The C-banded karyotypes of the four British species of Notonecta L. (Heteroptera: Notonectidae)

Chromosome preparations were made from mid-gut and ovarian cells of adult Notonecta glauca L., N. obliqua Thunberg, N. maculata F. and N. viridis Delcourt, using the acetic acid dissociation, air-drying method (Crozier 1968) with Giemsa staining. C-banding was obtained by treatment with barium hydroxide and salt-sodium citrate (2xSSC). The karyotypes of the first three species are very similar, with 11 pairs of autosomes plus XY sex chromosomes (plus sometimes a small 12th autosome pair in N. glauca), and the sequence of chromosome sizes very similar. However, the four longest pairs of autosomes, and the X chromosomes, have characteristic C-band patterns, which differ between the species. The karyotype of N. viridis is more distinct, with one pair of long autosomes, while the remaining chromosomes are much shorter. The long autosomes have distinct C-bands, but these are present in only one of the shorter pairs, as faint terminal bands. In warm conditions the long autosomes of N. viridis appear rod-like, but in cold conditions they have one end heavily condensed, giving a tadpole-like appearance.