Marc Gibernau

Chemosensory attraction of fig wasps to substances produced by receptive figs

In the mutualism between figs (Ficus spp., Moraceae) and their species‐specific fig wasp pollinators (Hymenoptera: Agaonidae), location of a receptive host tree by the adult insect is a critical step. The adult female wasp lives only a few days, and must usually fly to a different tree than her natal tree to locate receptive figs. Trees in receptive phase often occur at very low densities. Reproductive success of both fig and wasp depends on transmission of a very strong signal by the plant. Some evidence exists for the role of olfaction in location of receptive hosts by fig wasps, but very little work has been done on the chemical ecology of host location and host specificity. Here the first experimental evidence is presented for long‐distance olfactory attraction of wasps by volatile substances produced by receptive figs, and for short‐distance or contact chemostimulation by host volatiles that elicit entry of the wasp into the fig. In studies using Ficus carica L., pentane extracts of receptive‐phase figs attract the pollinator Blastophaga psenes L. from distances of at least 5 m in the field. Short‐distance chemostimulation was demonstrated in laboratory bioassays. Pentane extracts of receptive figs, when painted onto the ostiole of non‐receptive figs, elicit entry of pollinator wasps. Figs emit volatile compounds attractive to pollinating wasps only during the period of receptivity; pentane extracts of non‐receptive figs are not attractive. A simple reliable procedure is described to compare the attractivity of different types of extracts (total, internal, and external extracts) and of different fractions, in the first step towards identifying attractant substances.

Evolutionary responses of discontinuous gas exchange in insects

The discontinuous gas-exchange cycles (DGCs) observed in many quiescent insects have been a cause of debate for decades, but no consensus on their evolutionary origin or adaptive significance has been achieved. Nevertheless, three main adaptive hypotheses have emerged: (i) the hygric hypothesis suggests that DGCs reduce respiratory water loss; (ii) the chthonic hypothesis suggests that DGCs facilitate gas exchange during environmental hypoxia, hypercapnia, or both; and (iii) the oxidative-damage hypothesis suggests that DGCs minimize oxidative tissue damage. However, most work conducted to date has been based on single-species investigations or nonphylogenetic comparative analyses of few species, despite calls for a strong-inference, phylogenetic approach. Here, we adopt such an approach by using 76 measurements of 40 wild-caught species to examine macrophysiological variation in DGC duration in insects. Potential patterns of trait variation are first identified on the basis of the explicit a priori predictions of each hypothesis, and the best phylogenetic generalized least-squares fit of the candidate models to the data is selected on the basis of Akaikes information criterion. We find a significant positive relationship between DGC duration and habitat temperature and an important interaction between habitat temperature and precipitation. This result supports the hygric hypothesis. We conclude that the DGCs of insects reduce respiratory water loss while ensuring adequate gas exchange.

Beetle pollination of Philodendron solimoesense (Araceae) in French Guiana

The pollination of Philodendron solimoesense (subgenus Meconostigma) was studied in four populations of French Guiana. Flowering is asynchronous within each population during July, and the flowering cycle is a 2‐d process. Numerous insects visit Philodendron inflorescences, but the main pollinator seems to be Cyclocephala colasi (Scarabaeidae, Dynastinae). The pollination process displays aspects typical of beetle pollination: the production of heat and of a strong odor, the presence of a food reward (stigmatic secretion and sterile male flowers), and the presence of a copulation chamber. Flower heat production is important (ca. 11°C above the ambient air) and may help to volatilize the fragrance. Attraction and choice‐test experiments showed that C. colasi is not likely to depend on chemical information (such as pheromone) to localize conspecifics but may rely instead on stimuli produced by the inflorescences in order to meet mating partners.

Volatile compounds from extracts of figs of Ficus carica

Abstract Pentane extracts from figs of Ficus carica , the common fig tree, were analysed by GC-mass spectroscopy. Four series of extracts were prepared from receptive male figs, non-receptive male figs, receptive female figs and non-receptive female figs. Extracts from non-receptive figs are characterised by furanocoumarins (tentatively identified as angelicin and bergapten), sesquiterpene hydrocarbons (i.e. trans -caryophyllene, and a compound tentatively identified as germacrene D), oxygenated sesquiterpenes (i.e. hydroxycaryophyllene) benzyl alcohol and benzylaldehyde. Extracts from receptive figs of both sexes are characterised by benzyl alcohol, linalool and linalool oxides (furanoid), cinnamic aldehyde, cinnamic alcohol and indole. Extract from female receptive figs has in addition large amounts of pyranoid (linalool oxides), whereas an extract from male receptive figs contains eugenol and an unidentified sesquiterpene hydrocarbon. Differences between extracts from male and female figs appear to be mainly qualitative due to pyranoid compounds, sesquiterpenes 1, 2 and 3 for female figs and eugenol and sesquiterpene 5 for male figs.

Ant protection of a Heteropteran trophobiont against a parasitoid wasp

Trophobiotic associations between Caternaultiella rugosa (Heteroptera; Plataspidae) and two ant species, Camponotus brutus (Formicidae) and Myrmicaria opaciventris (Myrmicinae), were recorded at the base of the trunks of Bridelia micrantha (Euphorbiaceae). The bug colonies were generally sheltered in pavilions built by the ants, but during periods of proliferation, part of the colonies developed outside the pavilions. We examined the protective activity of the two associated ant species against an encyrtid parasitoid wasp that parasitized egg masses of the bug. Egg masses situated outside the pavilions were significantly less parasitized on trees occupied by either ant species than on experimental trees where ants were excluded by a sticky barrier. Egg masses were significantly less parasitized on trees occupied by C. brutus than on those occupied by M. opaciventris, both inside and outside the pavilions. Moreover, they were less parasitized inside than outside the pavilions when protected by C. brutus. Inside the pavilions, parental care of the egg masses and first-instar nymphs was abandoned to the ants. In contrast, outside the pavilions, the females of C. rugosa guarded egg masses and clusters of first-instar nymphs. Furthermore, adults and last-instar nymphs grouped around and above first-instar nymphs, forming a protective shield. These groups formed and disintegrated daily, according to the attending ants rhythm of activity.

Are olfactory signals sufficient to attract fig pollinators

AbstractFlower fragrances are important stimuli in attracting insect pollinators. Different odours attract different pollinators and can, in some cases, achieve specific relationships. Among highly...

Reproductive biology of Montrichardia arborescens (Araceae) in French Guiana

Data on the pollination biology of neotropical aroids are still scarce and concern only a few species (Beath 1999, Croat 1997, Gibernau et al . 1999, 2000; Mayo et al . 1997 and references cited therein). It appears from these studies that Anthurium , Monstera and Spathiphyllum are on the whole pollinated mainly by bees (but see Kraemer & Schmitt 1999), whereas Dieffenbachia , Homalomena , Syngonium , Philodendron and Xanthosoma are generally beetle-pollinated. Although araceous inflorescences may be visited by several insect taxa (Madison 1979), only a few are the legitimate pollinators for each species (Seres & Ramirez 1995, Valerio 1984, Young 1986).

Ant species that protect figs against other ants: Result of territoriality induced by a mutualistic homopteran

Abstract:Hymenoptera pollinators and figs (ripe or unripe) of Ficus vallis-choudae are protected from the predatory activity of myrmicine ants (Atopomyrmex mocquerisi; Crematogaster clariventris; Crematogaster sp.) by other ants (Camponotus acvapimensis and Camponotus brutus; Formicinae) who attack neither unripe figs nor the pollinator. On trees occupied by Atopomyrmex and Crematogaster, and on trees invaded by columns of workers after recruitment by scouts, the predatory activity begins when the fig wasps emerge. Then, the ants attack unripe figs (asynchronization in ripeness), destroying whole figs of certain trees. The male function of the trees through pollen dispersal by fig wasps is, therefore, severely reduced, while the female function (seed dispersal) is affected only on unripe figs before fig wasp emergence. We recorded 13 ant species on the 73 Ficus vallis-choudae of the Batchenga savanna (Cameroon) studied, but only the five previously cited species were able to occupy an entire fig tree. The...

The Key Role of 4-methyl-5-vinylthiazole in the Attraction of Scarab Beetle Pollinators: a Unique Olfactory Floral Signal Shared by Annonaceae and Araceae

Cyclocephaline scarabs are specialised scent-driven pollinators, implicated with the reproductive success of several Neotropical plant taxa. Night-blooming flowers pollinated by these beetles are thermogenic and release intense fragrances synchronized to pollinator activity. However, data on floral scent composition within such mutualistic interactions are scarce, and the identity of behaviorally active compounds involved is largely unknown. We performed GC-MS analyses of floral scents of four species of Annona (magnoliids, Annonaceae) and Caladium bicolor (monocots, Araceae), and demonstrated the chemical basis for the attraction of their effective pollinators. 4-Methyl-5-vinylthiazole, a nitrogen and sulphur-containing heterocyclic compound previously unreported in flowers, was found as a prominent constituent in all studied species. Field biotests confirmed that it is highly attractive to both male and female beetles of three species of the genus Cyclocephala, pollinators of the studied plant taxa. The origin of 4-methyl-5-vinylthiazole in plants might be associated with the metabolism of thiamine (vitamin B1), and we hypothesize that the presence of this compound in unrelated lineages of angiosperms is either linked to selective expression of a plesiomorphic biosynthetic pathway or to parallel evolution.

POLLINATION OF PHILODENDRON ACUTATUM (ARACEAE) IN THE ATLANTIC FOREST OF NORTHEASTERN BRAZIL: A SINGLE SCARAB BEETLE SPECIES GUARANTEES HIGH FRUIT SET

Philodendron acutatum (Araceae) is a hemiepiphyte common to the Atlantic Forest of northeastern Brazil. In two localities, we studied the species’ breeding system and associations with flower‐visiting insects, along with an analysis of its floral scent composition. The fruit set of self‐incompatible P. acutatum was high, more than 90%, and inflorescences were exclusively pollinated by one species of scarab beetle, Cyclocephala celata (Scarabaeidae, Dynastinae). Pollinators are drawn toward the inflorescences at dusk by strong floral fragrances given off during the female phase of anthesis, along with endogenous heating of the spadix, whose temperatures were recorded at more than 11°C above ambient air. Two other species of flower‐visiting Cyclocephala were also consistently recovered in blacklight trappings during the flowering period of P. acutatum. The fact that only C. celata was found in association with P. acutatum suggests a local reproductive dependence of the plant to this scarab beetle species. Dihydro‐β‐ionone and 2‐hydroxy‐5‐methyl‐3‐hexanone, a rare volatile molecule so far unreported as a floral compound, together accounted for more than 97% of the unique scent composition of P. acutatum and might be involved in specific attraction of C. celata.