212 BR. J. ENT. NAT. HIST., 13: 2001 



steady increase in antennal segmentation. It is now suggested that instars would be 

 more adequately described by a notation in which the numerical stage and 

 developmental pattern, when known, are both shown, as in 2/4 to indicate the 

 second in a four-stage sequence, thus emphasising the distinction between instars 2/4 

 and 2/5. Some of these stages for female C. brunneus can be diagnosed with 

 reasonable certainty although, as results for 1970 show, hind-femora measurements 

 alone may not be sufficient. Antennal segmentation of the adults records their 

 nymphal history and, for the last two nymphal instars, permits the identification of 

 3/4, 4/4, 4/5 and 5/5 individuals. Stage 3/5 may be deduced from a combination of 

 antennal features and the possession of pre-reversal wing-buds, although there 

 remains a remote possibility that this could be 3/6. Recognition of instar 2/4 among 

 typical 2/5 types has not been achieved, but may come about through fuller study of 

 the external genitalia. No means of distinguishing between instars 1/4 and 1/5 have 

 been found, if indeed the future developmental route is already predetermined at 

 hatching. 



There remains the question of the significance of the naturally-occurring four- 

 stage females and the factors influencing their production. Any effect comparable 

 with phase variation would require the four-stagers to be more frequent in dense 

 populations, or, at least, among the offspring of such populations (Albrecht, 1955). 

 No attempt was made to assess the population densities of the colonies studied here, 

 but the low incidence of four-stagers would not have permitted valid comparison. 

 For non-British grasshoppers, variable instar numbers have been associated with 

 temperature (Parker, 1930), geographical range (Shotwell, 1941) and food (Smith, 

 1959). Several workers since Richards & Waloff, rearing females of C. brunneus in 

 captivity, have clearly indicated a four-stage nymphal development (Moriarty, 1969), 

 strongly implied this (Kelly-Stebbings & Hewitt, 1972) or at all events made no 

 comment contrary to the prevailing view, so that Hassall & Grayson (1987) regarded 

 their finding of five stages as abnormal. It is difficult to assign common features to 

 accounts of captive rearing, but fairly widely reported are an elevated laboratory 

 temperature, artificial irradiation, grass specially grown for food, rearing in groups 

 and housing in better ventilated conditions than those described here. Sometimes the 

 specimens have been drawn from stock maintained in captivity for several 

 generations. Hassall & Grayson (1987) found that second-generation laboratory- 

 bred females from one site passed through only four nymphal stages when the quality 

 of their food was reduced. 



Such factors may not be the only influence, as both types of female were among 

 the siblings hatched in 1976 and reared under similar conditions; indeed one of each 

 type actually occupied the same jar throughout nymphal development. That these 

 were the offspring of a four-stage female might suggest a heritable effect, although 

 whether truly genetic or more akin to the transmission through the generations of 

 phase differences cannot be determined on this evidence alone. Whatever may be the 

 explanation for the presence of four-stage females in natural populations it would 

 seem that this is most likely to be provided by those encountering them routinely 

 during captive rearing. 



ACKNOWLEDGEM ENTS 



I wish to thank the Authorities of the Royal Russell School for allowing me to 

 work in the school grounds, and my son, Graham A. Collins, for preparing the 

 histograms. 



