Innovative Control Methods

In 2020, the invasive mosquitoes Aedes aegypti and Aedes albopictus, were found in Shasta County. Upon the initial detection, extensive surveillance and control strategies were implemented to control populations and limit their expansion into other District areas.

Invasive mosquitoes, which are permanently established throughout California (see map) are more than a nuisance and can pose a huge public health threat. These mosquitoes are efficient vectors of debilitating diseases such as dengue, Zika and chikungunya that kill thousands of people each year throughout the world. Therefore, finding and implementing innovative methods of controlling these mosquito populations and limiting their abundance is very important.

A novel approach that has been recently used by mosquito control districts in California in the fight against invasive mosquitoes is the use of the Sterile Insect Technique (SIT). SIT is an environmentally friendly insect control technique which involves the mass rearing and sterilization of male mosquitoes using different approaches followed by their release into designated areas to mate with wild female mosquitoes resulting in no offspring and a significant decline in mosquito populations.

METHODS OF SIT IN MOSQUITOESWOLBACHIA

Chart showing how Wolbachia works in mosquito population controlWolbachia is a safe and natural bacterium that is present in up to 60% of insect species including butterflies, dragonflies, moths and some mosquitoes. However, Wolbachia is not present in the Aedes aegypti mosquito and it is used to reduce the ability of mosquitoes to transmit viruses such as dengue, Zika and chikungunya.

How does SIT using Wolbachia work?

When male Wolbachia–carrying Aedes aegypti mosquitoes mate with female Aedes aegypti without Wolbachia, their resulting eggs do not hatch. This is because such matings are biologically incompatible. Thus, release of male Wolbachia–Aedes aegypti will lead to a decline in the Aedes aegypti population in the field over time. The outcome of this approach is consistent with our current emphasis on source reduction (removal of breeding habitats).

Infographic showing how wolbachia is introduced via injection into invasive Aedes mosquito eggsThis mosquito suppression strategy is species-specific. Release of male Wolbachia-Aedes aegypti will only impact the Aedes aegypti population in the field, and not other insects.

How is Wolbachia introduced into Aedes aegypti?

Wolbachia is not found in Aedes aegypti in the field. Wolbachia is introduced into Aedes aegypti eggs via microinjection. Female Wolbachia–Aedes aegypti mosquitoes that emerge from these eggs will pass Wolbachia to their offspring (maternal transmission). This process allows us to produce Wolbachia–Aedes mosquitoes easily.

IRRADIATED MALE MOSQUITOESThis SIT strategy involves the mass-rearing and sterilization of male mosquitoes using radiation followed by a wide release of the sterile males over defined areas. The irradiated males will mate with wild females resulting in no offspring and a reduction in mosquito populations that can pose a public health threat.

Key agencies have utilized this irradiated SIT technique
The California Department of Food and Agriculture (CDFA) successfully utilized this method to control Mediterranean fruit fly infestations in citrus and other fruit trees.
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The United States Department of Agriculture (USDA) has also had tremendous success using SIT to control screwworms, a devastating cattle pest.
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GENETIC MODIFICATION OF MOSQUITOESOxitec is a British company exploring biological insect control techniques in the fight against Aedes aegypti. This method can be applied to a variety of pests ranging from mosquitoes that transmit disease to other insects that can damage crops. This technique is currently being explored in the Florida Keys.

Non-biting and self limiting mosquitoes

Oxitec’s Friendly™ safe, non-biting male mosquitoes are designed to suppress local wild populations of disease-spreading mosquitoes. Friendly™ mosquitoes carry a self-limiting gene, which means that when Friendly™ mosquito males mate with wild females, their offspring inherit a copy of this gene, which prevents females from surviving to adulthood. Since these females do not mature to reproduce, there is a reduction in the wild pest population.

SIT IN SHASTA COUNTYThe Shasta Mosquito and Vector Control District supports the evaluation and research of SIT. Federal and State regulatory agencies will determine the safety of innovative approaches in California. Our agency may evaluate the use of these technologies only after it has been approved. Currently, no mosquitoes are being released using SIT in Shasta County.