Obstacle perception by insect antennae during terrestrial locomotion

Abstract. Insect antennae bear several types of sensilla including chemo-receptors, hygroreceptors, thermoreceptors and mechanoreceptors. A large proportion of sensilla is chemoreceptors, providing olfactory function. Pro-prioreceptors located on the antennae provide information on the position of these organs and are used in flight control. This type of sensillum is present in most insects and might serve other functions. We tested the hypothesis that antennae are used to perceive obstacles in the path of walking beetles. When adult Colorado potato beetles, Leptinotarsa decemlineata (Say), touch an obstacle with their antennae during terrestrial locomotion, they modify the angle of their body to allow the tarsi of one prothoracic leg to reach the top of the obstacle. Our results demonstrate that antennae, by their movements and their position ahead of the beetle, provide information on the presence of the obstacle necessary to initiate step-up behaviour. Furthermore, the change in the body angle needed to increase the reach of the prothoracic leg and step on the obstacle, is proportional to the height of the obstacle. Since the eyes are not involved in the process, normal behaviour can be performed in the dark.     

Visual control of cursorial prey pursuit by tiger beetles (Cicindelidae)

Target detection poses problems for moving animals, such as tiger beetles, that track targets visually. The pursuer's movements degrade target image contrast and induce reafferent image movement that confounds continuous detection of prey. In nature, beetles pursue prey discontinuously with several iterations of stop-and-go running. The beetle's dynamics were analyzed by filming pursuits of prey or experimenter-controlled dummies. Durations of stops are inversely related to prey visual angular velocity; as the prey image moves between neighboring ommatidial fields, the beetle relocalizes it and renews running. During subsequent runs, translation and rotation depend upon prey visual angular velocity and position, respectively, seen during the previous stop. The beetle runs, then stops, while prey continues moving. After two to three iterations of stop-and-go the beetle catches its prey, suggesting open-loop control of running. Computational model simulations produce good qualitative spatio-temporal fit with actual pursuits. However, when pursuing prey dummies, beetles track continuously and quickly follow changes in target position, suggesting closed-loop control using a position-sensitive servo mechanism. Differences between these types of pursuit control system are discussed with respect to limitations in signal detection, particularly spatio-temporal contrast, that may force beetles to use an open-loop system. Accepted: 7 April 1997     

Active tactile exploration for adaptive locomotion in the stick insect

Insects carry a pair of actively movable feelers that supply the animal with a range of multimodal information. The antennae of the stick insect Carausius morosus are straight and of nearly the same length as the legs, making them ideal probes for near-range exploration. Indeed, stick insects, like many other insects, use antennal contact information for the adaptive control of locomotion, for example, in climbing. Moreover, the active exploratory movement pattern of the antennae is context-dependent. The first objective of the present study is to reveal the significance of antennal contact information for the efficient initiation of climbing. This is done by means of kinematic analysis of freely walking animals as they undergo a tactually elicited transition from walking to climbing. The main findings are that fast, tactually elicited re-targeting movements may occur during an ongoing swing movement, and that the height of the last antennal contact prior to leg contact largely predicts the height of the first leg contact. The second objective is to understand the context-dependent adaptation of the antennal movement pattern in response to tactile contact. We show that the cycle frequency of both antennal joints increases after obstacle contact. Furthermore, inter-joint coupling switches distinctly upon tactile contact, revealing a simple mechanism for context-dependent adaptation.     

Pre-Mating Reproductive Isolation in Tiger Beetles (Carabidae: Cicindelinae): an Examination of the Role of Visual and Morphological Feedback

The biological species concept depends on mechanisms isolating reproduction to taxonomically define a species and to explain the disadvantages, and subsequent lack, of hybridization. In co-occurring tiger beetles (Carabidae: Cicindelinae), these between-species barriers are not readily apparent. To understand the characteristics potentially responsible for this isolation, we conducted behavioral and morphological experiments with two pairs of tiger beetle species. Choice trials showed males use visual cues to trigger the pursuit of potential mates and prefer females who appear similar in color. Geometric morphometric techniques allowed us to quantify shape differences in the mandibles of all four species. Previously, it was proposed that the mandible-coupling sulcus pairing acted as a lock-and-key mechanism to provide feedback necessary for species recognition. Our results, however, suggest that although there are significant differences in shape, these differences do not provide any feedback to the male or enhance his ability to retain his grasp on the female. Taken together, these findings suggest that vision, rather than the traditional mandibular lock-and-key hypothesis, may play a key role in reproductive isolation for co-occurring tiger beetle species.     

Status and conservation of an imperiled tiger beetle fauna in New York State,USA

New York has 22 documented species of tiger beetles (Coleoptera: Cicindelidae). Over half of these species are considered rare, at risk, or potentially extirpated from the state. These rare species specialize on three sandy habitat types under threat from human disturbance: beaches, pine barrens, and riparian cobble bars. In 2005, we began a status assessment of eight of New York’s rarest tiger beetles, examining museum records, searching the literature, and conducting over 130 field surveys of historical and new locations. Significant findings included (1) no detections of four of the eight taxa; (2) no vehicle-free beach habitat suitable for reintroducing Cicindela dorsalis dorsalis; (3) C. hirticollis at only 4 of 26 historical locations; (4) C. patruela patruela at only one site statewide; and (5) C. ancocisconensis at only 3 of 28 de novo survey sites. Additional species that might be declining deserve our attention, as do some threats to tiger beetle habitats, like lack of beach wilderness, fire suppression in pine barrens, and river damming. Rarity in tiger beetles is a result of varying ecologies, which suggest different conservation strategies. Future inventory and documentation of tiger beetle occurrences need to take into account the metapopulation structure and imperfect detectability of these rare insects.     

How unique is the tiger beetle fauna (Coleoptera,Cicindelidae) of the Balkan Peninsula?

The tiger beetle fauna of the Balkan Peninsula is one of the richest in Europe and includes 19 species or 41% of the European tiger beetle fauna. Assembled by their biogeographical origins, the Balkan tiger beetle species fall into 14 different groups that include, Mediterranean, Middle Oriental, Central Asiatic, Euro-Siberian, South and East European, Pannonian-Sarmatian, West Palaearctic, Turano-European and Afrotropico Indo-Mediterranean species. The Mediterranean Sclerophyl and the Pontian Steppe are the Balkan biogeographical provinces with the highest species richness, while the Balkan Highlands has the lowest Cicindelidae diversity. Most species are restricted to single habitat types in lowland areas of the Balkan Peninsula and only Calomera aulica aulica and Calomera littoralis nemoralis occur in respectively 3 and 4 different types of habitat. About 60% of all Balkan Cicindelidae species are found in habitats potentially endangered by human activity.     

夜行性昆虫微光视觉行为及其视觉适应机制

作为昆虫种群的重要组成部分,夜行性昆虫成功进化出了与其生存环境相适应的感觉机制,普遍认为夜行性昆虫主要依靠嗅觉和机械性感受等来探索环境,其视觉器官发生了退化或功能丧失。近年来,随着红外夜视、视网膜电位(electroretinogram, ERG)和视觉神经等生物新技术的应用,昆虫视觉生态学研究出现了突破性进展,自2002年以来陆续发现蛾类、蜜蜂和蜣螂等夜行性昆虫进化出了非凡的微光视觉(dim-light vision)能力,在夜晚(光照强度低于0.3 lx)依然可以如同在明亮的白天一样清晰、准确地感知目标物体特定的视觉特性,如明暗、颜色、形状、大小、对比度、偏振光和运动状态等,展现出视觉调控夜行性昆虫行为活动的巨大潜力。此外,这些夜行性昆虫复眼瞳孔、小眼焦距、视杆和色素颗粒等方面进化出了一些相应的形态生理特征,以提高光学灵敏度适应夜间微光环境。鉴于夜行性昆虫微光视觉行为及其视觉适应机制的研究尚处于起步阶段,仅见于少数访花昆虫或粪食性昆虫,建议加强以下几个方面的研究：(1)重大夜行性农业害虫的微光视觉及其应用的研究;(2)非典型重叠复眼的光学结构特征及其应对微光环境的适应机制研究;(3)夜行性昆虫响应微光环境的视觉适应机制研究;(4)基于夜行性昆虫微光视觉行为研发新型害虫防控技术。     

Species designation of the Bruneau Dune tiger beetle (Cicindela waynei) is supported by phylogenetic analysis of mitochondrial DNA sequence data

Beetles comprise nearly one quarter of described species and show high levels of morphological and ecological diversification. Because of their wide distribution, ease of detection, and correlation of species richness patterns with other taxa, tiger beetles have been recommended for use as a global indicator of regional biodiversity, requiring accurate taxonomic designations. The Bruneau Dune tiger beetle (Cicindela waynei), whose habitat consists of an isolated dune field in southern Idaho, was recently described as a distinct species from the St. Anthony Dunes tiger beetle (C. arenicola) based on morphological characteristics. While these characteristics include distinct differences in genital morphology that could indicate intrinsic reproductive isolation, morphological characteristics have sometimes been misleading in tiger beetle taxonomy. To evaluate genetic support for this species designation, we analyzed 1,751 base pairs of mitochondrial DNA sequence from 147 tiger beetles collected throughout the range of both C. arenicola and C. waynei. Maximum-likelihood and Bayesian phylogenetic analyses indicated monophyly for C. waynei on a well-supported, short branch nested within C. arenicola. Bayesian species delimitation analyses strongly supported C. waynei as a distinct species (speciation probability = 1.0) with the estimated time of divergence ca. 14,500–67,000 years ago. This lack of reciprocal monophyly and recency of speciation is consistent with C. waynei as a member of an evolutionary front where speciation has occurred at a rapid rate. Mitochondrial sequence data supports the species designation of C. waynei, emphasizing the need to determine appropriate management for this species and its restricted habitat.     

Diurnal Tiger Beetles (Coleoptera: Cicindelidae) Capture Prey Without Sight

Although much research has examined the process of prey capture by tiger beetles, an underlying assumption in this work is that tiger beetles are principally, or even exclusively, visual predators. Because this assumption is untested, we performed a series of experiments on four diurnally active tiger beetles in the Genus Cicindela. Individual beetles were placed in chambers in complete darkness and allowed to forage on apterous Drosophila for 6 h. Contrary to expectations, adults of all tested species captured more than 90% of prey items. These results show that other modalities can be used by tiger beetles during prey capture. Beyond potentially providing an explanation for observed night activity in tiger beetle species, the significance of these findings lies in the need to test underlying assumptions of even well-studied organisms.     

Additive and synergistic integration of multimodal cues of both hosts and non-hosts during host selection by woodboring insects

Host selection by herbivorous insects is primarily thought to depend on attraction to olfactory cues emitted from the host species. However, the discrimination of these hosts from non-host species may also arise from the adaptive detection and avoidance of non-host cues, including visual characteristics. Many generalist, conifer-colonising beetles, for example, use characteristic volatiles to identify and discriminate against non-host angiosperm trees such as aspens and birches while flying. These trees also differ in bark reflectance characteristics, which could also mediate host/non-host discrimination by interacting with semiochemicals. We tested this hypothesis by evaluating the responses of eight species of polyphagous woodboring beetles to traps which simulated the visual appearance of coniferous hosts (black) and angiosperm non-hosts (white), and which were baited with host or non-host volatiles. As predicted, three species of large woodboring beetle and a woodboring wasp all avoided white, non-host-simulating traps that were baited with attractive kairomones, and preferred black, host-simulating traps. Conversely, three ambrosia beetle species demonstrated weaker visual preferences, possibly because they preferentially colonise fallen hosts that would transmit less accurate visual information. However, the ambrosia beetle Trypodendron lineatum did show a greater preference for host-coloured traps when these released host-associated kairomones in addition to their pheromone, and also avoided white non-host traps, but only when these released non-host volatiles. To our knowledge, this is the first evidence that multiple non-host cues could synergistically mediate the adaptive discrimination of hosts and non-hosts. Our results suggest that successful host location by generalists arises from the complex integration of cues in multiple sensory modes, and that foraging herbivores evaluate both hosts and non-hosts during their search.     

Vision for navigation: What can we learn from ants?

The visual systems of all animals are used to provide information that can guide behaviour. In some cases insects demonstrate particularly impressive visually-guided behaviour and then we might reasonably ask how the low-resolution vision and limited neural resources of insects are tuned to particular behavioural strategies. Such questions are of interest to both biologists and to engineers seeking to emulate insect-level performance with lightweight hardware. One behaviour that insects share with many animals is the use of learnt visual information for navigation. Desert ants, in particular, are expert visual navigators. Across their foraging life, ants can learn long idiosyncratic foraging routes. What's more, these routes are learnt quickly and the visual cues that define them can be implemented for guidance independently of other social or personal information. Here we review the style of visual navigation in solitary foraging ants and consider the physiological mechanisms that underpin it. Our perspective is to consider that robust navigation comes from the optimal interaction between behavioural strategy, visual mechanisms and neural hardware. We consider each of these in turn, highlighting the value of ant-like mechanisms in biomimetic endeavours.     

Computational visual ecology in the pelagic realm

Visual performance and visual interactions in pelagic animals are notoriously hard to investigate because of our restricted access to the habitat. The pelagic visual world is also dramatically different from benthic or terrestrial habitats, and our intuition is less helpful in understanding vision in unfamiliar environments. Here, we develop a computational approach to investigate visual ecology in the pelagic realm. Using information on eye size, key retinal properties, optical properties of the water and radiance, we develop expressions for calculating the visual range for detection of important types of pelagic targets. We also briefly apply the computations to a number of central questions in pelagic visual ecology, such as the relationship between eye size and visual performance, the maximum depth at which daylight is useful for vision, visual range relations between prey and predators, counter-illumination and the importance of various aspects of retinal physiology. We also argue that our present addition to computational visual ecology can be developed further, and that a computational approach offers plenty of unused potential for investigations of visual ecology in both aquatic and terrestrial habitats.     

Ultra-Rapid Vision in Birds

Flying animals need to accurately detect, identify and track fast-moving objects and these behavioral requirements are likely to strongly select for abilities to resolve visual detail in time. However, evidence of highly elevated temporal acuity relative to non-flying animals has so far been confined to insects while it has been missing in birds. With behavioral experiments on three wild passerine species, blue tits, collared and pied flycatchers, we demonstrate temporal acuities of vision far exceeding predictions based on the sizes and metabolic rates of these birds. This implies a history of strong natural selection on temporal resolution. These birds can resolve alternating light-dark cycles at up to 145 Hz (average: 129, 127 and 137, respectively), which is ca. 50 Hz over the highest frequency shown in any other vertebrate. We argue that rapid vision should confer a selective advantage in many bird species that are ecologically similar to the three species examined in our study. Thus, rapid vision may be a more typical avian trait than the famously sharp vision found in birds of prey.     

Patterns of species assemblages and geographical distributions associated with mandible size differences in coastal tiger beetles in Japan

Nine species of tiger beetle (Cicindelidae) occur in coastal habitats in Japan, with two to four species co-occurring at each locality. To examine the patterns of coexistence and geographical distribution, the mandible size of co-occurring species at 17 localities in Japan was examined, based on the assumption that competition for food is an important factor in determining these patterns. The interspecific overlap of mandible length was absent or very low in localities with two or three species, whereas it was more or less evident in localities with four species. For four large coastal species, the geographical distributions of two species with similar mandible lengths are either allopatric or parapatric, whereas those of two species with different mandible lengths largely overlap. These results strongly suggest that size-assortment in mandible length is important in determining species assemblage and distribution in coastal tiger beetles in Japan.An erratum to this article can be found at     

Cockchafer Larvae Smell Host Root Scents in Soil

In many insect species olfaction is a key sensory modality. However, examination of the chemical ecology of insects has focussed up to now on insects living above ground. Evidence for behavioral responses to chemical cues in the soil other than CO₂ is scarce and the role played by olfaction in the process of finding host roots below ground is not yet understood. The question of whether soil-dwelling beetle larvae can smell their host plant roots has been under debate, but proof is as yet lacking that olfactory perception of volatile compounds released by damaged host plants, as is known for insects living above ground, occurs. Here we show that soil-dwelling larvae of Melolontha hippocastani are well equipped for olfactory perception and respond electrophysiologically and behaviorally to volatiles released by damaged host-plant roots. An olfactory apparatus consisting of pore plates at the antennae and about 70 glomeruli as primary olfactory processing units indicates a highly developed olfactory system. Damage induced host plant volatiles released by oak roots such as eucalyptol and anisol are detected by larval antennae down to 5 ppbv in soil air and elicit directed movement of the larvae in natural soil towards the odor source. Our results demonstrate that plant-root volatiles are likely to be perceived by the larval olfactory system and to guide soil-dwelling white grubs through the dark below ground to their host plants. Thus, to find below-ground host plants cockchafer larvae employ mechanisms that are similar to those employed by the adult beetles flying above ground, despite strikingly different physicochemical conditions in the soil.     

Morphological variability in Lophyra flexuosa (Fabricius, 1787) (Coleoptera,Cicindelidae) in desert countries is affected by sexual dimorphism and geographic aspect

Lophyra flexuosa, a eurytopic tiger beetle characterized by long phenological activity, wide geographic and altitudinal distribution, and occurring in the highest number of habitats among all Cicindelidae known from North Africa, was chosen to study its geographic variation in morphology and sexual dimorphism. Here, we found significant sexual dimorphism exhibited in larger body size of females and longer mandibles in males, which can be explained by different roles of particular sexes in courtship. Moreover, we recorded significant differences in body sizes between western and eastern Maghreb populations which could suggest genetic isolation between these populations. As the species is related to habitats placed close to the water reservoirs, which in the desert countries are under significant human pressure (including climate change), we expect a reduction of habitat occupied by this taxon. Therefore, the geographic morphological variability that we observe today in the tiger beetle Lophyra flexuosa in the future could lead to speciation.     

The Maghreb – one more important biodiversity hot spot for tiger beetle fauna (Coleoptera,Carabidae, Cicindelinae) in the Mediterranean region

The tiger beetle fauna of the Maghreb region is one of the richest in the Palaearctic, including 22 species and 5 subspecies and 19% of all Palaearctic species of Cicindelinae. Assembled to their chorotypes, the Maghreb tiger beetles fall into eight different groups that include Maghreb endemics (26% of fauna), Mediterranean (7%), West Mediterranean (40%), North African (4%), Mediterranean-Westturanian (4%), West Palaearctic (4%), Afrotropico-Indo-Mediterranean (4%), and Saharian (11%) species. The Mediterranean Sclerophyl and Atlas Steppe are the Maghreb biogeographical provinces with the highest species richness, while the Sahara Desert has the lowest Cicindelinae diversity. Twenty-five cicindelid species and subspecies (93% of Maghreb fauna) are restricted to only one or two habitat types in lowland areas. Only Calomera littoralis littoralis and Lophyra flexuosa flexuosa are recognized as eurytopic species and occur in three types of habitat. The highest tiger beetle diversity characterizes salt marshes and river banks (in both cases 11 species and subspecies or 41% of Maghreb fauna). Approximately 85% of all Maghreb tiger beetle species and subspecies are found in habitats potentially endangered by human activity.     

Visual orientation by the crown-of-thorns starfish (<Emphasis Type="Italic">Acanthaster planci</Emphasis>)

Photoreception in echinoderms has been known for over 200 years, but their visual capabilities remain poorly understood. As has been reported for some asteroids, the crown-of-thorns starfish (Acanthaster planci) possess a seemingly advanced eye at the tip of each of its 7–23 arms. With such an array of eyes, the starfish can integrate a wide field of view of its surroundings. We hypothesise that, at close range, orientation and directional movements of the crown-of-thorns starfish are visually guided. In this study, the eyes and vision of A. planci were examined by means of light microscopy, electron microscopy, underwater goniometry, electroretinograms and behavioural experiments in the animals’ natural habitat. We found that only animals with intact vision could orient to a nearby coral reef, whereas blinded animals, with olfaction intact, walked in random directions. The eye had peak sensitivity in the blue part (470 nm) of the visual spectrum and a narrow, horizontal visual field of approximately 100° wide and 30° high. With approximately 250 ommatidia in each adult compound eye and average interommatidial angles of 8°, crown-of-thorns starfish have the highest spatial resolution of any starfish studied to date. In addition, they have the slowest vision of all animals examined thus far, with a flicker fusion frequency of only 0.6–0.7 Hz. This may be adaptive as fast vision is not required for the detection of stationary objects such as reefs. In short, the eyes seem optimised for detecting large, dark, stationary objects contrasted against an ocean blue background. Our results show that the visual sense of the crown-of-thorns starfish is much more elaborate than has been thus far appreciated and is essential for orientation and localisation of suitable habitats.