.|  Baltimore Ecosystem Study
Ecological complexity and disease vectors: Phenology and composition of urban mosquito communities in Baltimore

Over the past 50 years many regions have experienced a (re)emergence of mosquito-vectored diseases, both due to novel pathogens and those previously eradicated. This phenomenon is increasingly evident in cities across the globe. Although developing nations still bear the heaviest burden of global mosquito-borne disease, countries like the United States are increasingly at risk. The emergence of West Nile virus (WNV) in New York City in 1999, reawakened many Americans to the threats of vector-borne infectious disease. In the past decade, WNV has had a persistent and dramatic impact on many North American bird species and has resulted in over 1000 human fatalities. The local intensity of avian and human incidence has been positively associated with human-dominated landscapes (LaDeau et al. 2007, 2008, 2011) and this is at least partially due to facilitation of vector mosquito production in urban habitats. Work at BES led by Dr. Shannon LaDeau of the Cary Institute of Ecosystem Studies investigates mosquito ecology and specifically, vector species production in urban communities.
 
Ongoing efforts by LaDeau and colleagues to understand mosquito ecology, disease vector dynamics, and potential human risk of vector-borne diseases in Baltimore address the following questions and has motivated two funded grants:
 
A. How is mosquito ecology and vector abundance supported by urban ecosystems?
 


Figure 1. Mosquito Sampling At Carroll Park
Photograph: Dan Dillon  
1. There are over sixty species of mosquitoes in the Mid-Atlantic region but only a few are important disease vectors. We collected data in 2010 to test the hypothesis that urban breeding habitats support fewer mosquito species but greater abundances of WNV vector species. Temporary pools of standing water near stream banks were sampled monthly from sites surrounded by urban (paved) and rural (forested) landscapes and both mosquitoes and potential predator species were identified. By mid-summer the predator (i.e., dragonfly larvae) to mosquito ratio was over three-times greater in rural versus urban samples. The overall abundance of mosquito larvae from rural samples was roughly one-third urban abundances, even though the urban sites were dry by August. The majority of increase in urban abundances was due to increased numbers of bridge vectors. Increased WNV risk in humans (and birds) in the Mid Atlantic that is associated with urban landscapes may be attributed to changes in mosquito communities. (Collaborator: John Wallace, Millersville University)
 

Figure 2. Mean mosquito abundance (left axis) and predator: mosquito ratio (right axis) from urban and rural water sources, early summer 2009. Enzootic (bird-feeding) and bridge (bird and human feeders) vectors are separated from other mosquito species.
 
Figure: Shannon LaDeau  

 
2. In 2010, 2011, and 2012 we collected weekly ovitrap samples from egg-laying mosquitoes at ten sites with decreasing impervious surface area from Baltimore City to a rural, reference watershed in the County. Seventeen species of mosquito larvae have been identified, including several medically important vector species and at least two species not known to feed on humans (Culex territans, Tox.septentrionalis). Species richness is highest in suburban sites, although diversity indices (i.e., Shannon-Weiner) decline higher impervious surface cover. Samples from the most urban settings (i.e., Watershed 263) supported a predominant invasive and human-biting community of mosquitoes (Ae. albopictus, Ae. aegypti, Culex pipiens), while the rural reference sites included both these species and native species. In general, the vector species that were sampled from more urban habitats reached higher peak abundances and did so earlier in the season.
 

Figure 3.Abundance data.
 
Figure: Shannon LaDeau  

 

Figure 4. Sampling
 
Photo: Shannon LaDeau  

 
B. What neighborhood characteristics (structural and socio-economic) and human behaviors support invasive mosquito infestations in the urban landscape?
 
1. Despite over a century of organized and often sophisticated efforts to control mosquitoes, nuisance complaints persist and mosquito-borne diseases are a persistent and growing concern in urban communities across the globe. The need for personal responsibility in managing urban pests at the scale of individual yards is increasingly viewed as the dominant paradigm for mosquito control in residential landscapes across the globe. This USDA-NIFA and the Northeastern Integrated Pest Management Center funded work (lead PI, Paul Leisnham at UMD, with LaDeau, Dawn Biehler (UMBC) and Guy Hager (Parks & People Foundation)) is designed to investigate ways to improve local management of the invasive Asian tiger mosquito (Aedes albopictus) in urban environments.
 

Figure 5. Asian tiger mosquito.
 
Source: source: http://phil.cdc.gov/phil/details.asp?pid=4487  
Ae. albopictus is one of the most problematic mosquito species in urban areas globally and arrived in the U.S. in the mid-1980's in tires imported from Asia. This species bites during the day and feeds predominantly on humans. Even in cities with active mosquito control programs, abatement efforts are often ineffective against the Asian tiger mosquito because it can reproduce successfully in most any water-holding container. Populations of this disease vector species have increased dramatically in Baltimore over the past decade. The goal of this project is to train citizens to recognize and remove mosquito breeding habitats in their yards and shared spaces. Researchers will (1) evaluate citizen understanding of mosquito biology, (2) monitor adult and larval mosquito populations in residential neighborhoods within the watershed and (3) develop 'citizen science' strategies. Our intent is to help communities reduce the numbers of containers and adult mosquitoes by promoting lasting behavior changes. A key goal of this work will be to better understand what types of mosquito education materials and training promote citizen involvement in better mosquito risk management.
 
2. LaDeau and colleagues (Paul Leisnham (UMD), Dawn Biehler (UMBC), Sacoby Wilson (UMD), and Rebecca Jordan (Rutgers) have received NSF funding to study links between urban decay, public health risks, and outdoor urban pests. [NSF-funded Coupled Natural Human Systems project: Urban disamenities and pests: Coupled dynamics of urban mosquito ecology and human activities across socio-economically diverse communities (Sept. 2012 - August 2016).] This research will investigate how mosquito and other pest infestations vary with physical and socio-ecological characteristics of neighborhoods and will broadly examine feedbacks between outdoor pest exposures, resident use of the outdoor environment, and sustainability of urban greening initiatives that could decrease pest production. Scientists will integrate ecological, environmental justice, and education theory to assess how symptoms of urban decay (e.g., empty buildings, unmanaged lots, garbage, etc.) may be both a mechanistic cause and unintended result of increased pest exposure, especially in lower socio-economic neighborhoods.
 

Figure 6. Urban Disamenities.
 
Source: source for panels a-c:LaDeau, http://phil.cdc.gov/phil/details.asp?pid=4487, LaDeau