Operations I
Operations I
Landing rate counts (LRCs), or the number of mosquitoes that land on an observer during a set time period, are a common mosquito surveillance method due to their quick turnaround time and realistic assessment of local biting pressure. At Collier Mosquito Control District (the District), LRCs had traditionally been collected for either two or five minutes depending on the time of day. When mosquito densities were high, however, it was difficult to accurately count the number of mosquitoes landing during the proscribed time period, leading to “binned” estimates of 25+, 50+ or 100+. While these estimates were sufficient to determine whether treatment was warranted, averages calculated based on the numeric values were artificially depressed. In addition, because the District evaluates treatment efficacy by comparing average LRCs before and after pesticide applications, the binned estimates tended to underestimate treatment efficacy.
The District took a two-pronged approach to addressing this issue. First, the LRC data collection protocol was revised to allow technicians to record counts over shorter time periods, increasing LRC sensitivity and facilitating detection of post-treatment mosquito population density changes that had previously been obscured by the binned estimates. Second, curves were fit to frequency distributions of the District’s historical LRC records. Averages for target years and areas were then recalculated using a hybrid method in which counts of less than 25 were treated as numbers, but binned values were replaced with randomly sampled integers from the relevant section of the fitted curve. The new averages were used to adjust the District’s baseline population estimates, resulting in treatment thresholds that more accurately reflected local conditions. Making these small adjustments has yielded substantial dividends, not only improving the accuracy and sensitivity of the District’s operational assessment tools but also creating new opportunities to use LRC data to answer quantitative research questions.