Host plant finding in the specialised leaf beetle Cassida canaliculata: an analysis of small-scale movement behaviour

Abstract.  1. Host plant finding in walking herbivorous beetles is still poorly understood. Analysis of small-scale movement patterns under semi-natural conditions can be a useful tool to detect behavioural responses towards host plant cues.
2. In this study, the small-scale movement behaviour of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) was studied in a semi-natural arena ( r = 1 m). In three different settings, a host ( Salvia pratensis L., Lamiales: Lamiaceae), a non-host ( Rumex conglomeratus Murr., Caryophyllales: Polygonaceae), or no plant was presented in the centre of the arena.
3. The beetles showed no differences in the absolute movement variables, straightness and mean walking speed, between the three settings. However, the relative movement variables, mean distance to the centre and mean angular deviation from walking straight to the centre, were significantly smaller when a host plant was offered. Likewise, the angular deviation from walking straight to the centre tended to decline with decreasing distance from the centre. Finally, significantly more beetles were found on the host than on the non-host at the end of all the trials.
4. It is concluded that C. canaliculata is able to recognise its host plant from a distance. Whether olfactory or visual cues (or a combination of both) are used to find the host plant remains to be elucidated by further studies.     

Role of olfaction in host plant selection and local adaptation of a polyphagous herbivore,Eucolaspis Sharp

Host plant cues are known to shape insect–host plant association in many insect groups. More pronounced associations are generally manifested in specialist herbivores, but little is known in generalist herbivores. We used a polyphagous native beetle from New Zealand, bronze beetle, Eucolaspis sp. ‘Hawkes Bay’ (Chrysomelidae: Eumolpinae) to explore the role of olfaction in locating host plants and local adaptation. We also tested the role of other cues in the degree of acceptance or rejection of hosts. Adult Eucolaspis beetles were attracted to fresh leaf volatiles from apple and blackberry (Rosaceae). Male and female beetles responded similarly to olfactory cues of host plants. An indication of evolutionary affiliation was observed in olfactory preferences of geographically isolated conspecific populations. We found that geographically isolated populations of the beetles differ in their olfactory responses and exhibit some degree of local adaptation. However, irrespective of geographical and ecological associations, blackberry was preferred over apple as a feeding plant, and another novel plant, bush lawyer (Rubus australis), was readily accepted by 53.25% of the tested beetles. We show that plant volatiles play an important role in host location by Eucolaspis, but the acceptance or rejection of a particular host could also involve visual and contact cues.     

Orientation behavior of Propylaea japonica toward visual and olfactory cues from its prey–host plant combination

The lady beetle Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae) is an important predator of aphids in agroecosystems. The inundative release of coccinellid beetles can be an effective biological control strategy. An understanding of how biological control agents perceive and use stimuli from host plants is the key to successfully implement commercially produced predators. Here, we studied the relative role of visual and volatile cues. Dual‐choice assays using foraging‐naïve and foraging‐experienced P. japonica adults were conducted using cotton plants [Gossypium hirsutum L. (Malvaceae)] with or without infestation by the cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae). Overall, experienced beetles were more attracted than naïve beetles toward cues associated with aphid‐infested plants. Experienced beetles were also more responsive to olfactory cues compared with naïve beetles. Both foraging‐naïve and ‐experienced lady beetles integrate olfactory and visual cues from plants infested with aphids, with an apparently greater reliance on olfactory cues. The results suggest that foraging experience may increase prey location in P. japonica.     

How do sex and sexual maturation influence the response of Monochamus galloprovincialis to host odours?

Finding the right host plant for feeding and reproduction is crucial for herbivorous insects. Usually they need both visual and olfactory cues to locate and colonize their host plants, but the respective role of the two types of stimuli is difficult to disentangle. Model plants mimicking the shape and colour of natural hosts, combined with odours dispensers, are relevant tools for this purpose. We used dummy pines and cut branches of natural pines to investigate host attraction in Monochamus galloprovincialis, the insect vector of the pine wood nematode in Europe. We compared the behavioural response of males and females, sexually mature or immature, in a large climatic chamber and in an olfactometer. Immature females were significantly attracted by the sole odours released by pines. Immature males and mature males and females needed a combination of visual and olfactory cues to find the host tree. These findings suggest that beetles use both visual and chemical cues to locate pine trees but that relevant stimuli likely differ between beetles of different sex and sexual maturation status. Our results question the implementation of precautionary clear‐cuts around infested trees for limiting the spread of PWN.     

Foraging behaviour at the fourth trophic level: a comparative study of host location in aphid hyperparasitoids

In studies of foraging behaviour in a multitrophic context, the fourth trophic level has generally been ignored. We used four aphid hyperparasitoid species: Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae), Asaphes suspensus Walker (Hymenoptera: Pteromalidae), Alloxysta victrix (Westwood) (Hymenoptera: Alloxystidae) and Syrphophagus aphidivorus (Mayr) (Hymenoptera: Encyrtidae), to correlate their response to different cues with their ecological attributes such as host range and host stage. In addition, we compared our results with studies of primary parasitoids on the same plant–herbivore system. First, the olfactory response of females was tested in a Y‐tube olfactometer (single choice: plant, aphid, honeydew, parasitised aphid, aphid mummy, or virgin female parasitoid; dual choice: clean plant, plant with aphids, or plant–host complex). Second, their foraging behaviour was described on plants with different stimuli (honeydew, aphids, parasitised aphids, and aphid mummies). The results indicated that olfactory cues are probably not essential cues for hyperparasitoid females. In foraging behaviour on the plant, all species prolonged their total visit time and search time as compared to the control treatment (clean plant). Only A. victrix did not react to the honeydew. Oviposition in mummies prolonged the total visit time because of the long handling time, but the effect of this behaviour on search time could not be determined. No clear correlation between foraging behaviour and host stage or host range was found. In contrast to specialised primary aphid parasitoids that have strong fixed responses to specific kairomones and herbivore‐induced synomones, more generalist aphid hyperparasitoids seem to depend less on volatile olfactory stimuli, but show similarities with primary parasitoids in their use of contact cues while searching on a plant.     

Close-range, in-flight integration of olfactory and visual information by a host-seeking bark beetle

A long‐standing controversy questions whether foraging bark beetles assess the suitability of individual host trees using cues at close range while flying or engage in random landing followed by contact assessment. In most cases, visual discrimination mechanisms are ignored. We show that pheromone‐responding mountain pine beetles (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), can visually discriminate between ‘host’ (black) and ‘non‐host’ (white) traps arranged in small clusters, in the absence of additional host olfactory information, and that males (but not females) demonstrate a greater preference for combined host visual and olfactory cues. However, white, non‐host traps baited with a host volatile were as attractive as unbaited, black host traps. Our results support the hypotheses that when deciding to land, the MPBs integrate visual and olfactory information and can process cues in both sensory modes at relatively close range (≤2 m). Thus, host selection mechanisms in this species are unlikely to be random with respect to either sensory mode.     

Integration of visual and olfactory cues of hosts and non-hosts by three bark beetles (Coleoptera: Scolytidae)

Abstract.  1. There has been a long-standing pre-occupation with how phytophagous insects use olfactory cues to discriminate hosts from non-hosts. Foragers, however, should use whatever cues are accurate and easily assessed, including visual cues.
2. It was hypothesised that three bark beetles, the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, the Douglas-fir beetle (DFB), D. pseudotsugae Hopkins, and the western balsam bark beetle (WBBB), Dryocoetes confusus Swaine, integrate visual and olfactory information to avoid non-host angiosperms (e.g. paper birch, trembling aspen), that differ in visual and semiochemical profile from their respective host conifers (lodgepole pine, Douglas-fir, interior fir), and tested this hypothesis in a series of field trapping experiments.
3. All three species avoided attractant-baited, white (non-host simulating) multiple-funnel traps, and preferred attractant-baited black (host-simulating) traps. In experiments combining white, non-host traps with non-host angiosperm volatiles, bark beetles were repelled by these stimuli in an additive or redundant manner, confirming that these species could integrate visual and olfactory information to avoid non-host angiosperms while flying.
4. When antiaggregation pheromones were released from white traps, the DFB and MPB were repelled in an additive-redundant manner, suggesting that beetles can integrate diverse and potentially anomalous stimuli.
5. The MPB demonstrated the most consistent visual preferences, suggesting that it may be more of a 'visual specialist' than the DFB or WBBB, for which visual responses may be more contingent on olfactory inputs.     

The effects of non-host plant essential oil volatiles on the behaviour of the pollen beetle Meligethes aeneus

The use of semiochemicals for manipulation of the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae) is being investigated for potential incorporation into a push‐pull control strategy for this pest, which damages oilseed rape, Brassica napus L. (Brassicaceae), throughout Europe. The response of M. aeneus to non‐host plant volatiles was investigated in laboratory assays to establish whether they have any effect on host plant location behaviour. Two approaches were used. First a novel, moving‐air bioassay using air funnels was developed to compare the response of M. aeneus to several non‐host plant essential oils. The beetles avoided the host plant flowers in the presence of non‐host volatiles, suggesting that M. aeneus uses olfactory cues in host location and/or acceptance. The results were expressed as ‘repellency values’ in order to compare the effects of the different oils tested. Lavender (Lavendula angustifolia Miller) (Lamiaceae) essential oil gave the highest repellency value. In addition, a four‐arm olfactometer was used to investigate olfactory responses, as this technique eliminated the influence of host plant visual and contact cues. The attraction to host plant volatiles was reduced by the addition of non‐host plant volatiles, but in addition to masking the host plant volatiles, the non‐host volatiles were avoided when these were presented alone. This is encouraging for the potential use of non‐host plants within a push‐pull strategy to reduce the pest colonisation of crops. Further testing in more realistic semi‐field and field trials is underway.     

Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

The relevance of visual and olfactory cues for host‐plant location is investigated in males and females of the oligophagous mustard leaf beetle Phaedon cochleariae Fabricius (Coleoptera: Chrysomelidae). Different objects are offered in a walking arena and the behaviour of beetles is observed. Beetles orient toward vertically or horizontally striped black and white pattern independent of stripe orientation. The results suggest that contrast facilitates orientation in the field, whereas the pattern itself may be less important for host location in dense vegetation. The response to green and yellow objects is tested to investigate discrimination abilities between young (green) and mature (yellow) leaves. Beetles prefer green over yellow independent of material (cardboard or leaves of Nasturtium officinale R. Br., Brassicaceae). Preference behaviour tested in a dual‐choice contact assay coincides with visual preferences, where adults prefer young, more nutritious leaves for feeding and oviposition. Furthermore, females discriminate between visual cues of green leaves and green cardboard, whereas males do not, indicating that females are more sensitive in colour discrimination. Differences in colour wavelength influence the choice of beetle behaviour more strongly than differences in intensity. Both sexes of P. cochleariae prefer volatiles of the host plant N. officinale, whereas only females respond to the main volatile compound 2‐phenylethyl isothiocyanate. Given a choice between visual and olfactory cues, males orientate towards the colour cues, whereas females do not show any preferences. In males, visual cues may thus override olfactory cues, whereas, in females, both are equally important, which may reflect different ecological requirements and/or physiological abilities.     

Visual cues override olfactory cues in the host-finding process of the monophagous leaf beetle Altica engstroemi

It is generally assumed that specialist insect herbivores utilize plant odours to find their particular host plants and that visual cues are of minor importance in the host‐finding process. We performed Y‐tube olfactometer bioassays and small‐scale field experiments to determine whether, under laboratory and field conditions, the monophagous herbivore Altica engstroemi J. Sahlberg (Coleoptera: Chrysomelidae: Alticinae) is guided to its host plant Filipendula ulmaria (L.) Maxim. (Rosaceae) by visual or olfactory cues. The olfactometer tests showed that A. engstroemi was never attracted to odours, either from undamaged or from damaged plants. Even starvation for 24 h did not change this behaviour. However, the field experiment showed that visual cues alone were sufficient to attract a significant number of starved beetles when offered a choice between bagged host plants and bagged green plastic control ‘plants’. Our findings contrast with the general view that plant odours constitute the major cue in the host‐finding process among specialized phytophagous insects. A review of the literature for the period 1986–2006 inclusive, relating to host‐plant finding in Chrysomelidae, identified studies of 19 chrysomelid species, all of which were guided by olfactory cues. No species were guided to their host by visual cues. Although some studies demonstrated that chrysomelids may exhibit orientation responses to colour or contrast, our study on A. engstroemi is the only one demonstrating that visual cues affect host‐plant selection in a chrysomelid species. We suggest that the use of visual cues in host‐finding may evolve among chrysomelids with limited dispersal ability in persistent habitats and may be found among species monophagous on abundant host plants that dominate the structure of the plant community, that is, where the host plant's presence is predictable in time and space.     

Integration of Visual and Olfactory Cues in Host Plant Identification by the Asian Longhorned Beetle,Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae)

Some insects use host and mate cues, including odor, color, and shape, to locate and recognize their preferred hosts and mates. Previous research has shown that the Asian longicorn beetle, Anoplophora glabripennis (Motschulsky), uses olfactory cues to locate host plants and differentiate them from non-host plants. However, whether A. glabripennis adults use visual cues or a combination of visual and olfactory cues remains unclear. In this study, we tested the host location and recognition behavior in A. glabripennis, which infests a number of hardwood species and causes considerable economic losses in North America, Europe and Asia. We determined the relative importance of visual and olfactory cues from Acer negundo in host plant location and recognition, as well as in the discrimination of non-host plants (Sabina chinensis and Pinus bungeana), by female and male A. glabripennis. Visual and olfactory cues from the host plants (A. negundo), alone and combined, attracted significantly more females and males than equivalent cues from non-host plants (S. chinensis and P. bungeana). Furthermore, the combination of visual and olfactory cues of host plants attracted more adults than either cue alone, and visual cues alone attracted significantly more adults than olfactory cues alone. This finding suggests that adult A. glabripennis has an innate preference for the visual and/or olfactory cues of its host plants (A. negundo) over those of the non-host plant and visual cues are initially more important than olfactory cues for orientation; furthermore, this finding also suggests that adults integrate visual and olfactory cues to find their host plants. Our results indicate that different modalities of host plant cues should be considered together to understand fully the communication between host plants and Asian longhorned beetles.     

Role of visual and olfactory cues from agricultural hedgerows in the orientation behavior of multicolored Asian lady beetle (Coleoptera: Coccinellidae)

Harmonia axyridis Pallas is an introduced lady beetle common in eastern North American agroecosystems. Two-choice behavioral bioassays were performed to determine whether visual and olfactory stimuli from prey and host habitats could elicit taxis in wild-collected H. axyridis adults and whether beetles exhibit a preference among stimuli. Soybean aphid (Aphis glycines Matsumura) spends much of the year in agricultural hedgerows residing on buckthorn (Rhamnus cathartica L), and H. axyridis is frequently observed feeding on aphids in this habitat. Olfactory bioassays were performed in a Y-tube olfactometer and tested the response of beetles to the odor of buckthorn leaves, apple leaves (Malus domestica Borkh.), and buckthorn leaves both naturally and artificially infested with A. glycines. No differences were observed between the numbers of beetles moving toward the odor of buckthorn artificially infested with A. glycines and uninfested buckthorn, but more beetles preferred naturally infested buckthorn over uninfested buckthorn. Visual bioassays were performed in an acrylic tube arena,and tested beetle response to silhouettes and to apple and buckhorn leaves. Beetles were significantly more likely to choose silhouettes over blank space in visual trials. Significantly more beetles moved toward buckthorn leaves than blank space, but beetles did not discern between apple and buckthorn until olfactory cues were also included. This study lays the foundation for future work examining the response of H. axyridis to visual and olfactory cues in Ontario agroecosystems, which could help enhance effectiveness of H. axyridis as a biological control and mitigate its impacts as a pest species.     

Behavioural plasticity and sex differences in host finding of a specialized bee species

Many animals feed on flowers, and visual as well as olfactory cues are considered as most important mediators in animal–plant interactions. However, the relative importance of these cues is not well understood. Bees are the most important animal pollinators worldwide and here, we determined the importance of decoupled and combined visual and olfactory cues of Lysimachia punctata (Primulaceae) for host plant location in both sexes of the specialized, solitary bee, Macropis fulvipes (Melittidae). Lysimachia-inexperienced female bees preferred olfactory over visual cues though visual cues increased the attractiveness of olfactory ones. In experienced females, the importance of visual cues was increased. Both Lysimachia-naive and -experienced males relied more on visual cues as compared to females. This study demonstrates that the relative weighting of cues used for host plant finding depends on the sex and experience of M. fulvipes. The latter finding reveals the presence of learning-induced behavioural plasticity in host plant finding for a bee species. It may allow the bee to forage highly efficient. Visually guided female detection on flowers by males is a likely functional explanation for the differences in the weighting of visual and olfactory cues between the sexes.     

The parasitoid fly Exorista japonica uses visual and olfactory cues to locate herbivore‐infested plants

Some parasitoid flies exploit odors derived from plants as olfactory cues for locating the food plants of host insects, but the role of visual cues associated with plants remains largely unknown. The generalist tachinid Exorista japonica Townsend (Diptera: Tachinidae) is attracted to odors derived from maize plants [Zea mays L. (Poaceae)] infested by the larvae of Mythimna separata (Walker) (Lepidoptera: Noctuidae). In this study, we examined the effects of visual parameters on the olfactory attraction of female flies to host‐infested plants. A paper plant model of one of four colors (blue, green, yellow, or red) was placed in front of a host‐infested plant, which was hidden behind a mesh screen in a wind tunnel. The landing rate of females was significantly higher on the green plant model than on the other three models. When an achromatic plant model of one of four gray scales (white, light gray, dark gray, or black) was tested, the response rate of females was significantly higher towards the white model and decreased as the brightness of models decreased. Few female flies responded to the green plant model without odors of the host‐infested plants. When the four color plant models were placed together in a cage filled with odors of host‐infested plants, females remained significantly longer on the green model than on the other three models. These results showed that E. japonica females preferred the color green when odors of the host‐infested plants were present and suggest that E. japonica uses visual as well as olfactory cues to locate the host habitat.     

Olfactory response of predatory mites to vegetative and reproductive parts of coconut palm infested by <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

The phytophagous mite Aceria guerreronis Keifer is an important pest of coconut worldwide. A promising method of control for this pest is the use of predatory mites. Neoseiulus baraki (Athias-Henriot) and Proctolaelaps bickleyi Bram are predatory mites found in association with A. guerreronis in the field. To understand how these predators respond to olfactory cues from A. guerreronis and its host plant, the foraging behavior of the predatory mites was investigated in a Y-tube olfactometer and on T-shaped arenas. The predators were subjected to choose in an olfactometer: (1) isolated parts (leaflet, spikelet or fruit) of infested coconut plant or clean air stream; (2) isolated parts of non-infested or infested coconut plant; and (3) two different plant parts previously shown to be attractive. Using T-shaped arenas the predators were offered all possible binary combinations of discs of coconut fruit epidermis infested with A. guerreronis, non-infested discs or coconut pollen. The results showed that both predators were preferred (the volatile cues from) the infested plant parts over clean air. When subjected to odours from different infested or non-infested plant parts, predators preferred the infested parts. Among the infested plant parts, the spikelets induced the greatest attraction to predators. On the arenas, both predators preferred discs of coconut fruits infested with A. guerreronis over every other alternative. The results show that both predators are able to locate A. guerreronis by olfactory stimuli. Foraging strategies and implications for biological control are discussed.     

叶甲科昆虫的定殖机制

在复杂的生态环境中,叶甲科昆虫利用寄主植物的挥发物作为嗅觉信号,并协同视觉信号共同作用以提高其远距离搜寻和定位寄主的效率。叶甲科昆虫也释放信息素来调节同种或者异种个体的行为反应;找到寄主植物后,叶子的形态学特性和化学组分的浓度等接触性因素就会影响叶甲科昆虫对寄主植物的最终选择。叶甲对上述这些信号物质的反应也受叶甲本身状态的影响,如生殖、滞育、饥饿、交配以及取食等。叶甲科昆虫对寄主植物的搜寻、辨识和接受、取食以及繁殖的过程受一种或多种因素协同影响。从嗅觉、视觉和触觉等方面对叶甲科昆虫的定殖机制做一综述。     

Olfactory host‐finding behaviour of Oulema melanopus (Coleoptera: Chrysomelidae) and its parasitoid,Tetrastichus julis (Hymenoptera: Eulophidae)

Behavioural responses to the host‐associated olfactory cues have not been completely understood for the cereal leaf beetle, Oulema melanopus, and its principal parasitoid, Tetrastichus julis. We, therefore, investigated the role of olfactory cues in the host‐finding behaviour of these species using olfactory bioassays. Behavioural responses of O. melanopus to odours emanating from intact host plants (wheat, oat, barley) vs. a clean‐air control were tested using multichoice and two‐choice bioassays. For T. julis, responses of naïve and experienced adult female wasps to odours associated with the faecal coat of O. melanopus larvae were measured under multichoice and two‐choice conditions. Our results indicate that olfactory cues are involved in the host‐finding behaviour of both O. melanopus and T. julis. Olfactory responses of O. melanopus were influenced by the sex of the beetle and the physiological stage of adults (reproductively active vs. in reproductive diapause). Females respond to olfactory cues in greater proportions than males, and reproductively active, overwintered adults show greater responsiveness than teneral adults in reproductive diapause. Behavioural responses to cues emanating from different crop species were different in multichoice bioassays but not in two‐choice bioassays. Further, we report for the first time that the olfactory cues associated with the faecal coat of O. melanopus evoke host‐finding behaviour of its parasitoid, T. julis. Naïve female wasps are more likely to use these cues to locate the potential host than experienced females. The results of this investigation provide insights into host finding by both the species and the nature of behavioural response brought about by olfactory stimuli, and the results can help to design strategies to improve parasitoid activity by enhancing the crop environment to generate cues for host finding and to manage O. melanopus populations.     

Evidence for the influence of conspecific chemical cues on <Emphasis Type="Italic">Aphthona nigriscutis</Emphasis> (Coleoptera: Chrysomelidae) behaviour and distribution

Although the distribution of biological control agents may have a significant effect upon their impacts, the mechanisms regulating these distributions are often unknown. Such is the case with Aphthona nigriscutis, a classical biological control agent of leafy spurge in North America. These beetles assume aggregated distributions at some sites but disperse rapidly at others. The potential influence of plant and insect-factors upon aggregation and dispersal was investigated to try to explain these observations. Male beetles produce a putative aggregation pheromone. Responses of conspecifics to male-associated cues are greater when beetles are feeding on host plants. Densities of beetle groups greatly impact their attractiveness. Males are more sensitive to dispersal cues and females are more sensitive to congregation cues.     

棉铃虫低龄幼虫对花香挥发物的联系性学习

鳞翅目昆虫的寄主选择主要是成虫的任务,但幼虫也可以精细调节取食部位。低龄幼虫记忆一些与食物伴随的化学信息能够提高适合度。当幼虫被迫离开寄主植物后,最好是搜索与此前取食过的寄主气味相似的植物,以便节省寄主转移的生理代谢成本。棉铃虫幼虫嗜食作物花器,因此推测花香挥发物可以代表幼虫食物的典型化学信息。采用人工饲料为无条件刺激,在条件化训练开始时,使初孵幼虫取食时暴露在7种花香挥发物下,随后7 d逐日测试低龄幼虫学习表现。结果发现,在7次测试中,苯乙醛选择频次有3次显著多于对照,芳樟醇条件化组在2次测定中处理被选频次显著或极显著多于对照,苯乙醇条件化组仅1次对处理选择频次显著多于对照,其他4种挥发物无论训练时间长短均不能造成嗅觉偏好性的改变,说明棉铃虫在取食过程中是选择性采集食物关键化学信息。然而,无经历组无论训练时间如何均不对苯乙醛表现出嗅觉偏好性,证实气味偏好性的改变并非生理性成熟所致。总之,和同种的成虫以及若虫期比较活泼的其他种类相比,棉铃虫低龄幼虫嗅觉联系性学习表现较差,并且嗅觉偏好性变化与条件化训练时长没有明确关系,结合棉铃虫的生态学习性讨论了可能的原因。     

The Role of Olfactory Cues for the Search Behavior of a Specialist and Generalist Butterfly

Searching for resources is often a challenging task, especially for small organisms such as insects. Complex stimuli have to be extracted from the environment and translated into a relevant behavioral output. A first step in this process is to investigate the relative roles of the different senses during search for various resources. While the role of olfaction is well documented in nocturnal moths, the olfactory abilities of the closely related diurnal butterflies are poorly explored. Here we investigated how olfactory information is used in the search for host plants and asked if these abilities varied with levels of stimulus complexity. Thus, we tested two nymphalid butterfly species with divergent host plant range in a two-choice olfactometer testing different combinations of host and non-host plants. The experiments show both the monophagous Aglais urticae and the polyphagous Polygonia c-album could navigate towards an odor source, but this ability varied with context. While mated females exhibited a preference for their host plant, unmated females of both species did not show a preference for host plant cues. Furthermore, both species showed inabilities to make fine-tuned decisions between hosts. We conclude that olfactory cues are important for butterflies to navigate towards targets. We argue that there are limitations on how much information can be extracted from host volatiles. These results are discussed in the light of neural processing limitations and degree of host plant specialization, suggesting the necessity of other sensory modalities to sharpen the decision process and facilitate the final oviposition event.