Jan Tengö

Mating structure and nestmate relatedness in a communal bee, Andrena jacobi (Hymenoptera, Andrenidae), using microsatellites

Complex eusocial insect societies are generally matrifilial, suggesting kin selection has been of importance in their development. For simpler social systems, factors favouring their existence, in particular kin selection, have rarely been studied. Communal nesting is one of these simple social organizations, and is found in a diversity of insect species. To examine whether kin selection may play a role in the evolution and maintenance of communality, we estimated genetic relatedness of nestmate females of the facultatively communal bee, Andrena jacobi. Microsatellite loci were developed for this species and used to analyse individuals from two populations. Loci were variable, they were in heterozygote deficit and showed positive inbreeding coefficients. This may arise from nonrandom mating; previous observations (Paxton & Tengö 1996) indicate that a large proportion of females mate intranidally with nestmate males in their natal nests before first emerging. Nestmate relatedness was low, no different from zero for all loci in one population and for three of four loci in the other population. The large number of nestmates sharing a common nest (up to 594) may explain the low relatedness estimates, although relatedness was also independent of the number of females sharing a nest. Lack of inclusive fitness payoffs could constrain social evolution in this communal species.

(S)-(+)-Linalool, a Mate Attractant Pheromone Component in the Bee Colletes cunicularius

Enantiomerically pure (S)-(+)-linalool was the main constituent in the extracts of the cephalic secretions of virgin females, mated females, freshly emerged males, and patrolling males of the solitary bee Colletes cunicularius. After copulation, the content of (S)-(+)-linalool emitted by the female was strongly reduced. Electrophysiological experiments revealed that both enantiomers of linalool elicited responses from the antennae of the males. Field tests using the pure enantiomers and the racemate of linalool showed that the number of male bees attracted was highest for (S)-(+)-linalool. The search flight activity in the mating flight area increased dramatically when patrolling males were presented with (S)-(+)-linalool vs (R)-(−)-linalool. Taken together, these data indicate a mate attractant pheromone function of (S)-(+)-linalool.

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.

Species, individual and kin specific blends in Dufour's gland secretions of halictine bees : Chemical evidence.

The compositions of Dufours gland secretions of four sympatric halictine bee species were chemically studied by combined gas chromatography-mass spectrometry. The secretion is composed of C16-C24 macrocyclic lactones, isopentenyl esters, and hydrocarbons. Comparative analyses have revealed that the blends of compounds are species specific. Studies of individual glands belonging to bees of the speciesEvylaeus malachurum have demonstrated that each bee exhibits a specific blend in its Dufours gland. Nestmate bees (considered as sister bees), however, are more similar to each other than nonrelated bees. The relative importance of species specificity, individual specificity, and similarities between kins are discussed.

All-trans-farnesyl hexanoate and geranyl octanoate in the dufour gland secretion ofAndrem (Hymenoptera: Apidae)

The volatile material which emanates from the Dufour gland of femaleAndrena bees has been examined in 13 species. In 11 of these, all-trans-farnesyl hexanoate is the dominating compound, whereas in two species geranyl octanoate is the largest component of the volatile secretion. Either of these two terpene esters were also found as major component in the cephalic secretion of some maleNomada bees. Bees of the genusNomada are nest parasites onAndrena. The chemical identification was carried out by capillary gas chromatography using a splitter-free intake system, alone and in combination with mass spectrometry. Some farnesyl and geranyl esters were prepared in the course of the work by reacting terpenol and acid with CDI (N, N′-carbonyldiimidazole). The secretion is thought to serve as a nest marking.

Do social parasitic bumblebees use chemical weapons? (Hymenoptera, Apidae)

The bumblebee Bombus (Psithyrus) norvegicus Sp.-Schn. is an obligate social parasite of B. (Pyrobombus) hypnorum L. Behavioural observations indicated that nest-invading B. norvegicus females may use allomones to defend themselves against attacking host workers. However, so far no defensive chemicals used by social parasitic bumblebee females have been identified. We analysed volatile constituents of the cuticular lipid profile of B. norvegicus females. Furthermore, we performed electrophysiological studies and behavioural experiments in order to identify possible chemical weapons. Coupled gas chromatography-electroantennography showed 15 compounds to trigger responses in antennae of the host workers. Using gas chromatography–mass spectrometry, the main compound among the cuticular volatiles of B. norvegicus females was found to be dodecyl acetate. A corresponding mixture of synthetic volatiles as well as pure dodecyl acetate showed a strong repellent effect on starved host workers. B. norvegicus females use dodecyl acetate to repel attacking B. hypnorum workers during nest usurpation and subsequently during colony development. Dodecyl acetate is the first repellent allomone identified in bumblebees.

Species specificity and complexity of Dufour's gland secretion of bumble bees

1. 1. Dufours gland secretions of nine westpalaearctic bumble bee species, representing Terrestribombus, Pyrobombus and Megabombus, were analysed by gas chromatography and mass spectrometry. 2. 2. The secretions were dominated by uneven numbered straight chain alkanes from heneicosane to hentriacontane, each alkane accompanied by up to 10 positional alkene isomers. 3. 3. Various esters dominate among the 64 oxygen-containing compounds found. 4. 4. This is the first report on Dufours gland secretion of bumble bees. The secretion is species specific. Subgeneric and tribe specific patterns are indicated. 5. 5. Characteristics for species separation of workers of the Terrestribombus group are presented. 6. 6. The possible communicative function of the secretion is discussed.

Odor mimetism? : Key substances inOphrys lutea-Andrena pollination relationship (Orchidaceae: Andrenidae).

The hypothesis of chemical mimesis in the relationship betweenOphrys orchids and their pollinators was tested experimentally using preparations ofOphrys lutea var.lutea odor and the males of the solitary beeAndrena fuscipes, a species constellation that does not coexist under natural conditions. Correspondence in odor production was shown to occur. Identification of the compounds in the cephalic secretion ofA. fuscipes, males and females, and the flower labella extracts, was performed by gas chromatography and mass spectrometry. Geraniol, nerol, citral,E,E-farnesol and 6-methyl-5-hepten-2-one were present in the extracts of both the orchid and one or both sexes of the bee. Extracts, TLC fractions of extracts, blends, and separate compounds were tested in the field in the mating flight areas ofA. fuscipes males. Extracts and blends containingE,E-farnesol, geraniol, and geranial showed the highest attractivity to the male bees. These compounds seem to be responsible for the release of the odor-guided mating behavior at theO. lutea labellum and can be regarded as general attractants for many species ofAndrena.

Odor correspondence betweenMelitta females and males of their nest parasiteNomada flavopicta K. (Hymenoptera: Apoidea)

Analyses have been performed with the help of combined capillary gas chromatography and mass spectrometry on volatile secretions emanating from the Dufour glands of femaleMelitta haemorrhoidalis andM. leporina and heads of maleNomada flavopicta, a nest parasite of theMelitta species. It was found that the cephalic secretions ofN. flavopicta males have definite similarities with the Dufour gland secretions of the two species ofMelitta. They all contain octadecyl butyrate as a major component. Monounsaturated alcohols of different chain lengths are also present in the secretions. Beside these compounds,Melitta has some other esters, notably C12-, C14-, C16-, and C20-butyrates as well as C12- and C16-acetates.

Host-parasite relationships in six species ofSphecodes bees and their halictid hosts: Nest intrusion, intranidal behavior, and Dufour's gland volatiles (Hymenoptera: Halictidae)

Nest invasion behavior was studied in six kleptoparasiticSphecodes species at four nesting sites of their respective social and solitary hosts.Sphecodes females preferred to enter unguarded nests. Nest intruding strategies observed in the differentSphecodes species did not depend on whether host species were solitary or social, as long as the nesting cycle of a social host was in the solitary stage (i.e., a single host female). Observation of intranidal behavior revealed thatSphecodes monilicornis females kill all host individuals within an usurped nest. They stay in the nest for several hours, laying eggs in adequately provisioned brood cells. Gas chromatography-mass spectrometry analyses of Dufours gland secretions revealed species-specific compositions. Qualitative comparisons of whole patterns and quantitative comparisons considering the predominant hydrocarbons common to both host and parasite contradict the hypothesis of chemical mimetism, a mechanism supposed to permit parasite intrusion by qualitatively similar odor bouquets in host and parasite females.