PHOTOPERIODISM IN INSECTS AND MITES 



A. D. LEES 



Agricultural Research Council, Unit of Insect Physiology, 



Cambridge, England 



The effects of day length on an aphid were reported by Marcovitch 

 (1924) only four years after the announcement of the fundamental 

 discoveries by Garner and AUard. Nevertheless, despite this encourag- 

 ing beginning, little more was accomplished in the field of arthropod 

 photoperiodism until the postwar years, which have witnessed a con- 

 siderable revival of interest. It is perhaps for this reason that physio- 

 logical analysis of this phenomenon is still at an early stage of develop- 

 ment. Sufficient species have now been examined to show that photo- 

 periodism is widespread, although certainly less ubiquitous than in 

 plants; and the adaptive significance of the response has come to be 

 appreciated. In the course of such studies useful information has been 

 accumulated which will have eventual utility in interpreting the photo- 

 periodic mechanism. However, it must be emphasized that the insect 

 physiologist is not yet in a position to present a satisfactory working 

 hypothesis of the controlling mechanisms in any one species. 



No "endogenous" annual rhythms, akin to the persistent diurnal or 

 tidal rhythms of Crustacea, have yet been described in insects. When 

 such seasonal rhythms occur, it has invariably been possible to relate 

 them to some component of the environment, the day or night length 

 being particularly pertinent in this respect. In general, the processes so 

 determined fall into two categories: the control of growth in species 

 that hibernate or estivate; and the control of differentiation in species 

 that show seasonal differences of form. The two are sometimes inter- 

 connected. In the following account some of the salient features of 

 arthropod photoperiodism are surveyed, with the emphasis on recent 

 work. 



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