Effects of early‐season insect herbivory on subsequent pathogen infection and ant abundance on wild cotton (Gossypium hirsutum)

Abstract

Abstract Plant‐induced defences play an important role in mediating interactions between plants, insects and pathogens. Yet, the plant traits underlying these effects, the extended consequences for higher trophic levels (i.e. predators), and the implications for plant growth and reproduction have received little attention. Here, we asked whether simulated early insect leaf damage on wild cotton (Gossypium hirsutum) affected subsequent damage by insect leaf chewers and pathogenic fungi, as well as ant abundance. To address the mechanisms behind such effects, we measured plant defensive traits induced by early leaf damage to determine which inducible traits might determine the effects on plant‐associates. We also evaluated whether early damage influenced plant growth and flower production, and if such effects were mediated by subsequent insect herbivory or pathogen infection. We show that simulated early leaf damage reduced damage by subsequent leaf‐chewing insects, increased plant fungal infections, but did not affect ant abundance. Leaf defensive traits (lignins and pubescence) were significantly induced by early damage and were negatively associated with insect herbivory and infection severity, but did not account for the effects of early leaf damage on either of these subsequent attackers. In addition, ant abundance was not associated with (or accounted for) subsequent herbivory or infection, suggesting they did not confer plant protection. Finally, early leaf damage negatively affected plant growth and flower production and analyses suggested that the effect on the latter was, at least partly, mediated by increased fungal infections. Synthesis. Overall, these findings show that early herbivory determines the outcome of cotton interactions with subsequent attackers, and such effects have an impact on plant growth and flower output.