Effects of soil conditions and drought on egg hatching and larval survival of the clover root weevil (Sitona lepidus)

Soil-dwelling insect herbivores are significant pests in many managed ecosystems. Because eggs and larvae are difficult to observe, mathematical models have been developed to predict life-cycle events occurring in the soil. To date, these models have incorporated very little empirical information about how soil and drought conditions interact to shape these processes. This study investigated how soil temperature (10, 15, 20 and 25 °C), water content (0.02 (air dried), 0.10 and 0.25 g g^?1) and pH (5, 7 and 9) interactively affected egg hatching and early larval lifespan of the clover root weevil (Sitona lepidus Gyllenhal, Coleoptera: Curculionidae). Eggs developed over 3.5 times faster at 25 °C compared with 10 °C (hatching after 40.1 and 11.5 days, respectively). The effect of drought on S. lepidus eggs was investigated by exposing eggs to drought conditions before wetting the soil (2–12 days later) at four temperatures. No eggs hatched in dry soil, suggesting that S. lepidus eggs require water to remain viable. Eggs hatched significantly sooner in slightly acidic soil (pH 5) compared with soils with higher pH values. There was also a significant interaction between soil temperature, pH and soil water content. Egg viability was significantly reduced by exposure to drought. When exposed to 2–6 days of drought, egg viability was 80–100% at all temperatures but fell to 50% after 12 days exposure at 10 °C and did not hatch at all at 20 °C and above. Drought exposure also increased hatching time of viable eggs. The effects of soil conditions on unfed larvae were less influential, except for soil temperature which significantly reduced larval longevity by 57% when reared at 25 °C compared with 10 °C (4.1 and 9.7 days, respectively). The effects of soil conditions on S. lepidus eggs and larvae are discussed in the context of global climate change and how such empirically based information could be useful for refining existing mathematical models of these processes.     

First sources of resistance to Sitona weevil (Sitona crinitus Herbst) in wild Lens species

Lentil is one of the important cool-season food legumes grown in many countries in the Mediterranean region. But a substantial yield loss is observed every year due to various biotic stresses. The Sitona weevil (Sitona crinitus Herbst) is a major insect pest limiting lentil productivity mainly in the countries of West Asia and North Africa region. The adult insects feed on the leaflets at seedling stage, and the plant suffers due to reduced photosynthesis. The larvae feed on the root systems and on the nodules, thus decreasing the ability of the plant to fix atmospheric nitrogen. Since sources of resistance to this pest in the cultivated lentil Lens culinaris Medikus subsp. culinaris are lacking, we searched for resistant sources in a collection of wild Lens species available in the ICARDA Gene Bank. We screened 315 accessions of wild lentil covering all known species/sub-species based on nodule damage at ICARDA’s main experimental station (Tel Hadya, Aleppo), a hot-spot for the pest in the region. Large variation was observed in the percent nodule damage among accessions across species. Eight accessions, ILWL 110, ILWL 136, ILWL 166, ILWL 203, ILWL 207, ILWL 245, ILWL 254 and ILWL 258 were identified as resistant, with ≤10% nodule damage, compared to >56% damage recorded on the cultivated lentil. This is the first report of resistance against Sitona weevil in lentil. One resistant accession ILWL 245 belongs to the species L. culinaris Medikus subsp. orientalis (Boiss.) Ponert, progenitor of the cultivated lentil, which is crossable with the cultivated lentil. This line is being used to introgress resistance genes to cultivated lentil and to understand the inheritance of Sitona weevil resistance.     

Dispersal power,home range and habitat preference of cantharid larvae (Coleoptera: Cantharidae) in arable land

The dispersal ability, home range size and habitat preference of sixth instar larvae of the widespread cantharid species Cantharis fusca (L.) and C. livida (L.) were studied in a mark–recapture experiment in a meadow–field (winter grain) area between autumn and spring in 1999/2000. The main results and conclusions were: (i) The mean dispersal velocity of C. fusca/C. livida larvae was 1.4/1.6 m d^–1 with a maximum of 3.2/2.3 m d^–1. The larvae were able to disperse more than 100 m during their larval development, demonstrating that larvae and not only adults contribute to spreading. (ii) The average home range area of seven C. fusca individuals was 12.9 m² (minimum 8 m²/maximum 19 m²). The low number of multiple recaptures and the large distances larvae can cover indicate that the real home range size was underestimated. (iii) C. fusca larvae significantly preferred the meadow area compared to the bare ground of the field. This can be explained by the meadow's higher plant cover and humidity C. livida specimens that were released one month later and recaptured only in low numbers showed no such preference. (iv) Due to the high dispersal ability of soldier beetle larvae, immigration from meadows and grass bulks of boundary strips into the crop margins and inner field areas is possible; it can be augmented by creating constant plant cover, e.g. through winter grain or cover crops.     

Effects of a plant parasitic nematode (Heterodera trifolii) on clover roots and soil microbial communities

We studied the effects of the root endoparasitic nematode Heterodera trifolii on rhizodeposition and the root architecture of white clover (Trifolium repens). Rhizosphere solutions were collected from the root systems of plants growing with and without H. trifolii (200 juveniles per inoculated plant) in sand-based microlysimeters. The organic carbon (C) content of these solutions was analyzed, and they were applied to plant-free soils to investigate microbial responses. Although plant biomass was unaffected by nematodes, the architecture of the root systems was significantly altered, with a decrease in overall root length and an increase in the density of lateral branches from the primary root. The presence of nematodes reduced the concentration of organic compounds in the rhizosphere solutions but only on the final sampling date (75 days). Analysis of microbial signature phospholipid fatty acids revealed no change in the structure of the microbial communities in soils to which rhizosphere solutions were applied. However, these microorganisms did respond with changes in substrate utilization patterns (community-level physiological profiles). Microbes in soils that received rhizosphere solutions from the nematode-infected clover showed lower utilization of most substrates but higher utilization of oligosugars. These responses appear to be related to changes in roots and rhizodeposition associated with nematode infection of clover roots. The results of this study suggest that root herbivory can negatively impact carbon-limited soil microbial communities via changes in root architecture that moderate rhizodeposition.     

Dispersal of the endangered flightless beetle Dorcadion fuliginator (Coleoptera: Cerambycidae) in spatially realistic landscapes

Habitat destruction and degradation are the major causes for the decline of the endangered grass-feeding beetle Dorcadion fuliginator in Central Europe. In the southern part of the Upper Rhine valley (border region of Switzerland, Germany and France) the habitat suitable for this flightless beetle has been reduced to small remnants of extensively managed dry grassland, usually surrounded by intensively cultivated agricultural fields or settlements. Using a mark-release-resight technique we examined movement patterns in three D. fuliginator populations to obtain basic information on the dispersal ability and longevity of this beetle. Estimated daily survival rates ranged from 88.8% to 90.8% in the populations examined. This corresponds to a mean life span of 10.5 days. Distances moved by D. fuliginator differed among populations. The beetles walked the largest distances in the verges of a field track. Several beetles moved distances of 20-100 m along the track, with a maximum distance of 218 m (a male in 12 days). The shortest displacements were recorded in the bank of the river Rhine, a narrow habitat surrounded by tarmac roads. We also assessed the spatial arrangement of 12 patches with D. fuliginator populations in two regions and estimated the size of each population over 4 years. Data on dispersal, daily survival, population size and spatial arrangement of patches were used to simulate patch-specific migration rates. The simulations suggested that in both areas the beetles regularly moved between neighbouring patches separated by distances shorter than 100 m, whereas patches separated by distances exceeding 500 m are isolated.     

Enhanced root nodulation of subterranean clover (Trifolium subterraneum) byRhizobium leguminosarium biovartrifolii in the presence of the earthwormAporrectodea trapezoides (Lumbricidae)

In a greenhouse study, the effect of the earthwormAporrectodea trapezoides on root nodulation in seedlings of subterranean clover (Trifolium subterraneum) was examined in the presence and absence of addedRhizobium leguminosarium biovartrifolii (strain NA 30). WhenR. trifolii NA 30 was inoculated into dung and placed on the soil surface, the total number of root nodules was five times greater (P<0.001) in the presence of earthworms than without earthworms and the number of nodules on the primary root of the plants 2–8 cm below the soil surface was 4 to 6 times greater (P<0.001) in the presence of earthworms. The additional nodulation did not affect plant growth or foliar N. When NA30 was dispersed through the soil at the beginning of the experiment, the presence of earthworms did not influence the level of root nodulation. The presence of earthworms increased root dry weight by 20–30%, plant top weight by up to 125% (P<0.001), and foliar N by 5–25% (P<0.001). Surface-applied dung increased the dry weight of plant tops (2-to 3-fold,P<0.001) but did not affect the concentration of foliar N (P<0.005).     

Effects of nutrient supply and below-ground herbivory by Diaprepes abbreviatus L. (Coleoptera: Curculionidae) on citrus growth and mineral content

Three-year-old citrus trees were grown in the greenhouse to study the effects of fertilizer concentration and root herbivory on plant growth and mineral concentration. In separate experiments, sour orange (Citrus aurantium L.) and Swingle citrumelo (C. paradisi Macf. × Poncirus trifoliate L.) plants were treated with a complete fertilizer diluted to provide 25, 100, 200, or 400 ppm N and grown for 7 weeks with or without Diaprepes abbreviatus L. larvae. Increased fertilizer concentration increased the shoot mass and the shoot:root ratio of both sour orange and Swingle citrumelo. Root herbivory also increased the shoot:root ratio by depressing root growth more than shoot growth. Effects of root herbivory on growth were consistent across the four levels of fertilizer concentration, indicating that tolerance is not a function of nutrient status. For both rootstocks, concentrations of nitrogen in roots and leaves increased with fertilizer concentration, and C:N ratios decreased. In sour orange, root herbivory most strongly affected the concentration of carbon in roots, whereas in Swingle citrumelo, root herbivory most strongly affected leaf nitrogen. In general, herbivory reduced mineral concentrations of roots but the strength, and sometimes the direction, of herbivore effects varied significantly among fertilizer treatments. This research indicates that application of excess, balanced fertilizer is unlikely to offset growth reductions due to root herbivory by D. abbreviatus, and suggests that supplementation of specific nutrients may be of value.     

From plant communities to landscapes in conservation inventories: A look at the nature conservancy (USA)

The Nature Conservancy (TNC—USA) has developed an efficient system for inventory and evaluation of ‘elements-of-diversity’. The major components of this system are a ‘fine filter’ for species inventory and a ‘coarse filter’ for community-type inventory. As in traditional vegetation science, community sampling and classification are restricted to relatively homogeneous stands and avoid edges, ecotones, and disturbed areas. TNC employs a habitat-based system of natural communities to complement plant community classification. This system is used to identify stands that cumulatively encompass the full range of variation within each defined natural community type. Ecological relationships among community-types in real landscapes, however, are not accounted for.This paper reviews some important ecological functions of heterogeneous landscapes, which are not necessarily protected by conservation strategies that focus on separate, homogeneous community-types. Recommendations to expand TNC's coarse filter to landscapes include: (1) Disturbance regime and regeneration patterns should be evaluated for each major community-type, and for each site representing a type or group of types; (2) Functional combinations of community-types and developmental stages (landscape mosaics) should be addressed in the TNC system; (3) Landscape context (e.g., surrounding habitat types and connectivity) for a site is as important as the habitat content (e.g., the rarity or quality of community-types present). Attention to landscape-level patterns and processes will be helful for evaluating large sites that are composed of many community-types, and in setting selection and stewardship priorities for sites for any size that are surrounded by dissimilar habitat.     

Volatile composition of coffee berries at different stages of ripeness and their possible attraction to the coffee berry borer Hypothenemus hampei (Coleoptera: Curculionidae)

The analysis of volatile emissions of coffee berries in different physiological states of ripeness was performed using dynamic headspace and gas chromatography/mass spectrometry analysis for Coffea arabica, var. Colombia. The composition of the volatiles emitted by coffee berries is dominated by very high levels of alcohols, mainly ethanol, in all stages of ripeness in comparison with other compounds. Overripe coffee berries have high volatile emissions and show a composition dominated mainly by esters followed by alcohols, ketones, and aldehydes. The lowest level compounds were monoterpenes. 2-Methyl furan was detected in various ripening stages; this compound has not been previously reported as a coffee berry volatile. The presence of ethanol and other alcohols in the volatile composition might explain the effectiveness of using traps with mixed alcohols for detection and capture of coffee berry borers.     

Measurement of pH at the root surface of red clover (Trifolium pratense) grown in soils differing in proton buffer capacity

Summary Measurements of pH were made at the root surface of Trifolium pratense, using Sb electrodes. Nodulated plants were grown in rhizotrones on a sandy soil free of carbonate and on a clay soil rich in carbonate. In the sandy soil, pH at the surface of root laterals was about 1 unit lower than in the bulk soil. The lowest pH values were found at the root tips. In the calcareous soil, pH measured at the root surface did not differ from pH in the bulk soil. This soil had a much higher H⁺ buffer capacity than the sandy soils. It seems likely that H⁺ ions excreted from the roots grown in the calcareous soil were directly neutralized by soil carbonate.     

Controlling factors of environmental flooding,soil pH and Diaprepes abbreviatus (L.) root weevil feeding in citrus: Larval survival and larval growth

The underlying influences of soil flooding, pH level and soil-inhabiting Diaprepes abbreviatus (L.) root weevil larval feeding in citrus were examined in two separate greenhouse studies, rootstock × flooding × Diaprepes-larvae (RFD) and liming × rootstock × flooding × Diaprepes-larvae (LRFD). Our objectives were to determine the combined effects of soil flooding and pH level on survival and growth of Diaprepes root weevil larvae to gain insights of insect-environmental relations for the weevil control. We used a Floridana sandy loam (pH 4.8) from a citrus grove infested by Diaprepes root weevil in center Florida. The RFD experiment consisted of two citrus rootstocks (Swingle and Smooth Flat Seville), three flooding durations (0, 20, and 40 days) and two larval infestation rates (0 and 5 larvae) for 40-day feeding. The LRFD experiment consisted of two citrus rootstocks (Swingle and Carrizo), three pH levels (non-limed control, and target pH 6 and 7), two flooding durations (0 and 40 days), and two larval rates (0 and 5 larvae) for 56-day feeding. Dolomite (54% CaCO₃ and 46% MgCO₃) was used for soil liming in the LRFD. Treatments were arranged with 15 replicates in a completely randomized design. In the RFD, flooded soil pH was 0.3 units higher than non-flooded soil and larval survival was the lowest in the longest flooded treatment (P < 0.05). In the LRFD, soil pH increased 0.5–0.9 units for the target pH 6, and 0.7–1.1 units for the target pH 7. The effects of rootstock, liming and flooding treatments and their interactions were significant on soil pH and larval survival (P < 0.05). Larval survival decreased from 80% to 60% with increasing soil pH from 4.8 to 5.7. Total larval weight per seedling decreased significantly from 0.060 g to 0.012 g when the soil pH increased from 5.1 to 5.7. Flooding reduced larval survival and growth, and increasing acidic soil pH by 1 unit would be an option for controlling soil acidity and for promoting integrated management of Diaprepes root weevil in citrus.     

Evaluating N/N and C/C isotope ratio analysis to investigate trophic relationships of elaterid larvae (Coleoptera: Elateridae)

Carbon and nitrogen isotope ratios in consumer tissues can be used to analyse the diet and trophic level of soil animals. However, life history traits may significantly influence stable isotope patterns. We evaluated in a series of experiments how stable isotope ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) at natural abundance can be used to study the diet and trophic position of long-lived macro-invertebrates, elaterid larvae, which are major below-ground herbivores. Small, but significant differences in δ¹³C signatures were found between the larvaes’ anterior and posterior body segments, whereas exuvia reflected the body's overall isotopic composition. The species-specific trophic shift (±SE) in δ¹⁵N for Agriotes obscurus and Agriotes sputator (1.62±0.24‰ and 1.08±0.27‰, respectively) was significantly lower than “mean enrichment estimates” reported in the literature, showing the limited applicability of such generalised estimates in studies of invertebrate trophic ecology. To avoid false-positive assignments to two trophic levels due to variation in δ¹⁵N values, a minimum sample size of three and five individuals for A. obscurus and A. sputator, respectively, was needed to reduce this risk to below α=5%. Keeping elaterid larvae for up to 128 days without food did not affect their isotopic signatures, in contrast to previous studies on starving animals. Switching wireworms to isotopically different diets induced changes in their isotopic signatures within 2 weeks. Changes, however, were significant only when the isotopic difference between diets was large. We conclude that experimental studies evaluating how specific life history traits affect stable isotope signatures in consumers have to precede any interpretation of stable isotope data gathered in the field.     

Characterization and partial purification of proteinases from the highly alkaline midgut of the humivorous larvae of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

Proteinases in the humus-feeding larva of Pachnoda ephippiata were partially purified and characterized. Proteinase activity from the midgut was alkali-stable and its pH optimum for activity was about pH 12. Nine proteolytic bands were visible on zymogram gels containing gelatin; one band of 19 kDa was dominant. P. ephippiata mainly employed serine proteinases for digestive proteolysis. The combination of strong midgut alkalinity and midgut proteinases with pronounced alkali stability, a high proteolytic activity on model humic acids, and a large tolerance to high humic acid concentrations would enable the P. ephippiata to gain nutrients from soil by digesting the proteinaceous component of soil humic substances.     

Kleptocopry of Aphodius coenosus (Coleoptera,Aphodiidae) in nests of Typhaeus typhoeus (Cleoptera,Geotrupidae) and its effect on soil morphology

Summary Kleptocopry is the behaviour of adults or larvae of a certain species whereby dung masses are utilized which had been provisioned by individuals of another species for the latter's own brood. Aphodius coenosus is a kleptocoprid in nests of Typhaeus typhoeus. This is the first record of kleptocopry by A. coenosus and of a kleptocoprid in the nest of T. typhoeus. In the laboratory, newly emerged A. coenosus adults moved to the surface while back-filling their burrows. Back-filled burrows (approximately 3 mm in diameter) were also found in the field, together with back-filled burrows from T. typhoeus (approximately 14 mm in diameter). Ancient (ca. 10 000 years old) back-filling traces of the Typhaeus type reported earlier were also accompanied by small back-filling traces, similar to those made by A. coenosus. The traces made by kleptocoprid A. coenosus thus offer support to the hypothesis that the ancient large traces originate from large geotrupid dung beetles.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Carabid beetle (Coleoptera: Carabidae) diversity in the black spruce succession of eastern Canada

This study provides the first assessment of carabid beetle diversity in a natural forest context that encompasses a complete black spruce (Picea mariana) natural succession. Boreal forest conservation has been based on several assumptions about forest age that only consider species richness without accounting for species composition. It has also been guided by studies of incomplete chronologies that do not include naturally burned or old-growth stages. Twenty-one forest stands of different ages following fire - from recently burned to old-growth stages (0-340 years of age) - were sampled, revealing a strong relationship between age of forest and diversity of Carabidae. Over time, species richness followed a parabolic U-shaped pattern both with observed (Obs) and predicted richness (ACE). Chronological clustering identified four groups of species in the succession: the ‘burned’ group characterized 0-2-year-old forests, ‘regenerating’ (21-58 year), ‘mature’ (70-170 year) and ‘old-growth’ (177-340 year). The time spans corresponding to each of these assemblages lengthen with age of forest at an exponential rate. Ward’s and K-means (clustering without constraint) provided support for the four assemblages but showed variation between individual successions, particularly for the ‘regenerating’ assemblage, identified as the most heterogeneous. The IndVal method identified characteristic species in every stage of the succession, particularly Sericoda spp. in the burned stage and Dromius piceus and Platynus mannerheimii associated with old-growth stands. The results obtained here show that diversity of Carabidae varies in primeval conditions according to age of forest and such variation should be taken into account when conservation issues are involved.     

Ecological stoichiometry of carbon, nitrogen, and phosphorus in estuarine wetland soils: influences of vegetation coverage, plant communities, geomorphology, and seawalls

Purpose

Little is known about carbon, nitrogen, and phosphorus stoichiometrical characteristics and influencing factors in estuary wetland soils. The purpose of this work is to study ecological stoichiometric characteristics of carbon, nitrogen, and phosphorus (R _CN, R _CP, and R _NP) in estuarine wetland soils of Shuangtaizi, northeast China and the potential affecting factors like vegetation coverage, plant communities, geomorphology, and seawall.

Materials and methods

During 2008–2010, soil samples in estuarine wetland were collected for soil organic carbon, total nitrogen and phosphorus, and other elements determination. Mole ratios of R _CN, R _CP, and R _NP were calculated.

Results and discussion

As a whole, R _CN was in the range of 8.26～52.97 (mean, 16.15), R _CP was in the range of 23.21～862.53 (mean, 90.66), and R _NP was in the 0.93～29.52 (mean, 5.07). R _CN, R _CP, and R _NP distribution were all with high spatial heterogeneities and significantly affected by vegetation coverage, plant communities, geomorphology, and seawalls. During the typical plant succession sequence of the halophytes–the mesophyte–the hydrophyte in estuarine wetland, P might be the primary limiting elements for nutrients stoichiometrical characteristics. R _CN, R _CP, and R _NP in soils of low-lying areas were all higher than that in highlands. Plant coverage and communities formation would help to reduce restriction from nitrogen, but to increase restrictions from phosphorus meanwhile.

Conclusions

C, N, and P ecological stoichiometry had high complexities. R _CN in estuarine wetland soils were generally high, whereas R _CP and R _NP were comparatively low, indicating that ecosystems in the estuary were limited by nutrients such as N and P, with the latter being the primary factor. Vegetation covers, plant communities, geomorphology, and seawall all affected nutrient stoichiometry in soils.     

Microfungal communities in soil,litter and casts of Lumbricus terrestris L. (Lumbricidae): a laboratory experiment

The anecic earthworm Lumbricus terrestris L. was kept in laboratory microcosms containing beech forest soil without litter, with beech leaf litter or with lime leaf litter. The structure of microfungal communities in soil, litter and fresh and aged (100 days) earthworm faeces was analysed using the washing and plating technique. The passage of mineral soil through the gut of L. terrestris affected the structure of the fungal community only little. In contrast, in the litter treatments the structure of the fungal community in fresh earthworm casts significantly differed from that in soil and litter. The majority of soil and litter inhabiting fungi survived passage through the gut of L. terrestris and the fungal community in casts consisted of a mixture of soil and litter inhabiting fungi. However, the frequency of Cladosporium spp., Alternaria spp., Absidia spp., and other taxa was strongly reduced in fresh casts. The degree of colonization of litter particles (number of isolates per number of plated particles) also decreased, but some fungi (mainly Trichoderma spp.) benefited from gut passage and flourished in fresh casts. During ageing of cast material the dominance structure of the fungal community changed. Both the degree of colonization of organic particles and the species diversity increased and approached that in soil. However, the structure of the fungal community in casts remained cast specific even after 100 days of incubation. It is concluded that the feeding and burrowing activity of L. terrestris accelerates the colonization of litter by the edaphic mycoflora but also extends the range of occurrence of litter-associated fungi into mineral soil layers.