Visual Lures Research Articles

Flowers ofCypripedium fargesii(Orchidaceae) fool flat-footed flies (Platypezidae) by faking fungus-infected foliage

Charles Darwin was fascinated by the orchid-pollinator interactions, but he did not realize that many orchid species are pollinated by deceit. Cypripedium, a model lineage of nonrewarding orchid flowers, is pollinated primarily by bees. Here we present both an example of floral mimesis of fungus-infected foliage in orchids and an example of flat-footed flies (Agathomyia sp.; Platypezidae) as pollen vectors for angiosperms. Cypripedium fargesii is a nectarless, terrestrial, endangered orchid from southwestern China that requires cross-pollination to produce the maximum number of viable embryos. All insects caught entering or leaving the labellum sac were Agathomyia sp. carrying conidia of Cladosporium sp. on their mouthparts and legs, suggesting mycophagy. Blackish hairy spots on the upper surface of foliage may imitate black mold spots, serving as short-term visual lures. Some odor molecules also associated with Cladosporium cultures were isolated in the floral scent. Mimesis of fungus-infected foliage probably represents an overlooked but important option in angiosperm diversification, because there are three to five more Cypripedium spp. in southwestern China with the same mode of floral presentation and black-spotted hairy leaves.

Rare white‐flowered morphs increase the reproductive success of common purple morphs in a food‐deceptive orchid

How floral colour polymorphism can be maintained in evolutionary time is still debated. In rewardless orchids, it is unknown whether rare white-flowered morphs differ in scent chemistry from pigmented morphs, and whether such intraspecific variation in floral signals may have an impact on reproductive success. We compared the chemical composition of floral volatiles emitted by white- and purple-flowered morphs of Orchis mascula, and recorded the fruit set of both colour morphs. We also used white ping-pong balls to mimic white-flowered morphs in field bioassays. We found that colour polymorphism was not associated with floral odour polymorphism. Surprisingly, when populations of purple-flowered plants included a few white-flowered individuals, the fruit set of the purple morph increased significantly (from 6 to 27%), while that of the white morph remained low. We obtained the same fourfold increase in fruit set when using ping-pong balls as visual lures, demonstrating the association between colour variation and fruit set, and the key role of visual signals in pollinator attraction. Our results are incompatible with negative frequency-dependent selection, a hypothesis invoked to explain colour polymorphism in other rewardless orchids. We propose several hypotheses to explain the maintenance of white morphs in O. mascula.

Comparison of two luring methods for trapping brushtail possums in non-forest habitats of New Zealand

A national trap–catch monitoring protocol been developed to standardise the settingand luring of leg-hold traps for monitoring brushtail possum control operations in New Zealand. The methods recommended were initially developed for use in forest and scrub areas, but a suitable luringsystem was needed to monitor possum populations in grassland (tall tussock) areas. A backing board in a metal frame was developed to which the standard dry flour and icing sugar lure could be applied. Because this added cost to monitoring operations, a trial was carried out to assess whether backing boards could be omitted and the lure placed directly on the ground. Results showed that traps with groundset lure had a capture rate of only about 50% of the rate achieved with lured backing boards. Traps with backing boards are more visually attractive, which probably explains their higher capture rate. To increase the capture efficiency of trapping, we recommend further research on improved visual lures rather than olfactory ones.

Novel visual‐cue‐based sticky traps for monitoring of emerald ash borers, Agrilus planipennis (Col., Buprestidae)

AbstractWe examined various methods of trapping emerald ash borers (EAB), Agrilus planipennis Fairmaire, using solely visual cues based on previous work that has documented the importance of visual cues in EAB mate location. Here, we give the results of two of these methods, coloured sticky cards (yellow or blue), or live ash leaves covered with spray‐on adhesive to which dead male EAB visual lures had been pinned. Feral male beetles were captured effectively on the sticky traps made from dead male EAB on ash leaves. These sticky‐leaf‐traps captured more male EAB when deployed in high‐population density areas than low‐density areas, but did capture EAB even at lower population densities. More feral males were captured on these traps when they were placed higher in the trees, regardless of the population density of EAB. Very few feral female EAB were captured using the sticky‐leaf‐traps. This novel method of EAB trapping may allow ‘real‐time’ population detection and monitoring of EAB adults during the active flight period rather than locating larval galleries during the autumn and winter after adult flight and attack. Feral male beetles were also captured using standard yellow‐ or blue‐coloured sticky cards to which male EAB had been affixed with adhesive; however, this type of trap was much less effective overall than using the sticky‐leaf‐traps. Furthermore, Agrilus cyanescens, a species similar in colour to EAB but smaller in size, showed a strong response to blue‐coloured sticky traps to which dead male EAB had been affixed with adhesive, suggesting a general use of visual cues in the mating systems of some of the other Buprestidae as well.

Function of bright coloration in the wasp spider Argiope bruennichi (Araneae: Araneidae)

There are two major competing explanations for the counter-intuitive presence of bright coloration in certain orb-web spiders. Bright coloration could lure insect prey to the web vicinity, increasing the spider's foraging success. Alternatively, the markings could function as disruptive camouflage, making it difficult for the insect prey to distinguish spiders from background colour variation. We measured the prey capture rates of wasp spiders, Argiope bruennichi, that were blacked out, shielded from view using a leaf fragment, or left naturally coloured. Naturally coloured spiders caught over twice the number of prey as did either blacked-out or leaf-shielded spiders, and almost three times as many orthopteran prey. Spectrophotometer measurements suggest that the bright yellow bands on the spider's abdomen are visible to insect prey, but not the banding on the legs, which could disguise the spider's outline. Thus, our results provide strong support for the hypothesis that bright coloration in the wasp spider acts as a visual lure for insect prey and weak support for the hypothesis that the arrangement of the banding pattern across the spider's body disguises the presence of the spider on the web.

Deceptive color signaling in the night: a nocturnal predator attracts prey with visual lures

The role color signaling plays in the nocturnal condition of the terrestrial ecosystem is currently poorly understood. In general, arthropods active in the night are inconspicuously colored. However, in addition to inconspicuously colored dorsum, several genera of nocturnal orb spiders also have conspicuous ventrum spots. In this study, we tested whether the inconspicuously colored dorsum functioned to reduce spiders‘ visibility to diurnal predators while the spiders were perching on bark with ventrum spots well concealed. We also evaluated when spiders sit on webs with conspicuous ventrum spots fully exposed, would they serve as deceptive color signals to lure visually orientated nocturnal prey. We first quantified how diurnal hymenopteran predators viewed the dorsum and nocturnal lepidopteran prey viewed the ventrum spots of nocturnal orb spiders Neoscona punctigera by calculating color contrasts. The diurnal color contrast of spiders’ dorsum when viewed by hymenopteran insects against bark was lower than the discrimination threshold. However, the nocturnal color contrasts of spiders‘ ventrum spots when viewed by moths were high. In the field, webs with N. punctigera intercepted significantly more insects than those without. When the color signal of ventrum spots was altered by paint, webs’ prey interception rates decreased significantly. These results demonstrate that even in the nocturnal condition certain terrestrial organisms exhibit visual lures to attract prey. Key words: color contrast, Neoscona punctigera, spider, visual ecology. [Behav Ecol]

Diurnal and nocturnal prey luring of a colorful predator

While animal color signaling has been studied for decades, we have little knowledge of the role conspicuous body coloration plays in the nocturnal context. In this study we explored animal color signaling in both diurnal and nocturnal contexts to arrive at a more comprehensive understanding of its function. We quantified how the brightly colored giant wood spiders Nephila pilipes are viewed by nocturnal insects, and performed field manipulations to assess the function of a spider's coloration in both diurnal and nocturnal conditions. Seen through the eyes of moths, the conspicuous body parts of spiders are quite distinctive from the vegetation background. The presence of N. pilipes significantly increased the diurnal as well as the nocturnal prey interception rates of their webs, but these rates were significantly reduced when the conspicuous color signals of N. pilipes were altered by black paint. A comparison of the diurnal and nocturnal hunting performances of spiders showed that their conspicuous coloration had a higher luring effect under dim light conditions. These results demonstrate that the conspicuous body coloration of N. pilipes functions as a visual lure to attract both diurnal and nocturnal prey. It seems that nocturnal insects are the major target of this colorful sit-and-wait predator. We suggest that the selection pressure to effectively exploit the color vision of nocturnal prey could be one of the major forces driving the evolution of spider coloration.

Signaling by decorating webs: luring prey or deterring predators?

Many organisms convey false signals to mislead their prey or predators. Some orb-weaving spiders build conspicuous structures on webs called decorations. Web decorations and spider colorations are both suggested to be important signals involved in interactions between spiders and other organisms. There are several hypotheses about the functions of signaling by decorations, among which prey attraction had received much support, but empirical evidence regarding predator defense is controversial. In this study, we conducted field experiments to investigate the effects of spider decoration and coloration on insect interception rates of webs built by Argiope aemula and to evaluate whether presence of decorations may decrease predation risk of spiders. Decorated webs with spiders present had the highest prey interception rate, followed by undecorated webs with spiders, and then undecorated webs without spiders. Such results indicated that decorations of Argiope spiders functioned as visual lures, and so did spiders’ bright body colorations. In the field, almost all wasp attack events occurred on medium-sized spiders rather than on large ones. Moreover, medium-sized Arg. aemula on decorated webs received far more attacks than those on undecorated webs. Results of this study thus show that the signals conveyed by decorations can visually lure prey but at the cost of an increased predation risk. [Behav Ecol]

Nocturnal hunting of a brightly coloured sit-and-wait predator

Many studies have shown that colour signals are important in spidereinsect interactions. The bright body coloration of certain orb-weaving spiders seems to serve as a visual lure to diurnal prey. However, no studies have examined whether this coloration affects spiders’ nocturnal hunting. Some nocturnal lepidopteran pollinators use colour vision to locate their food resources, so orb-weaving spiders’ bright coloration may also be attractive to visually oriented nocturnal insects. To assess the role of body coloration of the orchid spider, Leucauge magnifica, in luring nocturnal prey, we investigated whether: (1) these spiders actively hunt during the night; (2) nocturnal prey comprise a significant proportion of total prey intake; and (3) altering body colour signals significantly affect the nocturnal prey capture rate. Round-the-clock monitoring of L. magnifica activity patterns showed that they hunt more actively at night. Owing to the presence of relatively large moths in their diet at night, L. magnifica consumed higher prey biomass during nocturnal hunting, although this was not statistically significant owing to large variability. Painting over the spiders’ yellow ventrum stripes significantly reduced their moth capture rate. These results show that certain orb-weaving spiders with bright body coloration attract nocturnal prey, and they obtain larger prey from nocturnal hunting.

Function of being colorful in web spiders: attracting prey or camouflaging oneself?

Bright body colorations of orb-weaving spiders have been hypothesized to be attractive to insects and thus function to increase foraging success. However, the color signals of these spiders are also considered to be similar to those of the vegetation background, and thus the colorations function to camouflage the spiders. In this study, we evaluated these 2 hypotheses by field experiments and by quantifying the spiders’ visibility to insects. We first compared the insect interception rates of orbs constructed by the orchid spider, Leucauge magnifica, with and without the spider. Orbs with spiders intercepted significantly more insects than orbs without. Such a result supported the prey attraction but not the camouflaging hypothesis. We then tested whether bright body colorations were responsible for L. magnifica’s attractiveness to insects by manipulating the spiders’ color signals with paint. Alteration of color signals significantly reduced L. magnifica’s insect interception and consumption rates, indicating that these spiders’ bright body parts were attractive to insects. Congruent with the finding of field manipulations were the color contrasts of various body parts of these spiders. When viewed against the vegetation background, the green body parts were lower, but the bright parts were significantly higher than the discrimination threshold. Results of this study thus provide direct evidence that bright body colorations of orb weavers function as visual lures to attract insects. Key words: color contrast, Leucauge magnifica, orchid spider, visual ecology.

Novel Visual Lures for the Management of Brushtail Possums

Author(s): Ogilvie, Shaun C.; Sakata, Keisuke; Thomas, Malcolm D.; Maddigan, Fraser | Abstract: The successful management of vertebrate wildlife populations can be dependent on the availability of reliable monitoring methods, and, depending on the status of the species in question, effective methods of conservation or control. The brushtail possum, introduced to New Zealand from Australia, is considered New Zealand’s number one vertebrate pest. We assessed possum preferences for 3 types of visual lures and the potential use of this information for enhancing existing possum control technologies. Significantly more lures were interfered with by possums when the lures were associated with a luminescent strip, compared to lures that were plain white or UV-enhanced (P l 0.01 in both cases). In addition, more possums were killed when luminescent lures were attached to kill traps and bags of bait than when these devices were deployed without lures. This study has highlighted new information showing that luminescent lures could be a valuable new tool in the management of nocturnal marsupials, be they species considered pests (such as the brushtail possum in New Zealand), or species of conservation concern, such as many of Australia’s marsupial species.

Mechanical Mouse Lure for Brown Treesnakes

The importance of prey movement for stimulating feeding behavior of Brown Treesnakes was tested by using a mechanical mouse model in combination with and without prey odor. Prey movement was found to be important in stimulating brown treesnake feeding behavior. Prey movement combined with prey odor was not significantly different than prey movement alone. In the development of simple artificial lures based on the stimulus of live mice, visual lures lacking movement are likely to be ineffective. Lures that combine a visual moving stimulus with prey odor are likely to be the most effective artificial lure for trapping brown treesnakes.

Signal conflict in spider webs driven by predators and prey

Variation in the sensory physiologies of organisms can bias the receptions of signals, driving the direction of signal evolution. Sensory drive in the evolution of signals may be particularly important for organisms that confront trade–offs in signal design between the need for conspicuousness to allow effective transfer of information and the need for crypsis of the signal to unintended receivers. Several genera of orb–weaving spiders include conspicuous silk designs, stabilimenta, in the centre of their webs. Stabilimenta can be highly visible signals to predators, warning them of the presence of a noxious, sticky silk web. However, stabilimenta can also be used by prey as a signal in avoidance of webs, creating a trade–off in signal visibility. I argue that the derived spectral properties of stabilimentum silk have resulted in part from this conflict. The innate colour preferences of insects, their ability to learn colours, and the spectral properties of flowers all suggest that the reflectance spectra of stabilimenta renders them relatively cryptic to many insect prey, while maintaining their visibility to vertebrate predators.

Comparison of the attractiveness of acoustic and visual stimuli for brushtail possums

Population control of the brushtail possum using poisons and traps relies on their interaction with baits and trap mechanisms. It follows that lures that can consistently attract possums will help increase killing efficiency. We tested the effectiveness of two different types of stimulus (white light and an electronic pulse sound, “beep") for attracting possums. Seventeen wild‐caught possums were given a choice between two boxes, one of which had one of the stimuli associated with it and a plain control box. Attractiveness was assessed by scoring the incidence of three specific behaviours: approaching box, putting head into box, or entering box. Most animals interacted with at least one of the boxes, although there was a tendency for increased interest in both boxes when the light box was present. An equal number of possums entered the light and beep boxes, but a significant number repeatedly entered the beep box more often. Acoustic and visual lures may have a role in increasing the attractiveness of traps, thereby improving their effectiveness.

Control of Feral Cats for Nature Conservation. I. Field Tests of Four Baiting Methods

Four methods of baiting were evaluated on a radio-collared population of feral cats on Heirisson Prong, Shark Bay, Western Australia. Dried-meat baits, baiting rabbits to kill cats through secondary poisoning, a fishmeal-based bait and a bait coated in the flavour enhancer Digest were tested. All proved to be ineffective for controlling feral cats. Future research should explore baits more ‘natural’ in appearance and the effect of visual lures, and possibly bait over a larger area to increase the number of cats exposed to baits.

Field Evaluation of Olfactory Lures for Feral Cats (Felis catus L.) in Central Australia

Field trials were conducted in central Australia to evaluate the ability of various olfactory lures to attract feral cats (Felis catus L.). Ten food-based lures, one plant extract and two scent-based lures (anal-gland preparations from male and female cats) were evaluated on the basis of visitation rates and elicited behavioural responses. A visual lure composed of bird feathers was also tested in conjunction with the scent-based lures. One food-based lure (sun-rendered prawn) and both of the scent-based lures were found to attract feral cats. The visual lure did not enhance the attractiveness of the scent-based lures. The possible uses and relative advantages of these lures in control programmes and in ecological studies of cats are discussed.

Distinctive markings of sharks: Ethological considerations of visual function

Behavioral reports on free-ranging sharks or those held under semifield conditions almost invariably contain a section on social activities. The frequent inclusion of such information allows the cautious suggestion that most, if not all, sharks possess the means by which requisite information is transferred between individuals so that social functions can be achieved. Such transfer could be readily accomplished through the visual modality in conjunction with appropriate optical signals, the latter being specific motor patterns and/or specific body markings. Many sharks possess body markings that likely serve as effective camouflage, particularly among those animals dwelling on or near the bottom. Distinctive markings are found, however, also on fishes that inhabit open water (pelagic) regions and it is one group of these enigmatic markings, the distinctive, fin markings of sharks within the well-known families Carcharhinidae and Sphyrnidae that forms the subject of this report. This report summarizes various functions that such markings could subserve. It focuses, then, on the more probable functions in light of correlational data relating the intensity of such markings to certain water conditions. The report concludes by considering one of the most puzzling cases of fin markings, the large white tipped “paddles” of the oceanic whitetip shark Carcharhinus longimanus. Evidence suggests that such markings are, in fact, visual lures that aid in the capture of extremely rapid moving prey.

Pollination of Androdioecious Xerospermum intermedium Radlk. (Sapindaceae) in a rain forest

Xerospermum intermedium, a fairly common understorey species in the West Malesian lowland dipterocarp forest is androdioecious, with delayed self-compatibility. It flowers annually, and has an extended flowering period, with individuals flowering somewhat asynchronously, presenting small flowers with minimal visual lures. The flowers are visited by an unrestricted array of apparently imprecise opportunistic feeders, predominated by trigonid bees and butterflies. Most of these visitors exhibit low fidelity and forage opportunistically on numerous competing tree species. Presentation of nectar in alternating rhythms between the male and hermaphrodite trees appears to induce pollinator movement between them. Out of such alternating visits between the sexes, a low level of short-range inter-tree pollen transfer by trigonids and butterflies seems to occur. Despite the elaborate system which promotes pollinator movement between the sexes, this species has retained a low level of self-compatibility. The physical barriers to pollinator movement in the understorey, and high interspecific competition for pollinators by a large number of tree species, appear therefore to make it difficult to maintain an obligate outbreeding system. Hence, androdioecism may be one of the explanations for the survival of X. intermedium.