Background and objectives: The biocontrol agent Aphidius gifuensis has widely been released and applied since 1997 to control Myzus persicae in tobacco fields of Yunnan Province, southwestern China, but its ecological effects on the local insect community and diversity have not been described. Biological control agents may effect a diversity of organisms as well as the target for control but such trophic cascades have seldom been studied. This study aimed to explore the effects of A. gifuensis on the insect community and diversity in tobacco fields after long-term release and expansion of the biocontrol agent in Yunnan Province.
Materials and methods: The effects of A. gifuensis on species composition, importance value, species richness, diversity indices and evenness index were studied for insect community samples obtained via field surveys and malaise trap collection in Yunnan Province.
Results: A total of 39 insect species and 1 spider, principally belonging to 40 families and 13 orders in tobacco fields of Yunnan Province were identified. Among these, there were 20 pests, 14 natural enemies and 6 others, constituting 50, 35 and 15% of total species sampled, respectively. Within insect communities, M. persicae, Empoasca flavescens and Drosophila melanogaster were the dominant species and Spodoptera litura, one unidentified species (Ichneumonidae), Sphex haemorrhoidalis, Vespa veutinaauraris, Aedes albopictus, A. gifuensis and Liriomyza huidobrensis were the subdominant species. From June to August, the relative density of A. gifuensis gradually increased and concomitantly the total relative density of other natural enemies exhibited a slight decline in July and marked increase in August. The relative density of M. persicae significantly increased in July and then declined precipitously in August. Moreover, the values of Simpson index, Shannon-Wiener index and Pielou index were greater than 0.50, 1.50 and 0.50, respectively, indicating high insect diversity.
Conclusion: Beneficial insects, in addition to the biocontrol agent are relatively abundant in tobacco fields of Yunnan Province, marking improvement in the local insect community diversity after a long-term release of the biocontrol agent A. gifuensis, which, by land area, constitutes one of the largest natural enemy control programs in the world.
Keywords: Aphidius gifuensis release; Tobacco; biocontrol agent; insect community; natural enemies.