In the 11 years assistant district manager Erik Hawk has been with the Marin/Sonoma Mosquito & Vector Control District, he’s seen a substantial amount of change. Land development projects have replaced some naturally occurring vernal pools with residential and commercial buildings, and have introduced new opportunities for container-breeding mosquitoes. Habitat restoration projects throughout the district — while providing vital refuges for indigenous plant, fish, and wildlife species — are increasing the potential sources for vector insects, as well.
Marin/Sonoma district, with approximately 2,400 square miles of varying terrain, still has significant amounts of natural wetlands, both tidal and freshwater. The changing nature of these habitats, and the sheer number of acres they cover, can make vector surveillance and control difficult. That’s what makes residual efficacy so important to the district’s efforts in protecting the health of its 722,000 residents.
“Residual biological products, like VectoLex® and VectoMax®, provide a substantial benefit to the Marin/Sonoma Mosquito & Vector Control District, and we’re excited about the benefits MetaLarv® may provide,” Erik explains.
Longevity and residual control are beneficial in terms of staff time, equipment use, and conducting control operations in sensitive areas. “Some of the sites where we apply these products are large, problematic sources, and to get the residual of three weeks to 30 days is key. Plus, we don’t have to send our technicians back to constantly check and treat the areas.”
Currently, the district is using VectoMax® and VectoLex® larvicides on Culex mosquito species that carry West Nile virus. Testing for the presence of West Nile virus in adult mosquitoes is conducted at the district’s own laboratory through real-time PCR analysis.
For the Anopheles species, found on the top of algae in water sources, the district prefers VectoMax®. “We’ve been very impressed with VectoMax® and the additional options the product offers. For example, if we’re seeing late instars — third or fourth — it has a quicker knockdown because of the incorporation of Bti.
In working with late instars in the warmer weather, we feel there’s less chance of them surviving to the pupal stage because of the quick knockdown.”
Another benefit the district has found in using VectoMax® is the ability to use less product. Through field studies, general operational use, and back-checking, the district has found control can be achieved with 10 to 15 pounds of VectoMax® per acre at sites where they would have normally applied 20 pounds per acre of other products. Still, for sites with heavy vegetation canopies, such as wastewater treatment ponds with high densities of eight-foot-tall bulrush, they go with 20 pounds per acre.
MetaLarv®, an insect growth regulator, has also shown promise for the district’s efforts to control Aedes dorsalis, a tidal marsh mosquito. The district has completed two trials with MetaLarv®, and Erik says they are very pleased with the results. “We got 30 days’ control and are anticipating that we’ll incorporate the product into future operations. There are a high number of granules per square foot when applied, for a pellet (S)-methoprene product, and that has the potential to be a benefit to us. It worked very well when applied with a backpack unit. In the future, we anticipate that we also will apply this product aerially.”
Dealing with change in the world of vector insect control takes vigilance, attention to detail, and the flexibility to adopt new ways of thinking. Whether it’s changing seasons, changing habitat landscapes, or changing regulations like NPDES, Marin/Sonoma Mosquito & Vector Control District is well prepared to meet the challenges and protect public health in its community.