Arthropod Responses Research Articles

Kinetic properties of catecholoxidase activity of tarantula hemocyanin

Phenoloxidases occur in almost all organisms, being essentially involved in various processes such as the immune response, wound healing, pigmentation and sclerotization in arthropods. Many hemocyanins are also capable of phenoloxidase activity after activation. Notably, in chelicerates, a phenoloxidase has not been identified in the hemolymph, and thus hemocyanin is assumed to be the physiological phenoloxidase in these animals. Although phenoloxidase activity has been shown for hemocyanin from several chelicerate species, a characterization of the enzymatic properties is still lacking. In this article, the enzymatic properties of activated hemocyanin from the tarantula Eurypelma californicum are reported, which was activated by SDS at concentrations above the critical micellar concentration. The activated state of Eurypelma hemocyanin is stable for several hours. Dopamine is a preferred substrate of activated hemocyanin. For dopamine, a K(M) value of 1.45 +/- 0.16 mm and strong substrate inhibition at high substrate concentrations were observed. Typical inhibitors of catecholoxidase, such as l-mimosine, kojic acid, tyramine, phenylthiourea and azide, also inhibit the phenoloxidase activity of activated hemocyanin. This indicates that the activated hemocyanin behaves as a normal phenoloxidase.

Choice of metrics for studying arthropod responses to habitat disturbance: one example from Gabon

Abstract. The choice of metrics comparing pristine and disturbed habitats may not be straightforward. We examined the results of a study in Gabon including 21 arthropod focal taxa representing 16 855 individuals separated into 1534 morphospecies. Replication included the understorey of 12 sites representing four stages of land use after logging (old and young forests, savanna and gardens), surveyed for 1 year using three sampling methods.For all focal taxa, we calculated a suite of 13 metrics accounting for the intensity of faunal changes between habitats, namely: abundance; observed, rarefied and estimated species richness; proportion of rare species; additive diversity partitioning; evenness of assemblages; higher taxonomic composition; species turnover; ordination scores of multivariate analyses; nestedness; proportion of site‐specific species and ratios of functional guilds.Most metrics showed large differences between forests and non‐forest habitats, but were not equally discriminating for particular taxa. Despite higher taxonomic groups being present in most habitats, many insect species were site or habitat specific. There was little evidence that the disturbance gradient represented a series of impoverished habitats derived from older forests. Rather, entire suites of species were being replaced as habitats were modified.Metrics based on species identity had a high sensitivity to disturbance, whereas measurements describing community structure were less discriminating in this regard. We recommend using metrics based on abundance, estimated species richness, species turnover estimated by multivariate analyses and guild structure, to avoid misleading interpretations that may result from comparisons of species richness alone.

Monitoring arthropods in a tropical landscape: relative effects of sampling methods and habitat types on trap catches

To discuss the challenge of monitoring multi-species responses of tropical arthropods to disturbance, we considered a large dataset (4 × 105 individuals; 1,682 morphospecies representing 22 focal taxa) based on the work of parataxonomists to examine the effects of anthropogenic disturbance on arthropods at Gamba, Gabon. Replication included three sites in each of four different stages of forest succession and land use after logging, surveyed during a whole year with four sampling methods: pitfall, Malaise, flight-interception and yellow pan traps. We compared the suitability of each sampling method for biological monitoring and evaluated statistically their reliability for 118 arthropod families. Our results suggest that a range of sampling methods yields more diverse material than any single method operated with high replication. Multivariate analyses indicated that morphospecies composition in trap catches was more strongly influenced by habitat type than by sampling methods. This implies that for multi-species monitoring, differences in trap efficiency between habitats may be neglected, as far as habitat types remain well contrasted. We conclude that for the purpose of monitoring large arthropod assemblages in the long-term, a protocol based on operating a set of different and non-disruptive traps appears superior in design than summing a series of taxa-specific protocols.

Differential expression profiling of components associated with exoskeletal hardening in crustaceans

BackgroundExoskeletal hardening in crustaceans can be attributed to mineralization and sclerotization of the organic matrix. Glycoproteins have been implicated in the calcification process of many matrices. Sclerotization, on the other hand, is catalysed by phenoloxidases, which also play a role in melanization and the immunological response in arthropods. Custom cDNA microarrays from Portunus pelagicus were used to identify genes possibly associated with the activation pathways involved in these processes.ResultsTwo genes potentially involved in the recognition of glycosylation, the C-type lectin receptor and the mannose-binding protein, were found to display molt cycle-related differential expression profiles. C-type lectin receptor up-regulation was found to coincide with periods associated with new uncalcified cuticle formation, while the up-regulation of mannose-binding protein occurred only in the post-molt stage, during which calcification takes place, implicating both in the regulation of calcification. Genes presumed to be involved in the phenoloxidase activation pathway that facilitates sclerotization also displayed molt cycle-related differential expression profiles. Members of the serine protease superfamily, trypsin-like and chymotrypsin-like, were up-regulated in the intermolt stage when compared to post-molt, while trypsin-like was also up-regulated in pre-molt compared to ecdysis. Additionally, up-regulation in pre- and intermolt stages was observed by transcripts encoding other phenoloxidase activators including the putative antibacterial protein carcinin-like, and clotting protein precursor-like. Furthermore, hemocyanin, itself with phenoloxidase activity, displayed an identical expression pattern to that of the phenoloxidase activators, i.e. up-regulation in pre- and intermolt.ConclusionCuticle hardening in crustaceans is a complex process that is precisely timed to occur in the post-molt stage of the molt cycle. We have identified differential expression patterns of several genes that are believed to be involved in biomineralization and sclerotization and propose possible regulatory mechanisms for these processes based on their expression profiles, such as the potential involvement of C-type lectin receptors and mannose binding protein in the regulation of calcification.

Utilization of prey from the decomposer system by generalist predators of grassland

We investigated the linkage between the detrital subsystem and generalist predators of meadow ecosystems by manipulating prey availability in two different ways: we increased resource availability for the decomposer subsystem and thereby decomposer prey by adding mulch materials (detritus enhancement), and we added fruitflies (Drosophila melanogaster, Diptera; prey enhancement) to fenced plots. Both supplemented materials significantly differed in their (13)C/(12)C and (15)N/(14)N ratios from those of the natural litter. We measured density responses of detritivorous, herbivorous and predaceous arthropods to the increased resource supply. We used ratios of natural stable isotopes of N and C in arthropod tissues to trace the flux from the added resources to consumers and to relate density responses of consumers to changes in resource supply. Effects of resource enhancement propagated through at least two trophic levels, resulting in higher densities of major decomposer and predator taxa. Effects of detritus enhancement were much stronger than those of prey enhancement. Signatures of delta(13)C proved density responses of Collembola taxa to be related to the added mulch materials. Among generalist predators, densities of juvenile wolf spiders (Lycosidae) responded more to detritus-enhancement than to prey-enhancement treatments. In contrast, the density of the web-building linyphiid and the non-web gnaphosid spiders remained unaffected. Each spider taxon, including those which did not respond numerically, was significantly enriched in (13)C in detritus-enhancement treatments, suggesting that they gain energy from the decomposer system. Numbers of herbivores-cicadellids and aphids-were similar in each of the treatments, indicating that they were unaffected by changes in predator density. Our results indicate that the lack of a numerical response to resource supplementation is not necessarily due to the absence of a trophic linkage, but may be caused by compensatory changes in mortality factors such as cannibalism and intraguild predation.

Temporal dynamics in non‐additive responses of arthropods to host‐plant genotypic diversity

Genotypic diversity within host‐plant populations has been linked to the diversity of associated arthropod communities, but the temporal dynamics of this relationship, along with the underlying mechanisms, are not well understood. In this study, we employed a common garden experiment that manipulated the number of genotypes within patches of Solidago altissima, tall goldenrod, to contain 1, 3, 6 or 12 genotypes m−2 and measured both host‐plant and arthropod responses to genotypic diversity throughout an entire growing season. Despite substantial phenological changes in host plants and in the composition of the arthropod community, we detected consistent positive responses of arthropod diversity to host‐plant genotypic diversity throughout all but the end of the growing season. Arthropod richness and abundance increased with genotypic diversity by up to∼65%. Furthermore, arthropod responses were non‐additive for most of the growing season, with up to 52% more species occurring in mixtures than the number predicted by summing the number of arthropods associated with component genotypes in monoculture. Non‐additive arthropod responses were likely driven by concurrent non‐additive increases in host‐plant aboveground biomass. Qualitative differences among host‐plant genotypes were also important early in the season, when specialist herbivores dominated the arthropod community. Neither arthropod diversity nor flower number was associated with genotypic diversity at the end of the growing season, when generalist floral‐associated herbivores dominated. Taken together, these results show that focusing on the temporal dynamics in the quantity and quality of co‐occurring host‐plant genotypes and associated community composition can help uncover the mechanisms that link intraspecific host‐plant diversity to the structure of arthropod communities. Furthermore, consistent non‐additive effects in genotypically diverse plots may limit the predictability of the arthropod community based solely on the genetic make‐up of a host‐plant patch.

Short-term community-level response of arthropods to group selection with seed-tree retention in a northern hardwood forest

We examined the short-term effects of group-selection harvesting with seed-tree retention on ground-dwelling and bark-dwelling arthropod communities in a northern hardwood forest in the Upper Peninsula of Michigan. Arthropods were sampled in 16 group-selection openings and 8 closed canopy reference plots. Two opening sizes were examined—radii of 0.5 (320 ± 27 m 2, n = 8) and 1.0 (1217 ± 62 m 2, n = 8) times the mean canopy height (22 m). Each opening and reference plot was centered on a single Betula alleghaniensis Britt. (yellow birch). Ground-dwelling arthropods were sampled using pitfall traps that were opened for two 1-week periods (rounds 1 and 2), and bark-dwelling arthropods were sampled with sticky traps attached to the centrally located B. alleghaniensis trees. Family-level diversity of ground-dwelling arthropods was lower in reference plots than in the openings, but the only significant difference occurred during round 2, between the matrix and large openings ( P < 0.01). During both sampling periods, the ground-dwelling community exhibited a distinct clustering of family-level composition along environmental gradients such as opening size. Families such as Staphylinidae (rove beetles) and Trombidiidae (red velvet mites) were not favored by higher canopy openness while families such as Acrididae (grasshoppers) and Lycosidae (wolf spiders) were captured more in openings than in the forest matrix. Landing rates of wood-boring insects such as Buprestidae (metallic wood-boring beetles) and Xiphydriidae (wood wasps) were significantly higher on seed trees in group-selection openings than in reference plots ( P < 0.05). Our results suggest that integrating group-selection openings within northern hardwood forests can lead to an increase in the family-level diversity of ground-dwelling arthropods, at least in the short term. Furthermore, seed trees left in such openings may be more attractive to bark- and wood-boring insects, which warrants further investigation into the susceptibility of these seed trees to damage by certain insect pests.

Short- and medium-term effects of experimental nitrogen fertilization on arthropods associated with Calluna vulgaris heathlands in north-west Spain

We studied the short- and medium-term effects of experimental nitrogen fertilization (3 and 15 months after the treatment) on the arthropods of Calluna vulgaris heathlands in NW Spain. Three heathland sites were selected with two permanent plots per site: control and fertilized. Ammonium nitrate fertilizer (56 kg N ha −1 yr −1) was applied monthly and insects were caught using pitfall traps. We found mainly species-level responses to nitrogen addition. Seven species (e.g. Lochmaea suturalis) showed a consistent trend (benefited or harmed) in both periods and were proposed as possible reliable indicators of the effects of nitrogen deposition in these ecosystems. We also found variable arthropod trophic-group responses: (a) herbivores (leaf beetles, true bugs) increased in abundance on a short-term scale; (b) predators (carabid beetles, true bugs) showed opposite and less clear responses in both periods. Further long-term studies are needed to determine the mechanisms underlying the observed arthropod responses.

Responses of Plants and Arthropods to Burning and Disking of Riparian Habitats

Abstract: Alteration of Iowa, USA, landscapes for agricultural production has resulted in a loss of &gt;99% of the original prairie and &gt;95% of native wetlands. This conversion has included riparian areas, which, as interfaces between terrestrial and aquatic ecosystems, are important to many wildlife species. Farm Bill programs have resulted in the reestablishment of millions of hectares of grasslands and wetlands nationwide, including &gt;100,000 ha in riparian areas of the Midwest. We assessed plant and arthropod responses to burning and disking of riparian grasslands in east‐central Iowa in 2001 and 2002. Burning altered the plant community by removing litter and standing dead vegetation and had negative effects on several arthropod taxa, including Hemiptera and Lepidoptera. However, we observed no differences in vegetation or arthropods between burned and unburned fields during the second year postburning (P &gt; 0.05). Disking decreased the cover of grasses, litter, and standing dead vegetation and increased plant species richness and the cover of forbs and bare ground (P &lt; 0.05). Arthropod abundance and dry biomass were greater on disked than undisked portions of fields (P &lt; 0.05). Increases in the abundance and biomass of arthropods associated with changes in vegetation structure and composition likely improved habitat quality for a number of breeding bird species. Both burning and disking appear to be effective management options for maintaining or enhancing riparian grasslands for wildlife.

Arthropod response to prescription burning at the soil–litter interface in oak–pine forests

In the southeastern U.S., forest managers are returning repetitive fire to the landscape to facilitate regeneration of desirable species. The increased use of prescribed fire generates questions regarding the effects of single- and multiple-burning events on leaf-litter and ground-dwelling arthropods, and recovery of these arthropods following fire disturbance. In this study, the effects of early season single- and multiple-burns were assessed on leaf-litter arthropods and ground-dwelling arthropods in oak–pine forests for two growing seasons following fire disturbance. Arthropods were sampled by leaf-litter extraction and pitfall trapping, where pitfall trapping was restricted to single-burned areas. For each sampling method, arthropod abundance, diversity, richness, and evenness were calculated at the family or ordinal level. Forest characteristics were also surveyed to measure impacts from the prescribed fires and to assess variability in the forest environment. Leaf-litter arthropod abundance was devastated by burning, and resurgence of populations was not evident until the second growing season in the multiple-burned areas. In single-burned plots, litter arthropod abundance remained low for the duration of the study possibly due to greater fire intensity relative to the multiple-burn plots. Leaf-litter arthropod diversity was not affected by either burn regime. Burning decreased leaf-litter arthropod richness and increased leaf-litter arthropod evenness, but these effects were only marginally significant. Prescription burning had no impact on ground-dwelling arthropod abundance, diversity, or richness, but arthropod community evenness increased following the single-burn disturbance. In the principal components analysis (PCA), burning was a major gradient explaining 46% of the variation in the data. Burning decreased leaf-litter cover and depth and lower canopy cover, and contributed to the variance explained by PCA. Our data confirm that prescription burning is accomplishing its management goal of removing undesirable lower-canopy cover in the mixed hardwood forests of the Cumberland Plateau. Following early-season, low-intensity burns, recovery of leaf-litter arthropods was not evident until two-growing seasons after fire disturbance. Any differences we observed could be attributed to lower fire intensity in forests that are repeatedly burned. Prescribed burns should be utilized on a rotation greater than 2 years to allow resurgence of the leaf-litter arthropod community and recovery of the leaf-litter habitat.

Consumer‐specific responses to riverine subsidy pulses in a riparian arthropod assemblage

Summary1. Aquatic resource fluxes from streams can provide significant subsidies for riparian consumers. Because aquatic resource fluxes can be highly variable in space and time, the subsidy efficiency (i.e. transfer to the recipient food web) is controlled by the short‐term aggregative response of riparian consumers.2. Field manipulations of stream‐derived invertebrate prey subsidies were used to examine specific aggregative responses of ground‐dwelling arthropods to riverine subsidy pulses in a braided‐river (Tagliamento River, NE Italy). Subsidy manipulation comprised short‐term reductions of natural stream‐derived subsidies and increased subsidies of stream‐derived invertebrate prey during four seasons.3. We hypothesised that specific aggregative responses of riparian arthropods depend on their specialisation on aquatic insects which was inferred from stable isotope analysis. Natural riverine subsidy sources including aquatic insect emergence and surface‐drifting organisms were quantified.4. Arthropods responded significantly with a reduction in abundance by 51%, at reduced subsidies and an increase by 110% at increased subsidies, when averaged over all seasons. Different arthropod taxa responded differently to subsidy manipulations in relation to their specialisation on aquatic subsidies: ground beetles with a diet consisting predominantly of aquatic insects responded only to subsidy reductions, indicating that their local abundance was not limited by natural stream‐derived subsidies; lycosid spiders with a partly aquatic diet showed no significant response; and ants, although relying on a terrestrial diet, responded positively to added stream‐derived invertebrate prey, indicating that stranding of surface‐drifting terrestrial invertebrates represented an important subsidy pathway.5. Ground beetles and lycosid spiders were seasonally separated in their use of aquatic subsidies. Results indicate that the life‐history characteristics of riparian consumers can control the subsidy efficiency for the recipient community. By the effective uptake of pulsed riverine‐derived subsidies, riparian arthropods can enhance the transfer of riverine food sources to the riparian food web.

Arthropods as ecological indicators of sustainability in Canadian forests

The high functional and unmatched biological diversity represented by arthropods demand that these organisms be considered as ecological indicators of sustainable forest management. Successful use of arthropods in this capacity will require a systematic and rigorous process, including selection of potential indicators, definition of relationships between indicators and disturbance variables, optimization of the useful range of the indicator and application of the indicator(s) in monitoring. In Canada, the single greatest impediment to the use of arthropods as ecological indicators is the importance of accurate species-level identification and the difficulty achieving it. Consequently, most work has focused on a few relatively well-known groups (e.g., epigaeic carabid and staphylinid beetles and spiders, saproxylic beetles, butterflies and larger night flying moths).Many recent studies have provided baseline data about the range of natural variation and have begun to quantify arthropod responses to natural and anthropogenic disturbances in the context of preplanned experiments or through various retrospective approaches. Carabid beetles are the best-studied group and sufficient sets of data now exist to permit a meta-analysis of the robustness of carabids as indicators across multiple spatial scales and in terms of how well they represent broader ecological responses to disturbances. There is good potential to incorporate arthropod indicators into monitoring programs in Canada, but it is necessary to first complete a scientifically credible selection process for specific ecological indicators. Future research should focus on completing the process for taxa under current study as this develops the best presently understood opportunities for using arthropod indicators in assessing various aspects of environmental change. Researchers should also consider other means of monitoring arthropod biodiversity by the use of surrogate ecological parameters such as ecological land classification and habitat classification systems. Key words: arthropods, ecological indicators, monitoring, biodiversity, taxonomy, sustainability

Pesticides of Potential Ecological Concern in Sediment from South Florida Canals: An Ecological Risk Prioritization for Aquatic Arthropods

A two-tier ecological risk assessment was conducted for pesticides monitored in sediment at 36 sampling sites in south Florida freshwater canals from 1990–2002. For tier 1, we identified the chemicals of potential ecological concern (COPECs) as DDT, DDD, DDE, chlordane and endosulfan based on their exceedence of sediment quality standards at 20 sites. For 12 sites with data on the fraction of organic carbon in sediments, whole sediment concentrations of COPECs were converted to pore water concentrations based on equilibrium partitioning. In tier 2, a probabilistic risk assessment compared distributions of pore water exposure concentrations of COPECs with effects distributions of freshwater arthropod response data from laboratory toxicity tests. Arthropod effects distributions included benthic and non-benthic arthropod species for chlordane (n = 9), DDD (n = 12), DDE (n = 5), DDT (n = 48), and endosulfan (n = 26). The overlap of predicted pore water concentrations and arthropod effects distributions was used as a measure of risk. DDE was the most frequently detected COPEC in sediment at the 12 sites. Chlordane was present at only one site. The mean 90th centile concentration for pore water exposure was highest for endosulfan and lowest for DDT. The estimated acute 10th centile concentration for effects was highest for chlordane and lowest for DDD. The probability of pore water exposures of COPECs exceeding the estimated 10th centile concentrations for species sensitivity distributions of arthropod acute toxicity data was between 0 and 1%. The estimated NOEC 10th centile concentration from arthropod chronic toxicity distributions was exceeded by the estimated 90th centile concentration for pore water distributions at three sites. Endosulfan had the highest potential chronic risk at S-178 in the C-111 canal system, based on the probability of pore water exposure concentrations exceeding the arthropod estimated chronic NOEC 10th centile at 41%. The COPEC with the next highest probability of exceeding the chronic NOEC 10th centile was DDD at 17.7% and 19.8% in the Everglades Agricultural Area (at S-2 and S-6). DDT had minimal potential chronic risk. Uncertainties in exposure and effects analysis and risk characterization are discussed.

Arthropod responses to harvesting and wildfire: Implications for emulation of natural disturbance in forest management

Although natural disturbance has been widely adopted as a template for forest management that protects biodiversity, this hypothesis has not been adequately tested. We compared litter-dwelling arthropod assemblages (Coleoptera: Carabidae and Staphylinidae; Araneae) in aspen-dominated stands originating as clear-cuts or wildfires across three age classes (1–2, 14–15, and 28–29 years old) to test whether the post-harvest and post-fire assemblages converged following disturbances, and to compare faunal succession. These findings were compared to data about epigaeic arthropods in old and mature pyrogenic aspen stands (>70 years old) to determine whether diversity and community composition of arthropods from the younger age-classes approached what may have been typical pre-disturbance conditions. The resulting data-set of almost 27,000 arthropods and 230 species showed convergence in most taxa, and some general similarities between 28- and 29-year-old stands and old and mature stands. However, not all taxa responded similarly, and faunal succession following clear-cutting appeared to progress more rapidly than following wildfire. Rarefaction-estimated diversity was elevated in 1–2-year-old stands, compared to unharvested stands, reflecting a mix of closed-canopy and open-habitat species. Non-metric multi-dimensional scaling ordinations showed that samples from young wildfire disturbed stands (1–2 years old) included more variable assemblages than all other study sites, and contained species that may depend on unique post-fire habitat characteristics. The fauna of old and mature stands exhibited low diversity, but contained species with limited dispersal abilities, and species tied to old-growth habitats such as dead wood. Harvesting systems that do not allow adequate recovery following a first harvesting pass, or do not maintain microhabitat features associated with older fire-origin forests, may threaten persistence of some elements of boreal arthropod faunas.

Response of Ground-Dwelling Arthropods to Different Thinning Intensities in Young Douglas Fir Forests of Western Oregon

We evaluated the effect of four different forest management techniques, unthinned control and three thinning intensities (light, light with gaps, and heavy thin), on arthropod abundance, diversity, and community structure as an indicator of ecological processes affecting other forest fauna. Ground-dwelling arthropods were collected during 2000–2001, with pitfall traps in June (warm-wet season) and August (hot-dry season) 5 yr after a thinning treatment in 40- to 60-yr-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] trees in the Willamette National Forest. We found arthropod abundance and diversity was higher in heavy and light/gap thinning treatments than the other treatments. Additionally, four groups (ants, spiders, camel-crickets, and millipedes) preferred the more intense thinning treatment areas. The abundance of carabids, the third most abundant group, was higher at the unthinned control than any thinning treatment during the wet season, but not during the dry season. Although the immediate disturbance associated with thinning might be expected to decrease population density of fauna such as ground beetles, we hypothesized that the principal effect of thinning was to increase habitat heterogeneity in these uniform plantations and indirectly increase species richness and abundance of soil-dwellers. Nonmetric multidimensional scaling (NMS) of overall arthropod community composition revealed that both seasonality and thinning were highly significant, resulting in four separate clusters of points, with season dominating thinning. Both variables were correlated with litter moisture. The NMS results indicated that ants preferred heavy thinning intensity. Spiders, carabids, and millipedes were positively associated with litter moisture, and camel-crickets were negatively associated with litter moisture. Overall, our results suggest that some dominant groups of ground-dwelling arthropods are sensitive indicators of environmental change, such as forest thinning.

Response of Ground-Dwelling Arthropods to Different Thinning Intensities in Young Douglas Fir Forests of Western Oregon

Abstract We evaluated the effect of four different forest management techniques, unthinned control and three thinning intensities (light, light with gaps, and heavy thin), on arthropod abundance, diversity, and community structure as an indicator of ecological processes affecting other forest fauna. Ground-dwelling arthropods were collected during 2000–2001, with pitfall traps in June (warm-wet season) and August (hot-dry season) 5 yr after a thinning treatment in 40- to 60-yr-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] trees in the Willamette National Forest. We found arthropod abundance and diversity was higher in heavy and light/gap thinning treatments than the other treatments. Additionally, four groups (ants, spiders, camel-crickets, and millipedes) preferred the more intense thinning treatment areas. The abundance of carabids, the third most abundant group, was higher at the unthinned control than any thinning treatment during the wet season, but not during the dry season. Although the im...

CANOPY ARTHROPOD RESPONSE TO DENSITY AND DISTRIBUTION OF GREEN TREES RETAINED AFTER PARTIAL HARVEST

We measured canopy arthropod responses to six contrasting green-tree retention treatments at six locations (blocks) in western Oregon and Washington as part of the Demonstration of Ecosystem Management Options (DEMO) study. Treatments were 100% retention (uncut), 75% retention with three 1-ha harvested gaps, 40% dispersed retention, 40% aggregated retention with five 1-ha uncut aggregates, 15% dispersed retention, and 15% aggregated retention with two 1-ha uncut aggregates. Arthropods were sampled from upper, mid-, and lower crown levels of one overstory Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and from three understory vine maple (Acer circinatum Pursh) in each treatment unit during June and August each year to assess seasonal variation in abundances. Pretreatment data were collected in 1996 and posttreatment data in 1999– 2000. Arthropods showed little evidence of response to treatments, but the abundance of arthropods on both plant species showed significant variation among blocks, reflecting responses to environmental gradients at a regional scale. Arthropod abundance also varied significantly over time in unmanipulated (control) treatments, suggesting sensitivity to annual changes in weather. Our results suggest that disturbance at this intensity or scale has little influence on canopy arthropods in the short term. Future sampling will be necessary to evaluate the extent to which arthropods respond to changes in environmental conditions created by these treatments over longer time periods.

Soil Arthropod Responses to Different Patch Types in a Mixed-Conifer Forest of the Sierra Nevada

Abstract The Teakettle Ecosystem Experiment in the southern Sierra Nevada is using thinning and prescribed fire to recreate historical stand conditions. As part of Teakettle we assessed pretreatment diversity and density of the soil arthropod community in 1998 and 2000. We determined the density and diversity of soil microarthropods among treatment plots, the influence of patch type (closed canopy, canopy gaps, Ceanothus sp., and coarse woody debris [CWD]), and established baseline pretreatment data. Mites were the dominant microinvertebrates (78%). Canopy gaps had the lowest mite density and diversity, and were more sensitive to year-to-year changes in climate (1998 was an extremely wet year for the region). Soil organic matter as represented by bulk density appeared to be most closely associated with changes in species composition among different patch types. There was substantial overlap, however, in community composition among the different patch types as represented by nonmetric multidimensional scaling (NMS) ordination. No significant differences were observed for mite species richness and density among plots assigned to future treatments. The gap data suggest that in the characteristically hot, dry summers of the southern Sierra Nevada the rate of recovery of vegetation following thinning and fire treatments may have a significant influence on the recovery rate of microarthropods, not only by providing sources of energy inputs in the form of dead organic matter, but also by moderating the microclimate of the forest floor. FOR. SCI. 51(3):255–265.

Information use by the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae), a specialised natural enemy of herbivorous spider mites

Plants can respond to infestation by herbivores with the emission of specific herbivore-induced plant volatiles. Many carnivorous arthropods that feed on herbivorous prey use these volatiles to locate their prey. Despite the growing amount of research papers on the interactions in tritrophic systems, it has remained unclear how carnivorous arthropods use herbivore-induced plant volatiles in prey-location. We investigated three important aspects of information use by the predatory mite Phytoseiulus persimilis, a specialised natural enemy of herbivorous spider mites. First, we showed that the foraging efficiency of predatory mites was not hampered by the presence of volatiles induced by nonprey caterpillars on brussels sprouts plants. Second, we revealed an important role for the volatile compound methyl salicylate. Predatory mites appear to use the presence of this compound, rather than its relative contribution to a volatile blend, to discriminate between two volatile blends. Third, we demonstrated that the role of methyl salicylate in the foraging behaviour of P. persimilis depends on previous experiences of the predators with this compound. Our research improves the understanding of the selection pressures that act on the foraging responses of carnivorous arthropods, and consequently on the selection pressures on volatile emission by plants in response to herbivory.

Short-term effects of a nun moth suppression programme (Lymantria monacha), (Lepidoptera: Lymantriidae) on epigeic non-target arthropods

The short-term responses of non-target soil arthropods to insecticides (Nomolt: Teflubenzuron, Karate: lambda-Cyhalothrin) applied against the nun moth (Lymantria monacha L.) were investigated in 2003. This phytophagous pest infested 30–40-year-old monocultures of Scots pine (Pinus sylvestris L.) located at an active military training area in northeast Saxony (Germany). According to the non-target epigeic arthropods, extinction of a higher systematic taxon (family, order) was not observed. Activity densities of soil macroarthropods were lower on plots treated with Karate, while those of necrophagous ground beetles increased considerably. Nomolt revealed no distinct impact on soil invertebrate density. Statistical analysis did not prove any consistent insecticidal effects on non-target arthropods. Adjacent open-heathland arthropods were not affected by a possible drift of the agents.