Field studies in Ontario, Oregon, and California on interspecific attraction and inhibition among the coniferophagous species of Choristoneura (the spruce budworm and its allies) confirmed specific pheromonal differences among the species. Of the three species that are mutually attractive and whose males are attracted by blends of trans- and cis-11-tetradecenal, C. fumiferana, C. biennis, and C. occidentalis, catches of C. fumiferana males in traps baited with C. fumiferana females were significantly reduced by the presence of females from a second group in which it is believed the females produce trans-11-tetradecenyl acetate. Catches of C. occidentalis males by C. occidentalis females were not affected in this way. F1 hybrids and backcrosses between an aldehyde-producing species and an acetate-producing species produced females that were attractive to males of one or other of the parent species, although some females were not attractive to either. Individual females never attracted males of both parent species, and of those that were attractive, more were attractive to males of the aldehyde species than to males of the acetate species. The results suggest sex-controlled inheritance and expression.

Three classes of sex chromatin (SC) distribution have been encountered in a sample of Canadian Lepidoptera. In 78 of the 103 species examined, females were SC positive and males were SC negative. In another 24 species, females and males were SC negative. Females and males of a single species, Eucordylea resinosae, had two equal-sized SC bodies in interphase nuclei. In no species were females found to be SC negative and males SC positive. Usually presence of SC indicates an XX male and XY female sex determining mechanism, and its absence, XX male; XO female, but the exceptional occurrence of SC in females and males of a species suggests the need for caution in too universal an application of this interpretation. Chromosome numbers have also been determined for 53 of the 103 species. Male haploid numbers ranged from 11 to 61, but 30 was most frequently encountered.

Chromosome number and morphology have been examined in four established cell lines (Md63, Md66, Md108, and Md109) of the forest tent caterpillar, Malacosoma disstria Hübner, and one (Cf124) of the spruce budworm, Choristoneura fumiferana (Clemens). Chromosome number distributions of Md63 (mode = 112) Md108 (mode = 103), Md109 (mode= 103), and Cf124 (mode = 110) overlap sufficiently to prevent identification of individual lines by number alone. However, Md66 is exceptional in possessing a modal number of 157. One large chromosome occurs in cells of all lines. The presence of this chromosome, the lack of any distinct polyploid series among chromosome numbers encountered, and the general inverse relationship between number and size of chromosomes, suggest that the high level of heteroploidy characteristic of these and other lepidopteran cell lines reflects not only a possible polyploid origin but also extensive chromosomal rearrangement and fragmentation. Tolerance for such change is attributed to the holokinetic organisation of lepidopteran chromosomes. A distinct heteropycnotic body is present in about 10% of Cf124 cell nuclei, and can be used as a marker for this line. This body may represent the sex chromatin normally encountered in somatic cells of female C. fumiferana.

Chromosomes of six species of Chilocorus have been examined for their reaction to Quinacrine (Q), and to Giemsa (G) after a variety of 'Denaturation-Renaturation' schedules and digestion with trypsin. Four types of chromatin can be distinguished with these techniques: 1, moderately stained with both Q and G; 2, brightly stained with Q and darkly stained with G; 3, unstained with Q but darkly stained with G; 4, unstained with Q but moderately stained with G. The last three of these types are restricted in chromosomally monomorphic species to the pericentric heterochromatin, but are variably distributed in the heterochromatic arms of C. stigma. Euchromatin per se does not react differentially. The relationship between karyotype stability and uniformity of banding patterns is discussed.

The male meiotic karyotypic formula of Conophthorus coniperda (Schwarz) (Coleoptera: Scolytidae) is 9AA + XY. This karyotype differs from C. resinosae Hopkins and C. banksianae McPherson, both of which have the karyotypic formula of 8AA + XY. Supernumerary chromosomes were found in different populations of C. resinosae and C. banksianae but were absent in C. coniperda. No geographic variation in the karyotypes of the three species was observed. The karyotypic formulae confirm the designations of C. coniperda and C. resinosae by morphological characters, but do not support the designation of C. banksianae as a distinct species.