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Title: Cover crop mulches influence biological control of the imported cabbageworm (Pieris rapae L., Lepidoptera: Pieridae) in cabbage

item BRYANT, ALEXANDRIA - Michigan State University
item Coudron, Thomas
item BRAINARD, DANIEL - Michigan State University
item SZENDREI, ZSOFIA - Michigan State University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2014
Publication Date: 3/24/2014
Citation: Bryant, A., Coudron, T.A., Brainard, D., Szendrei, Z. 2014. Cover crop mulches influence biological control of the imported cabbageworm (Pieris rapae L., Lepidoptera: Pieridae) in cabbage. Biological Control. 73:75-83.

Interpretive Summary: The use of cover crops is increasing in vegetable production systems to improve soil health. However, our knowledge of how cover crops affect biological control of insects is very limited. The high use of biological control in vegetable production enhances the importance of this information. This article reports the effect of different cover crops and cover crop management practices on parasitism and predation of a pest caterpillar in a cabbage production system. Our results indicated that all cover crops do not elicit the same response from insects; that rye cover crop mulch resulted in increased pest populations compared to vetch mulch or bare soil; that cover crop mulch manifested some interference with short-range host finding by parasitoids but had little effect on canopy-foraging predators; and that small natural enemies played an important role in controlling pest caterpillars on cabbage. These findings will assist vegetable producers with selecting cover crop plant species and practices so as to improve biologically-based pest insect control within their vegetable crops.

Technical Abstract: Increasing structural complexity within crop fields can provide a way to manipulate pest abundance and biological control in agroecosystems. Here, we examine the effect of cover crop mulches in cabbage on the structure and function of an insect food web, investigating the role of cover crop species, structure, and volatile cues on important interactions. We focused on the imported cabbageworm (Pieris rapae L., Lepidoptera: Pieridae), and three of its natural enemies, the spined soldier bug (Podisus maculiventris (Say), Hemiptera: Pentatomidae), the convergent lady beetle (Hippodamia convergens (Guerin), Coleoptera: Coccinellidae), and the parasitoid, Cotesia rubecula Marshall (Hymenoptera: Braconidae). We measured the abundance of these insects in a field experiment and conducted a natural enemy exclusion cage study to determine the level of biological control of the imported cabbageworm in the field. Our field experiments indicated that cover crop species, but not structure, influenced insect abundance, with significantly more imported cabbageworm and C. rubecula in rye cover crop mulch plots compared to vetch mulch or bare soil plots. In the Y-tube assays we found some evidence that the increased parasitoid abundance did not result in increased parasitism because of interference of the mulch with short-range host finding odor cues. The natural abundance of the two predators was not different among our field plots with different cover crop treatments. Mortality and parasitism of sentinel imported cabbageworm larvae was not different in field cages among the different cover crop mulch treatments, but there was a significant difference among cage types indicating that small natural enemies play an important role in the biological control of this cabbage pest.