Mosquito populations booming after rains

Scott Anderson
Special to the Bulletin
Scott Anderson

Which species are present and whether mosquitoes are an annoyance or vectors for diseases likely depends on those conditions? Similarly, the temperature, availability of water and type of water available, such as clear floodwater in ditches, a wheelbarrow that has collected water or stagnant puddles in hot, dry weather are all contributing factors to what type of mosquito is visiting you and your family.

Rainfall, especially with multiple storm systems that have saturated and flooded areas around the state, can significantly contribute to a boom in mosquito populations.

People are seeing, and should expect to see, quite a bit more mosquito activity in the next days and weeks. Our focus is going to be disease carriers that typically become a problem in late summer and early fall. However, all this rain has created plenty of habitat for floodwater and container species.

Mosquitoes come in waves and can overlap as the season progresses.

First wave: floodwater mosquitoes

Floodwater mosquitoes are the first to emerge after rain events.

Heavy rains leave the ground saturated and create standing puddles in ditches and low spots in fields and lawns. Floodwater mosquito larvae emerge quickly after water becomes available. Eggs are placed there by females and wait for water, sometimes two to five years before rainfall reaches them depending on the species.

Floodwater mosquitoes are typically larger and are aggressive. These types of mosquitos are often the persistent biters from dawn to dusk.

Any location that is holding water, even in grassy areas, could be a breeding ground.

Second wave: container mosquitoes

Container mosquitoes, which include the Aedes species identified by its black and white body and white striped legs, typically emerge next. Female mosquitoes lay eggs in anything holding water – from tires, buckets and wheelbarrows to gutters, unkept pools and trash cans. They prefer clearer, fresher water, and females are constantly looking for good breeding sites.

Container mosquitoes like Aedes are daytime feeders but can be opportunistic at nighttime when large groups of people gather.

Any time after a rain, it is good to make a round on the property to look for anything that might be holding water. It just takes a matter of days for these mosquitoes to go from egg to biter, so they can become a problem pretty quickly.

Third wave: Culex mosquitoes

Culex, a mosquito species that prefers stagnant pools of water with high bacteria content, typically emerge as waters recede and dry summer conditions set in and create breeding sites in low-lying areas. They are the disease carriers that concern the public and health officials.

In rural areas, bogs, pooled creek beds or standing water in large containers such as barrels, trash cans or wheelbarrows can make a good habitat for Culex.

Reducing mosquito numbers in your location and the use of spray repellents are a good start when it comes to protecting yourself from bites. Covering exposed skin with long-sleeved shirts and long pants help as well.

Plants like citronella, geraniums, lemongrass, lavender, lantana, rosemary and petunias have been shown to repel mosquitoes, the distribution limits effectiveness for protecting a space.

Candles and other smoke-based repellents fall into a similar category as plants.

Protecting yourself with any spray-on, CDC-approved repellent like DEET, picaridin or lemon eucalyptus oil is my best recommendation anytime you go outside for an extended period,” she said. Personal protectants are the only certainty against bites.

Pets should be removed from areas with mosquito infestations. Small children should not be taken outdoors for long periods if mosquitoes are an issue because they can have adverse reactions to mosquito bites, and spray products should be used sparingly on them, especially babies. There are age restrictions for most repellents; no repellents on babies less than 2 months old and do not use lemon of eucalyptus oil on children 3 and under.

This time of year, it’s just best to limit their exposure to mosquitoes.

Controlling mosquitos after widespread, heavy rains is difficult because their habitat can be so unpredictable, Swiger said. Container mosquitoes are a bit easier – remove the habitat by dumping the water or treat the water with granular or dunk larvicides.

Sprays or barrier treatments that kill adult mosquitoes are another option, but effectiveness is limited, Swiger said. Products that homeowners can apply only last 24 hours.