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