Male sterility in Heliothis virescens x H. subflexa backcross hybrids: Evidence for abnormal mitochondrial transcripts in testes

The genetic architecture of a complex ecological trait: host plant use in the specialist moth, Heliothis subflexa

We used genetic mapping to examine the genetic architecture of differences in host plant use between two species of noctuid moths, Heliothis subflexa, a specialist on Physalis spp., and its close relative, the broad generalist H. virescens. We introgressed H. subflexa chromosomes into the H. virescens background and analyzed 1462 backcross insects. The effects of H. subflexa-origin chromosomes were small when measured as the percent variation explained in backcross populations (0.2-5%), but were larger when considered in relation to the interspecific difference explained (1.5-165%). Most significant chromosomes had effects on more than one trait, and their effects varied between years, sexes, and genetic backgrounds. Different chromosomes could produce similar phenotypes, suggesting that the same trait might be controlled by different chromosomes in different backcross populations. It appears that many loci of small effect contribute to the use of Physalis by H. subflexa. We hypothesize that behavioral changes may have paved the way for physiological adaptation to Physalis by the generalist ancestor of H. subflexa and H. virescens.

Hybridization between Helicoverpa armigera and Helicoverpa assulta (Lepidoptera: Noctuidae): development and morphological characterization of F1 hybrids

Reciprocal hybridizations between Helicoverpa armigera (Hübner) and Helicoverpa assulta (Guenée) were studied. The cross between females of H. armigera and males of H. assulta yielded only fertile males and sterile individuals lacking an aedeagus, valva or ostium bursae. A total of 492 larvae of the F1 generation were obtained and 374 of these completed larval development and pupated. Only 203 pupae were morphologically normal males, the remaining 171 pupae were malformed. Larvae and pupae that gave rise to morphologically abnormal adults exhibited longer development times. Sterility was not only associated with malformed external sex organs, but also a range of abnormalities of the internal reproductive system: (i) loss of internal reproductive organs, (ii) with one to three copies of an undeveloped bursa copulatrix; or (iii) with one or two undeveloped testes. Normal male hybrid adults showed higher flight activity in comparison with males of both species. In contrast, the cross between females of H. assulta and males of H. armigera yielded morphologically normal offspring (80 males and 83 females). The interaction of the Z-chromosome from H. assulta with autosomes from H. armigera might result in morphological abnormalities found in hybrids and backcrosses, and maternal-zygotic incompatibilities might contribute to sex bias attributed to hybrid inviability.

Identification and characterization of a testis-specific isoform of a chaperonin in a moth, Heliothis virescens

Two relatively abundant proteins having subunit molecular weights of 60,000 and 63,000 (p60 and p63, respectively) have been purified as a 16 to 18S complex from sperm mitochondria of a moth. Heliothis virescens. Although the function of these proteins had heretofore not been established, interest in the p63 polypeptide stemmed from its sperm-specific expression and its striking occurrence as a net charge variant among several insect species surveyed, using two-dimensional gel electrophoresis. Genomic and cDNA clones corresponding to the p63 protein have now been isolated and their sequencing has revealed extensive amino acid sequence identity with both the Escherichia coli GroEL protein and its eukaryotic homologues, the chaperonins. Immunoblot studies with a Tetrahymena chaperonin antiserum demonstrated that the p60 protein, which is expressed in all cell types, is structurally related to p63 and is itself a chaperonin subunit. While the chaperonin complex from Heliothis sperm shares certain properties with GroEL, including the ability to hydrolyze ATP and organization of its subunits into a seven-member ring, electron microscopic analysis revealed that its higher-order structure differed from GroEL (and other lower eukaryotic chaperonins) in that the native particle comprises one such ring rather than a doublet. It is not yet known whether the two chaperonin isoforms coexpressed in moth sperm assemble separately or give rise to hybrid particles. In either case, the existence of multiple chaperonin subunits in sperm leaves open the possibility that some aspect of mitochondrial biogenesis that is dependent upon the activity of these proteins is qualitatively or quantitatively different in this cell type.

Evidence from mitochondrial DNA that African honey bees spread as continuous maternal lineages

African honey bees have populated much of South and Central America and will soon enter the United States. The mechanism by which they have spread is controversial. Africanization may be largely the result of paternal gene flow into extant European populations or, alternatively, of maternal migration of feral swarms that have maintained an African genetic integrity. We have been using both mitochondrial and nuclear DNA restriction fragment length polymorphisms to follow the population dynamics between European and African bees. In earlier reports, we suggested that if African honey bees had distinctive mitochondrial (mt) DNA, then it could potentially distinguish the relative contributions of swarming and mating to the Africanization process. Because mtDNA is maternally inherited, it would not be transmitted by mating drones and only transported by queens accompanying swarms. Furthermore, the presence of African mtDNA would reflect unbroken maternal lineages from the original bees introduced from Africa. The value of mtDNA for population studies in general has been reviewed recently. Here we report that 19 feral swarms, randomly caught in Mexico, all carried African mtDNA. Thus, the migrating force of the African honey bee in the American tropics consists of continuous African maternal lineages spreading as swarms. The mating of African drones to European queens seems to contribute little to African bee migration.