According to officials with the Moab Mosquito Abatement District, mosquitoes will not be as bad this year as they had been in 2019, when flooding of the Matheson Wetlands reached a roughly 10-year high, leading to a mosquito hatch much larger than typical.
Although mosquitoes might not be as numerous this year as they were at times last year, there are lingering concerns about West Nile virus, which was detected in local mosquitoes last year, and an invasive species of mosquito that aggressively bites humans.
To suppress West Nile, get rid of standing water
There is a diversity of mosquitoes in Moab that present a diversity of challenges. The first kind is of the genus Culex; these mosquitoes carry West Nile virus, typically infecting and receiving the virus to and from birds.
A mosquito carrying West Nile can transmit the virus when it bites a human. That is the primary vector by which people contract the disease since the virus is blood-borne, in contrast with COVID-19, which spreads via respiratory droplets.
Mosquitoes that carry West Nile will lay their eggs in stagnant water found in backyards, the bases of potted plants, unscreened rain barrels, and anywhere else water collects unattended. Because of this, the numerosity of potential West Nile carriers can be unaffected by flood levels in the Colorado River.
Shanon Amsberry, the district manager, is hoping to recruit the help of locals to ensure that the mosquito is suppressed if not eradicated in Moab.
“This mosquito plays by a completely different set of rules than our other ‘local’ mosquitoes,” Amsberry said. “Getting community involvement is the best practice to fight it.”
Amsberry said that he encourages Moab citizens to survey their properties — back yards, front lawns and other outdoor locations — for places that could potentially be collecting stagnant water. Old boat tarps, buckets and even regularly used water feeds for chickens are among the places he said to check.
Cleaning any items like this that have standing water ensures that they don’t remain potential egg-laying sites, but also clear out the eggs that may have collected.
Aggressive biters also hatch in standing water
Another kind of mosquito found in Moab is from the species Aedes aegypti; these insects pursue humans aggressively to feed. Aedes aegypti specimens also lay their eggs in stagnant water. Because of this, the preventative measures that locals can take against West Nile carrying mosquitoes are the same that they can take against the aggressive biters: Get rid of standing water.
Residents clearing out small pools of water can identify Aedes aegypti eggs if paying close attention; Amsberry said they appear as small, black dots.
Mosquitoes and the river
There is a third category of mosquito in Moab: Those that lay their eggs in floodwaters, primarily the Matheson reserve. These mosquitoes are not known to carry West Nile virus, and they are not as aggressive toward humans as others. Still, they do bite.
“Last year, we had a sequence of flooding events stimulating egg-hatching of Aedes vexans,” said Tim Graham, chair of the mosquito abatement board. “The adult females then laid eggs in soil as the water dropped and these eggs hatched when the water rose again.”
Graham said he does not expect Aedes vexans to be as much of a problem this year as they had been last year, when sequential flooding events may have initiated multiple hatches throughout the early summer. He said some of the eggs that hatched last year may have come from eggs laid prior to 2018.
“Last year at about this time, the whole watershed snowpack was around 135% of average,” Graham said. “Currently we are at 101% of average snowpack.”
However, according to Graham, “There are still a lot of factors that can impact flooding patterns in the wetlands and how that translates into mosquito numbers. How quickly the snow melts in watersheds above Moab will affect when and how high the river peaks and thus how much flooding might occur in the wetlands and other areas along the river (like along Kane Creek Boulevard).”
Graham also said that the size of last year’s hatch could also mean more eggs laid in the wetlands than typical. Although the mosquito abatement district has been in the sloughs, applying larvicide to kill whatever larvae they can, it won’t be able to get to them all.
“The large populations that we experienced last year, of course, most likely greatly increased the egg bank,” Graham said. “Probably not all the eggs laid last year hatched last year, so even average flooding could result in greater numbers hatching this year, but if we have less flooding than last year some larvae may not reach adulthood before the water evaporates or infiltrates into the soil.”