Tag Archive for: Mosquitoes

Mosquito Disease Transmission: Just the Facts

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Notorious Disease Vectors

Mosquito disease transmission is something most people are aware of. Mosquitoes are some of the most notorious disease vectors in the world. Because of their worldwide distribution — they’re on every continent except for Antarctica — proximity to humans, and inclination to feed off of humans, mosquitoes have been able to spread viral (e.g. West Nile, Zika, Chikungunya) and parasitic (e.g. Malaria) diseases to people throughout the world. Mosquito-borne diseases account for over one million human deaths annually.

But how do they do this? It turns out female mosquitoes inject some of their own saliva into hosts such as humans. This stops the host’s blood from coagulating before the mosquito can retrieve the blood. If that mosquito has previously fed on a human or other animal infected with certain diseases, those diseases may have been able to replicate within the mosquito without harming it.

Yikes, right!? Thus, when an infected mosquito injects saliva into a host, that host can, in turn, become infected.

 

Mosquito Disease Transmission: Spectrum of Viruses

So, can mosquitoes pass all viruses and parasites to humans? The short answer is no.

Now for the longer answer: some viruses (like HIV) and parasites cannot survive the mosquito’s gut. Because of that inability, they’re unable to establish within the mosquito’s cells and replicate. Environmental conditions, predominantly temperature, can also affect how a capable a virus or parasite is at infecting and replicating within a mosquito.

Warmer temperatures generally mean that a pathogen can replicate at a higher rate within a vector. Finally, the amount of the virus or parasite ingested by the mosquito also determines the ability for the mosquito to transmit the pathogen – the vector competence. The greater the dose, the greater the vector competence, assuming the pathogen is able to infect and replicate within the mosquito.  The main diseases mosquitos can transmit within Canada are the California serogroup viruses, eastern equine encephalitis, and West Nile virus (WNv).

With mosquitoes being some of the most notorious disease vectors in the world, it’s no surprise we’re aware of many of these viruses. WNv is the most commonly transmitted mosquito-borne disease in Canada. In 2018, a total of 432 human cases of WNv were reported in Canada – the highest total since 2007. Large-scale, nation-wide surveillance efforts are conducted to keep track of WNv incidence in horses, birds, and humans. These data give program managers the ability to direct mosquito control efforts.

mosquito controlMosquito disease transmission can be mitigated in a number of ways.

Morrow BioScience offers mosquito control services, including nuisance mosquito habitat assessment, larval mosquito monitoring and treatment, and adult mosquito species identification.

Have questions? Contact us!

Mosquitos as Notorious Disease Vectors – additional resource:

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Integrated Mosquito Management Program

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How do we Control Mosquitoes?

Morrow BioScience uses an integrated pest management approach to controlling mosquitoes. The best time during the mosquito life cycle to control them is when they are larvae. For this reason, we place most efforts on finding larval development sites and treating the larva then. Mapping and monitoring the sites assists in the continued improvement of information.

Integrated Mosquito Management: Mapping and Monitoring

For mosquito control to be effective from year to year, we must map development sites and enter them into a database for reference.

During the fall and spring, technicians find new potential development sites to monitor during the summer. When we find new sites, we map them using Global Positioning System (GPS) and add them to the database. During the spring and summer, technicians monitor known development sites for larvae. We check most sites at least once every week, and more frequently as the weather warms. If we find sufficient larvae in the development sites, we treat them using larvicides. However, if there are no larvae in the development sites, no treatment occurs and we check the sites again within a week.

In addition, if there are any areas near your home which contain water but cannot be mechanically controlled, you can report them at any time by calling your municipality. This obviously is only effective if your area has a control program in place. They will send someone out to the area that will assess the sites to determine if they require further monitoring.

Larviciding

The use of larvicides such as B.t.i. has proven to be the most effective in decreasing mosquito populations. Larvicides are relatively environmentally friendly, target-specific, and very effective in killing larvae. We can apply these through the use of helicopters, boats, or by hand.

Whenever possible, our technicians hike into the mosquito development sites and apply the larvicide by hand. This is very effective for smaller channels, but not in larger areas when the water is high. When the water is too high, we use boats to access and treat otherwise inaccessible areas.

Finally, helicopters may be used to treat large development sites that are inaccessible or too large to treat by hand. This includes islands on the river as well as other large sites that become flooded when the river gets above a certain height.

For more info on integrated mosquito management or our services, please contact us.

Integrated Mosquito Management – additional resources:

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Mosquitoes in BC: Biology of Main Target Species

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Mosquitoes in BC

In our area of British Columbia, the primary mosquito targets are Aedes vexans and Aedes sticticus. Their biology is quite specific to floodwater habitats. Both are somewhat easily identifiable in the field as adults and, when combined with habitat, also easily identifiable in the field as larvae. Generally, if the mosquitoes are so numerous that you can’t help but breathe them in, and they are biting during the heat of the day, you may have at least one of these mosquito types.

Biology of Main Target Mosquito Species

Adult mosquitoes of both species have pointed abdomens. One has cool white bands on its legs and the other has black legs. That’s good enough 9 times out of 10 (that is, if you’re near a flooded area and the mosquitoes are aggressive).

A. vexans tend to come on first as rising water levels flood low-level grasslands associated floodplains. The trigger for their hatching is a rise in water temperature (in northern climes this can be as early as 4C but typically when the water reaches 6-8C).

A. sticticus tend to come on later as water levels reach the wooded riparian zones of the floodplain. The trigger for their hatching includes a decreased DO (and can happen in 1- 2 hours from wetting).

Both species lay their eggs on soils prone to seasonal flooding. As water levels rise the eggs are wetted (covered) and in appropriate conditions are triggered to hatch. This begins the progression to annoying biting adult. In cooler waters this process can take 2-3 weeks, from egg to adult. That provides a 10- 14 day window for effective treatments (we try to target 3rd instar larvae).

As the weather and water warms up, this timeline can be shortened considerably. From the time that eggs are first wetted until the end of the effective treatment window can be as little as 60-70 hours. However, both species can, under certain circumstances, skip the fourth instar and molt directly from third to pupa.

Each time the water levels progress higher, or as sustained water levels increases seepage areas not contiguous with the main river body, new batches of mosquitoes hatch.

A proportion of A. vexans eggs do not require diapause before they are able to hatch. The only requirement is that they are dry for a 3-5 day period. This means that, in suitable conditions, subsequent peaks in water levels that don’t reach the previous high can still produce mosquitoes.

BC Mosquito Control Solutions

These mosquitoes are extraordinarily successful. When field techs are looking for them it’s not uncommon to find them at densities of more than 1000/250ml of water. That can translate to roughly 80 million mosquitoes per hectare of water. Believe us, that’s a lot! In our experience, if you aren’t finding 100+ larvae per dip then you aren’t in the right place.

Have questions? Learn more about our services here or contact us for more info.

BC Mosquitoes: Biology of Main Target Species – additional resources (FAQs):

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BC mosquitoes - mosquito control services