Aivlé Cabrera

Organic geochemistry of seasonally flooded rain forest soils : molecular composition and early diagenesis of lipid components

Ten soil samples from the Orinoco River Basin, Venezuela, were studied in order to characterize the molecular distribution of lipids and to determine early diagenetic degradation processes in these environments. The sample set contained six soil samples that were collected directly adjacent to large tropical rivers, and that were, therefore, subject to seasonal flooding. Molecular evidence for the formation of anaerobic microenvironments in these soils during the flooding period was obtained; this was based on the presence of several ring-A-degraded higher plant triterpenoids, products of the anaerobic degradation of 3-oxy-triterpenoids. The molecular distribution of other lipid classes such as n-alkanes, n-alkanols, fatty acids and sterols are also reported here and compared to the organic matter of rivers from the Orinoco Basin.

Mandibular Gland Secretion in Different Castes of the Leaf-Cutter Ant Atta laevigata

Gas chromatography analyses and behavioral assays showed that Atta laevigata, a highly polymorphic ant species, has a mandibular gland secretion that varies with castes. All castes contain 4-methyl-3-heptanone as the main component and its concentration is proportional to head size. Small workers and soldiers, but not medium size workers, also contain 4-methyl-3-heptanol. Queens show variations in their chemical composition after mating, as virgin males contain a secretion dominated by 4-methyl-3-heptanol, and, in a lesser proportion, 4-methyl-3-heptanone. In mated males these proportions are inverted. The compounds 4-methyl-6-hepten-3-one, 4-methyl-4-hepten-3-one, 6-methyl-tetradecene, and 2,6-dimethyl-2-dodecene are found only in queens. The behavioral response elicited by the secretion is mainly alarm, which is elicited more strongly by glands of larger workers. The results suggest that chemical castes, behavioral castes, and morphological castes overlap in this species.

Mate selection in the moth Neoleucinodes elegantalis: evidence for a supernormal chemical stimulus in sexual attraction

We studied mate selection mechanisms in the tomato fruit borer moth Neoleucinodes elegantalis, and we found that males and females tended to mate monogamously. Males chose a female according to the blend of her sex pheromone, and they preferred heavier females for mating. Females that produced the preferred blend of the sex pheromone were heavier and had larger wings. Heavier males were more likely to initiate flight sooner and to be the first to copulate with the female. These results suggest that females compete for faster-responding males by producing an attractive blend of sex pheromone, and that males compete for females that synthesize the more attractive sex pheromone blend by responding to the calling female faster. We propose that the pheromone blend preferred by males constitutes a signal reflecting the genetic and physiological quality of the female that is difficult to achieve for biosynthetic reasons. We found that a synthetic ‘supernormal’ pheromone blend was more effective in attracting males than was the pheromone produced by calling females, thus providing a useful means of mass trapping of males (e.g. to control infestations in tomato plantations). The results support theoretical predictions that mate selection behaviour in both sexes regulates most sexual encounters, even those modulated by sex pheromones.

On insect attractants from pitcher plants of the genusHeliamphora (sarraceniaceae).

Examination ofHeliamphora heterodoxa andH. tatei from the Guayana Highlands of Venezuela reveals that the enol diacetal monoterpene, sarracenin, is the major volatile compound present in the spoon-shaped structures of leaves of the pitchers. In addition, erucamide, phenol, cinerone, phenylacetaldehyde, and a series of methyl esters also occur in extracts of the spoon-shaped appendages of pitchers at the time during which they attract insects.

Leaf-cutter ant species (Hymenoptera: Atta) differ in the types of cues used to differentiate between self and others

Nestmate recognition among most social insects is thought to be mediated by cuticular hydrocarbons. We found that among two closely related ant species, the chemical cues used for recognition vary between them and that they are not cuticular hydrocarbons. Experiments with free-living colonies of Atta laevigata and Atta cephalotes using live and dead dummies, some impregnated with glandular extracts, allowed us to reconstruct the cues by which A. laevigata differentiates itself from A. cephalotes workers. The results suggest that the same odour cues (chemicals from the alarm pheromones and from abdominal exocrine secretions) are used for both inter- and intraspecific recognition systems, achieving discrimination of self (i.e. a nestmate) from others, and that both species differ in the chemical nature of the odour cues used for recognition. Our results suggest that recognition mechanisms vary among ants, and may thus vary among other social insects, and are shaped by various evolutionary forces in addition to kin selection.

Secretory mechanisms for the male produced aggregation pheromone of the palm weevil Rhynchophorus palmarum L. (Coleoptera: Curculionidae)

Abstract Histological and chemical analyses of different corporal segments of the palm weevil Rhynchophorus palmarum , revealed the presence of two symmetrical glands (modified salivary glands) in the prothorax of males, but absent in females. Using gas chromatography and mass sepectrometry, we demonstrated the presence of rhynchophorol (aggregation pheromone) in extracts of this gland, as well as in the rostrum and digestive tract (rectum) of males. Olfactometric experiments showed that the release of the aggregation pheromone starts approximately 10 min after the insect detects ethyl-acetate and continues for several hours. The pheromone is secreted through the feces and more concentrated through the mouth to a depression on the dorsal part of the rostrum where, via hairs and the surface tension of the secretion, it collects in a complex structure consisting of various types of hairs, which help disperse the pheromone.

Seasonal sebaceous patch in the nectar-feeding bats Leptonycteris curasoae and L. yerbabuenae (Phyllostomidae: Glossophaginae): phenological, histological, and preliminary chemical characterization.

Many species of bats secrete a wide variety of substances, frequently associated with olfactory communication. We characterized a seasonal phenomenon of dorsal sebaceous secretion in the Curaçaoan long-nosed bat, Leptonycteris curasoae, in Venezuela, and the lesser long-nosed bat, Leptonycteris yerbabuenae, in Mexico. The phenology of the sebaceous patch was determined, a histological analysis of the affected area was conducted using specimens of L. curasoae from Venezuela, and finally, a preliminary chemical characterization of the substance secreted was performed combining histochemical techniques with gas chromatography and mass spectrometry analyses. The sebaceous patch was detected exclusively in male adult specimens. Individuals presenting it had a variable area of fur covered with a fatty and odoriferous substance at the level of the interscapular zone. Occurrence of the sebaceous patch was cyclical and coincided with the mating season in Venezuela and Mexico. The following histological changes associated with occurrence of the patch were observed: increase of epidermis thickness and decrease of dermis and hypodermis thicknesses, increase in density of sebaceous glands, increase of percentage of skin covered by sebaceous glands, increase of size of sebaceous glands previous to secretion followed, and increase of the sebum volume within sebaceous glands previous to secretion. Several compounds tentatively identified as fatty acids, cholestanes and cholesterol were present in the sebaceous secretion. Based on the evidence obtained, we hypothesize that the sebaceous patch could be involved in olfactory communication, possibly related to mating behavior in these bats.

Organic biogeochemistry of a hypereutrophic tropical, freshwater lake — Part 1: particle associated and dissolved lipids

Lipid components in both the dissolved and particle associated phases were analyzed in several samples taken at different depths in the water column of a hypereutrophic, tropical, freshwater lake (Lake Valencia, Venezuela). Quantitatively and qualitatively, the lipid fraction was found to vary with depth. Early diagenetic changes were clearly observed for several lipid classes in both stratified and mixed water conditions. The origin of the organic matter was primarily autochthonous (planktonic and bacterial). The dissolved lipid fraction was found to contribute a significant percentage of the total lipids in the lake. High primary productivity of specific species of phytoplanktonic organisms in the lake water resulted in an abundance of some lipid classes which are usually assigned a terrestrial (allochthonous) origin, but in this case seem to be microbially derived.

Organic compounds and heavy metals in the atmosphere of the city of Caracas, Venezuela — I: Atmospheric particles

Aliphatic and aromatic hydrocarbons, fatty acids and heavy metals (Pb, Cu, Ni, Zn, Fe and Cd) were analyzed in atmospheric particulate matter in the city of Caracas, Venezuela. Samples were taken from 6 stations within the metropolitan area of Caracas, characterized as industrial (one), urban (two), suburban (two) and rural (one). In addition, the concentration and composition of the organic compounds was monitored over a 5 month period at an urban site to determine seasonal and temporal variabilities.In general terms, the concentrations of pollutants decreased from industrial and urban sites to suburban to rural. A similar trend was observed for preliminary toxicity tests carried out on the particulate extracts. The concentration levels of most of the pollutants were high for the industrial and urban sites, and comparable with those of other major cities worldwide.

OLFACTORY BEHAVIOR AND ELECTROANTENNOGRAPHIC RESPONSES OF THE COCOA BEETLE, STEIRASTOMA BREVE (COLEOPTERA: CERAMBYCIDAE)

Abstract With the aim of studying the olfactory behavior of one of the main pests in neotropical cocoa plantations, the cocoa beetle Steirastoma breve (Sulzer) (Coleoptera: Cerambycidae), we studied behavioral and antennal responses towards different odor sources in a two-choice olfactometer and an electroantennographic system, respectively. Odor sources tested as stimuli in olfactometric experiments were chopped pieces of cocoa branches, adult males, adult females of S. breve, and combinations of these. Extracts of female and male body parts in n-hexane were tested in electroantennnographic experiments. Statistically significant attraction responses in the olfactometer were observed only when S. breve individuals were stimulated with odors from pieces of cocoa branches. Both sexes showed active EAG responses to odors of cocoa branches, and females showed active EAG responses to adult male odors. These results suggest that olfactory behavior of S. breve is mediated by volatiles derived from cocoa trees and from adult male insects.