Roesel's Bush-cricket Research Articles

Lagomorph grazing alters suitability of hillside grassland for Orthoptera

The effects of lagomorph grazing on the Orthoptera of a small hill at Lound Lakes (Suffolk, UK) were studied during the summer of 2020. The transect counts of Orthoptera revealed low sward height due to high rabbit Oryctolagus cuniculus (Linnaeus, 1758) grazing on the high slopes which led to the general absence of tall grass species such as the Common Green Grasshopper Omocestus viridulus (Linnaeus, 1758) and Roesel's Bush-cricket Roeseliana roeselii (Hagenbach, 1822). Only nymphs and Field Grasshopper Chorthippus brunneus (Thunberg, 1815) adults were found in any number on the higher slopes, perhaps utilising the short swards and bare earth as basking habitat. The lower slopes and pastures supported tall-grass Orthoptera due to the absence of rabbit grazing and tussocky grassland.

Evaluating range-expansion models for calculating nonnative species' expansion rate.

Species range shifts associated with environmental change or biological invasions are increasingly important study areas. However, quantifying range expansion rates may be heavily influenced by methodology and/or sampling bias. We compared expansion rate estimates of Roesel's bush-cricket (Metrioptera roeselii, Hagenbach 1822), a nonnative species currently expanding its range in south-central Sweden, from range statistic models based on distance measures (mean, median, 95th gamma quantile, marginal mean, maximum, and conditional maximum) and an area-based method (grid occupancy). We used sampling simulations to determine the sensitivity of the different methods to incomplete sampling across the species' range. For periods when we had comprehensive survey data, range expansion estimates clustered into two groups: (1) those calculated from range margin statistics (gamma, marginal mean, maximum, and conditional maximum: ˜3 km/year), and (2) those calculated from the central tendency (mean and median) and the area-based method of grid occupancy (˜1.5 km/year). Range statistic measures differed greatly in their sensitivity to sampling effort; the proportion of sampling required to achieve an estimate within 10% of the true value ranged from 0.17 to 0.9. Grid occupancy and median were most sensitive to sampling effort, and the maximum and gamma quantile the least. If periods with incomplete sampling were included in the range expansion calculations, this generally lowered the estimates (range 16–72%), with exception of the gamma quantile that was slightly higher (6%). Care should be taken when interpreting rate expansion estimates from data sampled from only a fraction of the full distribution. Methods based on the central tendency will give rates approximately half that of methods based on the range margin. The gamma quantile method appears to be the most robust to incomplete sampling bias and should be considered as the method of choice when sampling the entire distribution is not possible.

Contrasting patterns of macroptery in Roesel’s bush cricketMetrioptera roeselii(Orthoptera, Ensifera)

We studied the wing dimorphism in Roesel's bush cricket populations. A total of 410 individuals (77 macropterous and 333 brachypterous) were sampled in seven sites. We found a high frequency (≤ 53%) of macropterous individuals in some meadows surrounded by forests. We measured the body weight, thorax weight, and abdomen weight in connection with macroptery vs brachyptery. We could find a positive correlation between macroptery and thorax weight. The abdomen weight of females showed high individual variation; thus the supposed trade-off between macroptery and lower fertility of females was not supported.

Influence of linear versus network corridors on the movement and dispersal of the bush-cricket Metrioptera roeseli (Orthoptera: Tettigoniidae) in an experimental landscape

Linear landscape elements are generally considered beneficial for promoting the movements of species between isolated habitats. However, relatively little consideration has been given to the effect of interconnections (nodes) between these elements: e.g. a simple linear element offers limited options for movement, whereas a network of such structures provides an exponential increase in potential pathways. In this pilot study we compared two experimental landscapes (single versus a lattice of four interconnected linear elements) in terms of their effect on the movement of males of Roesel's bush-cricket (Metrioptera roeseli) (Orthoptera: Tettigoniidae). Emigration of released bush-crickets from experimental landscapes was greater if there was a single rather than a lattice of linear elements (corridors). In the landscape with a lattice of corridors, 50% of the bush-crickets changed their direction of movement at nodes at least once. There was also evidence that nodes were attractive to bush-crickets; a higher proportion of individuals were found in and around nodes than in adjoining corridors, with the strength of this effect (i.e. aggregation at nodes) increasing with time. Thus nodes may not only affect the direction of movement but may also act as a local attractant. These effects may have an important role in the movement of species and their success in colonizing fragmented landscapes. These results indicate that in future landscape planning more consideration should be given to the connectivity between linear landscape elements as it is likely to be important in determining the movement and distribution of species.

Limited gene flow may enhance adaptation to local optima in isolated populations of the Roesel’s bush cricket (Metrioptera roeselii)

Variation in morphological traits along latitudinal gradients often manifests as size clines. In insects, both positive and negative correlations are seen, and the mechanism behind the response is unclear. We studied variation in seven morphological traits of Roesel's bush cricket, Metrioptera roeselii, sampled from seven latitude-matched-pair populations that were either geographically isolated from or connected to the species continuous distribution range. The aim was to examine whether morphological traits differed between isolated and continuous populations, and whether latitudinal variation was apparent. The data were used to indicate whether variation in trait means originates from plastic responses to the environment or genetic adaptation to local conditions. To evaluate the influence of gene flow on trait means, we analysed the genetic variation in seven microsatellites. Data showed that individuals from isolated populations display a positive relationship between latitude and body size, whereas individuals from continuous populations show little or no such relationship. The combined morphological and genetic data suggest that the isolated populations have adapted to local optima, while gene flow between continuous populations appears to counteract this process.

Macropterism of Roesel's BushcricketMetrioptera roeseliiin Relation to Climate Change and Landscape Structure in Eastern England

Abstract There has been a considerable range expansion for Roesel's bushcricket Metrioptera roeselii in Essex since 1980, and it is often assumed that the macropterous (long-winged) form (f. diluta) has played an important role. A systematic study of the occurrence and distribution of this bushcricket in the county shows that this range expansion has corresponded with a significant increase in air temperature and the availability of tall grassland on farmland, due to the introduction of set-aside and agri-environment schemes such as Countryside Stewardship. These tall grasslands are particularly important for M. roeselii in areas of the county (e.g., the northwest) where hedgerow removal has been severe since the 1940s. This study indicates that the previous year's air temperature may be the most crucial climatic determinant of macroptery, hot weather leading to successful breeding and high population densities in the following year. These populations may then produce macropterous individuals in response ...

Landscape-scale Expansion of Roesel’s bush-cricket Metrioptera roeselii at the North-western Range Limit in Central Europe (Orthoptera: Tettigoniidae)

Range expansion linked to global warming is a widespread phenomenon among insects. This range expansion may be either gradual and on a broad-front or discontinuous following long distance dispersal. Many species of Orthoptera show a distinct wing-length dimorphism related to dispersal and rare long-wing individuals are assumed to contribute significantly to the colonisation of new habitat patches. Grid-based distribution surveys of Roesel's bush cricket Metriopera roeselii (Hagenbach 1822) at the edge of the species' range in NW' Germany were conducted in 1991, 1996 and 2004. Most newly colonised grid cells were directly adjacent to cells that were occupied in previous surveys or were connected to them by other colonised cells. The maximal distance between newly colonised grid cells and cells that were occupied in previous surveys was 6.3 km between 1991 and 1996 and 5.1 km between 1996 and 2004. The proportion of macropterous individuals sampled in 2004 was very low (1.4%). Macropterous individuals tended to occur in newly colonised, more isolated and low abundance grid cells. Hence, range expansion of M roeselii took place by short-distance colonisation from cells that were occupied in previous surveys rather than by single events of long-distance dispersal.

The effect of conspecifics on individual male movement in Roesel's bush cricket, Metrioptera roeseli

Abstract. 1. Individual movement behaviours of male Roesel's bush crickets were compared between individuals experimentally released with or without conspecifics.2. Differences in movement behaviour were recorded between the groups, with individuals released with conspecifics moving faster and further.3. The study shows that behavioural interactions between individuals need to be considered in population modelling. Empirical movement data derived from lone individuals would result in a significant underestimation of both population expansion (−38.1%) and inter‐patch movement (−35.8%).

Impact of Grazing on Individual Male Movement in Roesel's Bush-Cricket Metrioptera roeseli: One Possible Clue to Species Range Expansion

One aid to understanding species distribution patterns is to gather detailed information on individual movement behavior. To gather information on dispersal capabilities in Roesel's bush-cricket Metrioptera roeseli an individual-based study was carried out. In four areas with two different cattle grazing regimes 35 individuals were released and their movements recorded for a mean of 80 h. Bush-crickets in grazed areas moved significantly further between the censuses and more individuals in grazed areas moved >5 m from the release point. The further away an individual was from the release point, the more likely he was to continue moving away. There was also a positive correlation between distance from the release point and the step length of the individual. The movement pattern found may make it easier for the species to find and reach new favorable habitats and withstand the negative effects of fragmentation.

COLONIZATION SUCCESS IN ROESEL'S BUSH-CRICKETMETRIOPTERA ROESELI: THE EFFECTS OF PROPAGULE SIZE

Assessing the colonizing ability of a species is important for predicting its future distribution or for planning the introduction or reintroduction of that species for conservation purposes. The best way to assess colonizing ability is by making experimental introductions of the species and monitoring the outcome. In this study, different-sized propagules of Roesel's bush-cricket, Metrioptera roeseli, were experimentally introduced into 70 habitat islands, previously uninhabited by the species, in farmland fields in south- eastern Sweden. The areas of introduction were carefully monitored for 2-3 yr to determine whether the propagules had successfully colonized the patches. The study showed that large propagules resulted in larger local populations during the years following introduction. Probability of colonization for each propagule size was measured and showed that propagule size had a significant effect on colonization success, i.e., large propagules were more successful in colonizing new patches. If future introductions were to be made with this or a similar species, a propagule size of at least 32 individuals would be required to establish a viable population with a high degree of certainty.