The District uses chemical control products when source reduction and biological control are not possible or efficacious. Chemical control of mosquitoes is often grouped into larviciding and adulticiding. Larviciding is a general term for the application of nonliving natural materials or synthetic chemical products to aquatic habitats to kill mosquito larvae or pupae or to otherwise prevent emergence of adult mosquitoes. Larvicides can be applied in a wide variety of formulations using a broad range of application technologies. Adulticides target adult mosquitoes. Chemical control efforts in Orange County are largely confined to larvicides, as they are the most effective means of control in the majority of breeding sources found in the County. Breeding sources treated for mosquitoes can include, but are not limited to, gutters, underground storm drains, marshes, unused swimming pools, etc. In certain habitats, such as coastal marshes, larviciding and adulticiding are used to target larvae and adult mosquitoes.
Both of these microorganisms produce natural metabolic by-products that are only toxic to mosquitoes and show no toxic effects on organisms other than midges and buffalo gnats. The latter two groups of aquatic flies are considered pests, particularly buffalo gnats that are well known for their painful bites and human blood feeding habits.
The protein toxins produced by these two bacteria control mosquitoes by destroying (rupturing) the gut of the larva (wiggler). Once ingested, death usually follows quickly within 24 hours and sooner under ideal conditions. Unlike B. sphaericus, which remains in the water and regenerates from the corpses of dead mosquito larvae, Bti is short lived and only effective for one generation of control. Under suitable conditions, B. sphaericus can remain effective for several generations and even longer.
Recent studies have indicated that when Bti and B. sphaericus are combined, overall control is enhanced. Together, the Bti reduces natural resistance to B. sphaericus and at the same time extends the effective period of one application from 10 days to over three weeks. Unlike Bti, which is least effective in polluted water, B. sphaericus is unaffected by organics and therefore, preferred for controlling mosquitoes like the Southern House Mosquito (Culex quinquefasciatus), which breeds throughout Orange County in foul water situations (storm drains, catch basins, etc).
Methoprene, a juvenile hormone mimic, and insect growth regulator (IGR) is an active ingredient in vector products. This products acts as a "natural hormone" of insects and effectively retards the completion of the life cycle of the mosquito. The IGR works by preventing the larva from transforming to the pupa (stage between the larva and adult) and/or the adult from emerging from the pupa. Methoprene is formulated in ways to provide both short and long-term control by one-time application mixtures and slow release presentations using granules and briquettes.
For residents who currently have bait on their properties, this is the information for the rodenticide.
Note that on September 23, 2014, OCMVCD switched from using Contrac All-weather Cake to Contrac All-weather Blox.
Information for veterinarians can be found here.
The District's primary method for control of RIFA is the application of pesticide ant bait containing an insect growth regulator or toxicant. The District currently uses five pesticide ant bait formulations containing four active ingredients. The active ingredients work as an insect growth regulator (IGR) or a metabolic inhibitor (MI) as means of controlling the current adult population and emerging juvenile population. The metabolic inhibitor interferes with the metabolism of food, resulting in the death of the ants by starvation. The colony eventually dies out as a result of ants consuming the bait, then starving, and not being replaced. Results are sometimes visible within a week. The insect growth regulator essentially sterilizes the colony, as ants die through attrition, and they are not replaced. This is a slow acting material, and results may take a month or more to be recognized.
Prior to treatment, District staff confirms the identification of RIFA at a site. The District performs RIFA control in cooperation with private pest control companies at residential sites. In large area sites, such as commercial buildings, schools, parks, rights-of-way, and multifamily housing, the District performs RIFA control. In heavily infested neighborhoods, the District abates RIFA through community-wide management of the pest.
Many neighborhoods in Orange County are heavily infested with RIFA. Heavily infested neighborhoods are determined by analyzing reports of RIFA occurrence. District staff visits these neighborhoods and distributes notifications that a pesticide ant bait treatment will be made within the next week. Residents can opt out of the treatment by contacting the District or taping the notification to the door on the date of the treatment. District staff records the presence of RIFA mounds in the neighborhood. On the treatment day, pesticide ant bait is applied to the front lawns, and sometimes backyards, and communal areas of the neighborhood via a hand-held granular application device. Residents are instructed not to irrigate their property for 24 hours following treatment and to refrain from applying pesticides or other chemicals for 72 hours following treatment.
Broadcast treatments of pesticide ant bait are effective because ants from all colonies in the treated area can collect the bait. This is also easier than an Inspector trying to locate individual mounds. Pesticide ant bait not collected by the ants rapidly decomposes in the environment. Bait broadcast in the environment is effective for a short period of time as the active ingredients degrade in sunlight, and exposure to environmental factors can breakdown the food carrier.