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Title: Conserving carnivorous arthropods: an example from early-season cranberry (Ericaceae) flooding

Author
item VAN ZOEREN, JANET - University Of Wisconsin
item GUEDOT, CHRISTELLE - University Of Wisconsin
item Steffan, Shawn

Submitted to: The Canadian Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2017
Publication Date: 1/18/2018
Citation: Van Zoeren, J., Guedot, C., Steffan, S.A. 2018. Conserving carnivorous arthropods: an example from early-season cranberry (Ericaceae) flooding. The Canadian Entomologist. 1-9. https://doi.org/10.4039/tce.2018.11.
DOI: https://doi.org/10.4039/tce.2018.11

Interpretive Summary: This paper reports two years of research into the commonly practiced IPM tactic of flooding cranberries in the spring. While the practice of flooding is common, the efficacy and mechanisms by which it sometimes succeeds/fails are poorly understood. The research reported here showed that generalist predators are significantly conserved during the flood, compared to non-flooded, sprayed beds. This would suggest that predation levels are higher where predator populations are greater, especially considering that their primary prey source, detritivores, was largely removed in both the Flood and Spray treatments, forcing the predators to hunt for herbivores (the pests). There was not a significant difference in pest populations between the two treatments, suggesting that predation is just one of multiple factors shaping herbivore populations. Impact: Given that spring flooding is exceedingly common in Wisconsin, this work corroborates the opinions held by many growers, that flooding is effective and equivalent to a single pre-bloom insecticide spray. Our findings support current practice, and have helped to explain why the practice often works quite well in most years, but in some years, does not provide adequate pest suppression.

Technical Abstract: Biological control plays an important role in many IPM programs, but can be disrupted by other control strategies, including chemical and cultural controls. In commercial cranberry production, a spring flood can replace an insecticide application, providing an opportunity to study the compatibility of the flood (a cultural control) with biological control. We suspect that chemical controls will tend to reduce the number of natural enemies, while the flood, through removal of detritus and detritivores, may cause generalist predators to prey-switch to consume proportionally more pest individuals. We measured the abundance of lepidopteran herbivores, detritivores, arachnids and parasitoids every week for six weeks in Wisconsin cranberry beds following either an insecticide spray or a cultural control flood. We found that detritivore populations rapidly declined in both flood and spray treatments; conversely, carnivore populations (spiders and parasitoids) were more abundant in the flooded beds than in sprayed beds. Populations of key cranberry pests were similar between flooded and sprayed beds. Our results showed that early-season flooding preserved more natural enemies than an insecticide application. This increase in natural enemy abundance may allow for greater continuity in herbivore suppression, providing a basis for long-term cranberry pest management.