170 Temperature 



the white mayfly, Eplioron album, must be chilled to within a few de- 

 grees of freezing for several weeks (or subjected to a few days of 

 actual freezing) for good hatching to be assured. As a result, this 

 insect cannot extend its range in the eastern part of the United States 

 farther south than 40° N latitude. 



The eggs of the Australian grasshopper will not continue growth 

 beyond a certain stage unless they are exposed to low temperatures 

 within the range that will permit diapause development to proceed 

 rapidly (5-13°C), and later, to high temperatures (17-35°C) which 

 permit morphogenesis to go forward (Fig. 5.16). This dependency 



20 

 Temperature, °C 



From Andrewaitha, 1952, copyright Cambridge Univ. Press 



Fig. 5.16. The influence of temperature on (A) diapause development and (B) 

 post-diapause morphogenesis in the embryo of the grasshopper, Austroicetes 

 cruciata. Solid line: eggs from South Austraha; broken line: eggs from West 



Australia. 



on chilling is nicely attuned to the normal life cycle of this grasshop- 

 per. Since the insect reaches the diapause stage at the beginning of 

 winter, it is in the condition to endure best the severest cold weather 

 of the year and also to take advantage of low temperatures for the 

 completion of diapause development. Other species in which dia- 

 pause occurs during later stages of the life history exhibit a different 

 timing in their adjustments to the ecological conditions of their habi- 

 tat. The eggs of the moth, Euproctis, hatch during July, and dia- 

 pause does not take place until the larvae have reached the second 

 or third instar. By the time the animals enter diapause autumn has 

 arrived and the species overwinters in the larval stage. 



In New England the gypsy moth pupates in summer, and develop- 



