Host-specific cues cause differential attractiveness of Kenyan men to the African malaria vector Anopheles gambiae

Background  

Many studies have suggested that variability in the attractiveness of humans to host-seeking mosquitoes is caused by differences in the make-up of body emanations, and olfactory signals in particular. Most investigations have either been laboratory-based, utilising odour obtained from sections of the body, or have been done in the field with sampling methods that do not discriminate between visual, physical and chemical cues of the host. Accordingly, evidence for differential attractiveness based on body emanations remains sparse in spite of the far-reaching epidemiological implications of this phenomenon.     

The role of body fat in female attractiveness

The purpose of the present study was to investigate the role of body fat percentage (BF%) on female attractiveness. To this end, a series of female body images were selected from a collection of dual-energy X-ray absorptiometry scans. Images were stratified by three levels (low, mid, and high) of waist-to-hip ratio (WHR) and seven levels (15%–50%) of BF%. These 21 images were presented in a random order and rated for attractiveness. Results indicate that WHR, BMI, and BF% are all significant predictors of female attractiveness when regressed separately (R²= 0.19, 0.70, and 0.76, respectively). When regressed simultaneously, all three variables accounted for 87% of the variance in image attractiveness, with only BF% and WHR being significant predictors. Further analysis revealed that body fat might disrupt the negative linear relationship between WHR and attractiveness. Men and women differed significantly in most categories of WHR and BF%, with men generally rating images as less attractive than women. These data indicate that BF% appears to be a strong cue for attractiveness and that the impact of WHR and BMI on attractiveness is dependent, in part, on BF%. The appearance of body fat may provide disruption in the visual cues of both shape and size of the female body, potentially impacting behavior.     

Human body odour, symmetry and attractiveness.

Several studies have found body and facial symmetry as well as attractiveness to be human mate choice criteria. These characteristics are presumed to signal developmental stability. Human body odour has been shown to influence female mate choice depending on the immune system, but the question of whether smell could signal general mate quality, as do other cues, was not addressed in previous studies. We compared ratings of body odour, attractiveness, and measurements of facial and body asymmetry of 16 male and 19 female subjects. Subjects wore a T-shirt for three consecutive nights under controlled conditions. Opposite-sex raters judged the odour of the T-shirts and another group evaluated portraits of the subjects for attractiveness. We measured seven bilateral traits of the subject's body to assess body asymmetry. Facial asymmetry was examined by distance measurements of portrait photographs. The results showed a significant positive correlation between facial attractiveness and sexiness of body odour for female subjects. We found positive relationships between body odour and attractiveness and negative ones between smell and body asymmetry for males only if female odour raters were in the most fertile phase of their menstrual cycle. The outcomes are discussed in the light of different male and female reproductive strategies.     

Beer Consumption Increases Human Attractiveness to Malaria Mosquitoes

Background

Malaria and alcohol consumption both represent major public health problems. Alcohol consumption is rising in developing countries and, as efforts to manage malaria are expanded, understanding the links between malaria and alcohol consumption becomes crucial. Our aim was to ascertain the effect of beer consumption on human attractiveness to malaria mosquitoes in semi field conditions in Burkina Faso.

Methodology/Principal Findings

We used a Y tube-olfactometer designed to take advantage of the whole body odour (breath and skin emanations) as a stimulus to gauge human attractiveness to Anopheles gambiae (the primary African malaria vector) before and after volunteers consumed either beer (n = 25 volunteers and a total of 2500 mosquitoes tested) or water (n = 18 volunteers and a total of 1800 mosquitoes). Water consumption had no effect on human attractiveness to An. gambiae mosquitoes, but beer consumption increased volunteer attractiveness. Body odours of volunteers who consumed beer increased mosquito activation (proportion of mosquitoes engaging in take-off and up-wind flight) and orientation (proportion of mosquitoes flying towards volunteers'' odours). The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes.

Conclusions/Significance

These results suggest that beer consumption is a risk factor for malaria and needs to be integrated into public health policies for the design of control measures.     

Electrophysiological and behavioural responses of mosquitoes to volatiles of Silene otites (Caryophyllaceae)

In order to understand the biological significance of flower odour for attraction of mosquitoes, electrophysiological responses to headspace flower odour samples of Silene otites (L.) Wibel were investigated on Culex pipiens pipiens biotype molestus Forskal 1775 and Aedes aegypti L. using coupled gas chromatographic-electroantennographic detection (GC-EAD). No remarkable differences in antennal responses to the odour compounds have been found between these two mosquito species. Further, the behavioural attractiveness of the electrophysiologically active compounds, singly or as multiple odour mixtures, was evaluated with bioassay experiments with C. pipiens molestus. In bioassays, C. pipiens responded to 14 electrophysiologically active compounds in different magnitudes (65–20%) and acetophenone, linalool oxide (pyranoid), phenyl acetaldehyde and phenylethyl alcohol were found as more attractive in comparison to the least attractive compound, hexanol. In two-stimulus choice test, mosquitoes were significantly more attracted to the mixture of the four most attractive compounds compared to the mixture of all 14 compounds. The results of present study confirm that floral odours are attractive cues for mosquitoes.     

Vocal and visual attractiveness are related in women

We investigated the relation between visual and vocal attractiveness in women as judged by men. We recorded 34 women speaking four vowels and measured the peak frequency, the first five harmonic frequencies, the first five formant frequencies and formant dispersion. The women were also photographed (head shot), several body measures were taken and their ages were recorded. The voices were played to male judges who were asked to assess the women's age and vocal attractiveness from the recording. The men were then asked to assess the attractiveness of the photographs. Men were in strong agreement on which was an attractive voice and face; and women with attractive faces had attractive voices. Higher-frequency voices were assessed as being more attractive and as belonging to younger women (the lowest frequency produced is a good indicator of age in women in general). Larger women had lower voices and were judged as having less attractive faces and voices. Taller women had narrower formant dispersion as predicted. The results imply that different measures of attractiveness are in agreement and signal similar qualities, such as female age, body size and possibly hormonal profile. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Brief exposure to the odour of a parasitized male alters the subsequent mate odour responses of female mice

Parasites can affect mate choice, with females preferentially selecting parasite-free males. Prior exposure to, or experience with, males has also been suggested to influence mate responses. Here, we examined the effects of an immediate, brief (1 or 15 min) pre-exposure to the urinary and associated odours of either an uninfected male house mouse,Mus domesticus , or a male infected with the natural murine nematode parasite, Heligomosomoides polygyrus, on the subsequent responses of female mice to the odours of infected and uninfected males. Using an odour preference test we found that females displayed a marked overall preference for the odours of uninfected males. Pre-exposure to the odours of a parasitized male decreased female preference for nonparasitized males and increased female preference for parasitized males. This ‘prior male’ effect was evident for both the total odour preference and initial odour choice. Females pre-exposed to the odour of a parasitized male displayed decreased choosiness and made no particular initial choice of a male, while still maintaining an overall preference for the odours of uninfected males. These shifts in initial choice and odour preference were not directly associated with either female stress responses or stress-related odour cues of the males. Our findings show that female mice can distinguish between parasitized and nonparasitized males on the basis of odour and suggest that a brief exposure to the odours of infected males influences females' immediate odour preferences, and their subsequent preference for and choice of males. This rapid, infection-associated ‘prior male’ effect may contribute to the reported variations in female mate preference and choice. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Abdominal odours of young,low-ranking European rabbit mothers are less attractive to pups: an experiment with animals living under natural breeding conditions

Lactating rabbit females (Oryctolagus cuniculus) emit abdominal, ventral odour cues that are involved in guiding the pups to the nipples. We tested the impact of the females’ social rank and age on the emission of this odour signal; both factors are highly collinear in wild rabbits and we did not aim to disentangle them in our study. We predicted that the abdominal odours of young, low-ranking females, which are usually more stressed and have a comparatively lower body condition, should be less attractive to pups than those of older, high-ranking females. For the experiment, we caught females from a population of wild-type European rabbits living in a large field enclosure. Pairs of adult females were placed in boxes with wire-mesh floor fixed over an arena with three rabbit pups aged 4–7 days old. First, we evaluated the effectiveness of our two-choice design by testing lactating females (LF) against non-lactating (NLF) controls (n = 17 pairs). In accordance with recent studies, the pups showed a clear preference for lactating females by means of a higher exploration time and more local searching under the ventral region of these females. In a second experiment, the pups chose between lactating 1-year-old, low-ranking females (Y/LRF) and older, high-ranking females (O/HRF) (n = 10 pairs). These latter assays suggested a comparatively lower attractiveness of Y/LRF females to pups searching for milk. Although the pups showed no significant preference in exploration behaviour, they preferably directed local searching events to the abdominal region of O/HRF females. In conclusion, our study suggests that mother–offspring chemosensory communication is modified by the mother’s age and social rank, i.e., by a complex of factors that are strongly linked in rabbit females in the wild.     

Importance of the experimental setup in research on attractiveness of odours in moths: an example with Busseola fusca

Wind tunnel and Y‐tube olfactometer studies are useful for demonstrating the responsiveness of male moths to sex pheromones. However, in the cereal stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), wind tunnel bioassays yielded poor results when the behavioural responses of females to plant odours were tested. We demonstrated that for B. fusca females, the Y‐tube olfactometer was better suited for measuring the attractiveness of plant odours, compared with the wind tunnel. In particular, we showed B. fusca preference for odours of a host over a non‐host plant species using this apparatus. Behavioural responses for B. fusca after host finding are also discussed.     

Divergent responses of two cereal aphids to previous infestation of their host plant

The role of pollen odour in resource location by the pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a pollen-feeding insect regarded as a pest of oilseed rape, Brassica napus L., (Brassicaceae) crops, was investigated in a linear track olfactometer. Both male and female beetles were attracted to the odour of whole oilseed rape flowers, indicating that these insects can locate their host plants using floral odours as cues. The attractive odour of flowers was found to emanate from all floral parts tested: the petals/sepals, the anthers, and from pollen itself. Therefore, at least part of the attractive odour of oilseed rape flowers emanates from pollen. Beetles were more attracted to floral samples containing anthers than those without anthers when these odours were directly compared in a choice-test, and this indicates that there were detectable differences between them. Anthers and pollen may therefore release distinctive odours that are quantitatively and/or qualitatively different from the odour of the rest of the flower. These experiments support the hypothesis that pollen-seeking insects use pollen odour cues to locate this food source.     

The attractiveness of different odour sources from the fruit–host complex on Leptopilina boulardi, a larval parasitoid of frugivorous Drosophila spp.

In parasitoid insects, successful offspring development depends on the female’s ability to find a suitable host. Specific recognition is often based on responses to olfactory cues, but their source and nature have rarely been determined. –This paper deals with the recognition of odours involved in host location by Leptopilina boulardi[Barbotin, Carton & Kelner-Pillault] (Hymenoptera: Eucoilidae), a larval parasitoid of Drosophila species that develops in mature fruits. The nature and origin of volatile stimuli recognized among odours of the host–fruit complex, and the effect of learning on this recognition, were investigated. Oriented responses to these odours were observed in a four-armed olfactometer and were analysed with the observer software (Noldus Information Technology). Fruit odours alone (banana and pear) were not spontaneously attractive to naive parasitoids, whereas naturally-infested bananas were highly attractive. The attraction was related to the odour that adult Drosophila left on the substrate but not to Drosophila oviposition activity or larval development. A synergism between some fruit odours (banana and pear) and the odour left by adult Drosophila on damp filter paper was observed. However, when testing a non-fruit substrate (mushroom), no synergism was observed. Thus, female L. boulardi may innately recognize host–food substrate odours associated with odours from the adult stage of their host. In addition, an oviposition experience on an infested banana allows L. boulardi females to memorise the fruit odour itself through associative learning. The adaptive significance of this process is discussed.     

The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

鳄蜥对熟悉和陌生个体气味的辨别

个体辨别对于减少同种争斗以及配偶选择具有重要意义。我们用棉棒粘取鳄蜥(Shinisaurus crocodilurus)尿液作为气味源,以香水作为对照,测定鳄蜥对熟悉个体气味、陌生个体气味以及香水的舔舌次数和舔舌潜伏期,来探讨鳄蜥通过化学信息辨别熟悉和陌生个体的能力。结果显示,不论是雌性还是雄性,对不同个体尿液的舔舌次数均显著高于对香水的,舔舌潜伏期显著短于香水的;尽管雄性对陌生同性个体气味与熟悉同性个体气味的舔舌次数无显著差异,但对前者的舔舌潜伏期显著短于后者;雄性对陌生雌性气味的舔舌次数显著多于熟悉雌性气味的,对前者的舔舌潜伏期显著短于后者;雌性对陌生雄性气味的舔舌潜伏期显著短于对熟悉雄性气味的;雄鳄蜥对陌生雌性气味的舔舌次数显著多于雌鳄蜥对陌生雄性的。结果表明,鳄蜥能辨别同种个体的化学信息,并能通过化学信息来辨别熟悉和陌生个体,推测鳄蜥的这种辨别能力对其领域分配以及繁殖交配有重要作用。     

Detection of substrate-associated odour cues versus prey-associated cues by the oral veil in Tritonia diomedea

Our goal was to test two potential sensory roles for the oral veil in the nudibranch Tritonia diomedea (now synonymous with T. tetraquetra). First, we hypothesized this cephalic sensory organ could detect substrate-associated odours left behind by an odour plume flowing across sediment. In two experiments in a laboratory flow tank, however, T. diomedea did not show consistent crawling headings in response to either prey or predator odours associated with sediment substrate. In one of the experiments, the slugs did significantly decrease crawling speed in response to prey odours. Although slugs could thus detect at least some substrate-associated odours, these results suggest such cues are not used for navigation. We next considered the oral veil’s potential role in behaviours requiring responses to nearby cues. Our observations of animals before and after denervation of the oral veil suggest that, unsurprisingly, predatory bite-strikes do rely on sensory input from the oral veil. Overall, these data, combined with the results of earlier studies, are consistent with the oral veil detecting cues primarily from nearby stimuli (including both chemical and mechanical modalities), while having little or no role in detecting and responding to odour cues originating from distant sources used for navigation behaviour.     

Do more attractive women show stronger preferences for male facial masculinity?

Researchers have suggested that more attractive women will show stronger preferences for masculine men because such women are better placed to offset the potential costs of choosing a masculine mate. However, evidence for correlations between measures of women's own attractiveness and preferences for masculine men is mixed. Moreover, the samples used to test this hypothesis are typically relatively small. Consequently, we conducted two large-scale studies that investigated possible associations between women's preferences for facial masculinity and their own attractiveness as assessed from third-party ratings of their facial attractiveness (Study 1, N = 454, laboratory study) and self-rated attractiveness (Study 2, N = 8972, online study). Own attractiveness was positively correlated with preferences for masculine men in Study 2 (self-rated attractiveness), but not Study 1 (third-party ratings of facial attractiveness). This pattern of results is consistent with the proposal that women's beliefs about their own attractiveness, rather than their physical condition per se, underpins attractiveness-contingent masculinity preferences.     

Evaluating the Induced-Odour Emission of a Bt Maize and its Attractiveness to Parasitic Wasps

The current discussion on the safety of transgenic crops includes their effects on beneficial insects, such as parasitoids and predators of pest insects. One important plant trait to consider in this context is the emission of volatiles in response to herbivory. Natural enemies use the odours that result from these emissions as cues to locate their herbivorous prey and any significant change in these plant-provided signals may disrupt their search efficiency. There is a need for practical and reliable methods to evaluate transgenic crops for this and other important plant traits. Moreover, it is imperative that such evaluations are done in the context of variability for these traits among conventional genotypes of a crop. For maize and the induction of volatile emissions by caterpillar feeding this variability is known and realistic comparisons can therefore be made. Here we used a six-arm olfactometer that permits the simultaneous collection of volatiles emitted by multiple plants and testing of their attractiveness to insects. With this apparatus we measured the induced odour emissions of Bt maize (Bt11, N4640Bt) and its near-isogenic line (N4640) and the attractiveness of these odours to Cotesia marginiventris and Microplitis rufiventris, two important larval parasitoids of common lepidopteran pests. Both parasitoid species were strongly attracted to induced maize odour and neither wasp distinguished between the odours of the transgenic and the isogenic line. Also wasps that had previously experienced one of the odours during a successful oviposition divided their choices equally between the two odours. However, chemical analyses of collected odours revealed significant quantitative differences. The same 11 compounds dominated the blends of both genotypes, but the isogenic line released a larger amount of most of these. These differences may be due to altered resource allocation in the transgenic line, but it had no measurable effect on the wasps’ behaviour. All compounds identified here had been previously reported for maize and the differential quantities in which they were released fall well within the range of variability observed for other maize genotypes.     

Behaviour of juvenile mud crabs Scylla serrata in aquaculture: Response to odours of moulting or injured crabs

Behaviour of juvenile mud crabs, Scylla serrata (70–90 mm carapace width, CW) were observed in response to odours of moulting and injured conspecifics and food (pilchard) under controlled flow conditions using bioassay technique. This study was undertaken to better understand the role that chemical cues have in mediating the attraction of cannibal crabs to moulting crabs in an aquaculture growout facility and thus aid in more successful production. In response to moult odour juvenile S. serrata spent 5.6 ± 1.9% of the time in locomotion but this did not differ significantly (P > 0.05) from that of control odours (seawater, 2.6 ± 1.2%), however a tactile response was observed for moult odour not seen in controls. Juveniles exposed to the odour of injured conspecifics (12.2 ± 2.3% of time in locomotion) and to food (22.7 ± 3.1%) differed significantly from the seawater control (P < 0.05). The possibility that the active agent in moult water is relatively dilute was considered, however varying concentrations of food and crushed conspecific odour failed to demonstrate concentration dependant behavioural results. Variation in the form of size (carapace width) and sex was revealed, so too was preliminary evidence of behavioural differences between crab hatchings. For example, larger crabs (around 80 mm CW) increased tactile investigation of the odour inlet pipe in response to the crab-based odours of moulting (3.5 ± 1.7% of the time) and injured conspecifics (2.6 ± 1.0%), though response to food remained constant over all sizes (10.0% of the time). In another experiment, larger female crabs maintained a high frequency of tactile response to the odour of injured conspecifics. In males, the response was attenuated in larger individuals. Despite no differences being found between moult odour and controls some evidence exists to suggest that a small proportion of crabs were responding to the moult odour and that this still has the potential to cause a dramatic cumulative reduction in growout survival. Variation in size and subsequent behaviour of individuals poses the question of whether behaviour contributes to growth rate and might be a focus of genetic selection for more uniform growth.     

Kin recognition in golden hamsters: evidence for kinship odours

Differential treatment of kin and non-kin has been well documented, but much remains unclear about how kin are recognized. If kin are recognized by a phenotype-matching mechanism, there must be a correlation between genetic relatedness and the similarity of cues used for recognition. A habituation technique was used with golden hamsters,Mesocricetus auratus, to investigate the relative similarity of the odour quality of flank gland secretions from siblings and unrelated individuals. Hamsters discriminated between the odours of their own, same-sex siblings but also treated these odours as similar compared to odours of non-siblings (experiment 1). They did not discriminate between the flank gland odours of unfamiliar siblings from another family (experiment 2). They also did not discriminate between the flank gland odours of unfamiliar, paternal half-siblings from another family (experiment 3). These results indicate that subjects perceived odours from genetically similar individuals as similar and provide evidence for kinship odour cues. The discrimination between the flank gland odours of subjects’ own siblings, however, indicates that hamsters learn the subtle differences between the odours of their close kin, probably through experience with siblings in the nest. When only volatile components from flank gland secretions were available to subjects (experiment 4), they again discriminated between the odours of their own siblings, suggesting that the volatile components from the flank gland secretion were sufficient for recognition of individual litter-mates.     

Do house mice modify their foraging behaviour in response to predator odours and habitat?

Predator odours and habitat structure are thought to influence the behaviour of small mammalian prey, which use them as cues to reduce risks of predation. We tested this general hypothesis for house mice, Mus domesticus, by manipulating fox odour density via addition of fox scats and habitat via patchy mowing of vegetation, for populations in 15 × 15-m field enclosures. Using giving-up densities (GUDs), the density of food remaining when an animal quits harvesting a patch, we measured foraging behaviours in response to these treatments. Mice consistently avoided open areas, leaving GUDs two to four times greater in these areas than in densely vegetated patches. However, mouse GUDs did not change in response to the addition of fox scats, even immediately after fresh scats were added. There was no interaction between fox odour and habitat use. We then tested whether habituation to fox odours had occurred, by comparing the individual responses to scats of eight mice born into enclosures with fox scats to those of eight mice born into scat-free enclosures and five wild mice. In smaller enclosures, GUDs of trays with scats did not differ from GUDs of trays without scats for any treatment. We conclude that exposure to high levels of fox odours did not alter the foraging behaviour of mice, but that mice did reduce foraging in areas where habitat was removed, perceiving predation risk to be greater in these areas than controls. We suggest further that studies using the ‘scat-at-trap’ technique, which have shown avoidance of predator odours by mice and other small mammals, may overestimate the general avoidance of predator odours by free-living prey, which must forage with a constant background of predator odours.     

The potential of flower odours for use in population monitoring of Western flower thrips Frankliniella occidentalis Perg. (Thysanoptera: Thripidae)

Sticky blue traps are a suitable and important tool for Western Flower Thrips population monitoring in greenhouses. They can be used in vegetables and in ornamentals, and provide important information on the current status of the pest population. However, such traps cannot be used in some susceptible plant species when they are flowering because at that stage the plants are more attractive to Western Flower Thrips than the traps. We therefore tried to increase trap attractiveness by combining the colour cue with an attractive odour cue. In laboratory experiments, we found a significant additive effect on attractiveness for two odours in traps provided with both the visual and the olfactory cues as compared to traps with either cue alone. However, these results could not easily be reproduced in greenhouses. The main factors responsible for this failure seem to be (1) the only moderate, additive increase of trap attractiveness when using combined visual and olfactory cues, and (2) the problems associated with odour diffusion. Unless a more attractive odour is found and a suitable odour dispenser is available, the use of odours to enhance sticky blue trap attractiveness for Western Flower Thrips cannot be recommended and, given the added cost for the trap, may not be affordable for growers.