Influence of plant architecture on tritrophic interactions between winter canola (Brassicae napus), Aphids (Hemiptera: Aphididae) and Hippodamia convergens (Coleoptera: Coccinellidae)

Master of ScienceDepartment of EntomologyBrian P. McCornackWinter canola production in the south-central US is commonly threatened by a complex of aphid species that can cause up to 70% in yield loss. Aphid species vary in their life-history traits, performance (sequestration/excretion of secondary compounds; glucosinolates), vertical distribution within the plant, and temporal dynamics across the growing season. Colonizing behavior of these aphids may be affected by intrinsic characteristics of the host plant (bottom-up effects), such as nutritional value, secondary compounds, or plant architecture. Understanding bottom-up effects may enable the evaluation of plant-level interactions that are influencing predator-prey dynamics. The goal of my research project is to understand aphid population dynamics in different canola plant structures, assess whether aphid quality (sequestration/ excretion of glucosinolates) is influenced by feeding location on the canola plant, and if so, assess the impact on the existing predator communities, specifically the development and fitness of immature and adult Hippodamia convergens. A combination of filed and greenhouse experiments provided novel contributions that will help shape our understanding of key factors regulating aphid population growth in canola fields, which will lead to more judicious use of insecticides and better sampling strategies

Nosema bombi (Microsporidia: Nosematidae) and trypanosomatid prevalence in spring bumble bee queens (Hymenoptera: Apidae: Bombus) in Kansas

Citation: Tribodi, A., Cibils-Stewart, X., McCornack, B., & Szlanski, A. (2014). Nosema bombi (Microsporidia: Nosematidae) and Trypanosomatid Prevalence in Spring Bumble Bee Queens (Hymenoptera: Apidae: Bombus) in Kansas. Journal of the Entomological Society, 87(2), 225-233. https://doi.org/10.2317/JKES130730.1Several species of bumble bees are declining in the United States; these declining populations often show higher prevalence of Nosema bombi, a microsporidian pathogen. To date, surveys of bumble bee pathogens in the United States have only been conducted on workers and males, yet the health of a population is ultimately dependent on the success of colony-founding queens. We conducted a molecular-diagnostic survey of the prevalence of N. bombi and trypanosomatids, such as Crithidia bombi, in six species of spring queens (n  =  142) collected in 2011 and 2013 at three sites in central Kansas. Nosema bombi was found in 27% of Bombus pensylvanicus and 13% of B. auricomus but was not found in the other species sampled. Trypanosomatids were only found in B. pensylvanicus (9%) during the May 2013 sampling period. The high prevalence of N. bombi in B. pensylvanicus is consistent with other surveys for this pathogen in other castes, but the high prevalence of N. bombi in B. auricomus is a novel finding. Although the conservation status of B. auricomus has not been thoroughly assessed, two recently published surveys showed that B. auricomus were less common in portions of the species' range. Based on those findings and an oft-cited link between N. bombi prevalence and bumble bee species' decline (e.g., B. pensylvanicus) in other studies, our findings suggest B. auricomus populations in Kansas may warrant further scrutiny

Silicon accumulation suppresses arbuscular mycorrhizal fungal colonisation in the model grass Brachypodium distachyon

Purpose Silicon (Si) accumulation by grasses alleviates diverse biotic and abiotic stresses. Despite this important functional role, we have limited understanding of how root microbial symbionts, such as arbuscular mycorrhizal (AM) fungi, affect Si uptake and even less about how Si supply and accumulation affect AM fungal colonisation. Our objective was to determine the nature of this two–way interaction in the model grass, Brachypodium distachyon. Methods We grew B. distachyon with five levels of Si supplementation using wild-type plants and a mutant (Bdlsi1-1) that has little capacity for Si uptake. Half of the plants were colonised by AM fungi; half were free of AM fungi. We measured Si accumulation, AM fungal colonisation, leaf carbon (C), nitrogen (N) and phosphorus (P) concentrations. Results AM fungi did not affect Si accumulation, although small increases occurred when root mass was included as a covariate. Si supplemented soil promoted plant growth and P uptake. Si accumulation suppressed colonisation by AM fungi and C concentrations in wild type but not in Bdlsi1-1 plants. Si concentrations were negatively correlated with C and N concentrations, with correlations being stronger in wild-type plants than Bdlsi1-1 plants. Conclusions Our results indicate that Si accumulation in the plant, rather than Si availability in the soil, underpinned reduced AMF colonisation. We propose that Si accumulation is unlikely to be impacted by AM fungi in plants with inherently high Si accumulation, but Si accumulation may suppress AM fungal colonisation in such plants

Reciprocal effects of silicon supply and endophytes on silicon accumulation and Epichloë colonization in grasses

Cool season grasses associate asymptomatically with foliar Epichloë endophytic fungi in a symbiosis where Epichloë spp. protects the plant from a number of biotic and abiotic stresses. Furthermore, many grass species can accumulate large quantities of silicon (Si), which also alleviates a similar range of stresses. While Epichloë endophytes may improve uptake of minerals and nutrients, their impact on Si is largely unknown. Likewise, the effect of Si availability on Epichloë colonization remains untested. To assess the bidirectional relationship, we grew tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) hydroponically with or without Si. Grasses were associated with five different Epichloë endophyte strains [tall fescue: AR584 or wild type (WT); perennial ryegrass: AR37, AR1, or WT] or as Epichloë-free controls. Reciprocally beneficial effects were observed for tall fescue associations. Specifically, Epichloë presence increased Si concentration in the foliage of tall fescue by at least 31%, regardless of endophyte strain. In perennial ryegrass, an increase in foliar Si was observed only for plants associated with the AR37. Epichloë promotion of Si was (i) independent of responses in plant growth, and (ii) positively correlated with endophyte colonization, which lends support to an endophyte effect independent of their impacts on root growth. Moreover, Epichloë colonization in tall fescue increased by more than 60% in the presence of silicon; however, this was not observed in perennial ryegrass. The reciprocal benefits of Epichloë-endophytes and foliar Si accumulation reported here, especially for tall fescue, might further increase grass tolerance to stress

Elevated atmospheric CO2 suppresses silicon accumulation and exacerbates endophyte reductions in plant phosphorus

Many temperate grasses are both hyper-accumulators of silicon (Si) and hosts of Epichloë fungal endophytes, functional traits which may alleviate environmental stresses such as herbivore attack. Si accumulation and endophyte infection may operate synergistically, but this has not been tested in a field setting, nor in the context of changing environmental conditions. Predicted increases in atmospheric CO2 concentrations can affect both Si accumulation and endophyte function, but these have not been studied in combination. We investigated how elevated atmospheric CO2 (eCO2), Si supplementation, endophyte-presence and insect herbivory impacted plant growth, stoichiometry (C, N, P and Si), leaf gas exchange (rates of photosynthesis, stomatal conductance, transpiration rates) and endophyte production of anti-herbivore defences (alkaloids) of an important pasture grass (tall fescue; Lolium arundinaceum) in the field. eCO2 and Si supplementation increased shoot biomass (+52% and +31%, respectively), whereas herbivory reduced shoot biomass by at least 35% and induced Si accumulation by 24%. Shoot Si concentrations, in contrast, decreased by 17%–21% under eCO2. Si supplementation and herbivory reduced shoot C concentrations. eCO2 reduced shoot N concentrations which led to increased shoot C:N ratios. Overall, shoot P concentrations were 26% lower in endophytic plants compared to non-endophytic plants, potentially due to decreased mass flow (i.e. observed reductions in stomatal conductance and transpiration). Alkaloid production was not discernibly affected by any experimental treatment. The negative impacts of endophytes on P uptake were particularly strong under eCO2. We show that eCO2 and insect herbivory reduce and promote Si accumulation, respectively, incorporating some field conditions for the first time. This indicates that these drivers operate in a more realistic ecological context than previously demonstrated. Reduced uptake of P in endophytic plants may adversely affect plant productivity in the future, particularly if increased demand for P due to improved plant growth under eCO2 cannot be met. Read the free Plain Language Summary for this article on the Journal blog. © 2023 The Authors. Functional Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society

First record of Soybean Stem Fly Melanagromyza sojae (Zehntner, 1901) (Diptera, Agromyzidae) in Uruguay confirmed by DNA barcoding

Colloquially known as Soybean Stem Fly, Melanagromyza sojae (Zehntner, 1901) (Diptera, Agromyzidae) is an oligophagous pest of plants in the family Fabaceae, including Uruguay’s biggest commodity crop, Soybean (Glycine max (L.) Merr.). To our knowledge, this is the first scientific record of M. sojae in Uruguay, and we confirm its identity through using DNA barcoding. Characteristic damage to host plants and immature stages of M. sojae were confirmed in Dolores and Colonia, Uruguay

First record of Soybean Stem Fly Melanagromyza sojae (Zehntner, 1901) (Diptera, Agromyzidae) in Uruguay confirmed by DNA barcoding

Colloquially known as Soybean Stem Fly, Melanagromyza sojae (Zehntner, 1901) (Diptera, Agromyzidae) is an oligophagous pest of plants in the family Fabaceae, including Uruguay’s biggest commodity crop, Soybean (Glycine max (L.) Merr.). To our knowledge, this is the first scientific record of M. sojae in Uruguay, and we confirm its identity through using DNA barcoding. Characteristic damage to host plants and immature stages of M. sojae were confirmed in Dolores and Colonia, Uruguay

Advances in understanding plant root responses to root-feeding insects

In terms of the number of animal and plant species that occupy our planet, around 26% are herbivorous insects (Strong et al., 1984). They represent enormous diversity, particularly in terms of how they consume and exploit plant resources. A comparatively small proportion of herbivorous insects, limited to six orders, feed belowground on plant roots (Brown and Gange, 1990). While some root herbivores spend their entire lifecycle belowground (e.g. grape phylloxera), it is likely that the majority of species have aboveground life stages (usually adult) and it is the juvenile (larval) life-stages that attack roots. Rootfeeding insects differ markedly from shoot-feeding insects in terms of their ecology and life-history traits. While there are many exceptions to the rule, these differences can be broadly generalized (see Table 1) (Johnson et al., 2016b). In particular, root herbivores are probably represented in just 17% of families: they are predominantly chewers, have relatively long lifespans, live in highly aggregated populations and are in constant contact with the immense microbial communities found in the soil (Johnson et al., 2016b). As a group, there are still major gaps in our knowledge about how they interact with roots compared with our understanding of aboveground insect herbivore interactions (Hunter, 2001)

Agroecological consequences of silicon supplementation for a legume cultivation: Two-year-long field observations

Putra R, Islam T, Cibils-Stewart X, Hartley SE, Johnson SN. Agroecological consequences of silicon supplementation for a legume cultivation: Two-year-long field observations. Agriculture, Ecosystems & Environment. 2024;365: 108893.Supplementing plants with silicon (Si) often improves plant productivity and resilience to biotic and abiotic stresses, but this is mostly reported in highly controlled experimental environments. The ecological consequences of Si supplementation, including environmental benefits and potential risks, are therefore poorly understood and require field-scale evaluation of how Si supplementation affects the wider ecosystem, such as invertebrate communities and soil physicochemical properties. We conducted the first field assessment of how a legume (lucerne; Medicago sativa) agroecosystem and its associated invertebrate communities responded to two levels of Si supplementation (calcium silicate slag), over two years. We quantified seasonal changes in the abundance and diversity of aboveground arthropod communities, crop yield, elemental and nutritional chemistry, and soil pH as well as soil chemistry. The highest rate of Si supplementation increased bioavailable Si in the soil by 181% and soil pH from 5.2 to 6.3, relative to untreated plots, with a significant positive correlation between increased soil bioavailable Si and pH. Si supplementation led to an increase in crop yield by up to 52%; however, the magnitude varied with season. Foliar concentrations of Si tended to increase with Si supplementation, but this increase was marginally significant, potentially due to a dilution effect of higher shoot biomass. Si supplementation did not affect concentrations of most soil elements we quantified or forage quality of lucerne. We recorded over 13,600 arthropods; Si supplementation led to a shift in community structure and overall increased diversity of arthropod functional groups. Notably, the saprophytic fly family, Lauxaniidae was more abundant on Si-supplemented plots compared to untreated plots, potentially due to increased plant turnover. These results indicate that silicon supplementation of a legume agroecosystem, using a by-product of steel production, provides productivity benefits that outweigh some possible detrimental impacts on the ecosystem (i.e. decreased arthropod abundances, toxic metal contamination or reduced forage quality), which we did not detect in our current field study. This management intervention enhances crop yield, so could reduce the need for conventional fertilisers as well as changing soil pH to be more beneficial to crops and some arthropod groups