Cropping Systems, Insect Movement, and the Spread of Insect-Transmitted Diseases in Crops

Abstract

Food production in the tropics has undergone tremendous modification in the last several decades, with traditional small, diversified farming systems being replaced by large-scale, input-intensive monocultures. It is clear that insecticide abuse and widespread dependence on single crop genotypes have resulted in many problems for the farmer, the environment, and the health and safety of rural workers (Bull, 1982). Along with other insect pests, insects that transmit pathogens to crops have evolved resistance to widely-used insecticides and have escaped regulation by their natural enemies. It is essential that we use our understanding of basic ecological processes to address the need for low-input agricultural technology for the tropics. Ifwe are to encourage decreased use of pesticides, then we must offer alternative solutions to the problems of pest damage. These solutions depend on an adequate understanding of pest biology and behavior.The goal is to manipulate pest organisms to decrease the damage they cause. One of most direct methods of control is the alteration of the crop itself, through plant breeding or through planting arrangement. U nfortunately, varieties resistant to insect vectors are not available for many crops. Moreover, as new resistant varieties have been developed, vectors (like other insect pests) have evolved to overcome resistance traits in the plants (Pathak and Heinrichs, 1982). Where resistant varieties exist, it is S. R. Gliessman (ed.), Agroecology

The distribution and abundance of Delphacidae (Homoptera) in central Argentina

“…Coincident with the findings of Power (1990), the environmental diversity (in term of crop species per unit area) showed a positive relation with the delphacid species diversity and a negative relation with the abundance of individual species (i.e. higher environmental and delphacid species diversity coupled with low density populations in the north‐east and lower environmental and delphacid species diversity coupled with high density populations in the south‐west).…”

Movement of Bactericera cockerelli (Heteroptera: Psyllidae) in Relation to Potato Canopy Structure, and Effects on Potato Tuber Weights

“…These natural enemies seemed to concentrate near the release points in a density-dependent manner where hosts would have been more abundant, thereby reducing nymphal populations and dampening subsequent effects on tuber weights. Insect vector dispersal is a main component of many plant disease epidemics (Jeger 1999), because the extent of the epidemic is often proportional to vector abundance, range, and frequency of movement (Power 1987(Power , 1990Irwin 1999). It is critical that focus be directed in understanding how and why B. cockerelli adults move in solanaceous crops, how long they reside on individual plants, and how current management practices contribute to vector movement and disease incidence.…”

Host plant dispersion, leaf hopper movement and disease transmission

“…If the period required for virus transmission is very long relative to average tenure times, then leafhoppers might move before they have effectively transmitted the virus. In this case, higher rates of plant-to-plant movement would not be expected to lead to higher disease incidence, whereas longer tenure times might (Power, 1990). Although a direct comparison of the relative lengths of the inoculation periods required for the transmission of the maize rayado fino virus and the corn stunt spiroplasma has not been undertaken, the available data d o suggest that MRFV takes considerably longer to transmit, requiring a minimum of 8 h (Paniagua & Gamez, 1976) versus an hour for the spiroplasma (Alivizatos & Markharn, 1986).…”

“…(Kareiva, 1983a;Stanton, 1983;Power, 1990). Because mqvement patterns, including immigration, emigration, and plant-toplant movement ('trivial' movement sensu Southwood, 1962), play a fundamental role in the response of other herbivores to plant dispkrsion (Bach, 1980(Bach, , 1984(Bach, , 1988Risch, 1981;Kareiva, 1982Kareiva, , 1985Cain et al, 1985), it is likely that movement can help to explain the anomalous response of homopterans to plant density.…”

“…Previous studies have demonstrated that simple measures of vector abundance do not always successfully predict pathogen incidence (Power, 1988(Power, , 1989. This is because the spread of these pathogens depends not only on the abundance of insect vectors, but also on the movement patterns of those insects (Irwin & Ruesink, 1986;Power, 1987Power, , 1990.…”