Capture of Screwworm and Secondary Screwworm Flies (Diptera: Calliphoridae) in a Time-Interval Grid Trap and Correlation with Temperature and Humidity

A time-interval electrocuter grid trap was successfully modified to collect adult screwworms, Cochliomyia hominivorax , and secondary screwworms, C. macellaria , during 14 hourly diurnal periods. Peak captures of screwworms were made in the morning, but collections of secondary screwworms were made in larger and more uniform numbers throughout the day. The total numbers captured and the activity patterns were highly variable day to day. Seasonally, captures peaked around midday during cooler weather, but were more evenly distributed throughout the day during hotter weather. Hourly captures of both species were positively correlated with increasing temperature in the range 20° to 33 °C. Screwworm capture was very low at temperatures below 20 °C, peaked at ca 33 °C, and appeared to decrease when the temperature rose from 33° to 35 °C. Secondary screw worms were detected over a greater temperature range than were screwworms, possibly because secondary screwworms were present at much higher numbers. Captures of secondary screwworms did not decrease between 33° and 35 °C. Additionally, a high degree of variation occurred both in diurnal pattern of fly activity and in numbers captured of both species even between successive days having apparently identical temperature and humidity patterns. Relative humidity did not appear to influence captures, except that captures were zero or extremely low during rains.