Abiotic constraints shape elevational distributions of Andean frog-biting midges (Corethrellidae) despite persistent host availability

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Abstract 1. Frog-biting midges (Diptera: Corethrellidae) are hematophagous insects that locate hosts by eavesdropping on anuran vocalisations, creating a close ecological link between midge and anuran assemblages. Despite this association and the distinct elevational distribution patterns of anurans worldwide, the structure and distribution of Corethrella communities along elevational gradients remain poorly documented. 2. We investigated patterns of richness, abundance, and community turnover of Corethrella along a ~3000 m elevational gradient (500–3400 m a.s.l.) in the Kosñipata Valley, southeastern Peru. Using standardised frog-call baited traps and molecular barcoding, we quantified α- and β-diversity across 200 m elevational bands. 3. A total of 196 individuals were recorded between 400 and 2250 m a.s.l., with no specimens detected above ~2250 m. Species richness of Corethrella declined non-linearly with elevation, while Shannon diversity showed no monotonic trend with elevation, instead exhibiting a non-linear pattern with local minima at intermediate elevations. β-diversity was high across the gradient and driven primarily by species turnover rather than nestedness. 4. Community composition changed markedly among elevational bands, with cluster and ordination analyses separating lowland and montane assemblages. The highest occupied band (2200–2400 m a.s.l.) contained only phylogenetically distinct species absent from lower elevations, indicating strong compositional differentiation at the upper elevation range limit. 5. These results demonstrate a sharply bounded elevational distribution and strong turnover in Corethrella communities along a tropical montane gradient. The absence of midges above ~2400 m, despite the continued presence of amphibian hosts, suggests that abiotic constraints limit their distribution. Our study highlights the role of elevation on midge communities, revealing unique mid-elevation assemblages, a pattern likely to have important implications for their associations with anurans.

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