Investigation on the Reasons for Local Insects in Yunnan Feed on Invasive Eupatorium adenophorum

Some studies found that Crofton weed (Ageratina adenophora Sprengel or Eupatorium adenophorum Spreng) was eaten by local herbivores to different degree, but the cause and effect for local herbivores eating Crofton weed remain unknown. We used larvae of Prodenia litura Fabricius and Spodoptera exigua Hbner as materials, the former can eat Crofton weed and the later can not. We fed two insects using leaf discs soaked into aqueous solutions of different leaf juice concentrations of Crofton weed to measure the level of preference or aversion two insects to Crofton weed, the forage plants were Brassica oleracea L. and Lactuca sativa var. longifolia Lam.. We also tested head neurotoxin (acetylcholine) content of two insects when poisoning symptom arose in anyone after eating Crofton weed. The primary aim was to study the selectivity for two insects to Crofton weed as well as the accumulation of head acetylcholine after eating Crofton weed. The results suggested that (1) leaf weight eaten by larva of P. litura was not closely related to concentration of Crofton weed leaf juice, however, the leaf weight eaten by larva of S. exigua reduced with the increase in leaf juice concentration of Crofton weed. (2) Head acetylcholine content of S. exigua increased and there was no difference for P. litura after eating Crofton weed. These results suggest whether local herbivores attack Crofton weed or not relates to whether there is an improved detoxification mechanism in their bodies or not. In the process of co-evolution between local insects and Crofton weed, insects with an improved and perfect ability of detoxification would become enemies of Crofton weed.