Meeting Abstract
Studies have shown that organically farmed fields promote natural predator populations and often have lower pest populations than conventional fields, due to a combination of increased predation pressure and greater plant resistance to pest damage. It is unknown how pest populations and predator efficacy may respond in these farming systems as global temperatures continue to rise. To test this, we placed in eight alfalfa fields, four having been conventionally farmed and four organically farmed for 25 years. We stocked cages with pea aphids (Acyrthosiphon pisum) and one of three predator treatments (0, 2, or 4 of the ladybeetle Hippodamia convergens). Half of the cages per field were then either left at ambient temperature or plastic-wrapped to warm them by 2°C. Aphid abundances were similar in conventional and organic fields under ambient conditions, but were significantly higher in conventional than in organic fields when cages were warmed. Predator efficacy was reduced under low predator abundance (H. convergens = 2) in conventional fields under warming conditions; predation strength in organic fields was unaffected by warming. Our study suggests that organic fields may be more tolerant to global warming than their conventionally farmed counterparts, in terms of both pest populations and predator-prey dynamics.
