Container-breeding mosquitoes are increasingly important in public health due to recent outbreaks of Zika virus, chikungunya, and dengue. This paper documents seasonality of the most prevalent container-breeding mosquito species in Mississippi—Aedes albopictus. Ten sites in 5 counties in both northern and central Mississippi (20 sites, 10 counties total) were sampled by larval dipping and oviposition traps biweekly from September 2016 to June 2019, totaling 22 months and potentially yielding 440 egg or larval collections. However, 22 collections were missed due to inclement weather and personnel issues during the study period, so actually only 418 site visits were performed. Sites were chosen to maximize chances of finding Ae. albopictus. Of the total 1,310 mosquito larvae collected during the study period, 717 larvae and 50 positive egg papers belonged to Ae. albopictus. Aedes albopictus was found in all 10 northern and central counties. No eggs were collected at any of the sites from December through February, although larvae were occasionally collected during that time frame. This study demonstrates that Ae. albopictus is active in central and northern Mississippi beginning in March each year and continuing through November or December. There is little activity during the coldest months of the year (January and February). These data represent the first extensive analysis of Ae. albopictus seasonality in Mississippi, and as such, allow for better public health awareness of diseases transmitted by this species and design of more effective vector control programs.
Container-inhabiting mosquitoes are a timely topic in public health due to the Zika virus outbreak of 2015–17 in the Western Hemisphere (Anonymous 2016, Fauci and Morens 2016). Zika virus is primarily transmitted by the container-inhabiting Aedes aegypti (L.) (yellow fever mosquito), although Ae. albopictus (Skuse) (Asian tiger mosquito) is also a potential secondary vector (Wong et al. 2013, Grard et al. 2014). Previous surveys in Mississippi have revealed approximately 61 species overall (Goddard et al. 2010), with at least 16 of those species occurring in artificial containers around the state (Goddard et al. 2010; Yee et al. 2012, 2015). Records from 1989 show the first known presence of the introduced species Ae. albopictus in Mississippi (USAF 1989), which subsequently spread across the state and now occurs abundantly in every county (Goddard et al. 2010). A recent container-breeding mosquito surveillance program was initiated in Mississippi, focused on Ae. albopictus and (potentially) Ae. aegypti (Goddard et al. 2017). This current study complements that surveillance effort by documenting the seasonality of the primary container-inhabiting mosquito species in Mississippi, Ae. albopictus.
Twenty sites in 5 counties in northern Mississippi and 5 counties in central Mississippi were sampled biweekly from September 2016 through June 2019 (22 months) (Table 1). At each visit, a rural site and an urban site were sampled in each county, potentially yielding 440 individual collections (however, there were 22 times when sampling was impossible due to inclement weather or changes in personnel, so 418 visits were made). Sampling-site locations were designated prior to the onset of surveillance activity, and they did not change throughout the course of the work. Sites were chosen to maximize chance of finding Ae. albopictus and were mostly tire piles and cemeteries, although in some places, debris or trash (e.g., bottles, cans, buckets) were also sampled. Sampling at each site, including one oviposition cup placement and larval collections using a dipper, was previously described in a parallel study (Goddard et al. 2017). Back at the laboratory, the number of larvae in each collection was counted, then 1–3 larvae from each collection were preserved in vials containing 70% ethanol; the remaining larvae were reared to adults over approximately the next 2 wk. Larvae (in alcohol) and any adults reared from the collections were identified using standard keys (Darsie and Ward 2005, Harrison et al. 2016). Eggs were hatched and larvae reared to adults for identification.
A total of 1,310 mosquito larvae were collected during this survey; 717 of them (54.7%) were Ae. albopictus. In addition, 50 positive egg papers were collected. Several other mosquito species were collected as both larvae and eggs, but they are not the subject of this report. This project documented the presence of Ae. albopictus in all 10 counties. For our analysis, a positive result was defined as documenting Ae. albopictus in a county at either the urban or rural site for at least one of the visits to that site during the month (Table 2). Aedes albopictus was collected slightly more often in urban sites than in rural sites. Positive results were obtained 96 out of 209 times (45.9%) in rural sites sampled; and 104 out of 209 (49.7%) at the urban sites. As for seasonality, there were only 2 months out of the 22 months of the project, December 2017 and February 2018, when no evidence of Ae. albopictus was documented at any of the 20 sites, either rural or urban. During both January 2017 and 2018, there was only 1 positive collection made. No eggs were collected at any of the sites for the 3-month period, December through February, although larvae were occasionally collected during that time frame. Finding Ae. albopictus larvae during winter is not indicative of active populations as this species may overwinter as larvae, but finding eggs is evidence of adult Ae. albopictus activity. This study demonstrates that Ae. albopictus is active in central and northern Mississippi beginning in March each year and continuing through November or December. There is little activity during the coldest months of the year (January and February). These data are important as this species is a known vector of several human diseases, as well as dog heartworm to canines (Gratz 2004, Ledesma and Harrington 2011). Finding the species active in both rural and urban areas from March until December should be of concern to public health and vector control officials in the southern USA.
This study was funded by a grant from the Centers for Disease Control and Prevention to the Mississippi State Department of Health, “Epidemiology and Laboratory Capacity for Infectious Diseases” grant number U50\CCU416826-03.
Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, 100 Twelve Lane, Clay Lyle Entomology, Mississippi State University, Mississippi State, MS 39762.
Bureau of Environmental Health, Mississippi Department of Health, PO Box 1700, Jackson, MS 39215.