SOME OBSERVATIONS ON THE ROLE OF 

 DIAPAUSE IN THE PHENOLOGY OF INSECTS IN 



SEMI-ARID ZONES 



I. HARPAZ 



Department of Entomology, Faculty of Agriculture, 

 Hebrew University, Rehovot (Israel) 



A subtropical climate, in particular a Mediterranean climate, 

 is characterized by a long dry summer and a mild rainy winter. 

 Such an annual cycle induces in many insects a summer-heat 

 and/or drought diapause, and in a smaller number of cases a 

 winter-cold diapause. The latter is predominant in Central and 

 Western Europe, and its manifold aspects have already been 

 extensively studied there, so much so that hibernation and 

 diapause are often used as synonyms. On the other hand, heat 

 and drought quiescence of aestivating insects are phenomena 

 which have been much less considered, particularly heat- 

 diapause in its strictest sense. Incidentally, diapause, aestivation 

 and quiescence are not wholly synonymous, as Lees^ has 

 pointed out very clearly. Reference at this stage should be made 

 to Rivnay's paper-, which was the first appraisal of the problem 

 in this region. 



Let us take as an example the codling moth [Cydia pomonella 

 L.). It is essentially univoltine in Northern France and England, 

 where over 90 % of the fully-fed larvae enter diapause by the 

 end of summer and pupate only the following spring. In the 

 South of France, however, where the summer is warmer and 

 development is faster, about 70 % of the larvae pupate before 

 entering diapause and give rise to a second generation^. In 

 Israel, with an even warmer summer, where the flight of the first 

 generation takes place in April and May (as compared with 

 June and July in Western Europe, including Southern France) 

 there are even three generations a year^ with diapause setting in 

 as from mid-July and onwards. This situation can be satis- 



