by Joe Barile, BCE, Technical Service Lead, Pest Management & Public Health, Bayer Environmental Science
It has been hard to miss the media coverage regarding the Zika Virus outbreak. There have been over 50 confirmed human cases diagnosed in the U.S. as this document is being prepared, and the World Health Organization (WHO) has declared a Global Public Health Emergency. All U.S. diagnosed cases are in people who have recently traveled to countries where the virus is established.
Zika is a virus first isolated from the Zika Forest in Uganda in 1947. Humans can be exposed to the virus from the bites of certain species of day-flying Aedes genus mosquitoes, most commonly in the western hemisphere by the species Aedes aegypti and A. albopictus. Through the 1950s, virus activity was restricted to a narrow equatorial band in Africa and Asia. It has since spread through the Pacific Islands and in 2015 to South America, Mexico and multiple Caribbean Islands.
Symptoms of Zika include headaches, fever, a possible rash, joint pain and possible conjunctivitis (eye inflammation). In most cases, only one in five healthy, exposed individuals experience a mild illness and fully recover. Pregnant women exposed to the virus may pass the virus to their developing fetus, possibly resulting in a condition known as microcephaly (reduced head size in the infant with high likelihood of brain damage). Since the outbreak of Zika in Brazil, health authorities have reported abnormally high numbers of microcephaly in infants. Zika is also suspected to possibly cause neurological conditions including a condition known as Guillian-Barré.
Transmission of the virus is from human to human via the bite of an infected mosquito or, as recently confirmed, through sexual contact with an infected individual. Birds or other animals (other than primates) are currently not known hosts or carriers. Once infected, an individual with Zika virus can infect mosquitoes for only a short time, usually about a week. There is no vaccine for Zika; there is no cure or therapy for Zika-infected individuals other than symptomatic care.
Health experts report that Zika should not become widespread in the continental United States due to our temperate climate, with most of the country experiencing a winter season that prevents year-round vector (mosquito) activity. However, in areas of the country where the two mosquito species of concern (A. aegypti and A. albopictus) are established, there may likely be sporadic outbreaks. These areas include much of the southeastern U.S., especially along the Gulf Coast to Texas, and localized areas of the Southwest and California.
This outbreak will raise public awareness regarding the risk of exposure to a mosquito-borne disease, and may locally result in an increase in requests for mosquito control services by Pest Management Professionals (PMPs). Residual Barrier Treatments can provide residents relief from the nuisance of biting mosquitoes. However, we advise PMPs to be cautious in communicating the level of protection that typical PMP-provided mosquito services (residual barrier treatments) may provide. PMPs cannot promise or predict that their service will kill every potentially disease-bearing mosquito that is found in a customer’s property. Mosquitoes, including known Zika vectors, can travel great distances; even riding wind and air currents, from non-treated areas onto a customer’s property. Additionally, a PMP has no control of the potential exposure of a customer’s family members outside of the treated property. PMPs should not make any statement or promise of disease control or protection when offering their mosquito service.
Mosquito Control Protocol
Mosquito abatement service will be provided based on the following service categories:
1. Inspection of property for conditions conducive to mosquito development (i.e. breeding). Notify the customer contact of such conditions, and recommendations for modification to conditions on the property to eliminate or reduce mosquito development.
2. Applications of larvicides (where appropriate) to mosquito-bearing stagnant water and/or to areas subject to periodic flooding that will allow immature mosquitoes to develop.
3. Application of Suspend® PolyZone®Insecticide as a residual barrier treatment to foliage and structures where mosquitoes will shelter and rest.
4. Reporting to customer any changes in property conditions that may provide mosquitoes additional harborages or developing sites.
Evaluations and Treatment
On initial, and every, visit: Technicians will walk and inspect the property upon arriving (and before ANY application of pesticides). Inspect for natural and man-made conditions that allow water (rain or irrigation) to collect and lay stagnant (non-moving) on the property. Naturally-moving water (streams, rivers, brooks) can be ignored as mosquitoes will not develop in moving water. Man-made containments (maintained swimming pools, fountains, reflecting ponds, fish-bearing ornamental ponds) where the water is moving, agitated, contains fish or is chemically treated may be ignored as they will not support mosquito development. Abandoned or poorly-maintained swimming pools or ornamental ponds should be inspected for breeding. Key examples of natural breeding sites include: stagnant drainage ditches, septic sumps, tree holes, and ‘low spots’ on property that regularly flood and hold water after significant precipitation events. Key examples of artificial breeding sites include: neglected birdbaths, neglected fountains, neglected pet water bowl, discarded or unused vehicle tires, neglected swimming pools (including covers and child wading pools), toys (pails, sandboxes, riding toys), discarded beverage cans and bottles, flower pots and planters, blocked gutters, tarps, and boat and snowmobile covers.
Learn to identify mosquito larvae and pupae in habitat and point out activity to customer contact when found. Advise on recommendations to change standing water conditions (if possible) to eliminate the breeding source.
If larvaciding and/or adulticiding applications are appropriate, inspect to determine best application techniques to prevent potential runoff and/or drift of applications from target sites. Inspect for non-target presence or activity (all pets, children, visitors, pollinating insects, wildlife) that must be prevented before application. Refer to product labels for details.
Always read and follow all product label directions.
If conditions are appropriate (standing, stagnant water that will be continually, or regularly present, and is a source of developing mosquitoes) apply an approved larvicide according to the product directions.
Biological larvicides (Bti) and/or biorational larvicides (methoprene) present a reduced hazard to non-targets.
Formulations are available (solid granules, briquettes and donut-shaped ‘dunks’) that may be applied by hand. Apply at label rates, and at intervals as directed on the larvicide label.
Adulticide Barrier Treatment
Always read and follow all product label directions.
Suspend PolyZone Insecticide can be utilized as the residual insecticide product for barrier treatments. Best results will be realized when Suspend PolyZone is applied through powered ‘mist-blower’ equipment. Applications of Suspend PolyZone by power sprayers and/or hand-held sprayers (i.e. ‘back-pack’ or B&G® sprayers) are allowed by the label, but are not as efficient as mist-blowers. The high velocity of the blower propelling the product to the application site, as well as the small particle size, will allow the product to penetrate foliage and adhere to the underside of leaves where mosquitoes rest.
Outdoor residual mosquito control is maximized when applied from a powered backpack mist-blower that is calibrated to maintain small droplet size with high delivery velocity. This allows the product to penetrate dense foliage, provide more uniform coverage, and wet the target application area without excessive runoff. For example, when utilizing the Stihl® SR450 backpack mist-blower, the adjustable flow rate varies from a setting of 1 (lowest volume) to 5 (highest volume).
Utilizing a setting of “2” on the SR450 is optimal as it allows enough product to be delivered at an efficient pace while minimizing waste. When using a lower flow rate such as “2” on the SR450 with high velocity (maximum throttle), the droplets are broken up more than at high flow rates resulting in reduced droplet size and improved efficacy and distribution. It is important to note that application equipment and settings vary greatly between manufacturers and models, so care must be taken to establish what settings provide the optimal spray pattern for the selected equipment.
Tips of the Trade: Spray patterns from backpack mist-blowers can be further improved by utilizing a diffuser. This part is usually included with a mist-blower and is a simple plastic piece that is attached to the end of the discharge chute. Diffusers break apart the spray cloud, allowing the product to disperse, delivering it in hard-to-reach areas where mosquitoes may be resting.
Suspend PolyZone is formulated to be diluted in water only. Do not dilute in oil or solvents. The use of a spray additive (spreader/stickers or wetting agents) is not recommended. The polymer included in the PolyZone formulation helps to adhere the active ingredient to treated surfaces and resist wash-off from precipitation and/or irrigation. Dilution rates range from 0.01% to 0.06% active ingredient (Deltamethrin). Use the low or mid rates when service intervals are short (i.e. monthly service) and mosquito pressure (activity) is low or normal; use higher rates for longer service intervals and/or when mosquito pressure is high (‘every-other-month’, quarterly, or seasonal). The high rate (0.06%) is recommended for fast knockdown in sites with high population density or activity.
Dilute Suspend PolyZone, according to the label directions, in the sprayer. Apply the dilution, as a mist, to foliage of trees, shrubs, and ornamental plantings, as well as turf and ground cover, under decks, around building foundations and other places where mosquitoes may rest. Comply with all label directions regarding weather conditions and non-target exposure warnings.
Apply in a manner that allows the treated mist to penetrate foliage canopies and reach the undersides of leaves, the preferred resting location for mosquitoes. Be sure to include the ‘upper’ canopy of trees and ornamentals where possible. Mosquitoes harbor in areas close to bird roosting sites (birds are natural sources of blood meals for many pest species of mosquitoes). Whenever possible, make applications with your back to the property boundaries to avoid drift onto neighboring properties.
Label restrictions for outdoor pyrethroid treatments must be followed. Be aware of wind and weather conditions that may prevent or restrict treatment.
Structures may be treated for residual mosquito control; comply with label restrictions. Apply to sites where mosquitoes will rest. These sites are generally in shaded areas protected from direct sunlight and wind. Such sites may include: under decks and porches, under soffits and overhangs. Avoid runoff of sprays.
For more information, contact your local Bayer Pest Management & Public Health Representative.