Abstract:

Aims: Biodiversity in urban ecosystem is a prominent topic in scientific research. Many studies have documented urban biodiversity, but changes in species interactions within these ecosystems remain unclear. Our research aims to elucidate the effects of different types of urban green spaces on the diversity of Drosophilidae species and their parasitoids, as well as their interactions. This understanding is significant for the effective management and planning of urban green spaces and the conservation of urban biodiversity.

Methods: From August to October 2023, we collected Drosophilidae species and their parasitoids from park green spaces, residential green spaces, and road green spaces in Xianlin university town in Nanjing using trap bottles baited with bananas. Insect identification was guided by taxonomic monographs, and α-diversity was evaluated using the Shannon-Wiener diversity index, Pielou evenness index, and Simpson diversity index. Additionally, we collected Drosophilidae pupae and measured parasitism rates by counting the number of emerged parasitoids.

Results: A total of 2,228 Drosophilidae adults belonging to five species across two genera were collected from three types of green spaces. Four of these species preferred rotten fruits. Drosophila melanogaster was the most abundant species, accounting for 82.9% of the total. More Drosophilidae adults were trapped in residential green spaces than in park green spaces or road green spaces, whereas D. suzukii, which preferred fresh fruits, was not found in road green spaces. The species composition of Drosophilidae varied significantly among the green spaces. α-diversity analyses showed that diversity indices were higher in park green spaces than in residential green spaces, with the Shannon-Wiener diversity index significantly higher in park green spaces compared to road green spaces. Additionally, only 23 adult parasitoids were collected, including 15 Pachycrepoideus vindemiaeand 8 Trichopria drosophilae, the dominant parasitoid enemies of Drosophilidae species in the study area. We found 334 parasitoids that emerged from Drosophilidae pupae, with road green spaces having the lowest parasitism rate at an average of 22.7%. Trichopria drosophilaeaccounted for 6.7% of the total, which was significantly lower than in residential green spaces. This could be attributed to the scarcity of T. drosophilae, which has higher host exploration efficiency, as well as temperature fluctuations and restricted host availability that limit its survival.

Conclusions: Our study found that the diversity of Drosophilidae species and the parasitism rate vary across different urban green spaces, revealing the interactions between hosts and parasitoids in urban ecosystems. The decrease in parasitoid diversity may be a key factor contributing to the weakening of the top-down effect. These results enhance our understanding of how biodiversity and ecosystem functions change in urban ecosystem and could provide theoretical guidance for the management of urban green spaces and the conservation of species diversity.

Key words: Drosophilidae, parasitoid wasp, urbanization, top-down effect, ecosystem function