Introduced plants reduce species interactions

Specialist Herbivore Performance on Introduced Plants During Native Host Decline

Ash (Fraxinus spp.) is in rapid decline across the northeastern USA due to the invasive emerald ash borer (Agrilus planipennis Fairmaire). Three recently co-occurring confamilial species may serve as alternative larval host plants for ash-reliant Lepidoptera. These prospective hosts are nonnative shrubs often planted in managed suburban landscapes and are sometimes invasive or naturalized in North America. Given the imminent decline of ash trees, we considered potential downstream effects on insect herbivores historically specialized on ash foliage. We measured the performance of three ash-specialist hawkmoths (Lepidoptera: Sphingidae) on native white ash (Fraxinus americana L.) and alternative host plants: common lilac (Syringa vulgaris L.), weeping forsythia [Forsythia suspensa (Thunb.) Vahl], and European privet (Ligustrum vulgare L.). We found the nonnative host plants provided varied support for larval survival to pupation, with biomass and growth rate affected differently by both plant and insect identity. Nearly all caterpillars reared on one alternative host, European privet, exhibited distinct malformations of the wing buds at pupation. Given caterpillar presence on privet in the field, privet may constitute an ecological trap (i.e., when female moths select a sub-optimal host, offspring survival and fitness are reduced). This work demonstrates how performance testing can reveal species-specific effects of host plant loss on mono- or oligophagous insects. For some ash specialists, alternative nonnative host plants may be suboptimal, but some cultivated host plants may be able to support certain specialist insects during native host decline. We suggest that landscaping decisions can be tailored to support threatened insect species.

Measuring mass: variation among 3,161 species of Canadian Coleoptera and the prospects of a mass registry for all insects

Although biomass values are critical for diverse ecological and evolutionary analyses, they are unavailable for most insect species. Museum specimens have the potential to address this gap, but the variation introduced by sampling and preservation methods is uncertain. This study quantifies species-level variation in the body mass of Canadian Coleoptera based on the analysis of 3,744 specimens representing 3,161 Barcode Index Number (BIN) clusters. Employing the BIN system as a proxy for species allows the inclusion of groups where the taxonomic impediment prevents the assignment of specimens to a Linnaean species. By validating the reproducibility of measurements and evaluating the error introduced by operational complexities such as curatorial practice and the loss of body parts, this study demonstrates that museum specimens can speed the assembly of a mass registry. The results further indicate that congeneric species of Coleoptera generally have limited variation in mass, so a genus-level identification allows prediction of the body mass of species that have not been weighed or measured. Building on the present results, the construction of a mass registry for all insects is feasible.

Parasitism and Predation on Sentinel Egg Masses of Three Stink Bug Species (Hemiptera: Pentatomidae) in Native and Exotic Ornamental Landscapes

This study evaluated parasitism and predation on sentinel egg masses of three stink bug species, the spined soldier bug, Podisus maculiventris (Say), the brown stink bug, Euschistus servus (Say), and the invasive brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), in ornamental landscapes composed of either native or exotic plants. This study also compared the species composition of parasitoids attacking two native stink bug species (P. maculiventris and E. servus) with those attacking the invasive BMSB on the same tree species in the same habitat. Overall, egg parasitism and predation were much higher on the two native stink bug species compared with BMSB, with an average parasitism rate of 20.6% for E. servus, 12.7% for P. maculiventris, and only 4.2% for H. halys and an average predation rate of 8.2% for E. servus,17.7% for P. maculiventris, and 2.3% for H. halys. Egg predation was also significantly higher on P. maculiventris than on E. servus eggs. Eight parasitoid species attacked sentinel stink bug eggs in the ornamental landscaped plots. Trissolcus euschisti (Ashmead) (Hymenoptera: Scelionidae) was the predominant parasitoid for all three stink bug species. There were no significant differences in parasitism and predation rates on any of the stink bug species between native and exotic plots. Therefore, there is no evidence that ornamental landscapes composed of native plants increased parasitism or predation rates of sentinel egg masses of two native stink bug species or the invasive BMSB, compared with those composed entirely of exotic plants.

Few keystone plant genera support the majority of Lepidoptera species

Functional food webs are essential for the successful conservation of ecological communities, and in terrestrial systems, food webs are built on a foundation of coevolved interactions between plants and their consumers. Here, we collate published data on host plant ranges and associated host plant-Lepidoptera interactions from across the contiguous United States and demonstrate that among ecosystems, distributions of plant-herbivore interactions are consistently skewed, with a small percentage of plant genera supporting the majority of Lepidoptera. Plant identities critical for retaining interaction diversity are similar and independent of geography. Given the importance of Lepidoptera to food webs and ecosystem function, efficient and effective restoration of degraded landscapes depends on the inclusion of such 'keystone' plants.

Biogeographical comparison of terrestrial invertebrates and trophic feeding guilds in the native and invasive ranges of Carpobrotus edulis

Plant invasions impact on biodiversity by altering the composition of native communities by disrupting taxonomic and functional diversity. Non-native plants are often released from their natural enemies, which might result in a reduction of the attack of primary consumers. However, they can also be exposed to the attack of new herbivores that they might not be able to tolerate. Hence, invertebrate communities can be influenced by invasive non-native plants, which in turn modify interactions and change environmental conditions. In this study, we examined the compositional and trophic diversity of invertebrate species, comparing ecosystems with and without the plant species Carpobrotus edulis in coastal areas in its native (South Africa) and introduced (Iberian Peninsula) ranges. Results show that C. edulis has a clear impact on invertebrate communities in its non-native range, reducing their abundance in invaded areas, and particularly affecting certain trophic groups. Invasive C. edulis also alters the invertebrate diversity by not only reducing abundance but also by altering species composition. Overall, the physical dominance of C. edulis modifies the co-occurrence of invertebrate assemblages, reducing the number of trophic groups and leading to substantial effects on primary consumers. Results suggest that the lack of natural enemies might be an important driver of the expansion of C. edulis in its introduced range. Further work is needed to examine long-term changes caused by non-native plants on invertebrate assemblages and the subsequent modification of biological interactions.

Insect Declines in the Anthropocene

Insect declines are being reported worldwide for flying, ground, and aquatic lineages. Most reports come from western and northern Europe, where the insect fauna is well-studied and there are considerable demographic data for many taxonomically disparate lineages. Additional cases of faunal losses have been noted from Asia, North America, the Arctic, the Neotropics, and elsewhere. While this review addresses both species loss and population declines, its emphasis is on the latter. Declines of abundant species can be especially worrisome, given that they anchor trophic interactions and shoulder many of the essential ecosystem services of their respective communities. A review of the factors believed to be responsible for observed collapses and those perceived to be especially threatening to insects form the core of this treatment. In addition to widely recognized threats to insect biodiversity, e.g., habitat destruction, agricultural intensification (including pesticide use), climate change, and invasive species, this assessment highlights a few less commonly considered factors such as atmospheric nitrification from the burning of fossil fuels and the effects of droughts and changing precipitation patterns. Because the geographic extent and magnitude of insect declines are largely unknown, there is an urgent need for monitoring efforts, especially across ecological gradients, which will help to identify important causal factors in declines. This review also considers the status of vertebrate insectivores, reporting bias, challenges inherent in collecting and interpreting insect demographic data, and cases of increasing insect abundance.

Invasive Goldenrod (Solidago gigantea) Influences Soil Microbial Activities in Forest and Grassland Ecosystems in Central Europe

A giant goldenrod plant, Solidago gigantea, native to North America is rapidly spreading in Europe and may have serious impact on ecosystems that inhabit. There is a lack of information about the effects of this species on soil biochemical properties and distribution and activity of microbial community. We analyzed soil physicochemical properties (soil reaction, soil moisture content, organic carbon and total nitrogen content) associated with activity of microbial population (activity of fluorescein diacetate (FDA), beta-glucosidase, urease and phosphatases enzymes) between invaded and adjacent uninvaded control sites in two habitats, forest and grassland, in the lowland of southeast Slovakia during years 2016 and 2017. The results revealed that invasion of S. gigantea significantly altered several soil properties and is associated with different soil properties. Soil acidity increased, organic carbon and moisture content decreased, while total nitrogen content was not significantly affected by invasion. FDA and urease activity were significantly higher in uninvaded sites. In contrast, beta-glucosidase and alkaline phosphatase activity were enhanced by S. gigantea invasion in both ecosystems studied. Acid phosphatase was not affected by the invasion. Our study proved that S. gigantea can influence several soil microbial properties while others remained unaffected, despite its significant impact on basal soil physicochemical properties.