Vegetation and Invertebrate Community Response to Eastern Hemlock Decline in Southern New England

The introduction of Adelges tsugae (Hemlock Woolly Adelgid [HWA]) to the eastern United States has had a devastating impact on Tsuga canadensis (Eastern Hemlock). Although much research has been done to assess HWA impacts on ecosystem processes and vegetation structure, few researchers have examined community-level changes in highly infested forest stands. Here we assess the impact of Eastern Hemlock mortality on vegetation and invertebrate diversity and community structure by comparing low-impact (healthy) stands and stands heavily impacted by HWA. We sampled the vegetative and invertebrate diversity of 8 sites (4 low impact and 4 high impact) in the summer and fall of 2008. We found a shift in the understory plant community and the canopy and subcanopy arthropod communities. Herbaceous plant species richness was significantly higher at high-impact sites, with Betula lenta (Black Birch) being the most common woody species. Overall, forest invertebrate community diversity (measured using the Shannon-Weaver diversity index) was greater in high- versus low-impact sites. Of the 21 indicator species significantly associated with a given forest type, 14 and 7 species were associated with high- and low-impact forests, respectively. Variation in arthropod community structure was driven by above-ground differences; ground-level arthropod community composition did not differ between high- and low-impact sites. These results demonstrate some of the biodiversity impacts that can result from the invasion of an exotic insect into forested systems

The impact of lianas on 10 years of tree growth and mortality on Barro Colorado Island, Panama

1. Lianas compete intensely with trees, but few studies have examined long‐term effects of liana infestation on tree growth and mortality. We quantified the effects of lianas in tree crowns (n = 2907) and rooted within 2 m of trees (n = 1086) on growth and mortality of 30 tree species from 1995 to 2005 on Barro Colorado Island (BCI), Panama, documented liana infestation in tree crowns in 1996 and 2007 to determine the dynamics of liana infestation, and quantified liana infestation in the crowns of 3231 additional canopy trees (d.b.h. ≥20 cm) in 2007 to compare with the same metric determined by previous studies in 1967 and 1980. 2. Severe liana infestation increased tree mortality: 21% of liana‐free trees in 1996 had died by 2007, whereas 42% of trees with more than 75% of the crown infested by lianas in 1996 had died by 2007. 3. Liana infestation of tree crowns significantly reduced tree growth, particularly on sun‐exposed trees. The proximity of rooted lianas significantly reduced the growth of shaded trees. 4. Liana infestation was dynamic: 10.9% of trees with severe liana infestation in their crowns in 1996 had shed all of their lianas by 2007 and 5.3% of trees with no lianas in their crown in 1996 had severe liana infestation in 2007. 5. Liana infestation was common: lianas were present in 53% of trees of the 30 focal species. Including lianas rooted within 2 m of the tree increased this percentage to 78%. Using both above‐ and below‐ground measures may provide a better estimate of liana competition than either measure alone. 6. Liana infestation is increasing on BCI. Lianas were present in the crowns of 73.6% of canopy trees (d.b.h. ≥20 cm). Liana canopy infestation was 57% higher than in 1980 and 65% higher than in 1967, which is consistent with reported increases in liana abundance, biomass, and leaf and flower production. 7. Synthesis. We used one of the largest studies ever conducted on lianas to confirm the negative effects of lianas on tree growth and survival over 10 years. Liana infestation of trees was widespread, dynamic and increasing on BCI

The Barley yellow dwarf virus-Rhopalosiphum padi pathosystem: An examination of host plant-virus-vector interactions

Barley yellow dwarf disease is an important plant disease caused by a complex of plant viruses referred to as Barley/Cereal yellow dwarf virus (B/CYDV) which is comprised of eight viral species infecting cereal crops and over 150 other Poaceae species. B/CYDV is transmitted exclusively by aphids in a persistent, circulative manner. In the United States, the most widespread species is BYDV-PAV transmitted by Rhopalosiphum padi (L.). The effects of BYDV-PAV infection on host plant preferences were examined for viruliferous (virus-carrying) and nonviruliferous R. padi. Viruliferous aphids that acquired virus from either infected barley or through membranes infused with artificial diet containing purified virus, were used to examine direct (membrane feeding) vs. indirect (infected host plant) effects of virus acquisition. Nonviruliferous aphids significantly preferred BYDV-infected plants while viruliferous aphids significantly preferred virus-free plants. The shift in preference from infected to noninfected plants following virus acquisition could accelerate the rate of virus spread and was shown to be the result of direct effects of virus acquisition within the insect vector. The wheat producing region of northern Idaho and eastern Washington is characterized by fragmented native prairie and Conservation Reserve Program (CRP) habitats embedded in an agricultural matrix. The Palouse Prairie and CRP lands were surveyed to determine in which habitats and grass species B/CYDV occur and what B/CYDV species are present. Ten species of Poaceae that have not been reported as hosts of B/CYDVs were evaluated via laboratory inoculations. Nine of these species are found throughout the Pacific Northwest in Camas and Palouse Prairie habitats or CRP lands and one of these species is being proposed as a candidate for biofuel production. B/CYDV was found for the first time in Palouse Prairie and CRP habitats and BYDV-SGV and PAV were identified as the predominant viral species occurring in this region. Achnatherum occidentale, A. lettermanii, A. thurberianum, Danthonia intermedia, Poa fendleriana, Sporobolus airoides, S. cryptandrus, Ventenata dubia and Arundo donax were identified as new hosts of BYDV-PAV. Transmission of BYDV-PAV from some of these grass hosts to susceptible barley was demonstrated using R. padi. The ecological and epidemiological implications are discussed.Thesis (Ph.D., Plant, Soil and Entomological Sciences)--University of Idaho, June 201

Using citizen science programs to identify host resistance in pest-invaded forests

Threats to native forests from non-native insects and pathogens (pests) are generally addressed with methods such as quarantine, eradication, biological control, and development of resistant stock through hybridization and breeding. In conjunction with such efforts, it may be useful to have citizen scientists locate rare surviving trees that may be naturally pest resistant or tolerant. The degree of resistance of individual trees identified in this way can be tested under controlled conditions, and the most resistant individuals can be integrated into plant breeding programs aimed at developing pest-resistant native stock. Involving citizen scientists in programs aimed at identifying rare trees that survive colonization by pests provides a low-cost means of maximizing search efforts across wide geographic regions and may provide an effective supplement to existing management approaches. © 2010 Society for Conservation Biology

Data from: Domesticated tomatoes are more vulnerable to negative plant-soil feedbacks than their wild relatives

Domesticated plants can differ from their wild counterparts in the strength and outcome of species interactions, both above- and belowground. Plant-soil feedbacks influence plant success, and plant-associated soil microbial communities can influence plant interactions with herbivores and their natural enemies, yet, it is unclear if domestication has changed these relationships. To determine the effects of domestication on plant-soil interactions, we characterized soil microbial communities associated with various cultivars of domesticated tomato and some of its wild relatives. We measured the strength and direction of plant-soil feedbacks for domesticated and wild tomatoes, and the effects of soil on plant resistance to specialist herbivory by Manduca sexta, and the attraction of a parasitoid wasp, Cotesia congregata. Domesticated tomatoes and their wild relatives had negative plant-soil feedbacks, as conspecifics cultivated soil that negatively impacted performance of subsequent plants (longer germination time, lower biomass) than if they grew in non-tomato soils. Significant variation existed among domesticated and wild tomato varieties in the strength of these feedbacks, ranging from neutral to strongly negative. For aboveground plant biomass, tomato wild relatives were unaffected by growing in tomato-conditioned soil while domesticated tomatoes grew smaller in tomato soil, indicating effects of plant domestication. Overall, increased microbial biomass within the rhizosphere resulted in progressively less-negative plant-soil feedbacks. Plant cultivars had different levels of resistance to herbivory by M. sexta, but this did not depend on plant domestication or soil type. The parasitoid C. congregata was primarily attracted to herbivore damaged plants, independent of plant domestication status, and for these damaged plants, wasps preferred some cultivars over others, and wild plants grown in tomato soil over wild plants grown in non-tomato soil. Synthesis: These results indicate that crop tomatoes are more likely to show negative plant-soil feedbacks than wild progenitors, which could partially explain their sensitivity to monocultures in agricultural soils. Further, cultivar-specific variation in the ability to generate soil microbial biomass, independent of domestication status, appears to buffer the negative consequences of sharing the same soil. Last, soil legacies were relatively absent for herbivores, but not for parasitoid wasps, suggesting trophic level specificity in soil feedbacks on plant-insect interactions

Effect of Black Soldier Fly Larvae and Food Substrates on Weed Seed Emergence

Black soldier fly larvae (Hermetia illucens; BSFL) composting is biotechnology used for organic waste management and an alternative to traditional composting. We designed a two-phase experiment to evaluate the effect of BSFL composting on the emergence of the following six weed species: barnyardgrass (Echinochloa crus-galli), common ragweed (Ambrosia artemisiifolia), giant foxtail (Setaria faberi), ivyleaf morningglory (Ipomoea hederacea), redroot pigweed (Amaranthus retroflexus), and velvetleaf (Abutilon theophrasti). The first experiment phase was in the laboratory (laboratory composting phase), which consisted of 100 seeds of each weed species subjected to five composting treatments [two controls (nontreated and standard Gainesville diet alone) and three types of substrates (standard Gainesville diet, vegetable waste, food waste) + BSFL]. Live pupa weighed 179 mg with the standard Gainesville diet + BSFL and 205 mg with the food waste diet + BSFL. Dry pupa weighed 68 mg and 70 mg, respectively. The BSFL in the vegetable waste + BSFL treatment did not pupate. During the second experiment phase, the composting treatments were placed in a greenhouse to evaluate weed emergence. Emergence in the nontreated control was 62% for barnyard grass, 38% for common ragweed, 26% for giant foxtail, 66% for ivyleaf morningglory, 3% for redroot pigweed, and 69% for velvetleaf. Compared with the nontreated control, all treatments with BSFL reduced the emergence of each weed species to #1%, except for velvetleaf. This study suggests that BSFL composting may effectively reduce weed seed emergence of many weed species and could be a safe alternative to conventional composting processes to minimize weed pressure in compost. However, efficacy may vary by weed species and may be dependent on seed characteristics, such as an impermeable seedcoat

Implementing IPM in crop management simultaneously improves the health of managed bees and enhances the diversity of wild pollinator communities

Abstract Impacts of insecticide use on the health of wild and managed pollinators have been difficult to accurately quantify in the field. Existing designs tend to focus on single crops, even though highly mobile bees routinely forage across crop boundaries. We created fields of pollinator-dependent watermelon surrounded by corn, regionally important crops in the Midwestern US. These fields were paired at multiple sites in 2017–2020 with the only difference being pest management regimes: a standard set of conventional management (CM) practices vs. an integrated pest management (IPM) system that uses scouting and pest thresholds to determine if/when insecticides are used. Between these two systems we compared the performance (e.g., growth, survival) of managed pollinators—honey bees (Apis mellifera), bumble bees (Bombus impatiens)—along with the abundance and diversity of wild pollinators. Compared to CM fields, IPM led to higher growth and lower mortality of managed bees, while also increasing the abundance (+ 147%) and richness (+ 128%) of wild pollinator species, and lower concentrations of neonicotinoids in the hive material of both managed bees. By replicating realistic changes to pest management, this experiment provides one of the first demonstrations whereby tangible improvements to pollinator health and crop visitation result from IPM implementation in agriculture