Thesis Abstract of AGS Students

Effect of vegetation textures on the density and herbivory of the soybean stem fly, Melanaglomyza sojae (Zehntner) in soybean cropping systems

Tita L. Cayme (1990)

Populations of adult stem fly, Melanagromyza sojae (Zehntner) (Diptere : Agromyzidae) were greater in soybean monocultures kept weed free throughout the season than in soybean monocultures and polycultures (intercropped with corn) left weedy for two or four weeks after planting or throughout the season. Significantly more larvae were also counted in monocultures and polycultures kept weed-free for four weeks after planting or weed-free throughout the season. Stem fly densities and percent infestations were apparently lower in the more weedy monoculture and polyculture cropping systems.

Predaceous arthropods were significantly more numerous in polycultures than in monocultures. Eurytoma wasps parasitized M. sojae larvae more effeciently in the more weedy cropping systems than in weed-free monocultures. Four monoculture and polyculture cropping systems were compared on the basis of plant complexity and arthropod species diversity. Polycultures showed the tendency to support more diversity for natural enemy species and vegetation per habitat space than monocultures. Apparently, this trend was due to greater spatial heterogeneity and complexity.

There was significantly lower weed biomass in polycultures than in monocultures. Apparently, shading provided by overlapping soybean/sweet corn canopies helped to suppressed weeds.

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