CHROMOSOME NUMBER POLYMORPHISM IN THE SAWFLY JANUS INTEGER ( HYMENOPTERA , CEPHIDAE ) *

METHODS Male pupae of .lanus integer were obtained by allowing virgin females to oviposit on caged currant bushes t?rom which all the previous year’s growth had been remo.ved. Chromosome preparations were made from pupal or prepupaI testes using an air-drying technique (Crozier, I968, I97O). Each prepupa or pupa was punctured using a minuten pin and placed with the puncture touching a drop of a o.o5% solution of colcemid in an insect Ringer solution and let:t overnight. The. next day the testes were dissected out under a 1% w/v sodium citrate solution and left in the solution or 2o minutes; they were then fixed in 3: methanol-acetic acid fixative for at least 45 minutes. The cells were dissociated using a drop of 6o% acetic acid on a warm slide and the suspension spread using further methanol-acetic fixative before being dried by an air-flow and stained using aceto-lactic orcein. The preparations were dehydrated and mounted in ’Euparal’. The chromosomes of intact cells were counted using a hand counter. If a majority o cells had shown the same number after


INTRODUCTION
The Symphytan amily Cephidae has a special significance in the study o the evolution o the Hymenoptera, as it is belived to be the group closest to the stem rom which the Apocrita evolved.The chromosomes o only one cephid, Cephus cinctus, have been de- scribed previo.usly(Mackay,955); the Cephidae are therefore an important but cytogenetically little-known group.

METHODS
Male pupae of .lanusinteger were obtained by allowing virgin females to oviposit on caged currant bushes t?rom which all the pre- vious year's growth had been remo.ved.
Chromosome preparations were made from pupal or prepupaI testes using an air-drying technique (Crozier, I968, I97O).Each prepupa or pupa was punctured using a minuten pin and placed with the puncture touching a drop of a o.o5% solution of colcemid in an insect Ringer solution and let:t overnight.The. next day the testes were dissected out under a 1% w/v sodium citrate solution and left in the solution or 2o minutes; they were then fixed in 3: meth- anol-acetic acid fixative for at least 45 minutes.The cells were dissociated using a drop of 6o% acetic acid on a warm slide and the suspension spread using further methanol-acetic fixative before being dried by an air-flow and stained using aceto-lactic orcein.The preparations were dehydrated and mounted in 'Euparal'.
The chromosomes of intact cells were counted using a hand counter.If a majority o cells had shown the same number after 20 cells, and none had been found with a higher number, that num- ber was taken to be the chromosome number of that individual.
Otherwise, further cells were counted.

RESULTS AND DISCUSSION
The karyotypes of eight male Janus integer were determined.Two Manuscript recei,ed by the editor March 3, 1972.Nogusa, 1965; Waterhouse and Sanderson, 1958; Comrie,  1938; Maxwell, 1958; Mackay, 1955).Benson's (1950) review does not give sources for the counts given, and Sanderson's (1932) counts were later shown by her (Sanderson, 1971) to be in error; counts from before these two and pre-1932 sources have therefore been omitted.

Psyche
[March-June had a chromosome number o 22, three had one of 24, two had one o 25, and one had one of 26.Karyotypes o.f 22, :24 and 26 chromo- somes are shown in Figure I.Because o the small size o the chromosomes, we could not determine the nature o the poly- morphism, but Robertsonian changes do not appear to.be involved.The range of chromosome numbers between 22 and 26 is probably continuous, with the lack of a count of 23 being due to sample error.This is the second report o.t: intraspecific variation in chromosome numbers in Symphyta.Sanderson (I97I) reports that, w'hile English collections of Tenthredo acerrima consistently had a haploid number o 18, Scottish collections had haploid numbers ranging from 18 to 21.There is thus a geographic basis to.t'he T. acerrima polymorphism that remains to be searched for in J. integer.
Chromosome numbers in the .A_pocrita range from four to 28, which range is found in the single family Formicidae (Crozier,197o).The low haploid number (n 9) (Mackay, 1955) of Cephus cinctus, combined with the fact that generally lower num- bers have been reported for Parasitica than for Aculeata, suggested that low numbers might be primitive in the .A_pocrita.However, the discovery that anorher cephid, Janus integer, has high chromosome numbers indicates that high numbers are as likely to.be a primitive character in the Apocrita as low numbers.
Karyotype xCrequencies are best considered using the genus-karyo- type concept (Crozier, I97O), in order to minimize the effects of different intensities of sampling between genera.Under this con- vention, each chromosome number is counted once each time it oc- curs in a genus, irrespective of how many species it occurs in.The genus-karyotypes known for the Symphyta are shown in figure 2, where it can be seen that Janus integer has the highest chromosome number o any sawfly.The distribution of genus-karyotypes is strongly skewed, suggesting that low numbers might be primitive for the Symphyta.The ranges in chromosome numbers of the fa.m- ilies Tenthredinidae and Cephidae are particularly striking.The gaps in these ranges might indicate polyploidy, but the karyotypes of too ew species are known to give much support to this suggestion.

SUMMARY
Eight males of Janus integer had haploid numbers of :22, :24, 25 and 26; presumably a larger sample would have yielded counts of 23 as well.The polymorphism does not appear to be Robertsonian in nature.The significance of these results to considerations of hymenopteran karyotypic evolution is discussed.