Prior exposure to plants cues can enhance assortative mating in insects. We hypothesized that, as previously reported for females, males of Cotesia congregata would display inherent responses to plant cues that could be modified by postemergence experience and further, that males originating from two different host-plant complexes (HPCs) would display different behavioral responses to these HPCs. In no-choice contact assays with a non-host plant, searching responses of males and females increased sharply at Day 2 and remained stable through Day 4. In no-choice assays with potential host plants, males searched longer on catalpa than tobacco; responses were not modified by postemergence experience. In choice assays with both HPCs, naïve males did not display orientation preferences; however, males experienced with their natal plant preferred their natal HPC. Results indicate that postemergence experience on the natal host plant induces an orientation preference for the natal HPC and thus, can facilitate assortative mating.

Among the predicted impacts associated with global climate change, warming is of special interest because the rates of physiological processes are temperature-dependent. Insects and other ectotherms are likely to be affected due to their limited ability to control body temperature. In this study, I measured the tolerance to extreme high temperatures, i.e., critical thermal maximum (CTmax), of component species in a tri-trophic system, including an herbivore (Manduca sexta), a primary larval parasitoid (Cotesia congregata) and a hyperparasitoid (genus Silochalcis). For wild insects, the parasitoid had the lowest CTmax, the hyperparasitoid had the highest, and the herbivore was intermediate. For laboratory insects, the parasitoid had a lower CTmax than the herbivore. Results suggest that laboratory colonies can be used to predict relative thermal performance of interacting species in the field. Variations in tolerance to high temperature among component species could disrupt the outcome of interactions in multi-trophic systems.

As respostas dos nematoides entomopatogênicos, Steinernema carpocapsae (Weiser) e Heterorhabditis indica (Poinar, Jackson e Klein), aos voláteis emitidos por raízes de cana-de-açúcar (Saccharum officinarum L.) danificadas ou não danificadas por ninfas da cigarrinha-da-raiz, Mahanarva fimbriolata (Stål), foram estudadas em laboratório. Plantas de cana-de-açúcar foram transplantadas para câmaras laterais do olfatômetro de seis vias e submetidas ou não a herbivoria por M. fimbriolata. Cerca de 10000 nematoides entomopatogênicos foram liberados na câmara central do olfatômetro e após 24 horas os nematoides foram contabilizados em cada câmara lateral do dispositivo. Raízes de plantas previamente danificadas ou não danificadas por M. fimbriolata foram destacadas das plantas, congeladas com nitrogênio liquido e maceradas. O material foi então aerado por 8 horas para a coleta dos voláteis. O perfil dos voláteis dos extratos naturais foi analisado em um cromatógrafo gasoso acoplado a um espectrômetro de massas (GC-MS). Os nematoides de ambas as espécies foram atraídos pelos voláteis radiculares de plantas danificadas pela cigarrinha-das-raízes, em contraste com plantas não danificadas e areia umedecida (controle). As análises em GC-MS revelaram que não houve diferença qualitativa no perfil de voláteis radiculares entre os tratamentos. Por outro lado, dos 11 compostos presentes nas raízes não danificadas, di-hidro mircenol e Beta isso metioneno reduziram, significativamente, sua concentração após o ataque de M. fimbriolata. Estes resultados sugerem que o recrutamento de nematoides entomopatogênicos neste sistema pode ter sido influenciado pela diminuição da concentração destes dois compostos radiculares nas plantas sob herbivoria. / The responses of entomopathogenic nematodes Steinernema carpocapsae (Weiser) and Heterorhabditis indica (Poinar, Jackson e Klein), to volatiles emitted by sugar cane roots damaged or undamaged by Mahanarva fimbriolata (Stål) nymphs, were investigated under laboratory conditions. Thus, sugarcane plants damaged or undamaged by M. fimbriolata were transplanted to lateral arms of six arm olfactometer. Approximately 10000 entomopathogenic nematodes were released in the central chamber of the olfactometer and after 24 hours, the nematodes were counted in each arm. Roots of previously damaged or undamaged plants were detached, frozen with liquid nitrogen and macerated. The material was then aerated for 8 hours to collect volatiles. The volatiles profile was analyzed by a gas chromatograph-mass spectrometer. Most nematodes of both species moved to plants that had been previously damaged over undamaged plants, and there was no significant difference in the choice of undamaged plant and only moisted sand. The GC-MS analyzes showed no qualitative difference between the root treatments volatiles profile. In both treatments, the same 11 compounds were found. Although, two compounds, dihydro myrcenol and Beta-iso-methionene, showed quantitative difference between treatments, observing greater production in undamaged plants, i.e. herbivory caused reduction in tested sugar cane roots volatiles releasing. These data provide new information about the tritrophic relationships occurring in the soil which, in the future, can be used in order to develop field management for M. fimbriolata.

Parasitic wasps are highly diverse and play a major role in suppression of herbivorous pest populations, but relatively little is known of the mechanisms driving their diversity. Molecular studies indicate that cryptic species complexes resulting from adaptations to specific hosts or host-foodplants may be common. The gregarious endoparasitoid, Cotesia congregata (Braconidae), is a model system for understanding parasitic wasp biology. It is reported to attack at least 15 species of sphingid caterpillars, most of which are plant family specialists. Molecular studies have demonstrated genetic differentiation of two host-foodplant complex sources originating from Manduca sexta on tobacco (MsT) and Ceratomia catalpae on catalpa (CcC). Response to female pheromone and elements of their courtship songs differ. Wasps from both sources mated and produced F1 hybrid offspring in the laboratory; however, 90% of hybrid females resulting from one of the reciprocal crosses failed to produce offspring. I built on this previous work by evaluating an ecological barrier, the evolution of courtship songs within the genus, and patterns of hybrid sterility among four additional host-foodplant complexes, as well as differentiation of their symbiotic bracovirus. Tests of developmental tolerance to nicotine demonstrate that MsT wasps are highly adapted to hosts feeding on tobacco, whereas CcC wasps experience high mortality. Acoustic analysis of courtship songs among host-foodplant sources of C. congregata and eleven additional species of Cotesia demonstrates that songs are species specific and appear to be correlated with genetic relatedness. Cotesia congregata from all sources mated and produced F1 hybrid offspring in the laboratory; however, hybrid females resulting from specific reciprocal crosses failed to produce progeny. Dissections of hybrid females revealed that sterile wasps lacked mature ovaries and functional bracovirus, a symbiotic virus integrated into the wasp genome and necessary to suppress the host immune system. Relative in vivo expression of wasp bracovirus genes differs between MsT and CcC host-foodplant complexes. Cumulatively, these behavioral, ecological, and genetic barriers to reproduction indicate that C. congregata is diverged into two incipient species with limited gene flow, and provides insight into the role of varied reproductive barriers in speciation of parasitic wasps.

Solenopsis invicta, the red imported fire ant, has recently become associated with Antonina graminis, an invasive pest, and Neodusmetia sangwani, biological control agent, and maybe negatively affecting established biological control. A preliminary survey outlined the range of A. graminis and its parasitoids, and found N. sangwani was present at a reduced rate in South Texas and in the southeastern United States. A greenhouse experiment demonstrated that S. invicta decreased the rate of parasitism of A. graminis by N. sangwani, with S. invicta directly interfering with oviposition. Interactions between S. invicta and A. gaminis may be facilitating the spread and establishment of two invasive pests which has a negative impact on established classical biological control of A. graminis by N. sangwani.

To understand how plant defensive traits will evolve, we need to consider the biotic context for plant-herbivore interactions. I investigated how predators affect selection on defensive traits in plants. First, I established the timing of resistance in three soybean genotypes. Next, I examined the combined effects of resistance and predators on plant fitness. I reared Mexican bean beetles (MBBs) with or without spined soldier bugs (SSBs) on soybeans with constitutive resistance (CR) or no resistance (NR). SSBs fed more on MBBs that fed on NR than on CR plants, and this translated into an increased fitness benefit from predators for NR plants over CR plants. Selection for some types of resistance in plants should thus be stronger with lower predation rates. Similarly, I reared MBBs with or without SSBs on soybeans with early induced resistance (EI), late induced resistance (LI), or CR. SSBs fed more on MBBs reared on LI plants than on beetles raised on CR plants, but no more on beetles reared on EI plants than on beetles reared on CR plants. LI plants were the only of the three soybean varieties to receive a fitness benefit from predators, which could help explain the evolution of this type of plant defense. The results of both experiments also suggest that predator introductions may be more beneficial to LI or NR crop plants than EI or CR crops. Finally, I present a model that determines the optimum amount of induced resistance (IR) and CR for a plant growing with and without neighbors. Unlike earlier models, our plants have a probability of being attacked that is modified by short- and long-term feedback of plant defenses to herbivores. Higher costs of defense favor IR over CR, while increasing herbivore attack rates or increasing the overall effectiveness of defense results in more CR. Plants with neighbors might be selected to evolve higher or lower levels of CR than if they were growing alone. Adding neighbors also selects for more mixed induced/constitutive strategies for all parameters. Having defended neighbors could thus be part of the reason why plants have evolved such mixed defense strategies. / Dissertation

Solenopsis invicta, the red imported fire ant, has recently become associated with Antonina graminis, an invasive pest, and Neodusmetia sangwani, biological control agent, and maybe negatively affecting established biological control. A preliminary survey outlined the range of A. graminis and its parasitoids, and found N. sangwani was present at a reduced rate in South Texas and in the southeastern United States. A greenhouse experiment demonstrated that S. invicta decreased the rate of parasitism of A. graminis by N. sangwani, with S. invicta directly interfering with oviposition. Interactions between S. invicta and A. gaminis may be facilitating the spread and establishment of two invasive pests which has a negative impact on established classical biological control of A. graminis by N. sangwani.

Components of successful pest management programs must be complementary and not antagonistic. This project examined interactions between natural enemies of the black cutworm, Agrotis ipsilon (Hufnagel), an important turfgrass pest, and host plant resistance by endophytic grass. Agrotis ipsilon nucleopolyhedrovirus (AgipMNPV) was examined as a bio-insecticide for controlling A. ipsilon in turfgrass. Fresh (1-week-old) AgipMNPV residues killed 76−86% of neonates hatching from eggs on golf course tees, however, residual control of implanted larvae lasted no more than a few weeks. Combinations of AgipMNPV with adjuvants, such as optical brightener and lignin, failed to accelerate or extend efficacy of the virus. AgipMNPV seems better suited for targeted control of early instars than for season-long control. Several applications per growing season would likely be needed to maintain high enough titers on turfgrass to effectively control cutworms. The addition of a chitin synthesis inhibiting turfgrass fungicide failed to synergize AgipMNPV infectivity to A. ipsilon. Choice tests revealed the fungicide residues to be a mild feeding deterrent, the likely cause of slightly reduced mortality from virus infection seen in field trials. Combination applications in turfgrass might interfere with larval ingestion of a lethal virus dose, resulting in prolonged feeding in the field. I examined how feeding on perennial ryegrass (Lolium perenne) with or without Neotyphodium lolii, its alkaloid-producing fungal endophyte, affects susceptibility of A. ipsilon to AgipMNPV. Feeding on endophytic grass neither compromises nor synergizes infectivity of AgipMNPV in the cutworm midgut. However, reduced consumption or avoidance of less-palatable endophytic grass could decrease ingestion of virus and rates of subsequent mortality in the field. Host feeding on endophytic grass had differing effects on the tachinid fly, Linnaemya comta, a fast-developing solitary parasitoid, and the encyrtid wasp, Copidosoma bakeri, a slow-developing gregarious parasitoid. L. comta development did not appear to be affected when its host fed on endophytic grass; in contrast, C. bakeri suffered negative fitness effects. These results suggest that parasitoid life strategy and taxonomy play a role in endophyte mediated tritrophic interactions.

This thesis gives a general model formulation of discrete time individual-based models and two specific individual-based models for gregarious behaviour. A spatially explicit individual-based model for a predator, prey and plant ecosystem is the first specific model considered. The movement of the individuals is solely based on nearest-neighbour attraction/repulsion and reproduction is asexual. The second specific model considered is a spatially explicit individual-based model for schooling behaviour. The movement of the individuals is based on the physics of fluids and their reactions (repel/comfort/attract) are solely based on directional light intensities. In the ecosystem model emergent spatial organization of the individuals into clusters or groups is present even though all the individuals (predators and prey) are intra-specifically repelled by each other. The model ecosystem was used to determine whether an intra-specific attraction among the prey could increase their individual fitness. The attraction mechanism considered is such that when a prey is not affected by a predator or a plant then this prey is attracted to its nearest-neighbour prey. Under the assumptions of the parametrized model ecosystem, this mechanism seems highly selective on the individual level. The schooling model assumes that the individuals have absolutely no spatial reasoning and cannot discern other individuals as individuals. In particular, the individuals school without the capacity to match the velocities or orientations of other individuals. Individuals have the ability to perceive their environment using directional photo-sensors and adjust the direction of their acceleration in response to the values of these photo-sensors. This result should fundamentally change the way social aggregations are modeled. The main objective of this thesis is to formalize mathematically individual-based models with the intention that they become more prevalent in the scientific inquiry into assessing evolutionary aspects of social behaviour.

As respostas dos nematoides entomopatogênicos, Steinernema carpocapsae (Weiser) e Heterorhabditis indica (Poinar, Jackson e Klein), aos voláteis emitidos por raízes de cana-de-açúcar (Saccharum officinarum L.) danificadas ou não danificadas por ninfas da cigarrinha-da-raiz, Mahanarva fimbriolata (Stål), foram estudadas em laboratório. Plantas de cana-de-açúcar foram transplantadas para câmaras laterais do olfatômetro de seis vias e submetidas ou não a herbivoria por M. fimbriolata. Cerca de 10000 nematoides entomopatogênicos foram liberados na câmara central do olfatômetro e após 24 horas os nematoides foram contabilizados em cada câmara lateral do dispositivo. Raízes de plantas previamente danificadas ou não danificadas por M. fimbriolata foram destacadas das plantas, congeladas com nitrogênio liquido e maceradas. O material foi então aerado por 8 horas para a coleta dos voláteis. O perfil dos voláteis dos extratos naturais foi analisado em um cromatógrafo gasoso acoplado a um espectrômetro de massas (GC-MS). Os nematoides de ambas as espécies foram atraídos pelos voláteis radiculares de plantas danificadas pela cigarrinha-das-raízes, em contraste com plantas não danificadas e areia umedecida (controle). As análises em GC-MS revelaram que não houve diferença qualitativa no perfil de voláteis radiculares entre os tratamentos. Por outro lado, dos 11 compostos presentes nas raízes não danificadas, di-hidro mircenol e Beta isso metioneno reduziram, significativamente, sua concentração após o ataque de M. fimbriolata. Estes resultados sugerem que o recrutamento de nematoides entomopatogênicos neste sistema pode ter sido influenciado pela diminuição da concentração destes dois compostos radiculares nas plantas sob herbivoria. / The responses of entomopathogenic nematodes Steinernema carpocapsae (Weiser) and Heterorhabditis indica (Poinar, Jackson e Klein), to volatiles emitted by sugar cane roots damaged or undamaged by Mahanarva fimbriolata (Stål) nymphs, were investigated under laboratory conditions. Thus, sugarcane plants damaged or undamaged by M. fimbriolata were transplanted to lateral arms of six arm olfactometer. Approximately 10000 entomopathogenic nematodes were released in the central chamber of the olfactometer and after 24 hours, the nematodes were counted in each arm. Roots of previously damaged or undamaged plants were detached, frozen with liquid nitrogen and macerated. The material was then aerated for 8 hours to collect volatiles. The volatiles profile was analyzed by a gas chromatograph-mass spectrometer. Most nematodes of both species moved to plants that had been previously damaged over undamaged plants, and there was no significant difference in the choice of undamaged plant and only moisted sand. The GC-MS analyzes showed no qualitative difference between the root treatments volatiles profile. In both treatments, the same 11 compounds were found. Although, two compounds, dihydro myrcenol and Beta-iso-methionene, showed quantitative difference between treatments, observing greater production in undamaged plants, i.e. herbivory caused reduction in tested sugar cane roots volatiles releasing. These data provide new information about the tritrophic relationships occurring in the soil which, in the future, can be used in order to develop field management for M. fimbriolata.