We have found the following differences in the male meiosis among three triatomine species: (1) The three largest autosomal bivalents of Triatoma infestans are heterochromatic. Rhodnius prolixus has two autosoreal bivalents with heterochromatic blocks. Triatoma rubrovaria does not show any heteropycnotic autosomes. (2) Sex chromosomes in T. infestans form a chromocenter. At early prophase terminal associations are seen between sex chromosomes in T. rubrovaria, and they maintain a close association until diakinesis. An intimate association between the X and Y chromosomes is observed during early prophase in R. prolixus, but a distant association is maintained by the sex chromosomes at diffuse and diplotene stages in this species. (3) Polyploid nuclei of the nutritive cells are quite distinct. Numerous chromocenters of different shapes and sized are seen in those of T. infestans. In T. rubrovaria one chromocenter having two positively heteropycnotic elements is observed surrounded by homogeneous chromatin. Only one compact chromocenter is found amongst unevenly distributed chromatin, in R. prolixus.

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1985.Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271. Geographic variation has been studied on seven south Argentina populations of Trimerotropis pallidipennis polymorphic with respect to centromere position. Univariate and multivariate statistical analysis were used to assess interpopulation relationships by considering the inversion frequency, the chiasma frequency, and the population distance from the Andes, which is considered to be the hypothetical pathway of migration of this typically North American species to southern latitudes. A cluster analysis indicated strong chromosomal differentiation between the almost monomorphic populations in the Andes' "precordillera" and the highly polymorphic populations in more eastern locations. It also showed that chromosomal similarity between populations could be predicted by geographic proximity. No attempt has been made to relate such a pattern of chromosome variation to ecological data. The lack of any clear relationship with phytogeographic regions or climatic characteristics suggests that microenvironmental factors related to aridity may be important in this case. The presence of inversions within a population has a notable effect on chiasma frequency and position. Chiasmata are suppressed within the inverted region of both inversion heterozygotes and homozygotes. The allelic sequences in the inverted region are thus preserved from recombination and exchanges are limited to terminal regions. Key words: geographic variation, chromosome polymorphism, chiasma frequency, B chromosome, pseudomultiple associations. GONI, B., E. S. DE VAIO, M. BELTRAMI, M. S. LEIRA, M. CRIVEL, F. PANZERA, P. CASTELLANOS et A. BASSO. 1985. Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271.La variation geographique a ete etudiee chez sept populations de Trimerotropis pallidipennis du sud de 1' Argentine, qui sont polymorphes relativement a la position du centromkre. Des analyses statistiques a une ou plusieurs variables ont ete utilisees pour determiner les relations entre populations, en considerant la frequence d'inversions, la frequence de chiasmata et la distance des populations par rappot aux Andes, qui sont considkrees comme le sentier de migration hypothetique de cette espkce typiquement nord-americaine vers les latitudes du sud. Une analyse de groupes a mis en evidence une forte differenciation chromosomique entre les populations presque monomorphes des Andes "precordillkres" et les populations hautement polymorphes localisees plus a l'est. Cette analyse a aussi demontre que la ressemblance des chromosomes pouvait Ztre predite par proximitk gkographique. Ce mode de variation chromosomique n'a en aucune fason kt6 relik aux donnkes Ccologiques. Toutefois, l'absence de relations claires entre les regions phytogeographiques ou les caracteristiques clima...

Three species of Cassidines were cytologically studied. Chelymorpha indigesta and C. variabilis, with 10II + Xyp, have a relatively primitive Coleopteran karyotype and the sex chromosomes form a parachute-like bivalent. Botanochara angulata, belonging to the same tribe, Stolaini, presents an exceptional karyotype with a very high chromosome number (2n = 51 ♀) and multiple sex chromosomes XpneoXneoYp. This system has derived from the Xyp by a yp-to-autosome translocation.

This work includes the cytological studies of three species of Heilipodus (Coleoptera, Curculionidae, Molytinae, Hylobiini) that live on plants of the genus Eryngium (Umbelliferae). The three have the same chromosome number (2n = 30), but differ in the morphology of their autosomes and in their sex chromosomes.All specimens of Heilipodus erythropus (Klug) showed a typical parachute-like sex bivalent, some individuals of Heilipodus sp. possessed either a simple Xyp or a sex multivalent involving a telocentric autosomal pair and the parachute bivalent. Finally, Heilipodus scabripennis (Klug) has multiple sex chromosomes neoXpneoXneoYyp.

Chromosome numbers, meiosis and sex-determining mechanisms of three species of Chrysomelidae (Coleoptera) were studied. They belong to the tribe Stolaini of Neotropical Cassidinae. Stolas lacordairei and Botanochara sp. have high chromosome numbers (2n = 30~), the first with a primitive coleopteran sex chromosome system Xyt, and the other with a very complex one XlpXfineoXneo Y. Botanochara bonariensis shows an even higher chromosome riumber (2n = 44~) and multiple sex chromosomes as does B. sp. The possible tendencies in the karyological evolution of the Stolaine Cassidines are discussed.