Effects of Temperature and Host Density on the Rate of Increase of an Insect Parasite

1. The searching of the chalcid parasite Dahlbominus fuscipennis (Zett.) for its host Neodiprion sertifer (Geoff.) was examined in the laboratory at temperatures of 16, 20, and 24⚬C. when the host was uniformly distributed at seven densities ranging from 0.06 to 1.56 cocoons per square inch. 2. At lower host densities, the rate of increase of the parasite was rapid, but at the higher host densities it tended to level off. 3. Variations in area of search and in number of hosts available for attack did not account for the variation in parasite increase. 4. At 24 and 20⚬C. the rate of increase of the parasite, at the highest host density, was controlled by the effect of temperature on the parasite's oviposition but at 16⚬C. only half as many hosts were attacked and half as many eggs were laid as was possible. 5. In a single parasite generation, the relation between parasitism and host density approximated the curve y = a + b ln x. 6. Increase in temperature and in host density caused a large increase in the ratio of parasites emerging to hosts emerging in a single parasite generation.