618 PHOTOPERIODISM IN INVERTEBRATES 



in Metriocnemus knabi. Photoperiodic induction was optimal at inter- 

 mediate temperatures (23° to 25 °C); higli temperatures prevented 

 the response, while low temperatures (12° to 8°C) retarded the rate 

 of response on inductive photoperiods. The threshold temperature for 

 the response was not determined, but it was found to be below 8°C. 

 Most workers have found that long photoperiods and high temperature 

 both act toward the same effect, while short photoperiods and low 

 temperature also work in concert. Such is the case in Macrosiphum 

 (Shull, 1929), Bombyx (Kogure, 1933), Diataraxia (Way and Hop- 

 kins, 1950), and Metatetranychus (Lees, 1953a). In Grapholitha, 

 however, both high and low temperatures tended to prevent diapause, 

 which was initiated on short photoperiods only at intermediate 

 temperatures. Antheraea (Tanaka, cited by Lees, 1955) responded to 

 photoperiod almost independently of temperature. It would appear 

 that a critical evaluation of the significance of these different patterns 

 of day length-temperature interaction must await a better under- 

 standing of the processes involved. 



The critical day length range has been determined for a number of 

 arthropods — the aphid Macrosiphum (Schull, 1929). the lepidopter- 

 ous insects Bombyx (Kogure, 1933), Grapholitha (Dickson, 1949), 

 Diataraxia (Way and Hopkins. 1950), Acronycta (Danilyevsky, 

 cited by Lees, 1955). Antheraea (Tanaka, cited by Lees, 1955), and 

 Barathra (Otuka and Santa, 1955); and the red-spider mite Meta- 

 tetranychus (Lees, 1953a). All these organisms live in temperate 

 regions of the world, and the critical photoperiod ranges, which 

 separate effective short photoperiods from long, lie somewhere be- 

 tween 1 2 and 1 6 hr. However, for species from high latitudes there is 

 a clear tendency for the range to be shifted to longer photoperiods 

 (Lees, 1954). 



Little information is available in this regard concerning the possi- 

 bility of subspecific variation. Apparently only one case is described 

 in the literature for photoperiodic animals.^ Lees (1953a, 1955) 

 found the critical day length range for mites at Cambridge, England, 

 to be about 2 hr shorter than that reported by Bondarenko (cited by 



3 See the recent paper by Bondarenko and Hai-Yuan, in Doklady Akad. 

 Nauk S.S.S.R., 7 79 (6), 1247 ( 1958), and others cited by Lees in his contribu- 

 tion to this symposium. 



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