Insect larvae contain substances toxic to adults: the discovery of paralysins

Acidic methanolic extracts of larvae of nine different insect species were found to contain substances that cause a lethal effect in the adult stage of the same species and of other species. These endogenous toxic substances, apparently being widely spread over the class of insects, were designated as paralysins, because of their immediate and observable paralytic effect upon injection. The developmental concentration curves of five different species of insects (Galleria mellonella (Lepidoptera), Neobellieria bullata (Diptera), Spodoptera frugiperda (Lepidoptera), Tenebrio molitor (Coleoptera) and Schistocerca gregaria (Orthoptera) indicate that the toxins are not present throughout all the developmental stages in the same concentration. The strongest paralytic activity was found in late instar larvae or in the early pupal stage. The temporal distribution of paralysins during development suggests that they might be involved in metamorphosis.     

Implantable enzyme amperometric biosensors

The implantable enzyme amperometric biosensor continues as the dominant in vivo format for the detection, monitoring and reporting of biochemical analytes related to a wide range of pathologies. Widely used in animal studies, there is increasing emphasis on their use in diabetes care and management, the management of trauma-associated hemorrhage and in critical care monitoring by intensivists in the ICU. These frontier opportunities demand continuous indwelling performance for up to several years, well in excess of the currently approved seven days. This review outlines the many challenges to successful deployment of chronically implantable amperometric enzyme biosensors and emphasizes the emerging technological approaches in their continued development. The foreign body response plays a prominent role in implantable biotransducer failure. Topics considering the approaches to mitigate the inflammatory response, use of biomimetic chemistries, nanostructured topographies, drug eluting constructs, and tissue-to-device interface modulus matching are reviewed. Similarly, factors that influence biotransducer performance such as enzyme stability, substrate interference, mediator selection and calibration are reviewed. For the biosensor system, the opportunities and challenges of integration, guided by footprint requirements, the limitations of mixed signal electronics, and power requirements, has produced three systems approaches. The potential is great. However, integration along the multiple length scales needed to address fundamental issues and integration across the diverse disciplines needed to achieve success of these highly integrated systems, continues to be a challenge in the development and deployment of implantable amperometric enzyme biosensor systems.     

Phylogenetic structure predicts capitular damage to Asteraceae better than origin or phylogenetic distance to natives

Exotic species more closely related to native species may be more susceptible to attack by native natural enemies, if host use is phylogenetically conserved. Where this is the case, the use of phylogenies that include co-occurring native and exotic species may help to explain interspecific variation in damage. In this study, we measured damage caused by pre-dispersal seed predators to common native and exotic plants in the family Asteraceae. Damage was then mapped onto a community phylogeny of this family. We tested the predictions that damage is phylogenetically structured, that exotic plants experience lower damage than native species after controlling for this structure, and that phylogenetically novel exotic species would experience lower damage. Consistent with our first prediction, 63% of the variability in damage was phylogenetically structured. When this structure was accounted for, exotic plants experienced significantly lower damage than native plants, but species origin only accounted for 3% of the variability of capitular damage. Finally, there was no support for the phylogenetic novelty prediction. These results suggest that interactions between exotic plants and their seed predators may be strongly influenced by their phylogenetic position, but not by their relationship to locally co-occurring native species. In addition, the influence of a species’ origin on the damage it experiences often may be small relative to phylogenetically conserved traits.     

Tolerating herbivory: does the plant care if the herbivore has a backbone?

Differences in size-related ecology and behaviour between vertebrate and invertebrate herbivores lead to differences in the rates, tissue specificity, and spatial distribution of their damage, as well as in their indirect effects. As a result, many features of tolerance to herbivory by these groups also may differ. Tolerating vertebrate herbivory may demand the ability to tolerate sporadic non-specific impacts; this may be achieved by broad responses promoting regrowth and resource acquisition. In contrast, the diversity of different types of invertebrate damage seems likely to demand a correspondingly great variety of responses. These conclusions suggest that tolerance to invertebrates may involve a broader set of responses than tolerance to vertebrates; conversely, the greater specificity of these responses may make it more difficult for arthropod-tolerant plants to achieve cross-tolerance to other types of damage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of simulated grazing on different genotypes of Bouteloua gracilis: how important is morphology?

Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering, and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted as an adaptive response that reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing in morphological and reproductive characters were transplanted into a shortgrass steppe community near Fort Collins, Colorado. Replicates of each genotype were subjected to clipping treatments intended to realistically simulate three grazing intensities. After two growing seasons, different genotypes still maintained significant differences in a wide range of morphological and demographic characters. However, there were few significant effects of grazing treatment, and no significant genotype×treatment interactions. These results suggest that for B. gracilis clipped in simulation of natural grazing, defoliation has few short-term effects on fitness components, and intrapopulation morphological variation has few consequences for defoliation resistance. Received: 22 March 1999 / Accepted: 26 October 1999     

The effects of disturbance and enemy exclusion on performance of an invasive species, common ragweed, in its native range

Common ragweed (Ambrosia artemisiifolia) is an abundant weed in its native North America, despite supporting a wide range of natural enemies. Here, we tested whether these enemies have significant impacts on the performance of this plant in its native range. We excluded enemies from the three principal life-history stages (seed, seedling, and adult) of this annual in a series of field experiments; at the adult stage, we also manipulated soil disturbance and conspecific density. We then measured the consequences of these treatments for growth, survival, and reproduction. Excluding fungi and vertebrate granivores from seeds on the soil surface did not increase germination relative to control plots. Seedling survivorship was only slightly increased by the exclusion of molluscs and other herbivores. Insecticide reduced damage to leaves of adult plants, but did not improve growth or reproduction. Growth and survivorship of adults were strongly increased by disturbance, while higher conspecific density reduced performance in disturbed plots. These results indicate ragweed is insensitive to attack by many of its natural enemies, helping to explain its native-range success. In addition, they suggest that even though ragweed lost most of its insect folivores while invading Europe, escape from these enemies is unlikely to have provided a significant demographic advantage; instead, disturbance is likely to have been a much more important factor in its invasion. Escape from enemies should not be assumed to explain the success of exotic species unless improved performance also can be demonstrated; native-range studies can help achieve this goal.     

Enemy release but no evolutionary loss of defence in a plant invasion: an inter-continental reciprocal transplant experiment

Plant chemical defenses and escape from natural enemies have been postulated to select for dietary specialization in herbivorous insects. In field and laboratory bioassays, we evaluated the effectiveness of intact and chemically modified larval shield defenses of the generalist Chelymorpha alternans and the specialists Acromis sparsa and Stolas plagiata (Chrysomelidae: Cassidinae) against three natural predators, using larvae reared on two morning glory (Convolvulaceae) species. We assessed whether: (1) specialists were better defended than generalists when both were fed and assayed on the same plant; (2) larval shield defenses were chemical, physical, or both; and (3) specialists exploit chemistry better than generalists. Live specialist larvae survived at higher rates than did generalists in predator bioassays with the bug Montina nigripes (Reduviidae), but there were no differences among groups against two species of Azteca ants (Hymenoptera: Dolichoderinae). Solvent leaching by H₂O or MeOH significantly reduced shield efficacy for all species compared to larvae with intact shields. In contrast, freshly killed specialist larvae exhibited significantly lower capture rates and frequencies than the generalists. Although solvent leaching significantly reduced overall shield efficacy for freshly killed larvae of all species, the pattern of leaching effects differed between specialists and generalists, with H₂O-leaching having a greater impact on the specialists. The overall vulnerability of the generalists appears due to lower chemical protection, which is ameliorated by increased escape behaviors, suggesting a selective trade-off between these defensive components. These experiments indicate that shield defenses are essential for larval survival and that specialists are superior at exploiting plant compounds residing in the aqueous fraction. Our results support the hypothesis that diet-specialized herbivorous insects have more effective defenses than generalists when both feed on the same plant due to the differential ability to exploit defensive precursors obtained from the host. The evolution of dietary specialization may therefore confer the advantage of enhanced enemy-free space.     

Surveying biodiversity in protected and managed areas: Algae, macrophytes and macroinvertebrates in boreal forest streams

Extensive surveys of biodiversity in protected and managed areas have not been conducted for a majority of taxonomic groups and ecosystem types, which makes it difficult to assess how large a portion of biodiversity is at least potentially under protection. The situation is the same in boreal regions, and only preliminary analyses of the biodiversity patterns of less well-known organism groups, including many freshwater taxa, within the protected area network have been conducted. We studied patterns of species richness and community composition of algae, macrophytes (bryophytes and vascular plants), and macroinvertebrates of headwater streams draining protected areas and managed forests in a boreal drainage basin in Finland. We found no significant differences in the species richness and community composition of these organism groups between the protected and managed streams. Gamma- and beta-diversity varied strongly among the protected and managed stream groups, yet this variation was contingent on the organism group and the beta-diversity measure used. In general, there was much species turnover within both protected and managed stream groups, masking any between-group differences. However, we found a number of redlisted and rare species in our surveys. Of these species, several macrophyte species occurred more frequently in the protected streams. By contrast, rare species of algae and macrophytes did not generally show such inclinations to the protected streams. We found no strong congruence in species richness or community dissimilarity between algae, macrophytes, and macroinvertebrates, suggesting that the main anthropogenic gradient in terms of forestry is not strong enough to modify stream environmental conditions and thereby shape biodiversity in the focal drainage basin. This finding also suggests that surveys of aquatic biodiversity across protected and managed landscapes should not rely too heavily on the surrogate taxon approach, but instead should consider patterns shown by multiple taxonomic groups that represent biologically and ecologically disparate organisms. Our results indeed suggest that the levels of alpha-, beta-, and gamma-diversity show differing among-taxon responses to forest management and naturalness of headwater streams.     

Herbivores and the success of exotic plants: a phylogenetically controlled experiment

In a field experiment with 30 locally occurring old‐field plant species grown in a common garden, we found that non‐native plants suffer levels of attack (leaf herbivory) equal to or greater than levels suffered by congeneric native plants. This phylogenetically controlled analysis is in striking contrast to the recent findings from surveys of exotic organisms, and suggests that even if ‘enemy release’ does accompany the invasion process, this may not be an important mechanism of invasion, particularly for plants with close relatives in the recipient flora.