The influence of selection on the preferendum of a Chalcid ( Microplectron fuscipennis Zett.) and its significance in the biological control of an insect pest

Abstract

The preferred temperature of Microplectron fuscipennis Zett., a Chalcid parasite of the European spruce sawfly, has been investigated with special reference to (1) changes produced by selective breeding, and (2) the significance of such changes in the biological control of insect pests. The average preferendum of both sexes is between 21.2 and 22.8 degrees C, with two minor peaks, one at 15 degrees C and another at 9 degrees C. In midsummer three groups preferring temperatures at 25, 15 and 9 degrees C are nearly equal. Such changes were due to the selection of breeding stock and not related to seasonal or previous temperature experiences. Within four inbred generations a line was established in which most of the individuals preferred the low temperature selected by the parents. So far, two groups have been isolated; one preferring a temperature of 25 degrees C and another of 9 degrees C.