PLANT COMMUNITY DIVERSITY, INSECT MOVEMENT, AND THE DYNAMICS OF AN INSECT-TRANSMITTED PLANT DISEASE (LEAFHOPPERS, CORN STUNT, DALBULUS MAIDIS

This research developed a theoretical framework for understanding the ecology of plant diseases transmitted by insects and the results have important implications for the management of these diseases in agricultural systems. The spread of insect-vectored disease depends on insect abundance, the average time an insect spends on each host plant and the feeding period required for the insect to transmit the pathogen. Plant community diversity and vegetation texture have an important influence on disease dynamics through their effects on insect abundance and movement behavior (Chapter 1).;The influence of plant community diversity and vegetation texture on the insect vector of a plant disease and the resultant disease spread in plant communities were examined in manipulative field experiments carried out in Nicaragua. The spread of the corn stunt disease in maize, and the abundance and movement patterns of the corn leafhopper Dalbulus maidis, which transmits corn stunt, varied in different experimental plant communities.;Increasing plant species diversity by intercropping with beans or weeds led to lower leafhopper abundance per plant, slower insect movement rates, and a lower incidence of corn stunt (Chapter 2). Leafhopper densities per plant and corn stunt incidence were lower in high density maize monocultures than low density monocultures (Chapters 2 & 3). At a given plant density, the planning arrangement influenced disease incidence through its effects on insect movement (Chapter 3). Manipulating host plant quality by adding nitrogen fertilizer resulted in higher leafhopper densities and higher disease levels in the high nitrogen treatments (Chapter 2). Leafhopper abundance was lower in plots with high maize genetic diversity than in plots with less genetic diversity (Chapter 4).;These results demonstrate that manipulations of plant density and diversity, plant quality, and maize genetic diversity could be utilized in a program of cultural control for the corn stunt disease vectored by Dalbulus maidis. This research examines the mechanisms involved in the spread of insect-transmitted disease in plant communities and provides information useful for designing agroecosystems.