Impacts of timing of predation and landscape complexity on the suppression of horticultural pests in Australia

Landscape complexity has been shown to increase the ecosystem service of pest suppression, although the mechanisms responsible remain elusive. Ecological theory predicts that early predation by a few predators can result in higher pest suppression than late predation by many predators. Therefore, we tested the effects of earliness of predator impacts on the suppression of Aphis gossypii in 19 horticultural landscapes that differed in landscape complexity in the Lockyer Valley, Australia. Predator impacts were manipulated using exclusion cages on sentinel aphid populations in a factorial design: 1) early predation (only during week 1), 2) late predation (only during week 2), 3) continuous predation (during both weeks), and 4) predator exclusion control. Landscape context was quantified by mapping all habitats in a 2 km radius from focal fields. The role of habitats around focal fields as potential sources for natural enemies was assessed by sampling with sticky traps and vegetation clippings. We tested the expectations of lower aphid densities 1) when exposed to early predation, and 2) in landscapes with larger sources of predators and higher complexity. Our results will provide guidelines on landscape features that maximize pest suppression through early impacts of predators.