Resources in the soil are heterogeneously distributed. We know that plant species differ in their root responses to nutrient patches and that these differences in foraging can influence plant competition. However, most studies of root-resource interactions overlook the potential top-down influence of root herbivores. While root herbivores can influence plant community structure, the extent to which they influence ecosystem-scale factors such as net primary production is unclear. In addition, little is known regarding root herbivore foraging behaviors and, more importantly, whether these foraging behaviors can actually influence species interactions. In this dissertation, I present a conceptual model of soil-root-herbivore interactions in which soil resource heterogeneity structures both root dynamics and the abundance and influence of root herbivores. I conducted two field and one greenhouse experiment examining this proposed model. The dissertation includes an introductory chapter (Chapter 1), a field study examining root responses to manipulations of soil fertility and root herbivory (Chapter 2), a greenhouse study that used plant species responses to heterogeneity to develop predictions about the role of root herbivores in mixed-species neighborhoods (Chapter 3), and a field study of planted communities examining soil fertility and fauna effects on above- and belowground structure and function (Chapter 4). In all cases, there were significant effects of root herbivores on community structure and components of net primary production. Resource distribution had a strong effect in studies conducted in sandy, nutrient-poor soils (Chapter 2 and 3), but had a reduced effect in the study conducted at Kentland Farm in loamy soils (Chapter 4). Interactions between resource availability and root herbivory were common. These results support the theory that the potential benefit of resource-rich patches may be constrained by root herbivores. This research complements recent findings that demonstrate other potential costs of species foraging behaviors (such as exposure to soil anoxia and increased drought stress), as well as potential effects of root herbivores and other soil fauna on plant diversity. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The white grub Liogenys fusca is an important pest of soil Midwest Region of Brazil, his injuries have been recorded in crops such as corn, soybeans and oats. The objective of this study was to study the bioecological aspects of Liogenys fusca on Rio Grande do Sul and to determinate the economic injury level (EIL) of the insect on the soybeans. Chapter I emphasis on the characterization of the development phases of Liogenys fusca and the dynamic of this population on Rio Grande do Sul. The study was performed in Manoel Viana, RS, throughout soil sampling held on a monthly basis during 2010 and 2011 years. The insect period of occurrence throughout the year and the location of these in the soil were evaluated. Chapter II emphasizes the economic injury level (EIL) of L. fusca on soybeans. A field experiment was conducted in Santa Maria, RS, on the harvest year of 2010/2011, testing four different populational levels of second and third instars larvae of L. fusca (4, 8 and 12 larvae/m2). The evaluated parameters were: initial plant population, final plant population, plant height at 15, 30 and 60 DAE (days after emergence) and yield (kg/ha). The EIL was estimated through the equation adapted from Pedigo (1999). Liogenys fusca is an univoltine specie. Larvae were sampled between the months February to November. The pupae were found in the interior of galleys built in the soil at a profundity of until 20cm from September through November. The adults were sampled from December through February. The economic injury level (EIL) of L. fusca on soybeans was ranged from 0,12 to 0,44 larvae/m2 as varied cost control. Each increased larvae per m2 effected a yield loss of 151,30 kg/ha on the soybeans. / O coró Liogenys fusca é uma importante praga de solo da Região Centro-Oeste do Brasil, seus danos já foram registrados em culturas como milho, soja e aveia. O trabalho objetivou estudar aspectos bioecológicos de Liogenys fusca no Rio Grande do Sul, e determinar o nível de dano econômico desse inseto na cultura de soja. O capítulo I trata da caracterização das fases de desenvolvimento de L. fusca e sua dinâmica populacional em Manoel Viana, RS. A partir de amostragens de solo, efetuadas mensalmente em 2010 e 2011; avaliou-se o período de ocorrência do inseto ao longo do ano e a sua localização no perfil do solo. O capítulo II trata do nível de dano econômico de L. fusca na cultura da soja, realizado em campo, em Santa Maria, RS, na safra 2010/2011, no qual foram testados níveis populacionais de larvas de segundo e terceiro ínstar de L. fusca. Foram eles: zero; 4; 8 e 12 larvas/m². Avaliaram-se os parâmetros: população inicial de plantas, população final de plantas, estatura de plantas aos 15, 30 e 60 DAE (dias após a emergência) e produtividade (kg/ha). O nível de dano econômico foi estimado através de duas equações adaptadas de Pedigo (1999). Liogenys fusca caracteriza-se como uma espécie univoltina. As larvas são encontradas entre os meses de fevereiro a novembro. As pupas são encontradas no interior de câmaras construídas no solo a profundidades de até 20 cm, entre os meses de setembro a novembro. Os adultos são coletados entre os meses de dezembro a fevereiro. O nível de dano econômico (NDE) de L. fusca em soja variou de 0,12 a 0,44 larva/m², conforme variou o custo de controle. A cada larva de L. fusca acrescida por m² há uma redução de 151,30 kg/ha na produtividade da soja.

A regional IPM project was initiated with four rounds of sampling for white grubs on the fairways of nine golf courses located on the Lower Peninsula of eastern Virginia, from 2000 through 2002. Fifteen regressor variables were collected and measured that included local-scale variables, golf course management practices and spatial pattern metrics derived from satellite images that underwent two methods of a supervised classification of six land-cover types (turf, woods, wetland, urban, bare soil and water) on four landscape scales derived from 10 km x 10 km buffer zones surrounding each golf course. Pearson's correlation coefficients were calculated to reduce the number of variables to a few that were highly correlated with white grub densities. Mallow's C(p) calculations were performed on the reduced variable sets to extract those that would be highly predictive. A multiple linear regression was performed using the Mallow's variables to develop eight regression equations (two classification methods x four landscape scales) that were used to predict regional white grub presence and abundance in 2003 on six additional golf courses located on the Lower Peninsula. The best model was the 6 km x 6 km buffer zones model from the second classification method, which included one local-scale variable (golf course age) and three spatial pattern metrics (total turf area, total turf area-to-total urban area ratio, and a woods interspersion-juxtaposition index). The mean difference between actual and predicted values was -0.15, standard deviation = 0.79, R2 = 81.38%. Additionally, a study was conducted to determine whether the number of white grubs collected from transects of sampled golf course fairways was significantly different from those found in the roughs. White grub counts from the roughs were significantly higher (mean = 0.283 grubs/transect, standard error = 0.0135) than those from fairways (mean = 0.146 grubs/transect, standard error = 0.0188); t = -4.31, df = 735, P = 0.0001. / Ph. D.

White grubs (Coleoptera: Scarabaeidae) are important turfgrass pests in Virginia. Insecticides such as the neonicotinoid imidacloprid are commonly applied to turfgrass in order to control these pests. As an alternative to synthetic insecticides, entomopathogenic fungi (EPF), including Metarhizium brunneum (Petch) and Beauveria bassiana (Balsamo) Vuillemin may also be used for white grub control. The interaction of combining these two control tactics for white grubs in Virginia merits further investigation as does their effects on other soil organisms such as earthworms, which cohabitate with white grubs in turfgrass soil ecosystems. Herein, I investigate the following: 1) the efficacy of combined applications of the EPF, M. brunneum and B. bassiana with lower rates of imidacloprid or the diamide insecticide, chlorantraniliprole against white grubs; 2) interactions of earthworms with white grubs and EPF; and 3) the effect of white grub control products on earthworms. In the laboratory, a combined application of one half the recommended rate of chlorantraniliprole plus the full recommended rate of B. bassiana caused significantly higher mortality of third instar Cyclocephala spp. grubs than the untreated control. In the field, imidacloprid applied at lower rates as a single treatment or as part of a combined treatment with EPF resulted in significantly fewer grubs when applications were made in June. In the greenhouse, Japanese beetle, Popillia japonica Newman females laid a significantly reduced number of eggs in turf treated with lower rate of imidacloprid either applied as a single treatment or as part of a combined treatment compared with untreated control. In an earthworm-white grub interaction study, the earthworms Eisenia fetida (Savingy) and E. hortenis (Michaelsen) were shown to transfer B. bassiana spores from fungus-infected soil to uninfected soil in the laboratory. However, the presence of earthworms in fungal infected soil did not enhance the mortality of Cyclocephala spp. grubs. In bioassays conducted in the laboratory, only two neonicotinoids, dinotefuran and imidacloprid, caused significantly higher mortality to adult Lumbricus terrestris L. earthworms than untreated control consistently. When applied as a drench to turfgrass in spring, summer, and fall, none of the insecticides significantly reduced the earthworm densities compared with a water control. / Ph. D. / White grubs cause serious damage to turfgrass in Virginia and as a part of turf management programs, insecticides such as the neonicotinoid imidacloprid are routinely applied to eliminate these pests. However, there are environmental concerns over the excessive use of neonicotinoids. In addition, these insecticides are typically only effective when they are applied in the summer to target small grubs. Herein, I investigated if combining reduced rates of imidacloprid or another insecticide, chlorantraniliprole, with commercially-available insect-killing fungi <i>Beauveria bassiana</i> or <i>Metarhizium brunneum</i>, could enhance white grub control. Neither the insecticides alone, nor the aforementioned fungal biopesticides provided effective control of larger white grubs in lab bioassays and field experiments. Additional research was aimed at understanding the interactions of insecticides and fungi on both white grubs and earthworms, which cohabitate frequently with white grubs in turfgrass soil ecosystems. In a greenhouse experiment, Japanese beetle females laid fewer eggs in turf treated with imidacloprid, but that chlorantraniliprole or the insect disease causing fungi did not affect beetle egg laying. In another experiment, earthworms were shown to transfer insect disease causing fungi in the soil in the laboratory. However, the presence of earthworms did not increase white grub fungal infection in fungi-infested soil in the lab. Additional experiments showed that two neonicotinoids, dinotefuran and imidacloprid, killed more earthworms than other insecticides when applied to soil in the lab. However, when applied as a drench to turfgrass in spring, summer, or fall, neither of these insecticides nor several others registered for use on turfgrass resulted in fewer earthworms compared with a water control. The complex interactions between turf-damaging white grubs, the insecticides used to control them, insect disease-causing fungi in the soil and non-target beneficial organisms such as earthworms warrant further investigation to help us move toward more sustainable pest management approaches in the future.

This work aimed to study the occurrence of soil-dwelling melolontid species called white grubs (Coleoptera: Melolonthidae) and its geographic distribution in Planalto , Rio Grande do Sul State. Chapter I, describes the current species at larva and adult stadium, provides a taxa key for regional identification and characterizes geographic species distribution. Chapter II analyzes white grubs diversity and populational density in each wild and crop fields and the relation between pest and no-pest communities. Surveys were carried out during both winter 2009 and 2010 in 23 localities distributed in Planalto region. Samplings were made in crop and wild fields in every locality. Population density was estimated with the larvae collected from soil trenches and taxa identification was confirmed by the observation of taxonomic features. For geographic distribution characterization, CRIA Species Link System was used. Community characterization was carried out through diversity and equitability faunistic indexes, and through abundance, frequency, constancy and dominance parameters. For populational density comparations, bootstrap T- test were used. There were found 28 melolontid species, which nine of them are already cited for RS. D. abderus and C. flavipennis were the most abundant and current species. Richness is concentrated in northeast and in Planalto Médio region. White grubs abundance was higher in crop fields, but wild fields were more diverse. The community of no-pest species is larger than the pest one in every field, and there were no differences on populational density of pest and no pest species between crop and wild fields. / Este trabalho teve por objetivo estudar a ocorrência de espécies de melolontídeos edafícolas denominados corós (Coleoptera: Melolonthidae) e sua distribuição geográfica no Planalto do Rio Grande do Sul. No capítulo I são descritas as espécies ocorrentes em sua fase larval e adulta, é proposta uma chave de identificação regional e se caracteriza sua distribuição geográfica. No capítulo II é apresentada a diversidade e densidade populacional de corós que ocorrem sob área cultivada e campo nativo e se determina a relação entre espécies-praga e não-praga. Nesse sentido, foram feitos estudos no período de inverno dos anos 2009 e 2010 em 23 municípios localizados no Planalto do RS. Em cada local, foram realizados amostragens de solo em uma área cultivada e outra de campo nativo. As larvas foram identificadas mediante a observação dos caracteres taxonômicos e em função da contagem foi estimada a densidade populacional. Para caracterizar a distribuição geográfica foi utilizado o Sistema Cria/speciesLink. Com os dados de abundancia e riqueza específica foram utilizados índices faunísticos para descrever as comunidades. Para comparar os dados de densidade populacional de corós entre área cultivada e campo nativo, os dados foram submetidos ao teste t bootstrap. Foram encontradas 28 espécies, das quais apenas nove estão citadas para o RS. As espécies D. abderus e C. flavipennis foram as mais abundantes e com ocorrência em um maior número de locais. A riqueza de espécies se concentra no Nordeste e Planalto Médio. A abundância de corós é maior em áreas agrícolas comparadas com campo nativo, enquanto que esse último é mais diverso. A comunidade de espécies não-praga é maior em ambas as áreas, e não há diferenças na densidade populacional das espécies-praga entre as áreas cultivadas e de campo nativo.