Cuticular hydrocarbons of the paper wasp,Polistes fuscatus: A search for recognition pheromones

The cuticular chemicals of 124 individual wasps (foundresses and workers) from 23 colonies ofPolistes fuscatus were analyzed. The compounds identified, all of which were hydrocarbons, were similar to those of other vespid wasps in that the bulk of the hydrocarbons were 23–33 carbons in chain length. However, the hydrocarbon profile ofP. fuscatus differed from those of its congeners in its proportions of straight-chain alkanes, methylalkanes, and alkenes. Three of the 20 identified hydrocarbons, 13- and 15-MeC₃₁, 11,15- and 13,17-diMeC₃₁, and 13-, 15-, and 17-MeC₃₃, had properties postulated for recognition pheromones: colony specificity, efficacy in assigning wasps to the appropriate colony, heritability, lack of differences between foundresses and workers, and distinctive stereochemistry.     

Reevaluation of the Role of Mandibular Glands in Regulation of Reproduction in Bumblebee Colonies

Possible pheromonal control of worker reproduction was tested in Bombus terrestris. The mode of assay included exposure of callow workers to extracts originating from different queen parts and measuring the effect on the in vitro biosynthesis of juvenile hormone (JH), the apparent gonadotropin in this species. Both queen total body extracts applied to dummies consisting of oven-dried or Soxhlet-washed virgin queen bodies and cuticular washes applied to living virgin queens effectively inhibited the biosynthesis of JH in callow workers. None of the five exocrine glands (mandibular, hypopharyngeal, salivary, Dufour's, and tarsal) demonstrated inhibitory activity. Likewise, the use of synthetic 3-hydroxy acids, found in queen mandibular glands, were ineffective in blocking JH biosynthesis in queenless workers. The results suggest that the queen may use a primer pheromone spread on the epicuticle as a means to inhibit worker reproduction. However, our results are not consistent with the prevailing hypothesis that in B. terrestris the main source of the pheromone that inhibits worker reproduction is in the queen's mandibular glands.     

Cuticular Hydrocarbons of Polistes dominulus as a Biogeographic Tool: A Study of Populations from the Tuscan Archipelago and Surrounding Areas

In social insects, the types and proportions of epicuticular lipids may exhibit significant diversity as a result of factors such as age, sex, caste, rank, nest, and relatedness. It is known that these variations can be used by social insects to acquire information regarding conspecific individuals. Recent findings have shown that different populations of Polistes dominulus (Christ.) have distinctly different chemical cuticular profiles, and that wasps are able to recognize individuals of their own population. In this study, we showed that cuticular hydrocarbon patterns of Polistes dominulus are consistent with similarities among northern Tyrrhenian islands, as reported in previous biogeographic studies. Indeed, our findings indicate that cuticular hydrocarbon mixtures of P. dominulus from Capraia and Corsica are grouped together by cluster analysis, while those from Elba and Giglio cluster with cuticular profiles of the mainland wasps (Venturina).     

The Defensive Role of Volatile Emission and Extrafloral Nectar Secretion for Lima Bean in Nature

Lima bean (Phaseolus lunatus) features two indirect anti-herbivore defenses—emission of volatile organic compounds (VOCs) and secretion of extrafloral nectar (EFN)—which are both inducible upon herbivore damage. In a previous field study, Lima bean benefited from the simultaneous induction of the two defenses, yet it remained unclear whether both had contributed to plant protection. Our experimental approach aimed at studying the defensive role of both indirect defenses simultaneously. Tendrils were sprayed with jasmonic acid (JA) to induce both defenses, and performance was compared to that of others that were treated with a synthetic blend of either EFN or VOCs. Confirming earlier results, JA treatment and application of the VOC mixture induced EFN secretion in treated tendrils in quantitatively similar amounts. The composition of the applied synthetic blend of EFN was adjusted to match the concentration of EFN secreted from JA- and VOC-treated tendrils. Repeated application of either enhanced the performance of several fitness-relevant plant parameters such as growth rate and flower production. Tendrils treated with JA showed a similar trend, yet some fitness-related parameters responded less to this treatment. This suggests a minor importance of any putative JA-dependent direct defense traits or higher costs of JA-elicited responses as compared to VOCS and EFN, as otherwise JA-treated tendrils should have outperformed VOC- and EFN-treated tendrils. Moreover, the beneficial effect of applying synthetic EFN alone equaled or exceeded that of VOCs and JA. Ants were by far the dominant group among the arthropods that was attracted to JA-, VOC-, or EFN-treated tendrils. The results suggest that EFN plays a more important role as an indirect defense of lima bean than VOCs or any other JA-responsive trait. Electronic supplementary material The online version of this article doi: contains supplementary material, which is available to authorized users.     

Ant repellent effect of the sternal gland secretion ofPolistes dominulus (Christ) andP. sulcifer (Zimmermann). (Hymenoptera: Vespidae)

The long-chain carboxylic acids identified in the sternal gland secretion ofPolistes dominulus andP. sulcifer females were tested individually on three species of ants,Crematogaster scutellaris, Formica cunicularia, andLasius sp., in order to verify if they have a repellent effect. The unsaturated acids (palmitoleic, linoleic, and oleic) act as repellents of all three ant species, while the saturated acids (lauric, myristic, palmitic, and stearic) have no effect. The mixture reproducing the secretion of the sternal glands ofP. dominulus maintained its repellency for at least four days.     

Surface lipids of the social waspPolistes annularis (L.) and its nest and nest pedicel

Cuticular lipids were recovered fromPolistes annularis workers and characterized by combined gas-chromatography-mass spectrometry. These lipids were found to be straight-chain and methyl-branched hydrocarbons with the major components being 13,17-dimethylhentriacontane (18%), 3-methyl-nonacosane (13%), and 3-methylheptacosane (11%). Cuticular lipids with a very similar composition were found on the surface of the larvae, eggs, and adult males ofPolistes annularis as well as on the surface of the nest and nest pedicel of the wasp. Hexadecanoic acid and octadecenoic acid were also found on the surface of the nest pedicel and these acids and/or the hydrocarbons may play a defensive role for the wasps.     

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.     

Mandibular Gland Secretion of <Emphasis Type="Italic">Melipona beecheii</Emphasis>: Chemistry and Behavior

The mandibular gland secretion of Melipona beecheii contains a rich mixture of terpenoid and oxygenated compounds and unsaturated and saturated hydrocarbons. However, it differs markedly from the 11 other Brazilian species examined in previous studies, both by the absence of 2-heptanol and the presence of rose oxides. The most abundant compound was geranyl hexanoate, whereas the most volatile compounds were cis- and trans-rose oxide and geraniol. The complete blend and five individual components found in the gland secretion were tested by electroantennography (EAG) and behavioral assays. The complete mandibular gland extract and geraniol elicited the strongest EAG responses, whereas these and farnesyl acetate induced the strongest attack response from workers. The role of the rose oxides remains to be elucidated, as they do not appear to play a major role as an alarm pheromone of this species.     

The Role of Filippi’s Glands in the Silk Moths Cocoon Construction

Filippi’s glands (FGs), formerly also called Lyonet’s glands, are accessory secretory structures of the labial (silk) glands of lepidopteran caterpillars, which were implicated to play an important role in the maturation of the silk material and the construction of the cocoon. In our previous study, we have identified several species of giant silk moths that completely lack the FGs. Interestingly, the absence of FGs in these species correlates with the construction of a loose cocoon architecture. We investigated the functions of FGs by their surgical extirpation in the last instar larvae of the silkworm, Bombyx mori. We found that the absence of FGs altered the structure of the resulting cocoon, in which the different layers of silk were separated. In further experiments, we found no effects of the absence of FGs on larval cocoon formation behavior or on changes in cocoon mass or lipid content. Differential proteomic analysis revealed no significant contribution of structural proteins from FGs to silk cocoon material, but we identified several low abundance proteins that may play a role in posttranslational modifications of some silk proteins. Proteomic analysis also revealed a difference in phosphorylation of the N-terminal sequence of fibroin-heavy chain molecule. Thus, FGs appear to affect silk stickiness during spinning by regulating posttranslational modifications. This could also explain the link that exists between the absence of these glands and the formation of loose cocoons in some giant silk moth species.     

Chemical Composition of the Defensive Secretion of the Longhorned Beetle, <Emphasis Type="Italic">Chloridolum loochooanum</Emphasis>

Adults of the longhorned beetle, Chloridolum loochooanum Gressitt (Coleoptera: Cerambycidae) emit a white frothy secretion from their metasternal glands. This defensive substance contains cyclopentanoid monoterpenoids (iridodials), whose structures were elucidated by gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) analyses that compared the naturally occurring structures with synthesized versions. Optically active citronellals, [(S)-, (R)-, and (S)/(R)- mixture], were used as starting materials for synthesizing the corresponding iridodials for the determination of the absolute configuration of the natural product. The retention time of (2S)-iridodial, derived from (S)-citronellal, corresponded to that of C. loochooanum iridodial by enantioselective GC analysis. Thus, we suggest that the absolute configuration of C. loochooanum iridodial is (1R,2S,5S)-iridodial.     

Systemic Induction of Terpenoid Aldehydes in Cotton Pigment Glands by Feeding of Larval Spodoptera exigua

Pigment glands in cotton contain terpenoid aldehydes that are toxic and deterrent to feeding of several generalist lepidopteran insects. We hypothesized that previously observed systemically induced feeding deterrence may be associated with pigment glands. We conducted experiments to determine the dynamics and chemical nature of inducible feeding deterrents in leaves of cotton, Gossypium hirsutum L, to larvae of the beet armyworm, Spodoptera exigua. Production and/or filling of pigment glands was influenced by physiological age of Deltapine 90 cotton plants. In undamaged plants, successively formed leaves contained more pigment glands, up to the seventh or eighth true-leaf developmental stage. Feeding choice tests conducted one or seven days after initial feeding damage revealed that third instars of S. exigua consumed more of the two youngest leaves from control cotton plants than from plants whose two oldest leaves had been fed on previously for 24 hr by S. exigua. The preference for leaves from control plants was significant one day after initial damage and highly significant seven days after damage. Consumption of mature foliage (leaf immediately above initially damaged leaves) from control plants and damaged plants did not differ. More pigment glands were counted on the youngest leaf of damaged plants than on the youngest leaf of control plants one day after initial damage. HPLC analysis revealed greater amounts of hemigossypolone, heliocides 1 and 2 (H₁ and H₂), and total terpenoid aldehydes per gland in young foliage of damaged plants than control plants one day after initial injury. By seven days after initial injury, greater quantities of hemigossypolone and all heliocides except H₄ were detected in young foliage from damaged plants compared to control plants. Concentrations of H₁ per gland in young leaves from damaged plants increased the most of all terpenoid aldehydes measured (3.4× the amount found in leaves from control plants). Mature leaves from damaged plants did not contain more terpenoid aldehydes than mature leaves from control plants. We suggest that systemically induced feeding deterrence to S. exigua in young leaves of glanded cotton was due to increased amounts of terpenoid aldehydes in pigment glands.     

Mandibular gland secretions of the male beewolvesPhilanthus crabroniformis,P. barbatus,andP. pulcher (Hymenoptera: Sphecidae)

The composition of the territorial marking pheromones from mandibular glands of males of the beewolvesPhilanthus crabroniformis, P. barbatus, andP. pulcher have been determined. The structures of the components were elucidated by gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy. The major compound ofP. crabroniformis is isopropyl tetradecanoate, with somewhat lesser amounts of 2-tridecanone, 3-methyl-3-butenyl tetradecanoate, and 928 (Z)(E)-11-eicosen-1-ol. The major compounds ofP. barbatus are ethyl tetradecanoate and hexadecanal, which are present in approximately a 6040 ratio. These two compounds comprise over 95% of the neutral lipids. Also present in lesser amounts are ethyl dodecanoate, tetradecanal, hexadecan-1-ol, a ^x -octadecen-1-ol, and octadecan-1-ol. The major compounds ofP. pulcher are ethyl (Z)-7-hexadecenoate and geranylgeraniol acetate, which comprise nearly 90% of the neutral lipid fraction, with smaller amounts of tetradecanal, pentadecanal, and ethyl hexadecanoate; trace amounts of ^x hexadecenal, hexadecanal, and octadecanal are also present.     

Ultrastructural and chemical examination of paper and pedicel from laboratory and field nests of the social waspPolistes metricus say

The ultrastructure and chemical composition of paper and pedicel from nests ofPolistes metricus that were constructed in the laboratory from known building material were compared to paper and pedicel from nests constructed in the field. Scanning electron micrographs showed the addition of a gluelike secretion from the wasp to the construction material. Solid-state [¹³C]NMR, elemental analyses, and amino acid analyses indicate that this secretion is a silklike protein with serine, glycine, alanine, and proline comprising 65–73% of the identified residues.