Nerol: An alarm substance of the stingless bee,Trigona fulviventris (Hymenoptera: Apidae)

Bees of the genusTrigona and subgenusTrigona possess volatile materials in their mandibular glands, used as alarm substances and as marking pheromones. Heads of workers ofTrigona fulviventris were analyzed by gas chromatography-mass spectrometry. The two major volatile components were nerol ( 50%), and octyl caproate ( 20%). Relative to other substances tested at a Costa Rican nest, treatments containing 20 g of nerol attractedT. fulviventris, depressed numbers of bees leaving the nest by about 50%, and elicited wing vibration and biting. The responses were similar to those obtained with the contents of one worker head. Attraction and biting were also seen in response to captures of colony members by assassin bugs (Apiomerus pictipes) outside a nest entrance; one bee responded in about 15% of the captures. This alarm behavior, although weak, is of interest since it was thought thatT. fulviventris was unusual for its subgenus in its lack of nest defense behaviors.     

Intranidal worker reactions to volatile compounds identified from cephalic secretions in the stingless bee,Scaptotrigona postica (Hymenoptera,Meliponinae)

From pentane extracts of worker heads of the stingless bee (Scaptotrigona postica), 70 volatile compounds were identified by combined gas chromatographic-mass spectroscopic analyses. A bioassay was developed to evaluate intranidal reactions of workers to synthetic volatiles. Thirty-six of the cephalic volatiles were tested. Thirteen types of behavioral reactions were recorded in a semiquantitative manner. The test was run in the brood nest where mainly young nurse bees are present and also in the storage area of the nest with old foragers traffic. The results obtained were compared and discussed in order to understand the chemical communication system of this species. Especially in the dark interior of the nest, which in nature is found in hollow tree cavities, chemical messages obviously play a particularly important role in the communication systems of the bees.     

Host recognition and the study of a chemical basis for attraction by cuckoo bumble bees (Hymenoptera: Apidae)

Species ofPsithyrus (Hymenoptera; Apidae) are obligate bumble bee social parasites. In this study, females ofP. vestalis andP. ashtoni were presented with pentane extracts prepared from different body parts of queens of their respective host species,Bombus terrestris andB. terricola. Parasites of both species were capable of distinguishing host bees from other bumble bee species using chemical cues contained within extracts. Among extracts of several body parts presented to parasites, the abdomen produced the greatest behavioral response, with Dufour's gland and terminal tergal segments eliciting the greatest response among abdominal regions. Extracts of these two body parts obtained fromB. terrestris queens shared a number of compounds, identified by GC-MS. Among the identified compounds are a number that have been reported to be of importance in bee sociochemistry.     

Formic acid in caustic cephalic secretions of stingless bee,Oxytrigona (Hymenoptera: Apidae)

The cephalic extracts of two species in the stingless bee genusOxytrigona were analyzed. Extracts made in diethyl ether, and then derivatized with diphenyldiazomethane, revealed large quantities of formic acid, potentially a major defensive secretion of this stingless bee group. We additionally identify several hydrocarbons, aldehydes, ketones, and acetates. Novel diketones identified by others were detected in both species.     

Dufour's gland and its role in secretion of nest cell lining in bees of the genusColletes (Hymenoptera: Colletidae)

The liquid secretion of the Dufour's gland in mated females comprises a mixture of macrocyclic lactones, straight chain mono- and dicarboxylic acids, together with trace amounts of di- and trihydroxy monocarboxylic acids and a series ofn-alkanes. Polymerization of the liquid to form the membranous nest cell lining, which also contains alanine and glutamic acid as major constituents, may be mediated by an enzyme from the thoracic salivary gland and voided via the mouth. The composition and structure of the cell linings are similar to those of Wigglesworth's cuticulin.     

Alarm substances of the stingless bee,Trigona silvestriana

2-Nonanol, 2-heptanol, octyl decanoate, and octyl octanoate were identified from the heads ofTrigona silvestriana workers. When presented at the nest, 2-nonanol, 2-heptanol, and the mixture of the four compounds elicited angular flights, landing, and buzzing of guard bees. Octyl octanoate elicited a weaker response. No response was given to octyl decanoate, to the ether solvent, or to the control volatile, vanillin.     

Function of glandular secretions in fragrance collection by male euglossine bees (Apidae: Euglossini)

MaleEulaema cingulata (Fabricius) (Apidae: Euglossini) possess large cephalic labial glands that secrete a mixture of lipids. In the process of fragrance collection, males secrete the labial gland lipids onto the substrate. The mixture of lipids and fragrances is then taken up by the front tarsal brushes and transferred to the hind tibial organs. The labial gland secretions apparently serve as a nonpolar solvent and carrier that increases the efficiency of fragrance collection.     

Linalool in mandibular gland secretion ofColletes bees (Hymenoptera: Apoidea)

Uinalool was identified as the main component of the mandibular gland secretion in females and males of four species ofColletes bees, viz.,C. cunicularius, C. daviesanus, C. impunctatus andC. succinctus. It was also shown to be the dominant volatile compound in the same gland in maleC. floralis (the female of this species has not yet been investigated). Further, in another species,C. similis, linalool is present in the mandibular gland secretions of females and males, but the dominant volatile component in these secretions is geranial, together with neral. Females of the speciesC. fodiens seem to lack monoterpenes altogether; nonadecane is the dominant volatile compound of the cephalic secretion (based on analysis of a single individual). When linalool is put out in the area of nest aggregation ofC. cunicularius, where the males are patrolling, a distinct increase in flight activity is noted. The function of linalool is discussed on the basis of field observations.This report forms part XXI in the series Studies on Natural Odoriferous Compounds.     

Intensification and prolongation of host searching inLeptopilina heterotoma (Thomson) (Hymenoptera: Eucoilidae) through a kairomone produced byDrosophila melanogaster

A chemical cue (kairomone) of the host, larvae ofDrosophila, was found to influence patch-time allocation of the parasiteLeptopilina heterotoma. This kairomone is soluble in water and chloroform. The kairomone was purified using thin-layer chromatography. The concentration of the kairomone increases with an increasing number of hosts. The parasites may use presence and concentration of the kairomone as cues to determine patch-time allocation.     

Role of diet in host selection ofHeliothis virescens by parasitoidCampoletis sonorensis (Hymenoptera: Ichneumonidae)

Gas chromatographic analysis revealed that chemicals attractive toCampoletis sonorensis (Cameron), previously identified in cotton, were not present in wheat germ diet-rearedHeliothis virescens (F.) larvae. Diet-reared larvae fed cotton obtained the chemicals from cotton, with the consequence of enhanced kairomonal activity of the larvae and their frass toC. sonorensis. Parasitoids, presented a choice between cotton, cotton plus hosts, hosts alone, and control in an olfactometer, responded non-randomly, with the greatest number of responses to cotton plus hosts, and three times as many responses to cotton alone as to larvae alone. The role of the plant in the parasitoid-host relationship is discussed.     

Genetic component of variation in chemical defense ofOreina gloriosa (Coleoptera: Chrysomelidae)

Defensive secretions of adultOreina gloriosa, liberated at the surface of the pronotum and elytra, contain a complex mixture of cardenolides, and ethanolamine. Proportions and concentrations of constituents determined by reverse-phase HPLC show considerable variation among individual beetles. Heritabilities of proportions of five main components were estimated by mother-offspring regression providing a validation of the less reliable full-sib correlation estimates. Average heritabilities based on the two methods were 0.51 and 0.58, respectively, estimated by using offspring of two age groups. Regression estimates of 2- and 10-week-old offspring differed significantly for one secretion constituent (RT16). Heritability estimates of concentrations of 16 secretion components were calculated by full-sib correlation analysis. Average heritability was 0.45, indicating a significant genetic component. Estimates did not differ significantly between the two age groups. We also estimated heritabilities of concentrations by a two-way model including data from offspring of both age groups. Heritability estimates based on this model are thought to correspond approximately to estimates based on samples from natural populations. The average of these estimates was lower (h ² =0.31) than the average heritability of each age group separately (h ² =0.45), suggesting a developmental effect on variation in chemical defense ofO. gloriosa.     

Physiological sources of variation in chemical defense ofOreina gloriosa (Coleoptera: Chrysomelidae)

The defensive secretion of the alpine chrysomelidOreina gloriosa is a complex mixture of mainly cardenolides and tyrosine betaine. Individually sampled secretions of adult laboratory-reared and field-collected beetles were analyzed by reverse-phase HPLC; 16 secretion components were quantified. Quantities and concentrations of different components were significantly affected by the age, sex, and reproductive status of individual beetles. Aging was correlated with marked increases (up to 4.4-fold) and decreases (up to 2.7-fold) of quantities and concentrations of several components. Differences between the sexes were smaller, but quantities of all components and concentrations of several components were larger in laboratory-reared females than in males. There was less of one component of the secretion in mated than unmated females, but the concentrations of four secretion components were higher (up to 1.6-fold) in mated females.     

Evidence for chemical defense in tropical green algaCaulerpa ashmeadii (Caulerpaceae: Chlorophyta): Isolation of new bioactive sesquiterpenoids

Results of field feeding preference studies with 12 species of tropical green algae of the genusCaulerpa showed thatC. ashmeadii was preferred least by herbivorous fishes. Chemical investigations ofC. ashmeadii demonstrated the presence of high concentrations of sesquiterpenoid metabolites. The chemical isolation and structural elucidation of five majorC. ashmeadii metabolites, as well as the results of field feeding preference, antimicrobial, and ichthyotoxicity assays demonstrating the biological activities of these metabolites are reported here.     

A comparative study of the exocrine products of cleptoparasitic bees (Holcopasites) and their hosts (Calliopsis) (Hymenoptera: Anthophoridae,Andrenidae)

The cephalic secretion of females of the cleptoparasitic beeHolcopasites calliopsidis contains two main volatiles, 6-methyl-5-hepten-2-one and geranyl acetone. The mandibular gland secretion of its host,Calliopsis andreniformis, on the other hand, contains the two isomeric forms of citral (neral and geranial). Neral and geranial are also produced by mandibular glands of two other species ofCalliopsis and one species in the related genusNomadopsis. The Dufour's gland ofC. andreniformis contains an oily secretion composed of hydrocarbons that are deposited on the brood cell walls and pollen balls providing a waterproof lining for both.     

Variability of chemosensory stimuli within honeybee (Apis mellifera) colonies: Differential conditioning assay for discrimination cues

Differential training of honeybee workers using the proboscis extension reflex is applied to the problem of evaluating compounds that may potentially provide cues for kin recognition in the honeybeeApis mellifera. These cues were obtained by contaminating glass rods and steel needles with different materials found in the hive. In particular it is shown that workers discriminate between: cuticular waxes from different adult workers; eggs from the same and different hives; similar aged larvae within the same hive; and needles contaminated with the Nasonov gland secretions of different adult workers. It appears that some of these differences are due to phenotypic variation among individuals that cannot be directly attributed to environmental factors.     

Distribution of birch (Betula SPP.), willow (Salix SPP.), and poplar (Populus SPP.) secondary metabolites and their potential role as chemical defense against herbivores

Isoprenoids and phenolics, major metabolites of important browse species, are reviewed in regard to concentrations, distribution within tissues, and between species. Seasonal variation of specific substances and changes with age of the plant are also considered. The distribution of substances may affect food selection and feeding behavior of animals. Wild mammalian herbivores tend to avoid plant parts rich in these substances, in spite of high nutritional content of the plant tissue. Possible mechanisms for defense by plants against depredation by mammalian herbivores are discussed within the framework of the plants' biochemistry.     

Mediation of host selection by cuticular hydrocarbons in the honeybee tracheal MiteAcarapis woodi (Rennie)

Using a simple two-choice bioassay and video analysis of individual locomotory tracks, it was determined that a preference for young-bee hosts over old-bee hosts in female honeybee tracheal mites,Acarapis woodi (Rennie), is chemically mediated. When presented with a choice of cuticular extracts from 5-day-old and <1-day-old adult bees, mites showed a significant preference for the young-bee extract in three of four bee colony sources. This discrimination was due apparently to a greater positive response elicited by the young-bee extract rather than a deterrent effect of old-bee extract, as the extract of old bees evoked a significantly higher response than a hexane control. A bioassay of silica-gel fractions of young-bee extract indicated that cuticular hydrocarbons alone were responsible for tracheal mite response. Further fractionation of a hydrocarbon fraction by argentation chromatography demonstrated that both saturated and unsaturated hydrocarbons were involved in the mite response, but when presented in opposition, mites showed a stronger response to the saturated than to the unsaturated components. Mites placed in zones treated with cuticular extract of young bees exhibited higher angular velocities than those placed on hexane, causing them to remain in the extract-treated zones for extended periods. These results point to a possible control strategy whereby migration of tracheal mites to young-bee hosts could be disrupted by artificially altering the chemical profile of the honeybee cuticle.     

Chemistry of cephalic secretion of fire beeTrigona (Oxytrigona) tataira

Analysis of the volatile compounds derived from cephalic glands of the fire beeTrigona (Oxytrigona) tataira by GC-MS was undertaken. The following compounds were readily identified: hydrocarbons:n-C₁₁H₂₄,n-C₁₃H₂₈,n-C₁₄H₃₀,n-C₁₅H₃₂,n-C₁₇H₃₆,n-C₂₃H₄₈,_n-C₁₅H₃₀,n-C₁₇H₃₄,n-C₂₁ H₄₂, andn-C₂₃H₄₆; carboxylic acids: palmitic acid, linoleic acid, linolenic acid, stearic acid, and oleic acid; carboxylic esters: dodecyl acetate, tetradecyl acetate, hexadecyl acetate, octadecyl acetate, and dodecyl decanoate; monoketones: 5-hepten-2-one, 3-hepten-2-one, 2-heptanone, and 5-nonen-2-one. Two major components of the mixture were identified asE-hepten-2,5-dione andE-3-nonen-2,5-dione. Structures of these novel compounds were suggested by their GC-MS behavior and the GC-MS behavior of their dimethoximes and proved by comparison with authentic synthetic samples. Trace amounts of the corresponding Z isomers and the saturated analogs, heptan-2,5-dione and nonan-2,5-dione, were also found. The possible functions of these glandular constituents are discussed.In cooperation with the Louisiana State University Experiment Station, Baton Rouge, Louisiana 70803.Subspecies mellicolor.     

Response ofMeteorus leviventris, (Hymenoptera: Braconidae) to mustard oils in field trapping experiments

Trapping experiments were carried out near Saskatoon, Canada, from May through August 1990 to assess the response of the braconid wasp,Meteorus leviventris, to four selected mustard oils or isothiocyanates (IC) at a release rate of 4 mg/day, and for allyl IC only, at 40 mg/day. Only allyl IC at 4 mg/day was significantly attractive when trap captures were compared to the captures in the control traps. The others (n-propyl IC, 2-phenylethyl IC., and ethyl IC) were not attractive, nor was allyl IC at the higher dose, although trap captures with the latter bait were the second highest.     

Synergism between chemical attractants and visual cues influencing oviposition of the mosquito,Culex quinquefasciatus (Diptera: Culicidae)

Physical factors, such as the color of the oviposition substrate, have seldom been compared with chemical cues in their ability to elicit oviposition behavior in mosquitoes. The role of dyed oviposition waters in attracting ovipositingCulex quinquefasciatus was examined in laboratory experiments. Oviposition waters dyed with ink were found to be significantly attractive to ovipositingCx. quinquefasciatus when compared to distilled water controls. Experiments demonstrated that the mosquitoes were responding to the increased optical density of the dyed oviposition water rather than volatile components of the dye. Ink was also considered in combination with chemical oviposition cues. No comparative data exist on the effect of physical and chemical factors presented together on the oviposition behavior ofCx. quinquefasciatus. Waters dyed with ink acted synergistically with a five-component chemical attractant mixture (3-methylindole, indole, 4-methylphenol, 4-ethylphenol, and phenol) in inducing oviposition in a 2×2 factorial experiment.