Beetle Activity Density Research Articles

The effects of heterogeneity created by treefall, landslide, and stream on ground beetle assemblages in a primary beech forest

Old-growth forests play essential roles in maintaining biodiversity and providing ecosystem services. While heterogeneity produced by various natural disturbances and micro-topography is an integral part of old-growth forest ecosystems, the effects of such natural disturbances and heterogeneity on arthropod diversity in old-growth forests are not fully understood. In this study, we evaluated how the heterogeneity produced by treefalls, landslides, and streams influences ground beetle diversity in an old-growth beech forest in the Tadami Biosphere Reserve, Japan. Fourteen plots composed of five forest interior, three treefall gaps, three landslides, and three along a stream were established, with 15 pitfall traps installed in each plot. Traps were opened for two days in each season. The results showed that canopy openness was the highest in landslide gaps, whereas litter depth was the lowest along the stream. Species richness was lowest along the stream but was similarly high in the other three habitat types. The activity density of beetles was also lowest along the stream, but highest in the landslide gaps. Landslide gaps and streams had distinct species compositions and several indicator species, respectively, indicating that soil disturbances involved in landslides and repeated overflow by snowmelt and heavy rain along the stream provide specific environmental conditions that differ from the forest interior and treefall gaps. This study demonstrates that heterogeneity derived from natural disturbances and streams enhances biodiversity in old-growth forests. These findings can be used to develop management measures that mimic natural disturbances in order to conserve biodiversity in managed forests.

Ground beetles suppress slugs in corn and soybean under conservation agriculture.

Conservation agriculture practices such as eliminating tillage and planting high residue cover crops are becoming increasingly important in field crop systems in the US Mid-Atlantic. However, these practices have sometimes been associated with an increase in moderate to severe damage to field crops by slugs. Conserving natural enemy populations is a desirable way to manage slug infestations because remedial control measures are limited. Here, we tested the effects of conservation practices, weather, and natural enemies on slug activity-density measured by tile traps placed among 41 corn and soybean fields during the spring of 2018 and 2019 in the Northern Shenandoah Valley, Virginia, USA. We found that a positive effect of cover crops on slug activity-density was reduced by tillage and that slug activity-density declined with increasing ground beetle activity-density. Slug activity-density also declined with decreasing rainfall and increasing average temperature. Weather was the only significant predictor of ground beetle activity-density, which was reduced in sites and weeks that were relatively hot and dry or that were cool and wet. However, we also found a marginally significant negative effect of pre-plant insecticides on ground beetles. We suggest that the observed interacting effects of cover crops and tillage reflect favorable conditions for slugs provided by increased small grain crop residue that can be mitigated to some extent by even low levels of tillage. More broadly, our study suggests that implementation of practices known to promote recruitment of ground beetles in crop fields can improve natural suppression of slugs in corn and soybean that are being increasingly cultivated according to conservation agriculture practices.

Ground-dwelling arthropods as biodiversity indicators in maize agroecosystems of Northern Italy

Reliable monitoring of arthropod diversity in a given agroecosystem is essential for the conservation of the related ecosystem services, such as biological control. The often daunting complexity of arthropod collection and identification, however, highlights the need for surrogate taxa that can be easily sampled and be representative of a number of other taxa in term of diversity, general community features and specific composition.In this study, we used pitfall traps to sample three ground-dwelling arthropod taxa important as biocontrol agents (ground beetles, rove beetles and spiders) in 9 conventionally managed maize agroecosystems of Northern Italy over the course of two years, with the goal of characterizing their assemblages and evaluating their reciprocal potential as indicators of activity density, species richness, community turnover and species co-occurrence.Although dominated by few generalist species, sampled arthropod communities were relatively species-rich, and included the first Italian record of the spider Zelotes metellus (Roewer) (Araneae: Gnaphosidae). Ground beetles as a group were confirmed as promising indicators for the species richness and community composition turnover of rove beetles and spiders. Additionally, several abundant arthropod species acted as indicators of the species richness of their respective groups, and the ground beetle Pterostichus macer (Marsham) also worked as an indicator of overall rove beetle activity density. While the co-occurrence of individual arthropod species was limited for the studied taxa, a few species such as the ground beetle Parophonus maculicornis (Duftschmid) did show promise as species-specific bioindicators. Our results could be useful in improving the monitoring and management of these important natural enemies in maize-growing regions.

Long-term data reveal unimodal responses of ground beetle abundance to precipitation and land use but no changes in taxonomic and functional diversity

While much of global biodiversity is undoubtedly under threat, the responses of ecological communities to changing climate, land use intensification, and long-term changes in both taxonomic and functional diversity over time, has still not been fully explored for many taxonomic groups, especially invertebrates. We compiled time series of ground beetles covering the past two decades from 40 sites located in five regions across Germany. We calculated site-based trends for 21 community metrics representing taxonomic and functional diversity of ground beetles, activity density (a proxy for abundance), and activity densities of functional groups. We assessed both overall and regional temporal trends and the influence of the global change drivers of temperature, precipitation, and land use on ground beetle communities. While we did not detect overall temporal changes in ground beetle taxonomic and functional diversity, taxonomic turnover changed within two regions, illustrating that community change at the local scale does not always correspond to patterns at broader spatial scales. Additionally, ground beetle activity density had a unimodal response to both annual precipitation and land use. Limited temporal change in ground beetle communities may indicate a shifting baseline, where community degradation was reached prior to the start of our observation in 1999. In addition, nonlinear responses of animal communities to environmental change present a challenge when quantifying temporal trends.

Pest management and yield in spring oilseed rape without neonicotinoid seed treatments

Use of neonicotinoid insecticides as seed treatments has been prohibited in the EU. As a consequence, concerns of lost production have been raised among producers. It remains, however, unclear to what extent the ban has increased pest attacks and crop damage, and reduced yield and farm profit. It is also unclear to what extent alternative, non-chemical options can protect crops. Flea beetles (Chrysomelidae: Alticini) are the main pests targeted by insecticide seed treatments in spring oilseed rape (Brassica napus L.). Over three years, we conducted 23 field experiments in which we compared seeds treated with neonicotinoids with untreated seeds, grown at normal or doubled sowing rates. The experiments were established during a range of sowing times at the same time as the hosting farmer sowed, which also allowed us to assess the impact of sowing date. We measured flea beetle activity density, crop plant density, cotyledon damage, crop yield and relative economic performance. Flea beetle activity density was eight times higher in 2014 than in 2016, with intermediate activity in 2015. Neonicotinoid seed treatment, increased sowing rate and an earlier sowing date all reduced crop damage. Seed treatment decreased crop yield loss by 521 kg ha−1 and relative profit loss by 144 Euro ha−1 in 2014, but had no effect on yield or profit in 2015–2016. Increased sowing rate did not affect yield, but decreased profit in 2015 (−138 Euro ha−1) and 2016 (−114 Euro ha−1), mainly due to higher costs for seed. Earlier sowing date was consistently associated with higher yield and profit. Our results put prophylactic seed treatments in question, as they gave lower yield losses in only one year out of three. Earlier sowing and somewhat higher sowing rate emerge as viable alternative pest management practices. Because management outcomes depended on pest pressure, which varied from year to year, crop damage prognosis tools are needed based on improved understanding of the population ecology of crop pests, to support the growers’ decisions and avoid unnecessary use of insecticides.

Soil microbial and macrofauna dynamics under different green manure termination methods

No-till green manure (Gmr) termination creates a unique situation compared to conventional no-till crop management due to the surface mulch generated. However, the impact this practice has on soil biota has been little researched, despite the important role soil biota play in soil ecosystem functions such as decomposition and pest control. This study examines how termination management of Gmr can affect soil biota and their population dynamics. Over two trials, Gmr tillage regimes of fall tilled, spring tilled, or no-till were applied to a spring planted Gmr of hairy vetch/oat (HVO) along with a typical regional practice of tilled red clover Gmr within a four-year grain rotation. Soil microbial biomass (SMB), earthworm density, and beetle and spider activity density were assessed up to three years following Gmr termination. SMB was greatest in the spring for no-till and fall tilled HVO Gmr treatments, but the effect was transient, disappearing after two months. Earthworm densities were negatively affected by tillage (88% and 86% less than no-till in Trial 1 and 2, respectively) but densities recovered three years after tillage to that of the no-till treatment. Beetle activity density was largely unaffected by Gmr termination. Spider captures were more numerous in no-till plots compared to spring tilled in one trial. Impacts of Gmr termination on soil organisms vary by taxa and earthworms were the most sensitive, taking two years to recover from tillage. No-till Gmr termination does not show clear benefits to soil biota.

Effect of local and landscape factors on abundance of ground beetles and assessment of their role as biocontrol agents in the olive growing area of southeastern Madrid, Spain

Designing biological control strategies for the olive fruit fly (Bactrocera oleae (Rossi)) by predators requires the study of their biology and effectiveness. In this work, we have studied the relationship between ground beetle activity density and local (soil condition) and landscape factors in the olive area of southeastern Madrid, as well as the efficiency of the most abundant species, Orthomus barbarus (Dejean) (Coleoptera: Carabidae) by functional response experiments. Also, O. barbarus has been described for the first time by molecular methods through the barcode gene COI. The two dominant species, O. barbarus and Pterostichus globosus (Fabricius) (Coleoptera: Carabidae) showed different responses to landscape structure, but soil condition was more relevant than landscape structure for both species, and for activity density of ground beetles as a whole. P. globosus is more efficient than O. barbarus, and it is possible that in the study area other taxa are relevant as B. oleae predators.

Impacts of Dryland Farm Management Systems on Weeds and Ground Beetles (Carabidae) in the Northern Great Plains

Farming systems act as ecological filters impacting cropland associated biodiversity; however, the extent of these effects is largely unknown in the drylands of the Northern Great Plains (NGP), a key conventional and organic crop production region. In this 3-year (2013–2015) on-farm study, we addressed this knowledge gap by assessing the effects of conventional and organic farming systems on weed and ground beetle (carabidae) communities. We observed 25 weed species in conventional and 44 in organic fields. Weed species richness and weed species evenness were 237% and 137% greater in organic fields than in conventional fields. We collected a total of 1520 beetle specimens, representing 28 species in conventional and 37 in organic fields. Beetle activity-density and species richness were 220% and 156% greater in organic fields than in conventional fields. Both weed and ground beetle communities differed between conventional and organic fields, indicating that farming systems act as distinct ecological filters. We conclude that, in the drylands of the NGP, adoption of organic farming enhances weed abundance which could have potential management challenges, but provide floral resources to the pollinators and parasitoids. Similarly, greater diversity of ground beetles could enhance conservation biological control of crop pests, ultimately supporting for sustainable agriculture.

Dynamic effects of ground-layer plant communities on beetles in a fragmented farming landscape

Vegetation effects on arthropods are well recognized, but it is unclear how different vegetation attributes might influence arthropod assemblages across mixed-agricultural landscapes. Understanding how plant communities influence arthropods under different habitat and seasonal contexts can identify vegetation management options for arthropod biodiversity. We examined relationships between vegetation structure, plant species richness and plant species composition, and the diversity and composition of beetles in different habitats and time periods. We asked: (1) What is the relative importance of plant species richness, vegetation structure and plant composition in explaining beetle species richness, activity-density and composition? (2) How do plant-beetle relationships vary between different habitats over time? We sampled beetles using pitfall traps and surveyed vegetation in three habitats (woodland, farmland, their edges) during peak crop growth in spring and post-harvest in summer. Plant composition better predicted beetle composition than vegetation structure. Both plant richness and vegetation structure significantly and positively affected beetle activity-density. The influence of all vegetation attributes often varied in strength and direction between habitats and seasons for all trophic groups. The variable nature of plant-beetle relationships suggests that vegetation management could be targeted at specific habitats and time periods to maximize positive outcomes for beetle diversity. In particular, management that promotes plant richness at edges, and promotes herbaceous cover during summer, can support beetle diversity. Conserving ground cover in all habitats may improve activity-density of all beetle trophic groups. The impacts of existing weed control strategies in Australian crop margins on arthropod biodiversity require further study.

Spatial distribution of insect indicator taxa as a basis for peat bog conservation planning

Peat bogs are highly endangered ecosystems worldwide. In the Western Balkans, they represent fragmented habitat patches, where insect diversity and implications for the habitat loss are poorly known. Carabid beetles and ants, widely used environmental indicators, were sampled by pitfall trapping in the largest and oldest Croatian peat bog and at its edges. We found that tyrphobiontic—bog specialist—species were absent in both taxonomic groups, which is likely due to biogeographical limitation for dispersal of these species into this region. With this study, tyrphophilous—typical of bogs—species have been recognised as environmental indicators in the Western Balkans peat bogs. Assemblages of both taxa were strongly affected by specific conditions in the peat bog – high soil moisture and Sphagnum moss dominance, showing that edges are more favourable habitats for both taxa. Overall, carabid beetle activity density was significantly higher at the edge than at the peat bog, while species richness increased for both taxa at the edge, but not significantly. Spatial distribution of tyrphophilous species differed between studied taxa, with ants being more abundant in the peat bog, and carabid beetles at the edge. Additionally, some stenotopic and globally endangered species preferred edges. Occurrence of tyrphophilous and globally endangered species highlights the great conservation value of peat bog habitats in the Western Balkans. However, successional changes in vegetation are changing hydrological conditions of the peat bog. Here we suggest active conservation measures to preserve these unique soil invertebrate zoocoenoses.

Response of Pemphigus betae (Hemiptera: Aphididae) and Beneficial Epigeal Arthropod Communities to Sugarbeet Plant Density and Seed-Applied Insecticide in Western Nebraska.

This study investigated the impact of a neonicotinoid seed-applied insecticide (Poncho Beta) and two plant densities (86,487 and 61,776 plants per hectare) on the sugarbeet root aphid (Pemphigus betae Doane), beneficial epigeal arthropods, and selected crop yield parameters in sugarbeet (Beta vulgaris L. var. vulgaris). Ground beetles and centipedes were the most commonly collected taxa during 2012 and 2013, respectively. Centipede, spider, and rove beetle activity densities were not affected by the seed-applied insecticide, whereas plant density had a marginal effect on centipede activity density during 2012. Ground beetle species richness, diversity, and evenness were also not impacted by the seed treatments. However, during 2013, ground beetle activity density was significantly higher in plots planted with untreated sugarbeet seeds due to the abundance of Bembidion quadrimaculatum oppositum Say. Sugarbeet root aphid populations were significantly higher in the untreated plots during both years. In 2012, sugarbeet tonnage and sugar yield were higher under the low plant density treatment, while higher sugar content was recorded from the seed-applied insecticide plots (2013). Seed-applied neonicotinoids and plant density had little impact on beneficial epigeal arthropod activity density. Seed treatment did result in decreased root aphid populations; however, these reductions were not sufficient to be considered as an adequate control. This limited aphid control likely contributed to inconsistent effects on yield parameters.

Seasonal shifts in ground beetle (Coleoptera: Carabidae) species and functional composition maintain prey consumption in Western Oregon agricultural landscapes

Ground beetles (Carabidae: Coleoptera) are generalist predators that contribute to biological control of agricultural pests. Different ground beetle species vary in terms of size, feeding habits, and season of adult and larval activity. Species with similar biology and feeding habits may form a functional group if they are also similar in their effect on the overall risk to a potential prey item in an area. Farm surveys and laboratory studies were conducted to test whether ground beetle populations on Western Oregon vegetable farms were associated with the predation risk of a sentinel prey item. Pitfall traps were used to measure the activity patterns of adult beetles throughout the year. Along with the monthly pitfall traps, sentinel prey cards were deployed to measure the risk of predation to a potential prey item by a carabid beetle on the landscape. Additionally, beetles were collected after pitfall trapping to measure the amount of the sentinel prey items they would eat. The ground beetle species collected in the sampling were placed into three size based groups. The phenology and feeding habitats of the species within each sized based group tended to be similar. Sentinel prey removal rates in the field were significantly increased in areas with high activity of midsized beetles during the spring, when midsized beetles were the most active on the landscape but the explanatory power was somewhat low. In the summer, when large beetles were active in the landscape, sentinel prey removal rates were similarly associated with large beetle activity densities.

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 Linne, 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.

Assessment of the potential impact of a Bt maize hybrid expressing Cry3Bb1 on ground beetles (Carabidae)

The potential impact of a Bt maize hybrid expressing the coleopteran specific Cry3Bb1 on non-target organisms was assessed in a field release experiment. The study examined the relative abundance of ground beetles (Carabidae) in four maize varieties including the genetically engineered DKC 5143-Bt (event MON 88017), its near-isogenic line DKC 5143 and the two conventional varieties DK 315 and Benicia. Pitfall traps were used to collect the ground dwelling arthropods, which were analyzed to species level. Statistical comparisons showed no significant differences of ground beetle activity densities and diversity patterns between the Bt maize and the near isoline. The internal contents of the Bt protein Cry3Bb1 in ground beetles collected from the field were measured with ELISA. The Bt protein was found in 47% of the ground beetles sampled in Bt plots before the anthesis and in 66% of the individuals sampled after the beginning of maize anthesis.

Effects of riparian buffer strips on ground beetles (Coleoptera, Carabidae) within an agricultural landscape

Abstract Current restoration of stream and lotic freshwater systems to ‘good ecological status’ has focused on the creation of vegetated riparian buffer strips. Yet, despite this constituting a major land‐use change, surprisingly little is known about the effects of these strips on riparian organisms. We investigated the effect that widespread adoption of buffer strips may have on activity density, species diversity, and assemblage composition of ground beetles (Coleoptera, Carabidae). Over 2 years, we sampled carabids from 41 riparian margins within two river catchments in north‐east Scotland. We compared three types of riparian margin: unbuffered (i.e. ‘unimproved’), vegetated buffer strips, and wooded, the latter acting as reference sites. A range of site parameters including characteristics of soil, water, and vegetation were recorded and the extent to which they correlated with ground beetle assemblages was explored. Catchment and treatment effects were detected on ground beetle activity density and species diversity with unbuffered sites showing higher activity density and species richness. The assemblage structure differed according to catchment, treatment, and local characteristics. Multivariate analysis suggested that soil and vegetation parameters and stream width, together with buffer strip age and length were determinants of assemblage structure. Few riparian species were found in large numbers. This study shows that in intensively managed agricultural landscapes riparian buffer strips do not create the quality of habitat required by truly riparian species. They do, however, provide habitat for woodland and stenotopic species and with more careful planning could play a role in increasing habitat heterogeneity at a landscape scale.

Effects of Carbaryl-Bran Bait on Trap Catch and Seed Predation by Ground Beetles (Coleoptera: Carabidae)

Carbaryl-bran bait is effective against grasshoppers without many impacts on nontarget organisms, but ground beetles (Coleoptera: Carabidae) may be susceptible to these baits. Carabids are beneficial in agricultural settings as predators of insect pests and weed seeds. Carabid species and their consumption of weed seeds have not been previously studied in agricultural settings in Alaska. This study examined the effect of grasshopper bran bait on carabid activity-density, as measured by pitfall trap catches, and subsequent predation by invertebrates of seeds of three species of weed. Data were collected in fallow fields in agricultural landscape in the interior of Alaska, near Delta Junction, in 2008 and 2010. Bait applications reduced ground beetle activity-density by over half in each of 2 yr of bait applications. Seed predation was generally low overall (1-10%/wk) and not strongly affected by the bait application, but predation of lambsquarters (Chenopodium album L.) seed was lower on treated plots in 1 yr (340 seeds recovered versus 317 seeds, on treated versus untreated plots, respectively). Predation of dandelion (Taraxacum officinale G. H. Weber ex Wiggers) seeds was correlated with ground beetle activity-density in 1 yr, and predation of dragonhead mint (Dracocephalum parvifolium Nutt.) seed in the other year. We conclude that applications of carbaryl-bran bait for control of grasshoppers will have only a small, temporary effect on weed seed populations in high-latitude agricultural ecosystems.

Carabid beetle communities after 18 years of conservation tillage and crop rotation in a cool humid climate

AbstractAgricultural practices affect the biotic and abiotic conditions that determine food and shelter for carabid beetles (Coleoptera: Carabidae). We hypothesised that carabid communities would respond differently to 18 years of contrasted cropping practices in cereal-based rotations. We measured the effects of tillage (MP: moldboard plough; CP: chisel plough; NT: no-till) and previous crop sequence (cereal monoculture versus cereal–forage/cereal–oilseed rotation) on carabid beetle activity density, diversity, and community structure in corn (Zea mays Linnaeus, Poaceae) at La Pocatière, Québec, Canada. Carabid beetles were sampled monthly from May to September 2006, using pitfall traps. Although 19 carabid species were observed, assemblages were dominated by Harpalus rufipes (De Geer), particularly in the second half of the season. Multivariate analyses indicated a strong affinity of carabid species for the NT treatment throughout the season. Crop sequence and tillage had no effect on diversity (Shannon's H′ ≤ 1.3) and evenness of carabid assemblage, but species richness and activity density were greater in NT than in tilled systems. Peak activity density of dominant species occurred at different times during the season, generally in accordance with preferred breeding season. Many species had greater activity density in NT than in tilled treatments. Because of their granivorous feeding habit, carabid populations such as that of H. rufipes could be an important asset to NT, given the limited weed management options available for this system.

Effects of agri-environment management for stone curlews on other biodiversity

Two-hectare unsown, tilled fallow plots put in place under agri-environment schemes for stone curlews Burhinus oedicnemus in England were surveyed for other bird species, brown hares Lepus europaeus, carabid beetles, vascular plants, butterflies and bumblebees. The results were compared with those from surveys within the crop in the same field and in neighbouring fields. This was done to test whether agri-environment management targeted at a single species also provided benefits to wider biodiversity. All groups except carabid beetles were more abundant, more likely to be recorded, or more species rich on plots than within the crop. Carabid beetle activity–density and species richness did not differ between the plot and the crop; activity–density of one functional group (predators) was lower on plots than in the crop. Six rare arable plant species were recorded, predominantly from plots, and the plots are considered to perform comparably to other agri-environment options available in England designed specifically for arable plants. One red-listed bird species of conservation concern (skylark Alauda arvensis) was more abundant on plots than in the crop, and three other red-listed species (linnet Carduelis cannabina, yellowhammer Emberiza citrinella, corn bunting E. calandra) were more likely to be recorded on plots than in the crop. A fifth (lapwing Vanellus vanellus) was almost exclusively recorded from plots, and was more likely to be recorded on plots categorised as in good condition for stone curlews. These results demonstrate that fallow plots that have been put in place for the recovery of stone curlews have considerable value for a range of other farmland biodiversity, although management for stone curlews may be detrimental to some taxa, such as carabid beetles, that are sensitive to the relatively frequent spring tillage that these plots receive.

Cover Crops and Disturbance Influence Activity-Density of Weed Seed PredatorsAmara aeneaandHarpalus pensylvanicus(Coleoptera: Carabidae)

The activity-density ofAmara aenea(DeGeer) andHarpalus pensylvanicus(DeGeer) (Coleoptera: Carabidae) was monitored in an experiment that compared five management treatments representing a range of disturbance frequencies, crops, and aboveground biomass production. In 2004 and 2005, three treatments comprised of multiple summer cover crops were compared to bare fallow and soybean, the latter of which used mechanical cultivation to manage weeds. In 2005 weed seed predation was assessed from June to September in two of the treatments (bare fallow and oat–pea/rye–hairy vetch). Beetle activity-density varied with treatment, time of sampling, and year. In 2004 peak activity-density ofA. aeneawas highest in the mustard/buckwheat/canola, but there was no difference inH. pensylvanicusactivity-density. In 2005 activity-density ofH. pensylvanicuswas higher in oat–pea/rye–hairy vetch than in soybean treatment. Seed predation rates were relatively consistent across treatments, averaging between 38 and 63%. In fallow and oat–pea/rye–hairy vetch,H. pensylvanicusactivity-density accounted for 29 and 33% of the variation in seed predation, respectively. Our findings suggest cover crops have a positive effect on the activity-density ofA. aeneaandH. pensylvanicusand that disturbance negatively influences their activity-density in the absence of cover crops.

Molecular analysis of predation by carabid beetles (Carabidae) on the invasive Iberian slugArion lusitanicus

The invasive Iberian slug, Arion lusitanicus, is spreading through Europe and poses a major threat to horticulture and agriculture. Natural enemies, capable of killing A. lusitanicus, may be important to our understanding of its population dynamics in recently invaded regions. We used polymerase chain reaction (PCR) to study predation on A. lusitanicus by carabid beetles in the field. A first multiplex PCR was developed, incorporating species-specific primers, and optimised in order to amplify parts of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of large Arion slugs, including A. lusitanicus from the gut contents of the predators. A second multiplex PCR, targeting 12S rRNA mtDNA, detected predation on smaller Arion species and the field slug Deroceras reticulatum. Feeding trials were conducted to measure the effects of digestion time on amplicon detectability. The median detection times (the time at which 50% of samples tested positive) for A. lusitanicus and D. reticulatum DNA in the foreguts of Carabus nemoralis were 22 h and 20 h, respectively. Beetle activity-densities were monitored using pitfall traps, and slug densities were estimated using quadrats. Predation rates on slugs in the field by C. nemoralis in spring ranged from 16-39% (beetles positive for slug DNA) and were density dependent, with numbers of beetles testing positive being positively correlated with densities of the respective slug species. Carabus nemoralis was shown to be a potentially important predator of the alien A. lusitanicus in spring and may contribute to conservation biological control.