Alligator weed (Alternanthera philoxeroides) is one of the most serious exotic noxious weeds in China, the flea beetle (Agasicles hygrophila) has been introduced as a biocontrol agent for the management of alligator weed. Recent researches have found that the flea beetle also attacks the native congener sessile joyweed (A. sessilis). However, whether and how the flea beetle integrates into food webs within recipient habitats and influences native insects remains unclear. 

In order to reveal the indirect trait-mediated non-target effect of biocontrol agent on native tortoise beetle and related mechanisms, the Invasion Ecology Group led by Prof. HUANG Wei from the Wuhan Botanical Garden of the Chinese Academy of Sciences conducted related analyses. 

According to the field survey, the tortoise beetle abundance was independent with sessile joyweed coverage, but negatively related to flea beetles abundance. In addition, non-target effect of flea beetles decreased native insect abundance on native plant according to the common garden experiment.  

The influences of flea beetle herbivory on tortoise beetle development and oviposition, and sessile joyweed metabolites were also investigated.  

Results illustrated that biocontrol agent flea beetle inhibited the native insect tortoise beetle through exploitation competition on the shared native plant sessile joyweed, and such exploitation competition was likely due to trait-mediated effects by reducing sessile joyweed nutritional value and inducing repellent volatile production. 

These findings remind that great caution should be exercised in releasing a biocontrol agent, even without significant attack on non-target.  

This research has been published in Journal of Ecology entitled "Herbivory of a biocontrol agent on a native plant causes an indirect trait-mediated non-target effect on a native insect".     

This work was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Natural Science Foundation of Hubei Province and the Application Foundation Frontier Project of Wuhan.  

Herbivory of flea beetle on sessile joyweed causes an indirect trait-mediated non-target effect on tortoise beetle (Image by HUANG Wei)