Feeding by slugs on maize imposes variable productivity costs but can induce compensatory growth under some conditions

BACKGROUND: In contrast to herbivorous insect pests, relatively little attention has been given to how terrestrial mollusks affect plant productivity. This lack of attention is problematic because in some crop-growing areas, particularly those that have adopted no-till farming practices and get ample rain, slugs are often the most challenging invertebrate pests that farmers face, but there is a poor understanding of how slug feeding on young crop plants influences their growth. To address this knowledge gap, we conducted a greenhouse experiment that exposed two different ages of young maize plants to slug and mechanical damage and then tracked their growth and development for 6 weeks. To complement our greenhouse experiment, we also analyzed legacy data of slug damage and maize productivity from three field experiments conducted over six growing seasons in no-till crop fields in central Pennsylvania, USA. RESULTS: Results from our greenhouse experiment suggested that slug and mechanical damage are largely similar but also indicated that low levels of slug damage can induce compensatory growth. Notably, some of our field research corroborated that low levels of slug feeding can positively influence maize yield, whereas other results indicated that heavier levels of slug damage can have the expected negative influence on maize yield. CONCLUSION: Our data suggest that slug damage is similar to mechanical damage and that the influence of slug feeding on maize development or productivity depends on the amount of damage received and the local growing conditions.