BR. .1. INI NAI HIST., 13: 2<iui 



203 



THE NYMPHAL STAGES OF THE FIELD GRASSHOPPER, 



CHORTHIPPUS BRUNNEUS ( 1 HI \BI R(.) 



(ORTHOPTERA: ACRIDIDAE) 



Cj. B. Collins 



15, Hurst Way, South Croydon, Surrey CR2 7.1/', UK. 



Abstract. Hind-femora measurements of the Field Grasshopper, Chorthippm 

 brunneus (Thunberg), collected at all stages of development from three sites in the 

 Croydon area, showed that most females had five nymphal stages, while a small 

 proportion at two of the sites passed through only four. A simple correlation found 

 between antennal segmentation and numerical stage for nymphs of known 

 developmental history provided an independent means of assigning a number to a 

 nymphal stage when background details were lacking, and permitted assessment of 

 the nymphal histories of adults. These findings are discussed against a background of 

 the four-stage nymphal histories apparently widely found for females of this species 

 reared in captivity. 



Introduction 



Captive rearing of small numbers of nymphal grasshoppers found hatching on 

 Constitution Hill, Aberystwyth, Dyfed, in 1941, although far from successful, 

 showed reversal of the wing-rudiments for females of C. brunneus occurring at the 

 third moult, while the only female to reach the adult state passed through five 

 nymphal stages. Similar small-scale trials at Aberystwyth in the following years on 

 nymphs both taken in the field and hatched in captivity confirmed a" five-stage 

 nymphal development for females, as opposed to the four-stage sequence found for 

 males of this species and for both sexes of C. parallel™ (Zett.). Further rearing trials 

 in 1949 on C. brunneus collected as first-stage nymphs from Mitcham Common. 

 Surrey (now London Borough of Merton), led to similar results so that, although 

 numbers involved were still low, there seemed no reason to doubt that a five-stage 

 nymphal sequence was normal for females of this species. 



The publication by Richards & Waloff (1954) of the results of their intensive study 

 of British grasshoppers gave widespread currency to their view that both sexes of 

 C. brunneus had four nymphal instars, and called into question the validity of the 

 above conclusion. The possibility that a different developmental pattern prevailed 

 under more natural conditions had to be considered, and a study devised that would 

 minimise any spurious effects of captive rearing. Individual nymphs cannot readily 

 be monitored in the field, while the statistical study of wild populations is beset with 

 difficulties and uncertainties. The compromise adopted was to collect nymphs at all 

 stages of development; to measure their hind-femora, count the antennal segments. 

 note the aspect of the wing-rudiments and external female genitalia: and to retain 

 each nymph until it had completed at least one moult, so that these features could be 

 assessed for the next instar and thus compared with those observed in the field. 



Reversal of the wing-rudiments, with the costal margins becoming directed 

 upwards towards the mid-dorsal line and the hindwings overlapping the fo rowings 

 while presenting the undersurface to the exterior, normally marks the onset of the 

 penultimate nymphal stage (Uvarov, 1966); no exception to this was encountered in 

 the present study. In C. brunneus the reversed hindwing rudiments reach to the rear 

 end of the first abdominal tergite in the penultimate, and to the rear end of the thud 



