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The “environmental heterogeneity hypothesis” predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15‐yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post‐restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16–20 yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5‐yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N‐enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N‐enriched soil, but the magnitude of this response was small. Communities assembling under long‐term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass‐dominated communities in N‐enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect of environmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

The rate of kill of cereal aphids by larvae of Metasyrphus corollae (F.) (Diptera: Syrphidae) was measured in the laboratory with the aim of assessing the impact of this predator on field populations of cereal aphids. Daily measurements were taken of changes in both the larval weight and the biomass of aphids killed by M. corollae in conditions of constant temperature and humidity. A mean relative kill rate was defined and calculated for each larval instar of the predator from which estimates of field daily rates of kill can be made. Résumé Quantification de l'impact de Metasyrphus corollae sur Sitobion avenae sur blé d'hiver: taux de mortalité au laboratoire Le taux de mortalité de S. avenae provoqué par les larves de M. corollae a été mesureé au laboratoire pour évaluer l'impact de ce prédateur sur les populations de ce puceron dans la nature. L'évolution du poids des larves et de la biomasse de pucerons tués a été suivie tous les jours dans des conditions de température et humidité constantes. Un taux moyen de mortalité a été déterminé pour chaque stade larvaire du prédateur, il a servi à déduire les niveaux de mortalité quotidienne dans les champs.

Applied nucleation (i.e. planting vegetation patches) is a restoration strategy that better recreates natural ecosystem heterogeneity and requires fewer resources compared to planting the entire area. Whereas applied nucleation shows promise as a forest restoration strategy, this approach has received little study in grassland restoration, where the spread of planted vegetation nuclei may be impeded by aggressive non-native species. We compared the establishment and cover of restored native grass, forb, and rush species for 7 years in applied nucleation and full planting treatments in a former agricultural site dominated by non-natives along the central California coast. We planted seedlings of the same nine coastal prairie species in all treatments, but the applied nucleation plots had four nuclei with only 30% of the seedlings as the full planting plots. We also evaluated the effect of adding wood mulch to reduce non-native plant competition. Native forb cover increased over time and was similar across treatments in the final study year. Native grasses increased for the first 4 years and then declined sharply in all treatments. Native forb cover spread into unplanted areas in applied nucleation plots, whereas grasses showed minimal spread. Of the five planted forb species, the two that persisted until the final study year both spread via rhizomes. Wood mulch reduced non-native cover in the first 2 years and had a longer-term effect on species composition. Our results suggest that applied nucleation can be an effective restoration strategy at a small scale in non-native-dominated grasslands for species that spread vegetatively.

Brazilian verbena (Verbena brasiliensis, family Lamiaceae) is a highly invasive plant found throughout the southern portion of the United States. As suggested by its name, it originates in South America but has prospered in the US due to its highly ruderal growing pattern and its ability to tolerate drought and disturbance. During the summer of 2019, sixty-four V. brasiliensis plants were growing in the University of Houston’s temperature-controlled greenhouse (Houston, TX). Eight plants exhibited symptoms of powdery mildew infection on the stems and adaxial surface of the leaves. White circular powdery colonies with high numbers of aerially dispersing spores were observed on leaves, seemingly uncorrelated with leaf age. Upon examination, chlorosis of leaf tissue was detected in areas of infection. Conidiophores (n=25) were on average 210 μm in length and produced 6 to 9 conidia in true chains. Base-cells of conidiophores branched from hyphae forming right angles and averaged 35 μm long at the base. Conidia were hyaline, ovate, and measured 28-31 × 19-21μm. These structures are typical of the powdery mildew oidium anamorph of the genus Podosphaera. No chasmothecia were observed within colonies.The morphological characteristics and measurements were consistent with those of Podosphaera xanthii (Braun and Takamatsu 2000). Pathogenicity was confirmed by gently rubbing symptomatic V. brasiliensis leaves onto healthy leaves of V. brasiliensis plants (Lee 2013). Fifteen plants were inoculated, and five remained uninoculated to serve as negative controls. Inoculated plants developed powdery mildew symptoms between 6 to 12 days (averaging 10 days), whereas all controls remained disease-free. DNA was extracted from fungal tissue from the original plant, inocula sample, and the newly infected leaves. The internal transcribed region was amplified using the ITS1f and ITS4 primers (White 1990). Three samples, one from the original plant, the inocula, and the reisolated fungi were sequenced, identified using NCBI BLAST, and the resulting sequences were deposited in GenBank (MN818562, (inocula), MN818563 (re-isolate), MN818564 (original)). All three sequences had 98.7% similarity to the P. xanthii on Brazilian verbena reported in South Korea assession number KJ472787 (Cho et al 2014). All three samples were amplified using the mating type primer sets and PCR protocal described in Brewer et al 2011. All three samples were determined to be MAT1-1-1 based on positive and negative control used for MAT1-1-1 and MAT-1-2-1 Positive controls included DNA from confirmed isolates from MAT1-1-1 and MAT-1-2-1 and negative controls were sterile water. Podosphaera xanthii, a common powdery mildew species, has been reported on a large range of important agricultural hosts, especially cucurbits (McCreight 2006). This is the first formal report of P. xanthii in Texas as well as the first report on Brazilian verbena in the United States. While we did not explicitly measure the pathogen’s effect on host fitness, infection may result in a reduction in the plant’s invasiveness. As Texas is a large producer of cucurbits, this pathogen could impact agriculture in the state. Given the invasive nature of V. brasiliensis in areas of high disturbance, such as agricultural fields and restored prairies, this discovery has broad importance for both agriculture and the ecological conservation of native species. Acknowledgments This work was supported by the National Science Foundation (Award #DEB-1754287), Texas Ecolab, and the University of Houston. References Braun, U., Takamatsu, S. 2000. Phylogeny of Erysiphe, Microsphaera, Uncinula (Erysipheae) and Cystotheca, Podosphaera, Sphaerotheca (Cystotheceae) inferred from rDNA ITS sequences–some taxonomic consequences. Schlechtendalia 4:1-33. Brewer, M. T., Cadle-Davidson, L., Cortesi, P., Spanu, P. D., and Milgroom, M. G. 2011. Identification and structure of the mating-type locus and development of PCR-based markers for mating type in powdery mildew fungi. Fungal Genet. Biol. 48:704-713. Cho, S. E., Park, J. H., Hong, S. H., Kim, B. S., & Shin, H. D. 2014. First report of powdery mildew caused by Podosphaera xanthii on Verbena brasiliensis in Korea. Plant Dis. 98:8, 1159. Lee, H. B. 2013. First report of powdery mildew caused by Podosphaera xanthii (syn. P. fusca)n cocklebur in Korea. Plant Dis. 97(6), 842. McCreight, J. D. 2006. Melon-powdery mildew interactions reveal variation in melon cultigens and Podosphaera xanthii races 1 and 2. Journal of the American Society for Horticultural Science, 131(1), 59-65.

Both dietary protein (N) and sodium (Na) are essential nutrients for invertebrate growth and reproduction. Field studies show that insects aggregate in areas with both high protein and sodium and their abundance is co‐limited by these two essential nutrients, but the mechanism behind this aggregation is not well known. We examined a possible mechanism that dietary protein and sodium co‐limit insect herbivore growth and reproduction. To test this mechanism, we conducted a feeding experiment examining the effect of these two nutrients by using artificial diets with two levels of protein and three levels of sodium on a generalist herbivorous cockroach Blaptica dubia. Elevated levels of dietary sodium interacted with low protein level to increase cockroach nymph relative growth rate during earlier instars. Female cockroaches always weighed more and had a higher relative growth rate than males regardless of dietary treatment. When compared between different dietary treatments, female cockroaches' relative growth rates were higher when fed with a high protein diet, while male cockroaches reached the final instar faster when fed with a high sodium diet. Cockroach reproduction was not affected by protein or sodium alone, but the combination of a high protein and high sodium diet resulted in the heaviest offspring. Our results suggest that both protein and sodium may be important for both the growth and reproduction of insect herbivores. The interaction of these two nutrients to improve cockroach growth and reproduction indicate a level of co‐limitation.

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