The mode of meiosis in the Psyllina

Summary

• 1. The spermatogenesis of six psyllids and the oogenesis of Psylla försteri have been studied. The haploid number n=13 was found in 4 species, all with an XO system of sex determination. 13 may well be the modal haploid number in the genus Psylla.

• 2. The chromosome complement of the only XY species, Psylla corcontum, with n=11, is probably the result of two chromosomal rearrangements which have led to the formation of a neo-XY pair.

• 3. Psylla försteri is an XO species in which the haploid set consists of only 8 chromosomes, one of which is very large. As the amount of DNA in this species is approximately equal to that in the 13-chromosome species P. sorbi, the large chromosome obviously corresponds to 5 or 6 chromosomes of P. sorbi.

• 4. A diffuse stage, which leads to a considerable increase of nuclear size, is typical of late pachytene to late diplotene of spermatogenesis.

• 5. In contrast to the other cytologically studied Homoptera Sternorrhyncha, the bivalents of psyllids co-orientate at the first metaphase of spermatogenesis. The following anaphase is therefore prereductional.

• 6. In the oogenesis of Psylla försteri the bivalents always seem to have auto-orientation, which means morphological postreduction at first anaphase.

• 7. The karyological picture is that of an organism with a diffuse kinetochore.

• 8. The Hemiptera and the plant genus Luzula both have diffuse kinetochores. The reason that the chromosome numbers in Hemiptera vary far less than in the genus Luzula may lie in the existence in the Hemiptera of a delicate system of sex determination sensitive to any change in chromosome number and structure.

• 9. Cytologically, the Psyllina lie between the suborders Sternorrhyncha and Auchenorrhyncha.