Acorn Weevil Species Diversity and Host Affinity in the Semi-Humid Evergreen Broad-Leaved Forests of Southwest China

Abstract

Acorn weevils critically impact forest regeneration in semi-humid evergreen broad-leaved forests (SEBFs) by parasitizing and consuming acorns before dispersal. Despite their ecological significance, research on the species diversity of acorn weevils within SEBFs remains limited. To address this gap, we assessed the species diversity and host affinity of acorn weevils across six dominant oak species at 18 locations. We performed DNA extraction and mitochondrial COI gene sequencing on weevil larvae and analyzed acorn functional traits (AFTs) from host acorns. Six acorn weevil species across four genera and two families were identified within the dominant acorns of SEBFs. Curculio dentipes showed the lowest host specificity, while Niphades castanea and Cyllorhynchites ursulus were specialist species. Notably, the species diversity of acorn weevils was significantly lower in Quercus franchetii than in others. Acorn volume and three secondary metabolite contents, including total phenols, total flavonoids, and tannins, were the primary AFTs influencing weevil species diversity. This study not only advances our comprehension of acorn weevil species diversity and their ecological interactions with oak hosts, but also provides valuable insights for the ecological management of SEBFs in southwest China.

Keywords: acorn functional traits; acorn weevils; semi-humid evergreen broad-leaved forests; species diversity.

Figure 1

Host acorn sampling site distribution and field conditions in Central Yunnan Plateau. (A) Different symbols represent various host acorn sampling sites; (B) mature acorns of Quercus schottkyana, with some detached from their cupules; (C) Castanopsis orthacantha acorns enclosed in cupules on branches; and (D) C. delavayi acorns on the ground, predominantly enclosed in their cupules.

Figure 2

Status of weevil larvae within the acorn on the verge of boring out and those remaining inside. (A) Weevil larvae in Q. schottkyana biting through the pericarp for emergence; (B) weevil larvae in L. dealbatus emerging from the cupule at the cicatrix; (C) weevil larvae within C. delavayi that have not yet bored out; and (D) weevil larvae in Q. schottkyana that have emerged simultaneously in large numbers.

Figure 3

(A) Maximum likelihood (ML) phylogenetic tree of weevils based on COI DNA barcode sequences, with Cylas formicarius as the outgroup. Circles at nodes indicate the bootstrap values with 1000 iterations. Leaf node labels denote “larva/adult-host acorn-collection site-sample number”. Different colours denote weevil samples grouped by species. (B) Feeding relationships between host acorns and acorn weevils, with links indicating the presence of weevil species within specific acorns. Link width represents the number of weevils sampled per acorn species. The numbers in upper half circle indicate individual counts per weevil species; lower half numbers indicate counts per acorn species. (C) Species richness of acorn weevils plotted against acorn number using a sparse curve.

Figure 4

Sparse extrapolation curves show species diversity of acorn weevils in dominant acorns within SEBFs. Curves are plotted against sample number, with shaded areas indicating the 95% confidence intervals. Overlapping confidence intervals suggest no statistically significant differences in diversity indices among the species. (A–C) represent species richness, Shannon–Wiener diversity, and Simpson diversity, respectively.

Figure 5

Canonical correspondence analysis (CCA) of AFTs of host acorns and species diversity of acorn weevils, including (A) the CCA plot and (B) the explanatory power of functional traits to species diversity of acorn weevils. In the CCA plot, different coloured points represent distinct host acorns, arrows from the origin indicate various acorn traits, and red arrows highlight significant trait factors in explaining weevil diversity. Traits marked with an asterisk in the bar graph indicate statistically significant differences.