Abstract:

Crofton weed gall fly (Procecidochares utilis) has been used widely as a natural enemy to control the invasive plant, crofton weed (Eupatorium adenophorum), but the effectiveness and mechanisms of crofton weed gall fly in controlling and preventing the weed have not well been studied. In this paper, we surveyed parasitism of gall fly on crofton weed in ecosystems that had been damaged by crofton weed in the western Panzhihua Prefecture, Sichuan Province, Southwest China. We studied the effects of the gall fly on the growth and reproduction of crofton weed by comparing the parasitism rates of individuals and branches with different ages in different habitats. The diameter, quantity of blossom branches, capitula and seeds between parasitized and normal branches also were compared. The results showed that: 1) there were significant differences (p<0.05) in the parasitism rates based on individuals (71.67%) and branches (17.30%). There were, on average, 17.48 parasitized branches per square meter in the adult population; branches with one insect gall accounted for 92.30% of the total parasitized branches. 2) The parasitism rate of branches (20.27%) in the humid habitat was markedly higher than that in the drought habitat (p<0.05). 3) The parasitization rate of branches differed significantly among individuals of different ages. Parasitism rates of seedlings (36.36%) and one-year-old individuals (21.56%) were significantly higher (p<0.05) than older individuals (13.50%, 8.82%, and 12.16% for two-year, three-year, and four-year old individuals). 4) Crofton weed gall fly had no significant effect on the diameter of branches, quantity of blossom branches, capitula or seeds of crofton weed, suggesting that parasitism of crofton-weed gall fly would not impact the growth and reproduction of crofton weed.

Key words: Crofton weed gall fly (Procecidochares utilis), Crofton weed (Eupatorium adenophorum), Reproduction, Parasitism rate, Natural enemy