Tettigoniidae Research Articles

Distribution, density, diet and productivity of the Scops Owl Otus scops in the Italian Alps

The Scops Owl Otus scops is probably the least known European owl. We surveyed Scops Owls in the Trento region (6200 km2) of the central–eastern Italian Alps between 1995 and 2003 and we intensively monitored a subpopulation in a 50‐km2 plot between 2000 and 2003. In the whole region, we found 81 territories concentrated in 21, low‐elevation 100‐km2 quadrats. Most territories were associated with villages surrounded by extensively managed grassland (79%), arid areas with rocky outcrops and xerophytic vegetation (12%) and/or large urban areas and parks (6%). In the 50‐km2 plot, density varied between 52 and 64 territories/100 km2 annually. Territories were either solitary or clumped in loose colonies of 2–7 pairs. In contrast to previous studies, most nests used for laying were in holes and cracks of buildings (95%, n = 20). This may have been favoured by thermal and foraging advantages, but also involved some costs, such as predation by domestic cats and collision with cars. Median laying date was 29 May (n = 16) and the mean number of fledged young was 1.37 (n = 30), 1.95 (n = 21) and 2.00 (n = 20) per territorial, breeding and successful pair, respectively. The diet was dominated by grasshoppers of the family Tettigoniidae. Compared to previous studies, this population showed medium to high density and low productivity. The species seems to be dependent on traditional, extensive agro‐pastoralism and the main conservation threats include habitat loss through land abandonment and consequent forest expansion, which are probably best halted through subsidy schemes. From our results and published data, we estimate the population of the Scops Owl in the Italian Alps at 230–500 territories. There is an urgent need for further data on this largely overlooked species, especially from its Mediterranean strongholds.

Passive dispersal of Metrioptera bicolor (Phillipi 1830) (Orthopteroidea: Ensifera: Tettigoniidae) by transfer of hay

The transfer of hay from a donor site onto a receptor site is currently a widely accepted restoration procedure to establish grasslands with high biodiversity and rich in species. The impact of this procedure on vegetation has been well studied. However, its influence on the insect population has not been investigated. This study verifies that individuals of Metrioptera bicolor (Orthopteroidea: Tettigoniidae) were successfully transferred with hay. Three individuals transferred with the hay were still able to reproduce after the hay transfer. This result corresponds to 4.6% of the 65 marked individuals that were mapped on the donor site on the day of hay transfer. Of the estimated 1220–3013 individuals on the donor site (8300 m2), 56–139 reproductively able individuals were transferred with the hay. Suitable habitat structures presupposed, this number is sufficient to initiate a persistent colonisation of the species on the receptor site. The loss rate of M. bicolor due to grass cutting totalled 42%, which can be considered a very high mortality rate. Comparable studies on bush crickets show a medium loss rate of 21%, in relation to body size.

Changes in dispersal during species' range expansions.

Explanations for rapid species' range expansions have typically been purely ecological, with little attention given to evolutionary processes. We tested predictions for the evolution of dispersal during range expansion using four species of wing-dimorphic bush cricket (Conocephalus discolor, Conocephalus dorsalis, Metrioptera roeselii, and Metrioptera brachyptera). We observed distinct changes in dispersal in the two species with expanding ranges. Recently colonized populations at the range margin showed increased frequencies of dispersive, long-winged (macropterous) individuals, compared with longer-established populations in the range core. This increase in dispersal appeared to be short-lived because 5-10 years after colonization populations showed similar incidences of macroptery to populations in the range core. These changes are consistent with evolutionary change; field patterns persisted when nymphs were reared under controlled environmental conditions, and range margin individuals reared in the laboratory flew farther than range core individuals in a wind tunnel. There was also a reproductive trade-off with dispersal in both females and males, which could explain the rapid reversion to lower rates of dispersal once populations become established. The effect of population density on wing morphology differed between populations from the range core (no significant effect of density) and expanding range margins (negative density dependence), which we propose is part of the mechanism of the changes in dispersal. Transient changes in dispersal are likely to be common in many species undergoing range expansion and can have major population and biogeographic consequences.

The Orthoptera of Michigan: biology, keys, and descriptions of grasshoppers, katydids, and crickets

The Orthoptera of Michigan: biology, keys, and descriptions of grasshoppers, katydids, and crickets

Movement patterns of the bush cricketPlatycleis albopunctatain different types of habitat: matrix is not always matrix

Abstract. 1. Inter‐patch movement is usually assumed to be homogeneous across a landscape. As the intervening area between suitable patches is usually richly textured, it cannot be assumed to be uniform in real landscapes.2. In an experimental mark‐and‐resight study, the movement behaviour of the bush cricketPlatycleis albopunctatain four habitat types as well as at the border between two of these habitat types was observed.3. Analysis of recapture data indicated differences in mortality risk (or emigration rates) between habitat types.4. When released at the border between suitable habitat and a crop field,P. albopunctatadid not show a consistent preference for the suitable habitat. This suggests that the crop field is at least temporarily attractive forP. albopunctata.5. Movement in suitable habitat was not always different from movement in the matrix, and movement between different types of matrix also differed.6. The results indicate that the movement behaviour ofP. albopunctatais influenced not only by suitability for breeding but also by structural resistance and other factors (e.g. food availability or habitat‐specific mortality risk).

Biomechanics: froghopper insects leap to new heights.

An innovative leaping action propels these bugs to the top of the insect athletic league. There are two basic body designs for jumping that enable many animals to escape from predators, to increase their speed of locomotion or to launch into flight1. Animals with long legs (bush babies, kangaroos and frogs, for example) have a levering power that enables them to use less force to jump the same distance as short-legged animals of comparable mass, whereas those with short legs must rely on the release of stored energy in a rapid catapult action. Insects exploit both designs: bush crickets use the leverage provided by long legs2, fleas use stored energy to power their short legs3, and grasshoppers4 combine features of each. Fleas are considered to be the champion jumpers, but here I show that froghoppers (spittle bugs) are in fact the real champions and that they achieve their supremacy by using a novel catapult mechanism for jumping.

Jumping and kicking in bush crickets.

Bush crickets have long, thin hind legs but jump and kick rapidly. The mechanisms underlying these fast movements were analysed by correlating the activity of femoral muscles in a hind leg with the movements of the legs and body captured in high-speed images. A female Pholidoptera griseoaptera weighing 600 mg can jump a horizontal distance of 300 mm from a takeoff angle of 34 degrees and at a velocity of 2.1 m s(-1), gaining 1350 microJ of kinetic energy. The body is accelerated at up to 114 m s(-2), and the tibiae of the hind legs extend fully within 30 ms at maximal rotational velocities of 13500 deg. s(-1). Such performance requires a minimal power output of 40 mW. Ruddering movements of the hind legs may contribute to the stability of the body once the insect is airborne. During kicking, a hind tibia is extended completely within 10 ms with rotational velocities three times higher at 41800 deg. s(-1). Before a kick, high-speed images show no distortions of the hind femoro-tibial joints or of the small semi-lunar groove in the distal femur. Both kicks and jumps can be generated without full flexion of the hind tibiae. Some kicks involve a brief, 40-90 ms, period of co-contraction between the extensor and flexor tibiae muscles, but others can be generated by contraction of the extensor without a preceding co-contraction with the flexor. In the latter kicks, the initial flexion of the tibia is generated by a burst of flexor spikes, which then stop before spikes occur in the fast extensor tibiae (FETi) motor neuron. The rapid extension of the tibia can follow directly upon these spikes or can be delayed by as long as 40 ms. The velocity of tibial movement is positively correlated with the number of FETi spikes. The hind legs are 1.5 times longer than the body and more than four times longer than the front legs. The mechanical advantage of the hind leg flexor muscle over the extensor is greater at flexed joint angles and is enhanced by a pad of tissue on its tendon that slides over a protuberance in the ventral wall of the distal femur. The balance of forces in the extensor and flexor muscles, coupled with their changing lever ratio at different joint positions, appears to determine the point of tibial release and to enable rapid movements without an obligatory co-contraction of the two muscles.

Population dynamics in the Grey Bush Cricket Platycleis albopunctata (Orthoptera: Tettigoniidae) – What causes interpopulation differences?

We found sharply differing population dynamics in Platycleis albopunctata at two one-hectare study sites differing in vegetation cover and inclination of slopes. At one site, the population remained relatively constant (about 600 individuals) over the period observed, while at the other site the population size varied during the observation period between more than 3000 and less than 100 individuals. This field observation was analysed by an experimental study of embryonic development and reproduction, both of which are expected to largely influence population dynamics. These experiments revealed a close correlation between the temperature and the duration of egg development on the one hand and fecundity on the other. We concluded that the temperature dependence of development and reproduction is responsible for the weather dependence of population dynamics. Based on our results, we developed a hypothesis to explain the striking differences in the dynamics of the two study sites which attributes them to differences in microclimate and primary production. Additionally, we applied a simulation model to investigate the weather dependence of the population dynamics. Finally, we discuss the consequences of different population dynamics for conservation: (a) the example stresses the difficulties that arise when using demographic data of any population for the prognosis of the extinction risk of a population under study; (b) the dependence of population dynamics on habitat parameters means they can be influenced by management.

Increased dispersal rates and distances in density-stressed bush crickets (Metriophera brachyptera).

Der infolge der Habitatfragmentierung eingeschränkte Individuenaustausch zwischen Populationen gilt als einer der Hauptgründe für ein erhöhtes Aussterberisiko insbesondere bei standorttreuen Arten mit geringem Ausbreitungspotential. Einige Untersuchungen an Heuschrecken deuten jedoch an, dass das Ausbreitungsvermögen standorttreuer Arten bisher möglicherweise unterschätzt worden ist. Es wird angenommen, daß bestimmte Umweltbedingungen bei diesen Arten Ausbreitungsverhalten auslösen und ihr Ausbreitungsvermögen erhöhen kann. An der Kurzflügeligen Beißschrecke Metrioptera brachyptera (L., 1761) wurden in einem ersten Schritt die Emigrationsraten bei verschiedenen Populationsdichten in 'Mikrokosmen' (Käfigpopulationen) untersucht. Der Anteil der Individuen, die aus den Käfigen auswanderten, war positiv mit der Individuendichte in den Käfigen korreliert. In einem zweiten Schritt wurden sowohl Indivduen, die unter Dichtestress gehalten wurden, als auch Tiere, die keinen hohen Individuendichten ausgesetzt waren, auf einem Fußballplatz freigelassen und ihr Ausbreitungsmuster untersucht. 'Gestresste' Individuen dispergierten signifikant schneller und weiter als 'ungestresste'. Die Ergebnisse weisen darauf hin, dass Ausbreitungsverhalten induzierbar ist und auch bei standorttreuen Arten auftreten kann. Es ist bei diesen jedoch keine regelmäßige Erscheinung, sondern besitzt Ausnahmecharakter.StichwörterDispersal, emigration, experimental approach, metapopulation, microcosm.

Comments on the article by Katbeh Bader and Massa on Jordanian Tettigoniidae (J. Orthoptera Res. 10(1): 25–37)

Comments on the article by Katbeh Bader and Massa on Jordanian Tettigoniidae (J. Orthoptera Res. 10(1): 25–37)

Food availability dictates the timing of parturition in insectivorous mouse‐eared bats

Which of these two confounding factors, weather or food availability – that largely correlate and interact – controls the timing of parturition in insectivorous bats? To answer this question, we took advantage of a predator‐prey system that offers a unique opportunity to perform natural experiments. The phenology of reproduction of two sibling bat species that inhabit the same colonial roosts, but exploit different feeding niches, was investigated. Myotis myotis feeds mainly on carabid beetles, a food source available from the end of hibernation onwards, whereas bush crickets, the main prey of M. blythii, are not available early in the season due to their successive instars; cockchafers are actually the sole possible alternative prey for M. blythii at that time of the year, but they occur every third year only, independently of local weather conditions. By comparing the species responses to the presence/absence of cockchafers, we could test the hypothesis that food availability, rather than climate, influences the timing of bat parturition. Our data show that M. blythii gave birth, on average, 10 d later than M. myotis in years without cockchafers, whilst parturition (1) was synchronous during cockchafer years, and (2) did not show much among‐year time variation in M. myotis. This suggests that food availability is the chief factor regulating the timing of parturition in mouse‐eared bats.

Application of time domain signal coding and artificial neural networks to passive acoustical identification of animals

The development of a computer-based system capable of identifying animals automatically from sounds they generate is described. The system uses time domain signal coding techniques and artificial neural networks for discriminating between the sounds of different animal species within a group. Results for British species of Orthoptera (bush crickets and crickets) show that it is capable of discriminating 13 species with 100% success and zero misidentification under low noise conditions. Results are also given for noise tests using 25 species of Orthoptera (including grasshoppers). The approach can be applied to other animal groups such as birds, mammals and amphibia; preliminary results are also presented for tests with 10 species of Japanese bird. The approach is generic and has application in many fields including non-destructive testing and physiological signal analysis.

A letter from the frontier: forecasting species expansions

As the global climate changes, species will have to move to where the weather suits their needs. But can we forecast where that is – can we predict the future distribution of a species based on the anticipated distribution of its preferred habitat and the current ability of that species to move from one site to the next? Although several researchers have tried to do this, a new paper by Chris Thomas and co-workers 1xEcological and evolutionary processes at expanding range margins. Thomas, C.D. et al. Nature. 2001; 411: 577–581Crossref | PubMed | Scopus (501)See all References1 suggests that this approach might be too simplistic.Working on four insect species that have recently expanded their ranges in Britain, Thomas et al. show that populations at the range margin have enlarged the spectrum of habitat types that they can colonize, and have improved their potential for dispersal. Of two species of butterfly, the silver-spotted skipper Hesperia comma previously lived on warm, south-facing chalk hillsides in southeast England. With climate warming, the species now thrives on slopes of all aspects, resulting in more patches to colonize and shorter distances between them. This has led to a much faster rate of expansion than was expected based on the distribution of the original habitat of the butterfly. The second butterfly, the brown argusbrown argus Aricia agestis, has also benefited from warmer weather by increasingly turning to widespread host plants in habitats that were previously too cool for it. This has allowed the argus to cross previously unbridgeable gaps between patches of its original host plant. In two species of bush crickets Conocephalus discolor and Metrioptera roeselii, Thomas et al. found a much higher proportion of longer- than shorter-winged forms in recently established populations than in old ones. This, the researchers argue, reflects how populations at expanding range fronts can be dominated by particularly dispersive individuals, hence significantly increasing the rate of expansion. Behind the advancing front, less dispersive but more fecund forms might again be favoured.Fig. 1Brown argus Aricia agestis, Robert WilsonView Large Image | Download PowerPoint SlideClearly, the paper by Thomas et al. should not lull us into believing that we live in the best of all possible worlds, where all species are able to adjust their ranges even quicker than we ever thought possible. Rather, as emphasized by Stuart Pimm 2xEntrepreneurial insects. Pimm, S. Nature. 2001; 411: 531–532Crossref | PubMed | Scopus (21)See all References2, the results should make us distrust our prophetic abilities, because global climate change might affect different species in different ways and through processes that we did not know to expect. The particular processes described by Thomas et al. also require some initial expansion before they come into play, and many species might fail to take these first crucial steps. But once a population gets going, transient evolutionary changes in habitat range and migration rate might well turn out to be common phenomena. But just how common? That remains to be discovered.

Ecological and evolutionary processes at expanding range margins.

Many animals are regarded as relatively sedentary and specialized in marginal parts of their geographical distributions. They are expected to be slow at colonizing new habitats. Despite this, the cool margins of many species' distributions have expanded rapidly in association with recent climate warming. We examined four insect species that have expanded their geographical ranges in Britain over the past 20 years. Here we report that two butterfly species have increased the variety of habitat types that they can colonize, and that two bush cricket species show increased fractions of longer-winged (dispersive) individuals in recently founded populations. Both ecological and evolutionary processes are probably responsible for these changes. Increased habitat breadth and dispersal tendencies have resulted in about 3- to 15-fold increases in expansion rates, allowing these insects to cross habitat disjunctions that would have represented major or complete barriers to dispersal before the expansions started. The emergence of dispersive phenotypes will increase the speed at which species invade new environments, and probably underlies the responses of many species to both past and future climate change.

The influence of temperature model assumptions on the prognosis accuracy of extinction risk

For a species whose abundance is well-known to correlate on the degree of heat different temperature model assumptions may affect the prognosis accuracy of persistence. Likewise, year-to-year autocorrelations in weather fluctuations are known to decrease extinction risk. Thus, we investigated the grey bush cricket Platycleis albopunctata. For this species is known that growth and reproduction is mainly influenced by temperature. We developed a stochastic individual based model for the bush cricket. This day–degree model described the demographic growth of the species that depends on temperature. Daily temperatures were generated by five different methods: (i) temperatures were sequentially taken from a meteorological database. To analyse the influence of different levels of autocorrelation in temperature records (ii) the day-to-day correlations were reduced by randomly permuting the sequence of days within the months of successive years from the database, (iii) year-to-year correlations were reduced by randomly rearranging the sequence of the years held in the database, (iv) combined day-to-day and year-to-year correlations were reduced according to the submodel (ii) and (iii), and finally (v) temperatures were randomly generated on the basis of Gaussian normal distributions. The mean and the variance of these distributions depended on the date of the year. Distributions were derived from the above mentioned meteorological database. We estimated highly different minimum viable population sizes. These did severely depend on the chosen temperature model. Values ranged from 3000 adults to more than a million adults per generation. High amounts of autocorrelation in temperature values decreased the extinction risk of a bush cricket population. Permuting the sequence of the years in the database increased extinction risk less than reducing day-to-day correlations. A decrease in autocorrelation of temperature records can result in unrealistic phenologies of life stages. Decreasing day-to-day or year-to-year autocorrelation in temperature records resulted in an increase or a decrease of the duration of the egg development or the duration of larval development. For poikilothermic species general implications are presented that are relevant for the design of quantitative models used in conservation biology.

Using biological principles to design MEMS

In micromechanics the handling and positioning of micropartsinvolves sophisticated assembly procedures and a good understanding ofmicrotribological phenomena. Due to the very low object mass, adhesion betweenthe micropart and the handling tool (usually a mechanical gripper) becomes aperformance-limiting factor. Adhesion effects can be even larger than theforce that frees the micropart from the handling tool thus making correctpositioning impossible. Many useful design principles for optimized adhesionproperties can be found in biological systems. In this paper adhesion betweenthe foot of an insect and a surface was evaluated. The attachment pads of thegreat green bush cricket (Tettigonia viridissima) - used to attach theinsect safely to a variety of different surfaces - were investigated to drawconclusions that could be implemented in future technical microsystems. It isshown that the attachment pads are flexible micromechanical units capable ofself-adjusting to different scales of roughness. The erratic influence ofcapillary action due to adsorbed water is presumably suppressed by ahydrophobic layer on the pads. Attaching and releasing mechanisms as well asaccurate measurement of the adhesion force are discussed in detail.

An Individual Based Model of the Impact of Suboptimal Habitat on Survival of the Grey Bush Cricket, Platycleis Albopunctata (Orthoptera: Tettigoniidae)

We developed an individual based model that investigates the importance of suboptimal habitats for the survival of the grey bush cricket Platycleis albopunctata living in a core habitat. Our model consists of two submodels. The first describes the demographic growth of the cricket known to mainly depend on temperature. The second introduces a simple heterogeneous habitat that consists of two areas of variable size and different suitability for reproduction. An optimal habitat is surrounded by a suboptimal habitat and both together are located within an unsuitable area. Applying Monte Carlo simulations we demonstrate that the extinction probability of a bush cricket population is significantly lower in an optimal habitat with a surrounding suboptimal habitat than without. Even small suboptimal habitats are sufficient to significantly reduce the extinction risk of the core population. For a bush cricket population living in a heterogeneous habitat mean minimum viable population estimates range from 13 000 to 15 000 adults, whereas 30 000 adults are required for a population living in an optimal habitat without a surrounding suboptimal habitat. Thus, the presence of a suboptimal habitat can reduce minimum viable population by 50%. For any species, our model predicts that the type of dispersal between optimal and suboptimal habitat and the type of habitat selection determine whether suboptimal habitat is useful or detrimental for species persistence.

Microtribology of biological materials

This paper presents a study on friction and indentation of attachment pads of the great green bush cricket, using a system involving a biological material and a flat surface. The pads are evolutionarily optimized frictional devices that are adapted to attach the insect to a variety of natural surfaces. The attachment pads of both living and dead insects were tested and evaluated using several analysis techniques. These techniques included friction analysis by microtribometry, microindentation, scanning electron microscopy (SEM), histologic sectioning, and shock freezing. Microtribological analysis showed that the friction between pad and surface is anisotropic. The anisotropy increases with increasing normal force. Microindentation revealed that the pads respond very flexibly to applied loads leading to an optimized morphology with respect to contact area. All results make clear that the microtribological properties are a perfect combination of surface structure, lubrication and active interface control.

Females of the grasshopper Chorthippus parallelus (Zett.) do not remate for fresh sperm

The evolution of female multiple mating is still a largely debated field. Among the benefits that have been proposed to explain this risky behaviour is the replenishment of sperm reserves. Apart from an increase in total sperm number, it can be an expression of post-copulatory mate choice or can be directed towards the uptake of fresh sperm. Using fresh sperm for fertilization instead of sperm aged by storage in the female genital tract may avoid a lowered fertilization capacity, an increase in deleterious effects or a skewed offspring sex ratio. We investigated the influence of sperm age on female fitness in the grasshopper Chorthippus parallelus, a species where females mate multiply. After copulation, females store sperm over the course of weeks until fertilization. An average ejaculate of 250 000 spermatozoa exponentially declined with time within the female's spermatheca. The number of days since copulation better explained the variation in actual sperm number than the number of pods or eggs laid. We investigated differences in female fitness parameters in two treatments. In the first, females were mated only once, while in the second, females always had freshly ejaculated sperm available. Although in our experiment, multiply mated females had heavier offspring than singly mated females, egg number per pod, hatching and fertilization success, their composite effects and offspring sex ratio did not vary with respect to season or sperm age. We therefore reject the hypothesis that the reason for remating in females of this species is the uptake of fresh sperm.

Bats, insects, and the evolution of hearing

Insectivorous bats appeared in the fossil record about 50 million years ago, or long after certain insects had adopted nocturnal habits. Many of these nocturnal insect species already had complex ears used mainly for intra-specific communication. Due to their physically small size, insects can produce high-frequency sounds most efficiently. Thus many species were ‘‘preadapted’’ for hearing bats. Examples would be certain beetles and bush crickets. Some nonhearing insects presumably evolved the capacity to hear the ultrasonic signals of bats. One well-documented case is that of the green lacewing, where the first fossil records of ears appeared after bats evolved. Many species of moths have ears tuned to bat signals, an adaptation that has evolved independently in different families and presumably in direct response to bat predation. All evidence points to a substantial selection pressure applied by bats on nocturnal insects. With the preoccupation of hearing mechanisms to avoid predation, other responses of nocturnal insects to echolocating bats might be overlooked. One example could be the advantage for nocturnal insects to occupy the ‘‘clutter zone’’ near or in vegetation, which would mix echoes from the prey with those of clutter. [Work supported by the Danish National Research Foundation.]