Using Mulla's formula to estimate percent control

Abstract

In California, the endemic mosquito borne encephalitides, including West Nile virus, are contained by special districts using integrated vector management programs. These agencies combine public education, source reduction and proactive larval control to suppress mosquito abundance to the point where tangential transmission of virus to humans is rare or unlikely. However, when these methods in concert fail to prevent enzootic amplification and the risk of human infection becomes eminent or is on-going, emergency adulticide applications of pyrethrin compounds are used to interrupt transmission. The efficacy of these applications has become controversial and some cities have opted to not apply adulticides. The current paper describes how a formula developed Dr. Mir Mulla some 40 years ago is still useful in solving contemporary problems of estimating percent control, a statistic useful in evaluating intervention efficacy. This simple but effective equation accounts for changes in both control and treated populations and thereby can be applied in dynamic situations where abundance is not stable. Examples are presented from ground and aerial experimental applications in Riverside County and from emergency interventions in Sacramento County in 2005 and Yolo County in 2006. © Springer Science+Business Media B.V. 2010.