Abstract Forest canopy cover is one of the determinants of understory microhabitats and subsequently has fundamental impacts on the diversity and occurrence of plants and animals. As a group of pest controllers that are highly sensitive to microclimate changes, solitary wasps are likely to be strongly influenced by such canopy‐induced microhabitat variations. However, the distribution patterns of solitary wasp species between open and closed‐canopy habitats in subtropical evergreen forests remain poorly understood, especially regarding the underlying ecological mechanisms and phylogenetic background. To clarify this issue, we used standardized trap nests in a subtropical evergreen forest in southern China to investigate the changes in taxonomic diversity, species composition and phylogenetic diversity of solitary wasps under two contrasting canopy habitats (i.e., open canopy vs. closed canopy). We found that wasps of Pompilidae, Vespidae and Sphecidae showed a preference for open‐canopy habitats. Anterhynchium flavomarginatum and Auplopus sp.1 used more nest tubes and constructed more brood cells in open‐canopy habitats than in closed‐canopy habitats, whereas Chalybion hainanense showed higher nest‐box‐level nesting occurrence under open than closed canopies. The number of nesting tubes and brood cells, species richness ( q = 0), Hill–Shannon diversity ( q = 1), Hill–Simpson diversity ( q = 2) and Faith's phylogenetic diversity of solitary wasps were higher in open‐canopy areas than in closed‐canopy areas. The differences in species composition and phylogenetic composition between the two contrasting canopy habitats were due to the replacement of species and phylogenetic lineages, with lower phylogenetic diversity under closed‐canopy areas. Community structure of solitary wasp was significantly associated with elevation, slope and Moran's eigenvector maps (MEM1, MEM11, MEM12). Our results highlight that open‐canopy habitats significantly enhance solitary wasp diversity. Management of canopy openness may be important for conserving animal species with different phylogenetic lineages and enhancing the diversity and stability of the solitary wasp community. Community assembly of solitary wasps in a subtropical evergreen forest is jointly influenced by environmental factors and spatial factors. These findings provide important insights into the processes underlying species coexistence and community assembly in subtropical evergreen forests.
Abstract Landscape modification driven by forest loss and fragmentation represents a pervasive threat to tropical forests and is expected to reshape biodiversity and ecosystem functioning. We investigated how forest cover and edge density relate to ant assemblage structure and whether seed removal is associated with resource size, community dominance and weighted morphological traits across Atlantic Forest fragments in northeastern Brazil. Across 16 forest fragments, we recorded 55 ant species from 32 genera, with assemblages strongly dominated by seed predators (particularly Pheidole gp. diligens sp. 3 and Pheidole radoszkowskii ) while active dispersers remained relatively rare. Forest cover was positively associated with the abundance of both incidental individuals and individuals of species with no seed‐related role, whereas functional‐group richness was not significantly associated with either forest cover or edge density. Seed removal decreased markedly with increasing seed size, with medium and large seeds showing significantly lower removal probabilities than small seeds. Seed‐removal probability increased with community dominance but decreased with increasing community‐weighted mean mandible size. While ant species richness may appear resilient to landscape change, the functional composition and dominance structure of the assemblages may shift, with consequences for ecosystem functioning. Stable species richness can mask functional reorganization, and seed removal is primarily driven by trait composition and dominance, highlighting the need to prioritize functionally important species in modified landscapes.
Fungi associated with insects can influence host physiology and behaviour in ways that enhance their own persistence, survival and overall dispersal. Using a combination of behavioural, chemical and electrophysiological assays, we demonstrate that infection of the sugarcane borer (Diatraea saccharalis) by the plant-pathogenic fungus Fusarium verticillioides affects insect sexual signalling and mating preferences. In wind tunnel assays, males were consistently oriented towards sex pheromone-related odours emitted by infected calling female moths over those from non-infected calling females. This behavioural change was not explained by differences in the rhythm of female calling behaviour, which remained consistent regardless of fungal infection. However, chemical analyses revealed that gland extract from infected females showed a small increase in the amount of Z9-16:Ald, a minor component of D. saccharalis sex pheromone. Also, infected females preferentially accepted infected males as mating partners, whereas non-infected females showed no mating preference. Taken together, these results show that the infection by a plant-pathogenic fungus alters sexual signalling and mating behaviour in the sugarcane borer, expanding our understanding of the ecological factors that influence insect sexual communication.
Forest canopies are vertically stratified habitats in which microclimate and host tissue quality vary with height. Scale insects (Hemiptera: Coccoidea) are ecologically important components of temperate forest canopies, producing honeydew exploited by bees, wasps and lepidopterans. The spatial distribution of tree scale insects thus has direct consequences for the availability of these resources but has not been described in North American hardwood forests. We quantified the abundance of three scale insect species and unidentified crawlers across upper-, middle- and lower-canopy strata of 33 sugar maple (Acer saccharum Marsh.) trees in south-central Ontario. We tested whether canopy position, tree size and year-over-year growth predicted scale abundance using per-species negative binomial generalized linear mixed-effects models (GLMMs). Scale insect communities were strongly vertically stratified, with all taxa reaching highest densities in the upper canopy. Species differed in their association with internode age: Lepidosaphes ulmi (L.) and crawlers peaked on the current year's leader, while Parthenolecanium corni (Bouch & eacute;) peaked on the prior year's internode, particularly in large-diameter trees. Tree size had no significant main effect for any taxon, though species-specific patterns emerged within canopy strata. Shoot elongation was positively associated with subsequent scale abundance across multiple canopy positions and growth stages, while radial growth was negatively associated with abundance in the upper and mid canopy. After controlling for shared habitat use, Phenacoccus acericola King, Parthenolecanium and crawlers showed positive co-variation at the branch scale; the crawler pool was most closely associated with Parthenolecanium. Within-tree habitat heterogeneity, rather than tree-level traits, drives the spatial structure of scale insect communities, with implications for the distribution of honeydew resources supporting canopy-dependent arthropods.
Abstract The evolutionary constraints on host plant preferences of herbivorous insects are a question of theoretical and practical importance. Since larvae have limited mobility, natural selection pressures should promote host plant choices by adults that optimise larval survival. Such optimal host utilisation is predicted to reinforce the evolution of specialisation. This concept is expressed and tested as the ‘preference‐performance hypothesis’ (PPH), which predicts a positive relationship between adult preference and larval performance. Through a series of choice and no‐choice experiments, the preference‐performance relationship was examined for the oligophagous tortoise beetle, Cassida rubiginosa , used for biocontrol of thistle weeds. It was hypothesised that adult host plant choices based on olfaction, final location, feeding intensity and oviposition are adaptive and reflect the optimal hosts for larval performance (survival). In accordance with the PPH, there was a positive relationship between all measures of adult preference and larval performance. Adult preference based on olfactometer experiments showed a significant but weak correlation, explaining 27.6% of the variation in larval survival. The strongest correlation was found for adult preference measured as the amount of feeding, explaining 72.5% of the variation in larval survival. Adult preference based on location at the end of the experiment showed a similarly strong correlation, explaining 69.4% of the variation in larval survival. Adult preference based on oviposition and the number of hatched larvae was moderately correlated with larval survival, explaining 46.8% and 48.7% of larval survival, respectively. While there is a significant positive relationship between preference and performance, adult host preference is only a moderate predictor of larval performance. The adult beetle showed substantial flexibility in host plant selection, and equal performance across most Cardueae hosts. This is likely due to the larvae being more sensitive to physical and chemical defences, and possibly an evolutionary lag in the host range between the life stages. Any expansion of the realised host range will be limited by the ability of the larva to adapt to suboptimal hosts.
