People and pets around the Island may have found themselves enjoying an evening hike or backyard barbecue a little more than usual this summer. Without much rainfall, there were hardly any mosquitoes on the Vineyard, even in places where they are known to thrive.

“It was quite remarkable,” said Richard Johnson, a biologist who monitors both ticks and mosquitoes on the Island. “Places like North Neck on Chappaquiddick, which is famous for mosquitoes — [they] were not there this year.”

There were so few mosquitoes that the Dukes County Commission decided to extend its mosquito surveillance program an additional two weeks in September to continue testing for West Nile virus, an infectious disease that can spread to humans. Last year three mosquitoes collected on the Island tested positive for the virus.

This was Mr. Johnson’s second year running the program. He believes the low numbers were probably due to a lack of rainfall, since mosquitoes tend to breed in standing water. In a typical year, he said, the population will increase with each generation. But without many mosquitoes to begin with this year, “the population never exploded,” he said. During the 12-week program ending last week, 551 mosquitoes were captured in the six Island towns and sent to a state laboratory in Jamaica Plain for testing. Mr. Johnson said he captured two or three times that number last year in a 10-week period. West Nile virus was not detected in any of the samples this year.

Wet leaves and hay were used to attract the mosquitoes at each site, and a fan was used to force them into a plastic box. Mr. Johnson stored the mosquitoes in a freezer before sorting them according to species and sending them to the laboratory.

County manager Martina Thornton said there are not enough resources or funding to monitor and also control the Island’s mosquito population. Monitoring was previously done by the county’s Integrated Pest Management department, which ended last year, and is now funded by the Island boards of health. (The surveillance program this year was not extended in Aquinnah, which lacked the necessary funds to do so, Ms. Thornton said.)

Dukes County provides public information from the state Department of Public Health about West Nile virus and prevention measures on its website, as do some boards of health on their websites. Ms. Thornton said education efforts have increased since last summer, but she was unaware of any public programs to eradicate mosquitoes.

The town of Tisbury hires Gremlin Fog Pest control, an Island company, to spray Memorial Park every year, and maintains ditches that drain standing water around Lake Tashmoo. It also sprinkles pellets in swamps and other potential breeding grounds to kill the larva. Tisbury health agent Thomas Pachico said those efforts began at least 10 years ago.

Tisbury’s assistant health agent Maura Valley said the spraying helps, but not as much as having a dry summer. “Mosquitoes weren’t a big problem until later in the season when we had a little rain,” she said.

Board of health agents contacted in Oak Bluffs, Edgartown, Chilmark and West Tisbury this week said chemical control methods are not used in those towns. Aquinnah health agent Julie Sierputowski said she did not believe chemicals were being used in Aquinnah. West Tisbury health agent John Powers said the town had an emergency plan to pelletize catch basins in the event of an outbreak.

Edgartown health agent Matt Poole pointed out that spraying and pelletizing are themselves often viewed as health risks. “Spraying is pretty darn unpopular out here,” Mr. Poole said. Edgartown used spraying and pellets in the past, but no longer attempts to control the population with chemicals.

Mr. Johnson said it was unlikely that spraying and pelletizing in specific places around the Island would have increased enough from last year to cause the low numbers of mosquitoes this year.

“There are places I know, where I went, where there should have been a lot of mosquitoes and there weren’t,” he said. “I can’t believe those were heavily sprayed.” He said that although he is not an expert on the subject, “I would be surprised as a biologist, and just my general knowledge of the Island, if it were affected by the level of spraying.”

A similar story played out on Cape Cod this year, according to a spokesman for the Cape Cod Mosquito Control Project which also traps mosquitoes for testing every year. Gabrielle Sakolsky, assistant superintendent for the project, said far fewer mosquitoes were trapped at five sites in Barnstable County this year compared with 2013. “Weather is a major factor,” she said in an email to the Gazette this week. “Last year our freshwater swamps were flooded through most of the summer . . . this year everything was almost dry by the end of June.”

But Debbie Hills, owner of Gremlin Fog Pest Control, said over-spraying is a widespread problem that may have contributed to the low count this year.

“There is a lot of people spraying now, and a lot of people don’t really understand what they are doing,” she said. “They are using stronger [chemicals] than they should be, and they spray more often and not at the right times.” She said the best times to spray are at dusk and dawn.

Many pest control companies on the Vineyard do not advertise, she said: “That’s what scares me.” As a licensed practitioner, Ms. Hills attends local workshops and lectures on pest control, but she said that over her 40 years of working on the Island, she has seen only one other Island pest control worker at those events. She suspected that many of the companies were unlicensed. “That’s the unknown factor,” she said.

Ms. Hills said she remembers when mosquitoes were so bad on Chappaquiddick many years ago that some people couldn’t hang their clothes out to dry. “With regular spraying, after a few years it gets under control,” she said. When she began spraying for Tisbury, Memorial Park would require several treatments in a season. “Now it’s just a couple,” she said.

She said other control measures, such as removing vegetation, adding certain types of plants, or introducing predatory insects, have further reduced the local mosquito population over the years.

Mosquitoes collected this year were tested only for West Nile virus, although other mosquito-borne pathogens, such as eastern equine encephalitis, can cause illness and death in humans. But only a few cases of EEE are reported in the U.S. each year. Only about 20 per cent of those who become infected with West Nile show symptoms, and only about one per cent develop a serious or fatal illness.

People on the Vineyard are more concerned about deer ticks than about mosquitoes, Mr. Johnson said. “You don’t hear much about West Nile, and most people that get it don’t even know they have it,” he said. Lyme disease, however, which is carried by deer ticks, affects hundreds of people on the Vineyard every year.