BEHAVIOR OF SOME SOIL INSECTS. 1 77 



ammonia was rather decided. The majority of the individuals 

 tested showed considerable signs of disturbance and discomfort 

 but they were not very strongly negative to ammonia; one or two 

 continued to remain in the ammonia air although they were not 

 at ease. The adults moved hesitatingly and at random in the 

 ammonia air, stroking the antennae and occasionally the ab- 

 domen. 



D. Reaction to Carbon Dioxide. The reaction of the adults to 

 gradients of carbon dioxide was not very different from that of 

 the larvae. Graph 20 shows the reaction of an adult Pterostichus 

 stygicus to air containing carbon dioxide gradients of 7.2, 3.6, 

 and o.o per cent, with a temperature of 22 C. and a relative 

 humidity of 90 per cent. The adult tried the carbon-dioxide-free 

 air several times, but each time came to rest in the air containing 

 the largest amount of the gas. Graph 21 shows the reaction 

 of an adult of the same species to air containing carbon dioxide 

 gradients of 14, 7. and o.o per cent, with a temperature of 22.5 

 C. and a relative humidity of 86 per cent. In this instance the 

 adult showed a distinct negative reaction to the flow of air con- 

 taining the largest per cent, of carbon dioxide, spending most of 

 its time in the carbon-dioxide-free air. In most cases where the 

 carbon dioxide was about 6 or 7 per cent., or higher, the adults 

 either avoided it or were uneasy and distressed. With lower 

 percentages of the gas very little signs of uneasiness were shown. 



IV. SUMMARY AND DISCUSSION OF CONCLUSIONS. 



A thorough understanding of the behavior of the soil insects 

 to evaporation, temperature, and gases found in the soil necessi- 

 tates a knowledge of the conditions existing in their habitat. 

 This includes the physical condition of the soil, the temperature, 

 the moisture, and the gases. The physical structure of the soil, 

 i. e., size of soil particles, porosity, amount of organic material, 

 etc., is important, since it is upon these that the soil moisture, 

 temperature, and aeration is dependent. The temperature of 

 the soil is fairly constant. It does not have the range of vari- 

 ation and is not subjected to the sudden changes encountered in 

 the atmosphere. This is more noticeably so in soil which is 

 moderately moist to wet and is due, to a large extent, to the great 



