The Value of Pitfall Trapping in Comparing the Activity of Insect Communities

Abstract

The number of insects caught in pitfall traps in two habitats in Wyoming, a mixed woods and a sagebrush flat, may be considered a direct measurement of the insect activity in each of the two habitats. The trap catches showed that greater overall activity occurred in the habitat with diversified vegetation, the mixed woods, than in the habitat with uniform vegetation, the sagebrush flat. Both habitats displayed greater activity by day than by night, but slightly more activity occurred at night in the mixed woods than in the sagebrush flat, although the ratios of day to night activity in the Woods and in the Sage did not differ significantly. Daily fluctuations in activity were due mainly to fluctuations in the weather, as shown by the significant correlations of some air and soil temperature and relative humidity measurements with the day or night catches of insects in the two habitats. The observed changes in activity due to weather also affected the ratio of day to night activity in both habitats. The insects sampled in this study were caught in one-gallon jars 1/4 filled with dilute alcohol, and sunken into the ground to their rims. 16 jars were systematically placed in each habitat within an area of 25 m., and checked morning and evening on 3 consecutive days of each week, during the 4 weeks of July, 1973. 1,247 mature insects were collected and removed from the two habitats altogether. The results obtained by statistically evaluating the trap catches in the two habitats indicate that pitfall trapping is valuable in directly comparing the activity of insect communities.