Ramón Cisneros

Ultrastructural study of the midgut and hindgut in eight species of the genus Dendroctonus Erichson (Coleoptera: Scolytidae)

Abstract Chemical communication mediated by pheromones is a crucial aspect in the life cycle of beetles in the genus Dendroctonus. This communication plays an important role in mate location and in the colonization of host conifers. The study of the alimentary canal of these species is of importance not only because this organ is involved in the processes of digestion, detoxification, nutrient absorption, and transport, but also in the production of semiochemical compounds, such as pheromones. To better understand these functions and where they occur, the ultrastructural differences between the anterior and posterior midgut and the hindgut and their different cellular types were characterized. Adult specimens of both sexes from eight species were dissected and the alimentary canal was removed. It was sectioned into three parts: anterior midgut, posterior midgut, and hindgut, and analyzed by transmission electron microscopy. Results show that the epithelial tissue of the midgut possesses ultrastructural characteristics that permit differentiation of the anterior and posterior midgut. There are no ultrastructural differences within sexes of the same species, but differences exist among species. The ultrastructural characteristics of the hindgut do not differ between sexes or among species, but they do differ from those of the midgut.

Comparative Anatomical and Histological Study of the Alimentary Canal of the Dendroctonus frontalis (Coleoptera: Scolytidae) Complex

Abstract In this study we compared the anatomy and histology of the alimentary canal of Dentroctonus approximatus Dietz, D. mexicanus Hopkins, D. frontalis Zimmermann, and D. brevicomis LeConte. The results show that these species share similar characteristics, and their structural pattern is comparable to that observed in other Dendroctonus species. These 4 species have characteristics not found in other bark beetle genera in the esophagus, crop, proventriculus, and hindgut. The close relationship of the Malpighian tubules to posterior foregut, anterior midgut, and distal hindgut is also different. Additionally, the midgut of the D. frontalis complex species shows a great cellular diversity, which suggests that this region may be involved in pheromone production.

Anatomical and Histological Comparison of the Alimentary Canal of Dendroctonus micans, D. ponderosae, D. pseudotsugae pseudotsugae, D. rufipennis, and D. terebrans (Coleoptera: Scolytidae)

Abstract The anatomy and histology of the alimentary canal of Dendroctonus micans (Kugelann), Dendroctonus ponderosae Hopkins, Dendroctonus pseudotsugae pseudotsugae Hopkins, Dendroctonus rufipennis (Kirby), and D. terebrans (Olivier) were described and compared. Characteristics in the structural organization of the alimentary canal in these species are comparable with those in previously studied Dendroctonus species. However, important histological differences not found in other scolytids were observed in the esophagus, crop, proventriculus, midgut, and hindgut of these species. Particularly, spines in the esophagus and crop, chitinous plates in the proventriculus, great cellular diversity in the midgut, and fine spines located in the cuticle surrounding the hindgut valve in the anterior hindgut are unique characteristics of Dendroctonus species. In the species studied, the ratio of foregut, midgut, and hindgut in relation to the total length of the alimentary canal varied slightly. This ratio did not show a relationship with insect size. Differences among the diameters of each gut region were statistically significant (P < 0.05), and the largest diameters did not necessarily appear in the largest species.

Karyology, Geographic Distribution, and Origin of the Genus Dendroctonus Erichson (Coleoptera: Scolytidae)

Abstract Several revisions of the taxonomy of the scolytid genus Dendroctonus have been reported during the last century. These have been based on the external morphology and biology of adults, karyology, and most recently molecular genetics. Using karyological data—chromosomal number and mechanism of sex determination—from 119 Dendroctonus populations representing 16 of the 19 species currently recognized, we determined rate of chromosomal evolution and evolutionary phases of this genus. The karyological formulae vary from 5 AA + neo-XY (2n = 12) to 14 AA + Xyp (2n = 30). The modal number of chromosomes is 2n = 30, with a mean 2n value of 23.37 and coefficient of variation of 31.67%. These values indicate that Dendroctonus has a high rate of chromosomal diversity and that its evolutionary phase is of regression. Theoretically, the genus should be composed of specialist species with relatively low chromosomal numbers; however, this is not the case. We also used chromosomal evidence to examine the suspected Mexican origin for Dendroctonus. We posed two hypotheses to explain the karyological diversification and current distribution of Dendroctonus species. The first considered that diversification of the karyotype originated from species with 14 AA + Xyp during its dispersion southward with its hosts (Pinus spp.) in North America. The second assumed that karyological diversification of Dendroctonus occurred during the dispersion of the genus toward Eurasia and southward in North America and that the increases and decreases in number of chromosomes originated from an ancestral karyotype between 18 and 22 chromosomes. Evidence for each hypothesis is discussed.

Genetic Structure of Dendroctonus mexicanus (Coleoptera: Curculionidae: Scolytinae) in the Trans-Mexican Volcanic Belt

Abstract It is assumed that geographic isolation of Dendroctonus Erichson species populations or their plant hosts determines genetic structure. This structure can be analyzed with respect to the biogeographic pattern that describes the species in a region. The Trans-Mexican Volcanic Belt (TMVB) is located between the Neartic and Neotropical regions and is a center of diversification and endemism of trees in the genus Pinus L. Dendroctonus mexicanus Hopkins is polyphagous within Pinus species and has a continuous geographic distribution across the TMVB. We explored whether the population genetic structure of D. mexicanus is reflective of the distribution pattern of the Dendroctonus species that occur in the TMVB. Twelve gene loci were analyzed by isozyme electrophoresis in 17 populations found on pines from the Leiophyllae subsection. Allele frequencies, average heterozygosity, heterozygosity by locus, deviations from Hardy–Weinberg equilibrium (HWE), F-statistics among populations, and average genetic flow were calculated. Genetic structure was determined using the relationship between FST versus geographic distances among populations. Genetic relations among populations were established by neighbor-joining and principal components analysis by using Nei’s genetic distances. Dendrogram reliability was assessed by bootstrap analysis and cophenetic correlation coefficient by using the Mantel test. Results show that heterozygosity of D. mexicanus is similar to other scolytids. A high proportion of loci were out of HWE by homozygous excess, which may be explained by multiple factors. The scarce number of fixed alleles, the allele variation pattern, pairwise genetic distances, and F-statistics suggest a model of isolation by distance for D. mexicanus in the TMVB resulting from recent dispersal events.

Midgut Cell Culture from Larvae of Dendroctonus valens (Coleoptera: Scolytidae)

Abstract Isolated cellular nidi stem cells from the anterior and posterior midgut of larvae of the red turpentine beetle, Dendroctonus valens LeConte, proliferate and differentiate in vitro when cultured in RPMI 1640 medium, in the presence of 20-hydroxyecdysone, fat body extract from Zophobas morio (Blanchard) (Coleoptera: Tenebrionidae) pupae, and conditioned medium. Our data suggest that the stem cells did not increase exponentially as in typical cultures. However, the early presence of stem cells in larval cultures indicates that the proliferation process is higher than in cultures from adult D. valens. After 2 wk in culture, up to 10% of cells were observed in various stages of differentiation. The mean duration of midgut cultures was 82 d.