Kairomonal response of the parasitoid, Bracon hebetor Say, to the male-produced sex pheromone of its host, the Greater Waxmoth, Galleria mellonella (L.)

Bracon hebetor is a larval ectoparasitoid that utilizes several pests belonging to the family Pyralidae (Lepidoptera) as hosts. In the present study, we analyzed the kairomonal response of this wasp to the male-produced sex pheromone of a host, the greater wax moth Galleria mellonella, an economically important pest of honeybees, Apis mellifera. Coupled gas chromatography-electroantennographic detection (GC-EAD) revealed three compounds in headspace collections from male G. mellonella that elicited responses from B. hebetor antennae: decanal and the previously identified sex pheromone components, nonanal and undecanal. Y-tube olfactometer tests that used na < ve, mated wasps showed that females, but not males, were highly attracted to (a) male G. mellonella headspace samples, (b) two synthetic blends of nonanal and undecanal (in ratios matching that found in male moth samples), and (c) the two aldehydes tested individually. Further, female wasps did not discriminate between a blend of aldehydes and male G. mellonella headspace. In dose-response trials that used octanal, nonanal, decanal, and undecanal, no difference in EAG responses of the two sexes was observed, except for undecanal at the second highest dose, for which female antennae showed significantly larger responses than did male antennae. When the two binary blends were tested at different doses, female wasps were significantly attracted to the two highest doses (1 A mu g and 10 A mu g), but not to the lowest dose (100 ng). Our results show that females of this economically important parasitoid utilize the male-produced sex pheromone of a host as an indirect cue to guide them to potential oviposition sites

Larval sites of the mosquito <i>Aedes aegypti formosus</i> in forest and domestic habitats in Africa and the potential association with oviposition evolution

International audienceAdaptations to anthropogenic domestic habitats contribute to the success of the mosquito Aedes aegypti as a major global vector of several arboviral diseases. The species inhabited African forests before expanding into domestic habitats and spreading to other continents. Despite a well-studied evolutionary history, how this species initially moved into human settlements in Africa remains unclear. During this initial habitat transition, African Ae. aegypti switched their larval sites from natural water containers like tree holes to artificial containers like clay pots. Little is known about how these natural versus artificial containers differ in their characteristics. Filling this knowledge gap could provide valuable information for studying the evolution of Ae. aegypti associated with larval habitat changes. As an initial effort, in this study, we characterized the microenvironments of Ae. aegypti larval sites in forest and domestic habitats in two African localities: La Lopé, Gabon, and Rabai, Kenya. Specifically, we measured the physical characteristics, microbial density, bacterial composition, and volatile chemical profiles of multiple larval sites. In both localities, comparisons between natural containers in the forests and artificial containers in the villages revealed significantly different microenvironments. We next examined whether the between-habitat differences in larval site microenvironments lead to differences in oviposition, a key behavior affecting larval distribution. Forest Ae. aegypti readily accepted the artificial containers we placed in the forests. Laboratory choice experiments also did not find distinct oviposition preferences between forest and village Ae. aegypti colonies. These results suggested that African Ae. aegypti are likely generalists in their larval site choices. This flexibility to accept various containers with a wide range of physical, microbial, and chemical conditions might allow Ae. aegypti to use human-stored water as fallback larval sites during dry seasons, which is hypothesized to have initiated the domestic evolution of Ae. aegypti

Divergence in Olfactory Host Plant Preference in <i>D. mojavensis</i> in Response to Cactus Host Use

<div><p>Divergence in host adaptive traits has been well studied from an ecological and evolutionary perspective, but identification of the proximate mechanisms underlying such divergence is less well understood. Behavioral preferences for host plants are often mediated by olfaction and shifts in preference may be accompanied by changes in the olfactory system. In this study, we examine the evolution of host plant preferences in cactophilic <i>Drosophila mojavensis</i> that feeds and breeds on different cacti throughout its range. We show divergence in electrophysiological responses and olfactory behavior among populations with host plant shifts. Specifically, significant divergence was observed in the Mojave Desert population that specializes on barrel cactus. Differences were observed in electrophysiological responses of the olfactory organs and in behavioral responses to barrel cactus volatiles. Together our results suggest that the peripheral nervous system has changed in response to different ecological environments and that these changes likely contribute to divergence among <i>D. mojavensis</i> populations.</p></div

Changes in behavioral preferences with host plant fermentation stage.

<p>(<b>A</b>) <i>D. mojavensis</i> populations specialize on different host cacti across their range. Its sibling species, <i>D. arizonae</i> uses columnar cactus and <i>Opuntia</i> as hosts. (<b>B–E</b>) Two choice behavioral preferences of males (M) and females (F) of the Mojave, S. Catalina, mainland Sonoran, and Baja populations for their own respective host plants. Behavioral preferences for uninoculated (NI) host cactus in comparison to fermented host cactus and preferences for different stages of fermentation of a given host cactus are shown. Cactus tissues were fermented for one to nine weeks (W1– W9). For the mainland Sonoran population, comparisons between uninoculated and five week fermented organ pipe are shown as no significant difference between uninoculated and one week fermented organ pipe was found (data not shown). For panels <b>B–E</b>, behavioral preferences are shown as mean ± standard error and significance within a given sex and choice test is depicted by asterisks (*: <i>P</i><0.05; ** <i>P</i><0.01; ***: <i>P</i><0.001; ****: P<0.0001).</p

Typical gas chromatograms of headspace for the four cactus hosts.

<p>(<b>A–D</b>) Barrel, prickly pear, organ pipe and agria cactus headspaces, respectively, from fermented samples are shown. Peak numbers correspond to compounds identified in time course experiment presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070027#pone.0070027.s001" target="_blank">Figure S1</a>. (<b>E</b>) Principal component (PC) analysis of the volatile samples from all four cacti. The eigenvectors for the PCs are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070027#pone.0070027.s004" target="_blank">Table S3</a>. The fifty percent density eclipses for the cacti are indicated with different line styles.</p

Behavioral responses to single compounds.

<p>Dose response indices (mean ± std error) of males (M) and females (F) for single compounds. Significant differences among <i>D. mojavensis</i> populations are denoted by different letters above the bars.</p

Large-scale characterization of sex pheromone communication systems in Drosophila

Insects use sex pheromones as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Despite the profound knowledge of sex pheromones, little is known about the coevolutionary mechanisms and constraints on their production and detection. Using whole-genome sequences to infer the kinship among 99 drosophilids, we investigate how phylogenetic and chemical traits have interacted at a wide evolutionary timescale. Through a series of chemical syntheses and electrophysiological recordings, we identify 52 sex-specific compounds, many of which are detected via olfaction. Behavioral analyses reveal that many of the 43 male-specific compounds are transferred to the female during copulation and mediate female receptivity and/or male courtship inhibition. Measurement of phylogenetic signals demonstrates that sex pheromones and their cognate olfactory channels evolve rapidly and independently over evolutionary time to guarantee efficient intra- and inter-specific communication systems. Our results show how sexual isolation barriers between species can be reinforced by species-specific olfactory signals. Despite the profound knowledge of sex pheromones, little is known about the coevolutionary mechanisms and constraints on their production and detection. Whole-genome sequences from 99 drosophilids, with chemical and behavioural data, show that sex pheromones and their cognate olfactory channels evolve rapidly and independently

Data from: A Drosophila female pheromone elicits species-specific long-range attraction via an olfactory channel with dual specificity for sex and food

Background: Mate finding and recognition in animals evolves during niche adaptation and involves social signals and habitat cues. Drosophila melanogaster and related species are known to be attracted to fermenting fruit for feeding and egg-laying, which poses the question of whether species-specific fly odours contribute to long-range premating communication. Results: We have discovered an olfactory channel in D. melanogaster with a dual affinity to sex and food odorants. Female flies release a pheromone, (Z)-4-undecenal (Z4-11Al), that elicits flight attraction in both sexes. Its biosynthetic precursor is the cuticular hydrocarbon (Z,Z)-7,11-heptacosadiene (7,11-HD), which is known to afford reproductive isolation between the sibling species D. melanogaster and D. simulans during courtship. Twin olfactory receptors, Or69aB and Or69aA, are tuned to Z4-11Al and food odorants, respectively. They are co-expressed in the same olfactory sensory neurons, and feed into a neural circuit mediating species-specific, long-range communication; however, the close relative D. simulans, which shares food resources with D. melanogaster, does not respond to Z4-11Al. Conclusion: The Or69aA and Or69aB isoforms have adopted dual olfactory traits. The underlying gene yields a collaboration between natural and sexual selection, which has the potential to drive speciation