Independent evaluation of Wolbachia infected male mosquito releases for control of Aedes aegypti in Harris County, Texas, using a Bayesian abundance estimator

Abstract

Among disease vectors, Aedes aegypti (L.) (Diptera: Culicidae) is one of the most insidious species in the world. The disease burden created by this species has dramatically increased in the past 50 years, and during this time countries have relied on pesticides for control and prevention of viruses borne by Ae. aegypti. The small number of available insecticides with different modes of action had led to increases in insecticide resistance, thus, strategies, like the "Incompatible Insect Technique" using Wolbachia's cytoplasmic incompatibility are desirable. We evaluated the effect of releases of Wolbachia infected Ae. aegypti males on populations of wild Ae. aegypti in the metropolitan area of Houston, TX. Releases were conducted by the company MosquitoMate, Inc. To estimate mosquito population reduction, we used a mosquito abundance Bayesian hierarchical estimator that accounted for inefficient trapping. MosquitoMate previously reported a reduction of 78% for an intervention conducted in Miami, FL. In this experiment we found a reduction of 93% with 95% credibility intervals of 86% and 96% after six weeks of continual releases. A similar result was reported by Verily Life Sciences, 96% [94%, 97%], in releases made in Fresno, CA.

Fig 1. Average and observed daily cumulative rainfall, and temperature.

Rainfall for each area was recorded at the nearest Harris County Flood Warning System weather station. The Long-term Rainfall (LT rainfall) is a 20-year average (1981–2001) recorded at Houston’s George Bush Intercontinental Airport (IAH). The LT Maximum, Average, and Minimum are 20-year averages (1981–2001) recorded at IAH. The observed daily temperature (bar; top of the bar observed maximum; bottom of the bar observed minimum) was recorded at IAH. Red stars show days when the temperature broke or tied the LT maximum or minimum. The number of released WIMs per week is presented at the bottom of the plot (k = x 1000). Climate and Weather data Source: National Weather Service and Harris County Flood Warning System. Raw data in S3 File.

Fig 2. Location of the untreated and treated areas in Harris County, TX, and the closest weather station operated by Harris County Flood Control.

Only precipitation data was available from these stations. Map generated with ArcMap [51] contains information from OpenStreetMap and OpenStreetMap Foundation, which is made available under the Open Database License.

Fig 3. N-mixture fitted models for Ae. aegypti and Ae. albopictus from the untreated area by week.

Blue histograms are the best N-Mixture fitted models; Red histograms are the raw trapping data (bin width = 5); the number represent the sampling week. A properly fitted model will cover most of the trapping data histogram. For example, in week 28 the model underestimated the number of traps in the 10–14 and 40–44 Ae. aegypti category (the red bars are larger than the blue bars).

Fig 4. Relative abundance of Ae. aegypti females per week in the untreated and treated area.

The center dot denotes the most probable value. Error bars denote 95% credibility intervals (see the “Statistical Methods for Abundance Estimation” section for description of the mean and credibility intervals). Red dotted line represents the credibility interval for the UA abundance in week 28. Blue dotted line represents the credibility interval for the TA abundance in week 31. If the credibility intervals do not overlap the means are considered statistically different with a probability of 95%.

Fig 5. Relative abundance of Ae. albopictus females per week in the untreated and treated area.

The center dot denotes the most probable value of the estimate. Error bars denote 95% credibility intervals (see the “Statistical Methods for Abundance Estimation” section for description of the mean and credibility intervals). The red dotted line represents the credibility interval for the UA abundance in week 29. The blue dotted line represents the credibility interval for the TA abundance in week 29. If the credibility intervals do not overlap the means are considered statistically different with a probability of 95%.