Herbivory of a biocontrol agent on a native plant causes an indirect trait‐mediated non‐target effect on a native insect

Abstract Identifying food web linkages between biocontrol agents of invasive plants and native species is crucial for predicting indirect non‐target effects. Biocontrol insects can integrate into webs within recipient habitats influence through apparent competition (altering shared natural enemies) or density‐mediated exploitation (changing density plants). However, whether how trait‐mediated (modifying plant chemicals volatiles profiles) produce effects remains largely overlooked, despite phenotypic responses to insect herbivory being common widely documented. The flea beetle Agasicles hygrophila was introduced China management alligator weed Alternanthera philoxeroides , but it also attacks the congener sessile joyweed sessilis which may cause on tortoise Cassida piperata that feeds joyweed. Here, we examined relationships among abundances beetle, coverage in field. Then, investigated impact development oviposition, as well primary metabolites leaf volatiles. Tortoise abundance not related coverage, they were less abundant with more beetles field survey, produced fewer offspring prior damage cage experiment. inhibited by bioassays enemy‐free conditions preferred oviposit had experienced little no damage. Flea decreased foliar glucose protein, substantially changed its volatile blend. Synthesis . Our results show has major competition, rather than competition. demonstrate a new example agents. Furthermore, our indicate minor brief negative impacts might propagate higher trophic levels such strengthen increasing intensity direct effect.