Aphid cards – Useful model for assessing predation rates or bias prone nonsense?

Predation on pest organisms is an essential ecosystem function supporting yields in modern agriculture. However, assessing predation rates is intricate, and they can rarely be linked directly to predator densities or functions. We tested whether sentinel prey aphid cards are useful tools to assess predation rates in the field. Therefore, we looked at aphid cards of different sizes on the ground level as well as within the vegetation. Additionally, by trapping ground-dwelling predators, we examined whether obtained predation rates could be linked to predator densities and traits. Predation rates recorded with aphid cards were independent of aphid card size. However, predation rates on the ground level were three times higher than within the vegetation. We found both predatory carabid activity densities as well as community weighted mean body size to be good predictors for predation rates. Predation rates obtained from aphid cards are stable over card type and related to predator assemblages. Aphid cards, therefore, are a useful, efficient method for rapidly assessing the ecosystem function predation. Their use might especially be recommended for assessments on the ground level and when time and resource limitations rule out more elaborate sentinel prey methods using exclosures with living prey animals.     

Estimated density of four carabid beetle species in Mongolian oak and Korean red pine forest ecosystems on Baekdudaegan mountain range (Mt. Oade and Mt. Guryong) of South Korea

The estimation of animal population size is a primary field of interest for wildlife biologists, and such numerical estimation of wild animals is a very important factor in establishing national policy towards nature. Therefore, we performed this study to estimate the population density of carabid beetles preying on soil biota at the Mongolian oak (Quercus mongolica) forests and Korean red pine (Pinus densiflora) forests of two mountains, Mt. Odae and Mt. Guryong. We used the trapping web method with pitfall traps to collect the beetles. We calculated the estimated density of a total of four carabid beetle species in two specific regions and converted them to an estimated beetle population size within a certain area by using the study area. From our estimates, one beetle species, Leptocarabus seishinensis seishinensis L., displayed statistically significant results. Although there was no appreciable difference in the makeup of different carabid beetle species between the two forest communities, the population size of the beetle species was larger in Mongolian oak forests than in Korean red pine forests. The spatial distribution of carabid beetles by forest type did not show any preference for particular spots. Our results showed that carabid beetles did not have specific home ranges and that they were not density dependent. We expect to use the raw data to recognize the response of soil organisms to changes in the habitat environment and to track the patterns of change more accurately over long passages of time.     

Ground Beetles (Coleoptera, Carabidae) in Forest Fragments of the Manawatu, New Zealand: Collapsed Assemblages?

Botanically diverse and well-maintained, protected forest fragments in the Manawatu area of the North Island of New Zealand contained very species-poor carabid assemblages. In a nearby large forest tract, the potential source area, nine species were caught in pitfall traps, while the largest forest remnant had two species, and a well-managed suburban forest patch had three species but only one with a potentially reproducing population. Lack of grazing and high botanical diversity was insufficient to maintain the potential carabid assemblage in these fragments. Predation risk and a low dispersal power in endemic New Zealand ground beetles, combined with fragment size and degree of isolation could contribute to this collapse. Active management of ground-active invertebrate species seems necessary to protect them in isolated forest fragments in New Zealand.     

Complete mitochondrial genome of a carabid beetle,Damaster mirabilissimus mirabilissim (Coleoptera: Carabidae)

In the present study, we report the 16 823‐bp long complete mitochondrial genome (mitogenome) of a carabid beetle, Damaster mirabilissimus mirabilissim (Coleoptera: Carabidae), which is endangered in Korea. The gene arrangement of D. m. mirabilissim mitogenome is identical to the most common type found in insects. The start codon of the D. m. mirabilissim COI gene is a typical ATN codon. On the other hand, the initiation codon for ND1 gene is TTG, instead of ATN. All transfer RNAs (tRNAs) exhibit a stable canonical clover‐leaf structure, except for tRNA^Ser(AGN), the dihydrouridine arm of which forms a simple loop. The 1703‐bp long A+T‐rich region is the second longest among the complete adephagan mitogenome sequences, next to Macrogyrus oblongus belonging to Gyrinoidea. One of the unusual features of the genome is the presence of a tRNA^Leu(UUR)‐like sequence in the A+T‐rich region. This sequence displays the proper anticodon sequence and the potential to form secondary structures, but also harbors many mismatches in the stems.     

Manipulating carabid beetle abundance alters prey removal rates in corn fields

Generalist natural enemies such as carabid beetles have the potential to maintain a variety of pests below outbreak levels in annual crops. To assess the relationship between carabid beetle abundance and field rates of prey removal, we created plots surrounded by different boundaries that selectively affected dispersal of edaphic arthropods, primarily carabids. Three treatments were established: (1) naturally occurring communities, (2) augmented communities using ingress boundaries, and (3) reduced communities using egress boundaries. Selective boundaries altered carabid communities with minimal habitat alteration and without use of insecticides. Three times during the growing season, a fixed number of onion fly pupae were placed in plots to evaluate the impact of carabid abundance on predation rates. A combination of vertebrate and invertebrate exclosures allowed us to evaluate prey removal by invertebrates alone. In comparison to the no boundary treatment, carabids increased 54.2% and decreased 83.1% in plots surrounded by ingress and egress boundaries respectively. Predation rates were positively correlated with carabid abundance (r² = 0.70, p < 0.0001). Significantly more pupae were removed from exclosures allowing access to invertebrates alone than from total exclosures, suggesting that invertebrates represented an important group of predators. Laboratory trials tested the feeding potential of the four most abundant carabid species and showed that they readily consumed onion fly pupae, supporting our hypothesis that carabids were the main predators in field tests. This study corroborates and extends previous observations of the importance of carabid beetles as generalist predators of insect pests in agricultural fields.     

Hybridization and speciation in the carabid beetles of the subgenusOhomopterus (Coleoptera, Carabidae, genusCarabus)

Natural hybridization among wingless carabid beetles of the subgenusOhomopterus (Carabidae, genusCarabus) is reviewed, and its significance in the evolution of this subgenus discussed. Natural hybridization occurs between parapatric species of similar size. Two case studies of natural hybridization suggest that natural hybridization could have affected the evolution of this subgenus in different ways. When there is a large difference in genital morphology between hybridizing species, interspecific copulation often results in genital injuries that causes mortality of copulating individuals, and hence reduces the fitness of hybridizing individuals greatly. In such a case, hybridization may be effective in maintaining the parapatric distribution of the two species, and in the long term, may promote reinforcement selection for traits which are effective in prezygotic reproductive isolation. When the morphological difference in genitalia is not so large as to cause genital injury, a hybrid population may be established at the intermediate zone between two parental species, provided that the immigration rates of the two species into the intermediate zone are small. Thus, natural hybridization may have contributed to both divergence and reticulate evolution in this subgenus.     

Gut microbial community response to herbicide exposure in a ground beetle

Gut microbiota plays a key role in physiological processes of insects, including nutritional metabolism, development, immunity and detoxification. Environmental stressors such as herbicides, used to optimize and improve crop yields, may interfere with the mutualistic relationships causing negative consequences for the host health. Dinitroaniline herbicides, for example pendimethalin, are used worldwide in pre-emergence application to control grass and some broadleaf weeds. They target microtubules to arrest cell division and inhibit the development of roots and shoots. Effects of a pendimethalin-based herbicide were assessed on the gut microbial community of Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae). The exposure effect was tested in vivo by using a recommended field rate (4 L per ha, 330 gL⁻¹ of active ingredient) and evaluating the variability of responses in 21 days, corresponding to the half-life of pendimethalin. The 16S rRNA sequencing data showed that the gut lumen was dominated by Proteobacteria, Firmicutes, Fusobacteria, Tenericutes and Bacteroidetes. The exposure interfered with the bacterial community richness and diversity associated with the gut from 2 days after the treatment. The differential abundance analyses highlighted a shift involving Lactobacillaceae, Streptomycetaceae, Neisseriaceae, Ruminococcaceae and Enterobacteriaceae. An increase in species such as Enterobacter sp., Pseudomonas sp., Pantoea sp and Paracoccus sp. involved in the herbicide degradation was also recorded after 21 days of exposure. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis indicated that the exposure has effects on the most predicted functional categories of gut microbiota related to metabolic function including carbohydrate, amino acid and lipid metabolism. These results demonstrate that pendimethalin can impact microbial communities associated with generalist predators inhabiting croplands leading to severe implications for the species’ ecological role. Understanding the effects of herbicides such as pendimethalin on ground beetles may help to protect beneficial soil insects that have a crucial role in the ecosystem services.