New World Screwworm Analysis

Image of adult screwormThe new world screwworm (Cochliomyia hominivorax (Coquerel)) was eradicated in North America, Libya and other locations using the sterile insect technique (SIT).  A physiologically-based demographic model (PBDM) was developed and used to characterize its range of year-round persistence and to examine the role of weather in its eradication. Published data on developmental times, fecundity and mortality rates on temperature were used to parameterize the model. Lower and upper thermal thresholds are 14.5°C and 43.5°C, and the optimal temperature for survival is 27.2°C. A survivorship index based on annual rainfall was used to estimate the limiting effects of moisture in arid areas.

Maps depicting areas of new world screwworm average geographic distribution in North America and the perspective distribution in the Mediterranean Basin
Average geographic distribution of new world screwworm in North America and the in the Mediterranean Basin (perspective)

The open source GIS software GRASS was used to map the simulation results, and county level myiasis incidence data for Texas during the 1962-1983 SIT eradication programme.

Winter temperatures and rainfall are shown to have a strong influence on screwworm outbreaks and in facilitating eradication in North America and Libya. Prospective analysis for the Mediterranean Basin suggests that eastern areas are most favorable for screwworm establishment (e.g., Nile River area of Egypt).  The SIT eradication programme and its possible extension into South America are discussed.

Predicted +2°C climate warming would increase the potential year-round range of screwworm in the southeastern United States.


Gutierrez, Andrew Paul and Luigi Ponti (in press)The new world screwworm: prospective distribution and role of weather in eradication. Agricultural and Forest Entomology

Gutierrez A.P., Ponti L., 2013. Eradication of invasive species: why the biology matters. Environmental Entomology,