Top-down and bottom-up regulation of codling moth populations in cider apple orchards

Abstract

The success of biological control by natural enemies in agricultural crops relies on an understanding of the trophic interactions between natural enemies, pests and host plants. Top-down and bottom-up trophic effects, together with potential landscape and local-scale factors, may regulate pest populations. For two years, we analyzed codling moth populations (Cydia pomonella), their crop damage and their parasitoid communities in 26 low-input cider apple orchards in northern Spain. Codling moth abundance was estimated from overwintering larvae sampled with cardboard traps on trees, parasitism was estimated from parasitoids emerged from lab-reared moth larvae, and pest damage was assessed in apples before ripening. Codling moth abundance differed between orchards across years, and was positively correlated with apple production and the cover of apple plantations in the surrounding landscape. The effects of the apple production on codling moth abundance suggest bottom-up pest regulation. Apple damage in individual orchards reached 71%, but decreased with apple production, indicating codling moth satiation. Seven parasitoid species were recorded on codling moth larvae. Parasitism rate in individual orchards reached 42.5% of codling moth larvae. The number of parasitized larvae per orchard was positively related to parasitoid richness, but also to codling moth abundance, suggesting simultaneous top-down and bottom-up effects between parasitoids and pest. This study highlights the need to tackle the whole parasitoid-pest-plant system in order to better manage codling moth damage in orchards. The conservation of complementary parasitoid species through biodiversity-friendly actions should be combined with the control of apple production at the orchard- and landscape scale.