FLEA BEETLE (COLEOPTERA, CHRYSOMELIDAE) POPULATIONS AND CROP YIELD IN-FIELD PEA AND OILSEED RAPE INTERCROPS

The influence of an intercropped agroecosystem of oilseed rape, canola -type (Brassica napus L.), and field pea (Pisum sativum L.) on the pop ulation level of the flea beetle, Phyllotreta cruciferae (Goeze), was evaluated for 3 yr in east-central North Dakota. Treatments included t wo monocultures of oilseed rape (8 kg/ha of live seed) and field pea ( 200 kg/ha of live seed) and three intercropped mixtures of field pea t o oilseed rape (150:2, 100:4, and 50:6 [kg/ha]). Flea beetle counts pe r 0.5 m2 were highest in the oilseed rape monoculture in all 3 yr of t he study but significantly higher from the other treatments in only on e year. The sex ratio of P. cruciferae adults collected was not influe nced by the treatments. The land equivalent ratios (LER = [intercroppe d yield for pea/monoculture yield for pea] + [intercroppe yield for ra pe/monoculture yield for rape]) for the intercrop treatments did not e xceed 1.0, indicating that the intercrops selected were not as efficie nt for yield as the monocultures. This intercrop system was not effect ive in reducing flea beetle loads on a per-plant basis, nor was there a yield advantage from this intercrop system.