Development of an Ecological Trap for American Cockroach Metapopulations
John C. Carlson and Mark S. Fox

Specific Aims
The over-all goal of this project is the manipulation of American cockroach metapopulations in order to significantly reduce their numbers inside houses using the ecological concepts of “source-sink” and “ecological traps.”  Ecological traps are generated accidentally by human activity, endangering beneficial species.  I intend to deliberately generate such a trap in order to cause a collapse of the American cockroach metapopulations.

Specific Aim 1: Document the “source” niches of urban cockroach metapopulations
Specific Aim 2: Describe the movement of cockroaches from sources into houses
Specific Aim 3: Blunt the movement of cockroaches into houses by management of source niches, and generate an ecological trap in those niches by drawing in cockroaches from other subpopulations

Background and Significance
Environmental exposure to a number of substances increases the probability that children will develop asthma.  Of these, sensitization to cockroach proteins combined with high concentrations of cockroach proteins in house dust are the strongest correlates of asthma severity in young children (Rosenstreich et al.  1997; Gruchella et al. 2005; Morgan et al. 2005).  Effective control of German cockroaches by indoor baiting leads to lower rates of sensitization in Northern US cities (Arbes et al. 2004; Morgan et al. 2005), however this is ineffective against American cockroaches, common in the southern US and tropical areas.  The impact of the different roach species on the development of asthma has not been fully investigated in the US, however both American and German cockroaches are implicated in asthma development, and share significant homology in major allergens (Pomes et al. 1998). In warm, humid regions, American cockroaches can become the predominant cockroach found in homes and are linked with high rates of sensitization in children (Tungtrongchitr et al. 2004).

While German cockroaches do not reproduce outside human habitation, American cockroaches are capable of maintaining large populations in outdoor niches.  Several studies have implicated sewer systems as the major source of urban American cockroaches (Eads 1954; Schoof and Siverly 1954; Jackson and Maier 1955).  Migration from sewers into houses can occur via aboveground and belowground routes, and has been experimentally linked to fluctuations in niche population pressure (Jackson and Maier 1955). Increasing population pressure drives outward migration, while areas with low populations attract migrating roaches. Population movements into houses may also be motivated by escape from cold or inclement weather (Eads 1954).

Where sewers are the major source for American cockroaches, and migration into houses from these sources is the predominant method by which household populations are sustained, these habitats present an opportunity for population-level control with methods specifically tailored to this type of niche (Rust et. Al 1991). In contrast to the difficulties in sustaining control efforts against German cockroaches (Morgan et al 2005), area-wide control measures against American cockroaches could be effectively done by local governments treating sources on public property. 

German cockroaches are very sensitive to indoor baiting systems that deliver slow-acting insecticides to a few roaches that return to nesting sites to share their food with other roaches (Arbes et al., 2004).  Despite the effectiveness of these systems, there is difficulty in sustaining them because treatment of individual homes is needed to prevent re-colonization (Peters 2007).  This is a particularly difficult problem in apartment buildings and low-income housing projects, where rates of asthma are very high.  Preventing asthma through environmental control has been economically viable in areas affected by German cockroaches (Morgan et al 2005).  Assuming equal efficacy, outdoor, area-wide control of American cockroaches would represent significant savings for governments that would otherwise pay for the chronic treatment of this preventable, potentially fatal disease.   While home repair and maintenance are believed to be helpful in preventing colonization of homes by American cockroaches, even with ideal maintenance, American cockroaches from sewers are able to swim through toilet water seals (Eads 1954). 

Metapopulation theory is used to describe the interactions among different sub-populations of a species.  Habitats are variable in quality, such that some are high quality and have population increases (sources) and others have low quality, such that population decreases (sinks).  If source habitats and sink habitats are sufficiently connected by migration, sink habitats may remain populated, despite low levels of reproduction, due to immigration from source habitats (Pulliam and Danielson 1991).  Members of a species generally can determine habitat quality, although when environmental cues lead to misidentification of poor quality habitats as high quality habitats, the sink is termed an “ecological trap” (Robertson and Hutto, 2006).  This study seeks to describe the population of American cockroaches in terms of source-sink metapopulation models, and ultimately generate an ecological trap using undetectable baited insecticides placed in source habitats.  Depletion of cockroaches within the preferred habitats should draw in cockroaches from less preferred habitats, ultimately leading to a collapse of the meta-population, if interconnectivity of subpopulations is sufficient.

Current control measures for American cockroaches focus on their potential role in mechanical transmission of a formidable list of infectious agents.  Unfortunately, the degree of control required to diminish allergen levels in house dust must fall to a much lower level than is generally targeted by current pest management strategies that use roach visualization as a main outcome (Sever et al 2007).  The effective maintenance of an ecological trap on government property would be economically sustainable by governmental organizations with a financial incentive to prevent sensitization of young children who would otherwise be at risk for developing acute and chronic allergic diseases.

References cited

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