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Title: SEASONAL OCCURRENCE OF APHIDS AND NATURAL ENEMIES IN WHEAT AND ASSOCIATED CROPS

Author
item French, Bryan
item Elliott, Norman - Norm
item Kindler, Dean - Dean
item ARNOLD, DON - OKLAHOMA STATE UNIVERSITY

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2001
Publication Date: 3/1/2001
Citation: N/A

Interpretive Summary: Diversifying cropping systems is thought to be one way to increase the effectiveness of natural enemies in biocontrol of crop pests. This is because natural enemies require prey and other resources that are not always present in the crop for which biocontrol agents are targeted. Natural enemies of cereal aphids in winter wheat must find alternate hosts or prey during the period between wheat harvest and planting, and during periods when cereal aphids are rare, if they are to be able to exert biocontrol over cereal aphids. We monitored experimental plantings of winter wheat and 12 other grain and forage crops for aphids and aphid natural enemies. Sorghum and winter canola provided sources of aphids for cereal aphid predators and parasitoids during summer months. Cotton also served as summer habitat for cereal aphid natural enemies. Winter canola also harbored aphids, and cereal aphid parasitoids and predators during autumn and winter. Legumes harbored aphids virtually year-round. However, the parasitoid species that attacked aphids in legumes did not parasitize most cereal aphid species in winter wheat fields. Thus, cereal aphid predators could benefit from diversifying cropping systems by planting legumes, but cereal aphid parasitoids would not find hosts in legumes, and their populations would not be enhanced. Overall, the study demonstrated that potential exists to improve biocontrol of cereal aphids in wheat by diversifying cropping systems.

Technical Abstract: Natural enemies of cereal aphids in winter wheat in Oklahoma must find alternate hosts or prey during the period between harvest and planting, and during periods when cereal aphids are rare. We monitored experimental plantings of winter wheat and 12 other grain and forage crops for aphids and aphid natural enemies throughout the growing season of each crop for three years. Sorghum and winter canola provided sources of aphids for cereal aphid predators and parasitoids during summer months. Cotton also served as summer habitat for cereal aphid natural enemies. Winter canola also harbored aphids, and cereal aphid parasitoids and predators during autumn and winter. Legumes harbored aphids virtually year-round. However, parasitoid species that attacked aphids in legumes did not parasitize cereal aphids in winter wheat fields except for the English grain aphid, Sitobion avenae Fabricius, which was an uncommon species in winter wheat. Thus, cereal aphid predators could benefit from diversifying cropping systems by planting legumes, but cereal aphid parasitoids would not find hosts in legumes, and their populations would not be enhanced.