The screwworm (Cochliomyia hominivorax) has been a serious economic pest in southern sections of the United States for many years. Recently, a U.S. Department of Agriculture eradication program has significantly reduced the number of reported infestations in the Southwest, although periodic outbreaks continue to occur. This study investigated the relationship between reported screwworm cases and weather conditions, with the objective of establishing guidelines for the use of real-time weather data as input to the eradication program. Because of several complicating factors the results were largely qualitative. The screwworm activity/rainfall relationship was quite variable. Periods of moderate or heavy precipitation were often followed within several weeks by an increase in reported screwworm cases. In other instances, there were wet periods with no resulting increase in screwworm activity. Some of this variability was believed due to a temperature factor, since insect activity appeared to be diminished by extremely high temperatures. This study suggested a critical threshold temperature of approximately 95 Β° F. Palmer Crop Moisture Index values were a useful indicator of screwworm activity, with above normal CMI values often, but not always, associated with increased infestation reports in following weeks. Periods of moderate or heavy rainfall, or persistent light precipitation, accompanied by temperatures remaining below the mid-90's should be a signal to the eradication program of an increased potential for screwworm outbreaks.
INTRODUCTI ON
For many years, southern regions of the United Slates experienced severe economic loss in livestock operations due to the insect pest Cochliomyia hominivorax, commonly known as the screwworm, a parasite of warm-blooded animals. The adult fly lays eggs in open wounds and the resultant larvae feed on the live tissue of the host, often resulting in the death of the animal. After about 6 days the larvae drop from the animal and burrow into the soil where they pupate for about one week in warm weather, but up to several weeks under cooler conditions. Although the insect overwintered only in Florida and southern areas of Texas, New Mexico, Arizona, and California, during the warm season it attacked cattle as far north as South Dakota and Minnesota in the Great Plains, and Tennessee, Virginia, and New Jersey in the eastern United States.