Movement of carabids from grassy strips to crop land in organic agriculture

The colonisation process of carabid beetles from field margins to crop fields under organic agriculture was investigated in 2010 and 2011 in northern Germany in order to find the supporting effects of grassy strips in the agricultural landscape. Displacement and speed of Pterostichus melanarius, Carabus auratus and Poecilus spp. were higher in the crops than in the grassy strips, except for the speed of C. auratus. Among the four species C. auratus, P. melanarius, Pterostichus niger, and Poecilus spp., C. auratus revealed the highest displacement and speed, whereas no significant differences were found between the other three species. P. melanarius showed higher displacement and speed in wheat than in red-clover or pumpkin. Speed and displacement of P. melanarius differed between spring and autumn generations in wheat or red-clover. When they were released at a junction of arable crop and field strips, C. auratus moved indifferently to either arable field or field margins/strips, whereas P. melanarius moved directly to crop centres. At the field margin, Poecilus spp. preferred to move along a grassy strip, while it moved irrespective from the grassy strips in a central site. C. nemoralis and P. niger preferred to move within the grassy strips. Our studies reveal that grassy strips do not affect the dispersal of typical arable field species; however, the species demanding grass vegetation can only overcome the barriers of arable fields either by grassy strips alone or by grassy strips with an adjacent hedge.     

Movements of carabid beetles (Coleoptera: Carabidae) inhabiting cereal fields: a field tracing study

Summary The individual movements of four carabid species were investigated by tracing beetles in the field using a portable radar system (harmonic radar). The field-inhabiting a Pterostichus melanarius Illiger, P. niger Schaller and Harpalus rufipes De Geer were traced in cereal fields. The movements of P. melanarius Mnd P. niger were also tracked in a wood and then compared with the movements of the forest-species Carabus nemoralis Müller. P. melanarius and P. niger displayed directed movements in cereal fields, although P. niger moved faster than P. melanarius. The movement pattern of H. rufipes in the field, and C. nemoralis and P. malanarius in the wood can be described as a c correlated random walk. In cereal fields, P. melanarius burrowed actively into the soil, and P. niger searched out crevices. In contrast, none of these two carabids burrowed in the forest soil, whereas C. nemoralis did. No statistically significant difference was observed between the movements of hungry and satiated beetles, although starved beetles tended to disperse shorter distances per move and turned back more often (especially P. niger). The significance of the various movement patterns exhibited by the species studied for their reproduction and survival on arable land is discussed.     

Habitat choice of some field-inhabiting carabid beetles (Coleoptera: Carabidae) studied by recapture of marked individuals

ABSTRACT.

• 1 Habitat choice of some field-inhabiting carabid beetles was studied in the field, and included the adult-overwintering Bembidion lampros Herbst, Pterostichus cupreus L. and Agonum dorsale Pontoppidan, and the larval-overwintering Trechus secalis Paykull, Pterostichus melanarius Illiger, P.niger Schaller and Harpalus rufipes De Geer. These were compared to the forest-inhabiting and adult-overwintering species, Carabus nemoralis Müller.
• 2 Marked beetles were released in the centre of a circular enclosure which was placed on the edge between a cereal field and a wood. The direction of movement in this circle was compared with that in a control circle placed entirely in the cereal field.
• 3 In the field/wood circle, adult-overwinterers and the larval-overwin-terer H.rufipes choose to move into the cereal field. The majority of T.secalis. P.melanarius and C.nemoralis, however, moved into the wood, while P.niger exhibited no preference.
• 4 In the field circle, adult-overwinterers moved towards the more sun-exposed parts of the circle, whereas the movements of larval-overwin-terers were random.
• 5 Some species-specific characteristics considered important for habitat choice by these carabid beetles, and the relevance of these characteristics for their dispersal behaviour are discussed.

     

Even the Smallest Non-Crop Habitat Islands Could Be Beneficial: Distribution of Carabid Beetles and Spiders in Agricultural Landscape

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.     

Activity and satiation state in Pterostichus melanarius: an experiment in different agricultural habitats

1. A capture–recapture experiment was conducted to examine the effects of satiation state on the activity and foraging efficiency of the carabid beetle Pterostichus melanarius Ill., in four different habitats (a hedge, a transition zone between the hedge and the adjacent wheat crop, the margin of the wheat crop, and the centre of the wheat crop) in an agricultural ecosystem in France. 2. Prey biomass and density decreased from the centre of the hedge to the crop margin and to the centre of the crop, where prey density was low but prey biomass was moderate. Starved and satiated beetles were released in circular enclosures and recaptured using pitfall traps for 6 days. 3. Immediately after release, starved P. melanarius were significantly more active than satiated beetles, but this difference disappeared after the first day. At each recapture date, starved individuals had gained weight whereas satiated individuals had lost weight. The analysis of activity and weight variation at the end of the first day indicated that the centre of the crop seemed to be the most favourable habitat for starved individuals to find food rapidly, whereas the behaviour of satiated individuals was identical in all habitats. 4. This experiment shows that habitat use of P. melanarius is flexible. The results are discussed in the context of the classical view of foraging behaviour in carabid beetles. The activity and foraging efficiency in P. melanarius in different habitats can be explained as the result of the interaction between individual satiation state, prey availability in the habitat, and particular preferences of the species.     

Movement Behaviour of the Carabid Beetle Pterostichus melanarius in Crops and at a Habitat Interface Explains Patterns of Population Redistribution in the Field

Animals may respond to habitat quality and habitat edges and these responses may affect their distribution between habitats. We studied the movement behaviour of a ground-dwelling generalist predator, the carabid beetle Pterostichus melanarius (Illiger). We performed a mark-recapture experiment in two adjacent habitats; a large plot with oilseed radish (Raphanus sativus) and a plot with rye (Secale cereale). We used model selection to identify a minimal model representing the mark-recapture data, and determine whether habitat-specific motility and boundary behaviour affected population redistribution. We determined movement characteristics of P. melanarius in laboratory arenas with the same plant species using video recording. Both the field and arena results showed preference behaviour of P. melanarius at the habitat interface. In the field, significantly more beetles moved from rye to oilseed radish than from radish to rye. In the arena, habitat entry was more frequent into oilseed radish than into rye. In the field, movement was best described by a Fokker-Planck diffusion model that contained preference behaviour at the interface and did not account for habitat specific motility. Likewise, motility calculated from movement data using the Patlak model was not different between habitats in the arena studies. Motility (m² d⁻¹) calculated from behavioural data resulted in estimates that were similar to those determined in the field. Thus individual behaviour explained population redistribution in the field qualitatively as well as quantitatively. The findings provide a basis for evaluating movement within and across habitats in complex agricultural landscapes with multiple habitats and habitat interfaces.     

Predator interference limits fly egg biological control by a guild of ground-active beetles

We examined whether predator interference could prevent effective conservation biological control of Delia spp. flies, important pests of cole crops, by an assemblage of carabid and staphylinid beetles. In laboratory feeding trials we found that the smaller (<1 cm) beetle species common at our site readily ate dipteran eggs, while the most common large carabid species, Pterostichus melanarius, rarely did. However, P. melanarius did eat several of the smaller beetle species. We conducted two field experiments where we manipulated immigration rates of the ground predator guild and then measured predation on fly eggs. Predation rates were consistently higher in cages where predators were added at ambient densities, compared to cages where ground predators were removed. However, in the second field experiment, when we quadrupled predator immigration rates neither beetle activity-density nor predation rate increased. High immigration rate plots had a higher proportion of P. melanarius in the predator community, compared to plots with beetles added at ambient densities, suggesting that P. melanarius was reducing activity-densities of the smaller beetles, perhaps through intraguild predation. Thus, tactics to improve the biological control of Delia spp. by conserving generalist predators, such as providing in- or extra-field refuges, could be thwarted if the primary predators of fly eggs, small carabids and staphylinids, are the targets of intraguild predation by also-conserved larger predators.     

Do smaller islands host younger populations? A case study on metapopulations of three carabid species

Aims To test a new concept for island ecology and metapopulation studies: if population persistence is a result of colonization and extinction processes, one would expect remarkable variability in the age of neighbouring populations – there would be both old and young (recently established) populations. Location The lake Mamry archipelago, Poland. Methods Forty trap transects with a total of 114 Barber traps were operating from June to September in 1997 and in 1998. The traps (0.5‐L plastic beakers, mouth diameter 120 mm, with a 20 × 20 cm wooden roof) were placed by applying a stratified sampling design into 13 habitat types on the 16 islands and two mainland sites. The frequency of macropterous individuals in wing‐dimorphic populations of three carabid species (Pterostichus melanarius, P. anthracinus and Carabus granulatus) was used as an indicator of population ‘age’. Results The frequency of macropterous individuals in the populations varied from 0% to 100% for P. melanarius (18.5% on average), from 0% to 91% for P. anthracinus (12.6%) and from 0% to 29% for C. granulatus (8.9%). Populations hosted more long‐winged individuals (and were therefore interpreted as being younger) on smaller islands, compared with those inhabiting large islands and the mainland sites. The results also revealed that the viability of the populations of the autumn‐breeding P. melanarius might be more affected by population size than that of the two studied spring breeders. Island connectivity did not have a significant effect on the frequency of macropterous individuals in the studied populations. Main conclusions The inverse relationship between the proportion of macropterous individuals and island size contrasts with the accepted theory of dispersal, which assumes that there is selection against dispersal on small islands. A regression analysis for population age and habitat characteristics reveals the extinction probability of a given population. I suggest that investigations based on variability in population age can help in studies of colonization–extinction processes that would otherwise face logistic and methodological obstacles.     

Augmentation of beneficial arthropods by strip-management

The effect of strip-management on surface activity, movements and activity density of abundant carabid beetles during two vegetation periods in a cereal field was investigated using mark-recapture techniques. Significantly higher recapture rates, indicating higher activity, were found in the strip-managed area than in the control area, especially in Poecilus cupreus and also in Carabus granulatus and Pterostichus melanarius. Several observations led to the conclusion that this higher activity is generally due to a prolongation of the reproductive period in the strip-managed area. Significantly higher activity densities were found for P. cupreus, Pterostichus anthracinus, C. granulatus and Pt. melanarius in the strip-managed area than in a bordering control area. P. cupreus is greatly attracted to the strips during its migrations, as can be deduced from the high percentage of movements that contact the strips. Also, significantly more marked individuals moved from the control to the strip-managed area than vice versa. Pt. melanarius and Pt. anthracinus show less preference for the strips in their movements than P. cupreus. However, significantly more individuals of Pt. melanarius also moved from the control to the strip-managed area. C. granulatus, on the other hand, kept mainly to the cereal areas. After harvest only Pterostichus niger and Harpalus rufipes distinctly preferred the strips. The generally marked degree of attraction exercised by strip-management on carabid beetles is discussed.     

Influence of within‐field position and adjoining habitat on carabid beetle assemblages in winter wheat

• 1 The influence of within‐field position and adjoining habitat on carabid beetles was studied in 20 winter wheat fields in ten different Swiss agricultural landscapes. In each landscape, two winter wheat fields (one with adjoining sown wildflower area and one with adjoining grassy margin) were investigated.
• 2 Carabid beetles were caught in pitfall traps 3 and 30 m from the edge in each of the 20 wheat fields. Significantly more individuals were found in the centres (30‐m position) than at the edges (3‐m position). Conversely, species richness was significantly higher at the field edges than in the centres.
• 3 Of the ten most abundant species, Poecilus cupreus, Agonum muelleri and Pterostichus melanarius were significantly more abundant in the field centres than at the edges. Harpalus rufipes was significantly more abundant in the fields adjoining sown wildflower areas than in the fields adjoining grassy margins.
• 4 In conclusion, the response of carabid beetles to within‐field position and adjoining habitats was species specific. This needs to be taken into account in habitat management for biodiversity conservation and pest control.

     

Carabid beetle diversity and distribution in Boston Harbor Islands national park area (Coleoptera, Carabidae)

As part of an All Taxa Biodiversity Inventory in Boston Harbor Islands national park area, an inventory of carabid beetles on 13 islands was conducted. Intensive sampling on ten of the islands, using an assortment of passive traps and limited hand collecting, resulted in the capture of 6,194 specimens, comprising 128 species. Among these species were seven new state records for Massachusetts (Acupalpus nanellus,Amara aulica,Amara bifrons, Apenes lucidulus, Bradycellus tantillus, Harpalus rubripes and Laemostenus terricola terricola-the last also a new country record; in passing we report also new state records for Harpalus rubripes from New York and Pennsylvania, Amara ovata from Pennsylvania, and the first mainland New York records for Asaphidion curtum). For most islands, there was a clear relationship between species richness and island area. Two islands, however, Calf and Grape, had far more species than their relatively small size would predict. Freshwater marshes on these islands, along with a suite of hygrophilous species, suggested that habitat diversity plays an important role in island species richness. Introduced species (18) comprised 14.0% of the total observed species richness, compared to 5.5% (17 out of 306 species) documented for Rhode Island. We surmise that the higher proportion of introduced species on the islands is, in part, due to a higher proportion of disturbed and open habitats as well as high rates of human traffic. We predict that more active sampling in specialized habitats would bring the total carabid fauna of the Boston Harbor Islands closer to that of Rhode Island or eastern Massachusetts in richness and composition; however, isolation, human disturbance and traffic, and limited habitat diversity all contribute to reducing the species pool on the islands relative to that on the mainland.     

Taxon specific response of carabids (Coleoptera,Carabidae) and other soil invertebrate taxa on invasive plant Amorpha fruticosa in wetlands

False indigo (Amorpha fruticosa L.) is an invasive exotic plant introduced to Europe in the early eighteenth century. Its spread has been rapid, particularly in disturbed wetland habitats, where it forms dense impermeable monospecific stands and modifies habitat conditions. The impact of A. fruticosa on native plant communities has been well analyzed, however knowledge concerning the possible effects on soil invertebrates and particularly carabid beetles is completely lacking. This study analyzed the impact of an A. fruticosa invasion on carabid beetles and other soil invertebrates. Soil fauna was sampled by pitfall traps at natural habitats, initially colonized by A. fruticosa, and habitats largely invaded by A. fruticosa. In total 2,613 carabid beetles belonging to 50 species and 72,166 soil invertebrates were collected. The invasion of A. fruticosa strongly affected the carabid beetle species composition, which clearly differed between all studied sites. Widespread euritopic carabid beetle species showed positive responses to A. fruticosa invasion, while the activity density of open habitat species strongly declined. Mean individual biomass was significantly higher at invaded sites due to increased incidence of large carabids (genus Carabus Linné, 1758). Carabid beetle activity density and abundance of soil invertebrates were considerably higher at invaded sites than in natural sites. Conversely, the impact of A. fruticosa on carabid beetle species richness and diversity was less pronounced, most likely due to immigration from adjacent habitats. Changes in carabid beetle species composition and abundance of soil invertebrates were most likely due to changes in vegetation structure and microclimate. The results suggest that A. fruticosa invasion considerably affected carabid beetles, an insect group that is only indirectly related to plant composition. Therefore, severe future changes can be expected in invertebrate groups that are closely related to plant composition, since A. fruticosa cannot be completely removed from the habitat and covers relatively large areas.     

Abundance-age-area relationships in an insular plant community

Two processes are thought to generate positive relationships between species richness and island area. The areaper se hypothesis states that larger islands maintain larger populations, which are less susceptible to extinction. The habitat hypothesis states that larger islands contain more habitats, and therefore a greater number of habitat specialists. However, the importance of each mechanism is debated. I tested the areaper se and habitat hypotheses by comparing relationships between plant abundance, age and island area in five shrub species on islands off the coast of British Columbia, Canada. Results showed that two shrub species increased in both abundance and age with island area. The remaining three species showed no differences in abundance and age with island area. Conifer abundances increased with island area, which generated differences in habitat availability. Smaller islands were dominated by open habitat, while larger islands contained both open and forested habitats. Changes in habitat availability with island area could explain patterns in plant abundance and age. The two species that increased in abundance with island area were commonly found in conifer forest on the mainland, and their distributions were consistent with the distribution forest habitat. Positive relationships between plant age and island area in these two species may result from lower survivorship in the open habitat, which dominated small islands. The three species that showed no relationship between abundance and island area are commonly found in open habitat on the mainland, and their island distributions paralleled the availability of open habitat on islands. Similar plant ages on different sized islands may result from their occurrence in open habitat on both large and small islands. Overall results support the habitat hypothesis and indicate that species distributions result from the interaction between habitat affinities and changes in habitat availability with island area.     

Carabids of differently aged reforested pinewoods and a natural pine forest in a historically modified landscape

We studied the responses of carabid beetles to Pinus sylvestris ageing in four plantations aged 2–3, 10–12, 40–45 and 80 years, and one mature natural pine forest – in NW Spain. In 2003, a total of 16,866 carabid individuals (50 species) were collected using pitfall traps. Overall carabid abundance and species richness differed significantly among the five age classes with the highest values occurring in the youngest age class. The carabid assemblages of the initial stages of the ageing sequence differed considerably from the later stages that were relatively similar to each other – a consequence of differences in species dominance at specific age classes. Yet, the carabid assemblage of the 80-year-old stage did not approach that of the natural pine forest, but, unexpectedly, the 40–45-year-old age class did. Canopy cover and soil pH were the main environmental variables that affected the carabid distribution. We also detected species-level responses to the ageing process, with open habitat species more abundantly collected at the youngest stages and forest specialists at the older stages. We conclude that carabid beetles responded predictably to the pine plantation ageing process, and that although pine forests in NW Spain do not seem to provide habitat for unique species, they act as secondary habitats for forest specialist species.     

Effects of urbanization on ground beetle assemblages (Coleoptera, Carabidae) of grassland habitats in western Canada

We pitfall-trapped carabid beetles across an urban-rural gradient in central Alberta, Canada to assess the relative contributions of landscape structure and habitat quality in explaining variation in composition of assemblages. The gradient ranged from the "urban" zone in the city of Edmonton, through a "suburban" zone just outside the city, into a "rural" zone 25–60 km east of the city. We trapped beetles at three replicated sites for each of two habitats (unmanaged grasslands and highly managed graveyards) in each of the three zones. Most of the 24 species (3162 individuals) captured were commonly associated with open habitats. Pterostichus melanarius , an introduced species, made up 80% of the total catch. Carabid assemblages of grasslands and graveyards were distinct, with lower species richness and lower catch rates of native, introduced and brachypterous carabids in graveyards. Graveyard assemblages also had proportionally fewer brachypterous carabid individuals (32 vs 52%) and species (20 vs 36%), suggesting that populations recruit locally from elsewhere after disturbances. Native carabids were least abundant in the urban areas. Brachypterous carabids were similarly abundant across the gradient, but more occurred in the urban zone than elsewhere (32 vs 5–10%). Samples from graveyards were characterized by lower beta diversity (variation among samples) than those from grasslands, but beta diversity was more-or-less equally variable across the gradient within habitats. The amount of unmanaged grassland habitat and the degree of urbanization significantly influence carabid assemblages, and therefore are relevant to management and conservation of urban grassland areas.     

Impact of predatory carabids on below- and above-ground pests and yield in strawberry

The impact of adult carabid beetles on below- and above-ground pests and fruit yield was examined in the laboratory and a two-year strawberry field study. In the laboratory, adults of Carabus nemoralis Muller, Nebria brevicollis (F.), Pterostichus algidus LeConte, Pterostichus melanarius (Illiger), and Scaphinotus marginatus Fischer (Coleoptera: Carabidae) consumed black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae) eggs, larvae and/or pupae placed on the surface. The same five carabid species showed no impact or low removal rates of O. sulcatus larvae that had burrowed into the root of potted strawberry plants. In an assay with only P. melanarius, adults consumed O. sulcatus larvae placed on the soil surface more frequently than larvae buried 1.3 or 5?cm below. In a field study, the density of adult carabids, predominantly P. melanarius, was manipulated with augmented, exclusion, and open control plots (2?×?2?m). Manipulating carabid density had no impact on the removal of sentinel O. sulcatus larvae and pupae that were buried belowground which is consistent with laboratory observations. Increasing carabid density within augmented plots led to greater removal of red clover seeds, Trifolium pratense L., placed on the soil surface in the first?year. Decreasing carabid density within exclusion plots resulted in fewer marketable fruits compared to control plots in both years. These results suggest that certain adult carabids may have limited impact belowground, and some beneficial impacts above-ground with pest control and crop protection.     

Impact of the invasive moss Campylopus introflexus on carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) in acidic coastal dunes at the southern Baltic Sea

Campylopus introflexus is an invasive moss in Europe and North America that is adapted to acidic and nutrient-poor sandy soils with sparse vegetation. In habitats like acidic coastal dunes (grey dunes) it can reach high densities, build dense carpets and modify habitat conditions. While the impact of the moss invasion on the vegetation is well analyzed, there is a lack of knowledge regarding possible effects on arthropods. In the present study we analyzed the impact of Campylopus introflexus on the ground-dwelling arthropods carabid beetles and spiders, as both taxa are known to be useful indicator taxa even on a small-scale level. In 2009 we compared species composition in a) invaded, moss-rich (C. introflexus) and b) native, lichen-rich (Cladonia spp.) acidic coastal dunes by using pitfall traps. A total of 1,846 carabid beetles (39 species) and 2,682 spiders (66 species) were caught. Species richness of both taxa and activity densities of spiders were lower in invaded sites. Species assemblages of carabids and spiders differed clearly between the two habitat types and single species were displaced by the moss encroachment. Phytophagous carabid beetles, web-building spiders and wolf spiders were more abundant in native, lichen-rich sites. Shifts in species composition can be explained by differences in the vegetation structure, microclimate conditions and most likely a reduced food supply in invaded sites. By forming dense carpets and covering large areas, the moss invasion strongly alters typical arthropod assemblages of endangered and protected (EU-directive) acidic coastal dunes.     

宁夏盐池荒漠草原步甲物种多样性

采用巴氏罐诱法于2009年3月到10月对盐池四墩子3种不同类型荒漠草原的步甲物种组成、数量分布进行了系统调查,共获得步甲标本1318号,分属于9属15种,其中直角通缘步甲Pterostichus gebleri、蒙古伪葬步甲Pseudotaphoxnus mongolicus、径婪步甲Harpalus salinus和短翅伪葬步甲Pseudotaphoxnus brevipennis为优势种,个体数量分别占个体总数的33.08%、19.73%、15.94%和8.04%。多样性分析表明适度干扰荒漠草地的Shannon-Wiener多样性、丰富度和均匀度均高于低干扰和强干扰荒漠草地。群落相似性分析显示猪毛蒿和甘草混交带与围栏放牧带及柠条带有较高的相似性,蒙古冰草带和苜蓿与柠条混种带相似性较高。从时间动态上看,步甲群落的个体数量在8月份达到最高。4种优势种季节性变化分别是直角通缘步甲盛发期为8月,径婪步甲发生的高峰期为8、9月,短翅伪葬步甲在5月和8月,蒙古伪葬步甲7-10月个体数量均多;不同物种在不同类型荒漠草地出现的高峰期是不一致的。典范对应分析(CCA)分析表明土壤含水量是影响步甲分布的最重要环境因子,植物生物量和植被密度次之;土壤含水量与步甲的Shannon-Wiener多样性、均匀度显著负相关,与优势度呈显著正相关。     

Predation by the Carabid Beetles Pterostichus melanarius and Poecilus cupreus on Slugs and Slug Eggs

Predation on slugs, Arion lusitanicus (Mabille) and Deroceras reticulatum (Müller), and their eggs by the carabid beetles Pterostichus melanarius (Illiger) and Poecilus cupreus (L.) was investigated in the laboratory. Slugs of different size and slug eggs were offered to the beetles in petri dishes with and without several alternative prey. Pterostichus melanarius destroyed eggs of D. reticulatum and A. lusitanicus, with a clear preference for D. reticulatum eggs. The availability of some alternative prey types adversely affected feeding on D. reticulatum eggs by P. cupreus and feeding on A. lusitanicus eggs by P. melanarius. Yet consumption of D. reticulatum eggs by P. melanarius was not significantly influenced by any alternative prey. Only P. melanarius killed small D. reticulatum in the presence of alternative prey. This suggests that P. melanarius and P. cupreus may have the potential to reduce slug populations in the field by destroying slug eggs and, in the case of P. melanarius, killing freshly hatched slugs.