crews deployed, revving up their brush saws and carving out access paths to water channels. The goal is to spray Bti — Bacillus thuringiensis subspecies israelensis — a soil bacterium that produces toxins that kill the larvae of the mosquito, blackfly, and fungus gnat, according to the webpage of the Environmental Protection Agency devoted to mosquito control.
In stagnant water, mosquito eggs are constantly hatching, but the soil surrounding the Herring River basin also contains droves of dormant eggs. These are just waiting for the right conditions; some have been patiently incubating for up to 10 years. Next week may well awaken them. The high tide on Aug. 23 is expected to crest at 11.6 feet, bringing salt water further inland from Duck Harbor. When the basin is inundated, Mosquito Control’s Gabby Sakolsky expects soil-bound eggs to hatch en masse.
Normally, flooding should drain back into the harbor as the tide recedes. But as people in Wellfleet know too well, the dike built at the mouth of the Herring River in 1909 means tidal flow is nearly absent. Now, while storm-flattened dunes are allowing more water in, that water is lingering in the basin, and the result is an expanded habitat for further egg laying.
Sakolsky, an entomologist, said she wishes the Seashore’s green light had come earlier, giving crews more time to clear brush and apply larvicide before this next overwash occurs.
The National Seashore, however, moves cautiously when it comes to disturbing the sensitive Herring River ecosystem. “I know that sometimes it seems like it takes a while to come to these decisions, but the onus is on us to make sure that we fully understand all of the activities that are going to take place,” said Geoff Sanders, the chief of natural resource management and science at the Seashore.
Since larvicide treatments began in easier-to-reach areas, Mosquito Control has detected a notable drop in its traps for Ochlerotatus cantator, a brackish-water species. The number of captured insects declined from 2,662 in one day in the last week of July to 90 in the first week of August.
Sakolsky hesitated to call this good news. While O. cantator is reaching the tail end of its season, she is bracing for surges in Ochlerotatus sollicitans, another saltmarsh species that flourishes later in August.
“They are much more aggressive,” she added, shuddering.