Dispersal is a key ecological process affecting community dynamics and the maintenance of populations. There is increasing awareness of the need to understand individual dispersal potential to better inform population-level dispersal, allowing more accurate models of the spread of invasive and beneficial insects, aiding crop and pest management strategies. Here, fine-scale movements of Poecilus cupreus, an important agricultural carabid predator, were recorded using a locomotion compensator and key movement characteristics were quantified. Net displacement increased more rapidly than predicted by a simple correlated random walk model with near ballistic behaviour observed. Individuals displayed a latent ability to head on a constant bearing for protracted time periods, despite no clear evidence of a population level global orientation bias. Intermittent bouts of movement and non-movement were observed, with both the frequency and duration of bouts of movement varying at the inter- and intra-individual level. Variation in movement behaviour was observed at both the inter- and intra- individual level. Analysis suggests that individuals have the potential to rapidly disperse over a wider area than predicted by simple movement models parametrised at the population level. This highlights the importance of considering the role of individual variation when analysing movement and attempting to predict dispersal distances.

Disentangling trophic interactions among species is important for elucidating mechanisms underlying ecosystem functioning and services. Carabid beetles are an important guild of predators that may regulate pest populations in arable landscapes, but their generalist feeding behavior hinders predictions about their actual contribution to pest control. In order to assess carabids’ potential for pest control, we simultaneously analyzed the carbon and nitrogen stable isotope ratios of a community of 45 co-occurring species in wheat and oilseed rape fields. With the expectation to identify distinct trophic groups based on the mean and the variance of carabid isotopic signatures, we observed a high degree of overlap in trophic positions between species. However, we also observed that species could be successfully categorized into two groups according to whether or not their carbon signatures varied independently from variations in the crop baseline. We interpret these results as differential primary resource uptake or by differential mobility aptitude in foraging. Accordingly, we propose that the isotopic signal can inform us on the presence/absence of links between generalist predators and cultivated plants through the trophic networks they belong to, and consequently on their potential role as pest natural enemies. We therefore suggest the complementarity of stable isotope analysis for obtaining a time-integrated assessment of carabid trophic behavior that may be combined with more direct molecular diet analysis allowing the simultaneous quantification of specific trophic links within agricultural landscapes.

The utility of biological control for weed management in agroecosystems will increase with a greater understanding of the relationships between common weed and granivore species. Giant foxtail is an introduced, summer annual grass weed that is common throughout the United States and problematic in numerous crops. Harpalus pensylvanicus (DeGeer) (Coleoptera: Carabidae) is a common, native, omnivorous carabid beetle with a range that overlaps giant foxtail. In 2004 and 2005, H. pensylvanicus was captured from farm fields in Centre County, PA, and subjected to laboratory feeding trials to test the preference of giant foxtail and other species on predation by H. pensylvanicus. Weed species seed preference experiments that included “Choice” and “No Choice” treatments were conducted using giant foxtail, common lambsquarters, and velvetleaf. When given a choice amongst the three weed species, H. pensylvanicus preferred giant foxtail and common lambsquarters seeds equally compared to velvetleaf seeds. When given the choice, H. pensylvanicus preferred newly dispersed giant foxtail seeds over field-aged seeds. Phenology of giant foxtail seed shed relative to H. pensylvanicus activity density was also quantified in field experiments in 2005 and 2006. Giant foxtail seed rain was determined by collecting shed seeds from August through October using pan traps. Activity density of H. pensylvanicus was monitored for 72-h periods using pitfall traps from June to October. Peak activity density of H. pensylvanicus occurred at the onset of giant foxtail seed shed in both years; however, giant foxtail seed shed peaked approximately 30 to 50 d after H. pensylvanicus activity density. Future research should focus on management practices that enhance and support H. pensylvanicus populations later in the growing season to maximize suppression of giant foxtail and other weeds that shed palatable seeds later in the season.

A standard method for evaluating weed seed predation is needed to facilitate generalizations across studies. Identification of general trends could allow practical recommendations for enhancing weed seed predation in agricultural systems. The objective of this study was to compare the commonly used sandpaper and soil substrate methods for offering weed seeds when assessing seed predation rates. Invertebrate seed predators and associated weed seed predation levels were measured in June to July, August, and September of 2005 and 2006 within a conventionally managed corn system. Seed predation levels of three common weed species, velvetleaf, giant foxtail, and common lambsquarters, were estimated using feeding trials in which 40 seeds of each species were offered over a 48 h period using the two substrates. Exclosures were used to distinguish total predation from predation by invertebrates alone. In addition, we investigated the use of geospatial analysis to estimate spatial autocorrelation of invertebrate populations and seed removal rates. Results suggest caution in using synthetic substrates, such as sandpaper, when assessing seed predation, especially when investigating small-seeded species (< 1 mg seed−1) or when seed predators are predominantly invertebrates. By contrast, predation of the larger-seeded species, velvetleaf, was less affected by substrate, perhaps because of removal predominately by vertebrates. One way to overcome problems with the sandpaper substrate method is for studies to include some soil substrate samples for on-site calibration of the sandpaper substrate. If necessary, data could then be corrected by multiplying by the ratio of soil substrate measured-predation rate to sandpaper measured-predation rate. Spatial autocorrelation explained between 6 and 9% of the variation in giant foxtail and common lambsquarters removal rates attributed to invertebrates alone. Researchers should, therefore, be careful not to neglect the impact of clustered invertebrate populations and associated seed removal rates.

Field experiments were conducted near Boone, IA, to quantify postdispersal seed predation of common lambsquarters and common waterhemp in corn (2003) and soybean (2004) managed with conventional, reduced, and zero-tillage systems. Seed predation in each tillage regime was quantified using selective exclusion treatments during July through September 2003 and June through October 2004. In addition, the activity density of ground-dwelling invertebrates was estimated with pitfall traps. Choice and no-choice feeding trials were conducted in the laboratory using the most abundant weed seed predators found in the field to determine seed preferences of the potential predator organisms. The greatest seed loss occurred during July and August. In 2003, seed predation was lower in zero tillage than in conventional and reduced tillages, but no differences in seed predation between tillage regimes were observed in 2004. Maximum seed predation for common lambsquarters was 53% in 2003 and 64% in 2004. Common waterhemp seed predation reached 80% in 2003 and 85% in 2004. The majority of seed predation was by invertebrate organisms. The most common invertebrate species captured with pitfall traps were field crickets (Gryllus pennsylvanicus De Geer [Gryllidae, Orthoptera]) and ground beetles (Harpalus pensylvanicus Burmeister [Coleoptera, Carabidae]). In 2003, field crickets were relatively more abundant in conventional and reduced tillage than in zero-tillage plots. In 2004, field crickets were more abundant in the reduced tillage than in the other two tillage regimes. No differences were detected for ground beetles among tillage regimes (P = 0.57). Choice and no-choice feeding experiments confirmed the preferences of field crickets and ground beetles for common lambsquarters and common waterhemp seeds over the larger seeds of giant foxtail and velvetleaf. Under field conditions, the activity density of field crickets was a significant predictor of common lambsquarters (r2 = 0.47) and common waterhemp (r2 = 0.53) seed predation. Positive relationships were also detected between the activity density of ground beetles and common lambsquarters (r2 = 0.30) and common waterhemp (r2 = 0.30) seed predation. This research demonstrated that weed seed predation is an important component affecting weed seedbanks and that crop management practices that favor the activity of predators such as field crickets or ground beetles could influence weed populations. Also, the results suggested that tillage is more important in determining the number of weed seeds available on the soil surface to predators than directly affecting predator activity density.

The activity-density of Amara aenea (DeGeer) and Harpalus 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 of A. aenea was highest in the mustard/buckwheat/canola, but there was no difference in H. pensylvanicus activity-density. In 2005 activity-density of H. pensylvanicus was 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. pensylvanicus activity-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 of A. aenea and H. pensylvanicus and that disturbance negatively influences their activity-density in the absence of cover crops.

In the present study, body length and dispersal ability were examined in carabid beetles (Coleoptera: Carabidae) sampled in the Peruvian Andes along two altitudinal gradients: old-growth forest and anthropogenically disturbed region. Dispersal ability was estimated by the flight-wing condition (i.e. macropterous or brachypterous) and the cuticular length of the flight muscle (medial length of the metasternum). The relationship between body length and altitude for combined gradients varied by tribe; all possible relationships were found: positive; negative; no relationship. At the family level, a negative relationship between altitude and insect body length was found; this was predicted because of a decrease in the diversity of resources, habitat area and primary productivity, and the increase in the unfavourable environment observed at high altitudes. Flight muscle length was also highly variable among tribes; however, for combined gradients, a negative correlation with altitude was found at the family level. Some tribes were either completely macropterous or brachypterous, but at the family level, the percentage of brachyptery increased with altitude. We suggest two hypotheses that may explain the increased incidence of flightlessness observed with increasing altitude: constraints of energy use and reduced need for dispersal potential. At the family level, carabid beetles tended to have a greater body length and decreased brachyptery in disturbed regions compared with old-growth forests. Increased dispersal ability was expected because of the need to find a suitable habitat in disturbed areas. Observed relationships may depend upon which tribes are examined and whether the forest on an altitudinal gradient has been disturbed.