Mosquito Control: Spraying vs. IPM

Editor’s Note: This article was reprinted with permission from Pinto & Associates.

IPM is the best way to control any pest over the long term. But not every job is suited for IPM. Mosquito control is a good example. In our industry there are two distinct types of mosquito jobs: one is quick and dirty, one is management over the long term. As a result, we have two types of mosquito control.

1. One-Shots

A "one-shot," for lack of a better term, is when a customer calls on Wednesday because he is having an outdoor function on Saturday evening and the yard is loaded with mosquitoes. Maybe it's a party or a wedding in a back yard, maybe it's a church function.

Whatever, the customer doesn't want to hear about integrated pest management, monitoring, source reduction and the like. He wants you to "get rid of the damn mosquitoes" so that guests are not bitten on Saturday. This is a spray job to kill adult mosquitoes, pure and simple (although this customer could be a hot prospect for a mosquito IPM program in the future).

There are two effective ways to apply insecticide to kill adult mosquitoes. In traditional "fogging," you apply an aerosol of very fine insecticide droplets using a thermal fogger or ULV cold aerosol generator. The goal is to spray so that the insecticide contacts the adult mosquitoes.

More commonly in our industry, we apply insecticide treatment of a residual insecticide onto mosquito resting areas. As the mosquitoes “stage” in their resting areas, most typically in and on vegetation, they land on treated surfaces and pick up a lethal dose of insecticide. This is often called a mosquito "barrier treatment."

The most effective way to apply a barrier treatment into vegetation is with a powered mist blower. However, the application can also be made with a power sprayer, backpack sprayer, and even a regular compressed air sprayer. When treating vegetation it is critical to get the insecticide residue onto the underside of leaves where mosquitoes most commonly rest.

A wide range of insecticides are suitable for mosquito barrier treatments. Some EPA-exempt products, such as botanical oils, have also been used successfully to kill mosquitoes. One-shot mosquito control jobs are by their nature short term and only partially effective, ranging 50-90% reductions depending on the field study. Limitations include (1) not all mosquito resting areas are treatable or reachable, (2) it is difficult to get complete coverage inside thick vegetation, and (3) mosquitoes can fly in from untreated sites.

2. Mosquito IPM Programs

The most effective way to control mosquitoes effectively over the entire mosquito season is through IPM. The space remaining in this feature is too short for a complete discussion of mosquito IPM but, briefly, the essential components are these:

Inspections and Surveillance. IPM programs for mosquitoes require regular inspections. Mostly, inspectors should be looking for active breeding sites (with mosquito larvae, eggs, or pupae) or potential breeding sites, but also for adults (biting counts, traps, resting mosquitoes), potential offsite problems, and sensitive areas.

Source Reduction. All mosquitoes need water to breed. Long-term effective control usually requires a reduction in the number and attractiveness of mosquito breeding sites...called "source reduction" in mosquito control work. Source reduction includes removal of mosquito-breeding containers, elimination of standing water, and, in rare cases, modification to bodies of water (elimination of organic debris, ditching, and draining).

Vegetation Management. An often overlooked component of mosquito IPM, vegetation management can greatly reduce a site's attractiveness to mosquitoes. Yards with lots of overgrown vegetation, weeds and brush provide many mosquitoes resting sites. Customers need to remove weeds and brush, thin ornamental plantings, trim tall grass, etc. to lessen mosquito pressure. 

Larvaciding. For standing water that cannot be altered or drained, larvacides are the key control tool. They kill the larvae or they prevent larval development so that biting adults are not produced. They are either applied to standing water, or to a site that will flood later (to control flood-water mosquitoes). The common larvacides are methoprene, B.t.i, and thin surface oils.

Other components of mosquito IPM programs are biological control (I quito fish), mosquito traps, adulticiding (the last resort, often indicating a p somewhere), and, of course, education and communication with the customer.