José Vicente Hernández

Chemical ecology of the palm weevil Rhynchophorus palmarum (L.) (Coleoptera: Curculionidae): attraction to host plants and to a male-produced aggregation pheromone.

Attraction to host plants by adultRhynchophorus palmarum (L.) palm weevils was studied in the field and in the laboratory. Chemical analysis revealed the presence of ethanol and ethyl-acetate in stems of coco palms and in pineapple fruits and of pentane, hexanal, and isopentanol in coco stems. In the olfactometer, the first two compounds and isoamyl-acetate were attractive to the insects and the last three compounds, although not attractive by themselves, increased attractiveness when mixed with the first two compounds. Mixtures of these compounds, in proportions similar to the one occurring in attractive plant tissue, were as attractive as natural coconut tissue. In the field, the chemical compounds, either presented alone or as a mixture, did not attract the weevil. Males produce an aggregation pheromone when smelling ethyl-acetate. Rhynchophorol, 2(E)-6-methyl-2-hepten-4-ol, the known active component of the aggregation pheromone, attracts weevils in the olfactometer and in the field only if plant tissue, ethyl-acetate, or the above-mentioned odor mix are present. We propose that a complex mix of ethanol, ethyl-acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered. Rhynchophorol can be considered to be a Synergist, having an anemotactic action at a distance. We recommend the use of retention traps baited with rhynchophorol, ethyl-acetate, and sugar cane as an alternative control method for the pest.

Nestmate recognition signals of the leaf-cutting ant Atta laevigata

Behavioral tests with field colonies of Atta laevigata were performed in order to identify the source of the odors used in nestmate recognition. We tested the postpharyngeal (PPG) and mandibular glands (MG) as putative organs producing chemical signals for nestmate recognition. Chemical analyses of PPG were also undertaken. With a series of bioassays, we confirmed that nestmate recognition is based on cephalic odors and that these odors come mainly from the mandibular gland secretion. We show chemical evidence that odors from MG are dispersed all over the cuticle. Although odors from PPG elicited colony-specific behavioral responses, the types of behaviors they elicited differed from those of nestmate recognition of whole ants or MG extracts. PPG secretion was characterized by long-chain alkanes and methyl branched alkanes of low volatility, whereas MG contained volatile ketones and alcohols.

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.

EXTERNAL MORPHOLOGY OF ABDOMINAL SETAE FROM MALE AND FEMALE HYLESIA METABUS ADULTS (LEPIDOPTERA: SATURNIIDAE) AND THEIR FUNCTION

Abstract Hylesia metabus is a species of moth, distributed principally in northeastern Venezuela. Female moths use their abdominal setae to cover their egg masses. Contact with these setae can cause a severe dermatitis in humans. Setae from males do not produce these symptoms. The external morphology of the abdominal setae in male and female moths was described and the effect of the setae on ant behavior was studied. We classified the setae into four types, S1, S2, S3 and S4. In females, two of these types were found in the dorsal region; S1 and S2 show a porous structure and measure 2000 μm and 155 μm in length, respectively. In the ventral part of the abdomen we observed three setae types, S1, S3 which are 190 μm long and have small barbs along their length directed towards the apex, and S4 which have numerous barbs at the base, but further up flatten out, with barbs along both sides, before tapering off at the apex. S4 also were found in the lateral zones of the abdomen and were the predominant type of setae covering the egg masses. Only S1 setae were found in males. Egg masses not covered by setae were examined and transported by Pheidole ants, whereas covered eggs were largely avoided. The morphology of the S3 and S4 setae types suggests that these may be related to the urticating properties reported for the moth. Ant avoidance of setae covered eggs suggests that these protect the eggs from at least some predators.

Growth of Atta laevigata (Hymenoptera: Formicidae) Nests In Pine Plantations

We evaluated the survival, mortality and colony growth over time after worker emergence in colonies of Atta laevigata (Fr. Smith) ants in young pine tree plantations of Pinus caribaea (Mor) located in Estado Monagas, Venezuela. One hundred forty-four colonies were inspected during a 41-month period. Colony mortality one month after worker emergence was 45%. A small mortality peak was evidenced when colonies were 24 months old, coinciding with a dry season. About 23% of the colonies marked survived more than 3 years. During the first two years, colony growth was faster than during the next two years, as measured by the total number of nest entrances and the nest surface area. Multiple regression analyses showed a closer correlation between nest age and nest area than between nest age and number of nest entrances. Most of the nests grew in an eccentric way with respect to the site where the queen first established the nest. These results allow for a more rational pest management of pine plantations by using the knowledge on nest growth for decisions on pest control.

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.

Larvae-pupae parasitoids of Hylesia metabus Cramer (Lepidoptera: Saturniidae) in northeastern Venezuela: a case of natural biological control

The moth Hylesia metabus Cramer is considered a public health pest due to the release of urticating hairs by adult females during periodic invasions of towns and villages, producing dermatits in humans. We reported natural parasitism levels for this moth during six life cycles in two localities in northeastern Venezuela. Pupae were collected in the field and maintained under laboratory conditions (27 masculineC, 65% RH, 12L:12D photoperiod) until eclosion. In Mapire, parasitism increased from 33.0% to 91.1% in the three cycles studied, with the dipterans Belvosia spp. (Tachinidae) and Sarcodexia lambens Wiedemann (Sarcophagidae) and species from Ichneumonidae, Chalcidae, Perilampidae and Eulophidae being the most common. In Pedernales, parasitism decreased from 29.5% to 16.1%, and Belvosia spp. was the most abundant parasitoids, reaching parasitization levels between 70.7% and 96.2%. A significative parasitization by Neotheronia sp. (Hymenoptera: Ichneumonidae) (27.1%) occurred only in third life cycle. All natural enemies observed were koinobionts, larval-pupa parasitoids. The variations in the populations of H. metabus and its parasitoids in the areas studied are discussed. Belvosia spp. and S. lambens may have potential for use in integrated management program of H. metabus.