Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2003
Publication Date: 1/20/2004
Citation: Phillips, P.L., Welch, J.B., Kramer, M.H. 2004. Seasonal and spatial distributions of adult screwworms (Diptera: Calliphoridae)in the Panama Canal Area, Republic of Panama. Journal of Medical Entomology. 41:121-129. Interpretive Summary: In this paper we present the remote sensing and geographic information system (GIS) research within the ARS Screwworm Research Unit. The objectives of the remote sensing program are to develop methods to predict screwworm fly (Cochliomyia hominivorax) distributions and strategies for monitoring the barrier zone at the Panamanian - Columbian border (Darien Gap) as well as areas that could become reinfected which include all of Central America and the Southern United States. This research directly benefits the USDA Animal Plant Health Inspection Service (APHIS) Screwworm Eradication Program. The Screwworm Eradication Program uses a method of sterile male releases to control populations of the screwworm fly, an economically important pest of domestic cattle. Such biological control effectively leads to the extinction of native screwworm populations. The USDA ARS research unit has developed methods to identify screwworm habitats in a tropical landscape using a combination of field data and satellite imagery. These methods are based on data collected in the Panamá Canal Area, Panamá. We feel these results will be applicable to most tropical habitats in Central America and parts of South America. The ability to identify screwworm fly habitat and map these distributions with satellite imagery will greatly increase the efficiency of the Screwworm Eradication Program.
Technical Abstract: The distribution of screwworms, Cochliomyia hominivorax, (Coquerel) was studied in a tropical wet zone in the Republic of Panamá using a combination of field collections and satellite imagery. Flies coming to rotted liver were collected at 82 sites in ten vegetation types (open areas, edge forest, dry scrub forest, forest successional stage 1, forest successional stage 2, forest successional stage 3, forest successional stage 4, forest successional stage 5 and mature forests, palm swamp forest, forest along streams) over three seasons (dry, transitional, wet). Nine of the vegetation types (excluding dry scrub forest) were identified and mapped using SPOT XS and Landsat TM satellite data. Most flies occurred during the transitional seasons. Most screwworm flies were in successional forests with trees 20 to 30 meters in height and a fairly open canopy composed of many deciduous species that shed their leaves during the dry season. Screwworm numbers were also high in palm swamp forest, edge forest and mature growth forest during the transitional season. Females accounted for 87.82 % of the total fly counts. This study further substantiates the importance of forests in the ecology and behavior of screwworm flies. We demonstrated that different forest types could be distinguished and mapped using remotely sensed data, thus providing a spatial distribution of high fly activity in a tropical landscape and discuss implications of this information to the screwworm eradication program.