Temperature Influence on Aedes aegypti Oviposition in the San Joaquin Valley of California.

Abstract

The establishment and oviposition of Aedes aegypti can vary from one location to another partially due to differing temperature and precipitation. In 2017, Ae. aegypti was first detected in Merced in the Central Valley of California. The objectives of this study were to examine the influence of temperature and precipitation on oviposition of Ae. aegypti, and to determine the beginning and end of the seasonal activity of Ae. aegypti in Merced. The study site consisted of a residential area in the north-east region of Merced where Ae. aegypti was first detected in Merced County. Fifty-four residences were randomly selected as ovitrap sites. Ovitraps were placed at field sites weekly for 12 months, from September 27, 2017, to September 27, 2018. Each week, ovitraps were inspected for the presence of mosquito eggs. Egg counts were used to calculate the following oviposition indices: the ovitrap index (OI) (percent of traps positive) and the egg density index (EDI) (eggs/positive traps). Oviposition occurred primarily from May through October, above a minimum temperature of 10°C, and when almost no rainfall occurred (0.5 mm total). During the year, the percent of positive traps per month ranged from approximately 1.2-67.3%, with highest values in June to October (43.9-67.3%). The highest mean monthly EDI was from July to October (34-44.6) and peaked in October at 44.6 eggs/trap. The EDI values are similar to other locations where Ae. aegypti transmits endemic vector-borne disease. These findings provide baseline data for Ae. aegypti control in Merced and the Central Valley of California.