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Abstract
Increasing plant diversity in agroecosystems strengthens pest suppression yet predicting which non-crop diversity type best supports biocontrol remains challenging. Farmers often supplement non-crop diversity with managed flowers or by allowing weed persistence both of which may bolster natural enemy communities that provide biocontrol. Concurrently, natural enemy balance and biocontrol effectiveness may be compromised by dominant invasive predators co-benefitting from non-crop diversity. We examined whether flowers or weeds had stronger balancing effects on insect predator communities by surveying plants and insects on zucchini at 37 organic farms. Neither flowers nor weeds affected natural enemy evenness. Invasive red imported fire ants (Solenopsis invicta Buren) were the single significant and negative predictor of non-invasive insect predator evenness. Fire ant activity increased with floral resource availability; neither fire ants nor non-invasive predators predicted prey removal, suggesting floral diversity may not reliably predict biocontrol when invasive predators interfere with non-invasive predator community structure and function.