Feeding Site Specificity in Frog-biting Midges (Corethrellidae)

J Insect Behav https://doi.org/10.1007/s10905-022-09807-2 Feeding Site Specificity in Frog‑biting Midges (Corethrellidae) Jonas Virgo · Thomas Eltz Received: 11 May 2022 / Revised: 1 September 2022 / Accepted: 16 October 2022 © The Author(s) 2022 Abstract Hematophagous arthropods often choose predictable feeding sites on their hosts´ body, presumably to maximize blood uptake while minimizing costs. Feeding sites can be host-specific, mediated by intrinsic host characters and/or specific preferences of the blood feeder. We investigated feeding site specificity in a community of frog-biting midges (Corethrella spp.) and frog hosts in La Gamba, Costa Rica. Midge distribution on hosts differed significantly between 12 investigated frog species, indicating that intrinsic host properties influence potential feeding sites. However, realized feeding sites were also significantly different between four investigated Corethrella morphotypes, across all hosts but also within certain shared hosts, indicating feeding site partitioning among Corethrella. We propose that the diversity of feeding sites in Corethrella-frog associations is determined by an interaction of host traits, e. g. calling site, defensive behavior or skin thickness, and midge traits, especially body size and corresponding mouthpart size/structure. Keywords Corethrellidae · host specificity · hematophagy · feeding site J. Virgo (*) · T. Eltz Department of Animal Ecology, Evolution and Biodiversity, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany e-mail: Introduction Differential feeding-site specificity has been described for a broad range of both permanent and periodic blood-sucking arthropods (see Lehane 2005). Biting often occurs on body areas that facilitate blood uptake due to certain morphological host traits, such as skin thickness and density of hairs/ feathers (e. g. Mullens and Gerhardt 1979). Bloodfeeders themselves are constrained by morphological features such as the size and structure of mouthparts (Krenn and Aspöck 2012) or adhering structures such as claws and tufts (Haarløv and Haarlov 1964). Furthermore, numerous ecological and behavioral traits on both sides may determine feeding associations, shifting the tradeoff between a minimal energetic expenditure for blood sucking and the evasion of host defenses (e. g. active repellent movements or grooming; Edman et al. 1972; Murray 1987). Here, we investigate feeding site specificity among a community of frog-biting midges (Diptera: Corethrelidae) and their frog hosts in La Gamba, Pacific Costa Rica. Female Corethrella eavesdrop on the mating calls of male frogs, their primary blood hosts (Camp and Irby 2017; McKeever and Hartberg 1977). Despite a rather generalist acoustic foraging behavior (Grafe et al. 2008; Virgo et al. 2019), midges partition among the host community by using unknown (but see da Silva and Breviglieri 2021) close-range recognition cues (Virgo et al. 2021; also see Grafe et al. 2019). Further observations indicate yet unrevealed Vol.: (0123456789) 13 J Insect Behav levels of specificity, as realized feeding sites on the host body may vary between frog species (Borkent 2008; Borkent and Grafe 2012; De Silva et al. 2014) and possibly among midge species (this paper). Based on midge catches from frog hosts collected over three years, we tested whether feeding site specificity exists in frog-biting midges and evaluated whether it is mediated by variable properties of frog hosts or variation of biting preferences among species of Corethrella, or both. Methods The data represents a subset of midges collected for a study on Corethrella host specificity at the La Gamba research station in the Golfo Dulce area, Pacific Costa Rica (Virgo et al. 2021), for which we had recorded information on feeding site (2018 to 2020). Female Corethrella spp. were collected during blood uptake from frogs with a handheld aspirator. We recorded the feeding site, differentiating between four feeding site categories: (1) nostrils, (2) head and dorsum, (3) hindlegs, and (4) toes (Fig. 1). Counts are based on the specimens collected. Note that on some occasions observed midge infestation on hosts was higher than Fig. 1  Female Corethrella spp. biting male frogs, showing differences in feeding site selection. A Corethrella spp. aggregating around the nostrils of Incilius coniferus; B Corethrella spp. aggregating in patches on head and thoracic dorsum of Smilisca phaeota; C Corethrella spp. aggregating on hind legs of Scinax boulengeri; E Corethrella spp. approaching and biting toes of Dendropsophus ebraccatus Vol:. (1234567890) 13 realized catches, as not all feeding individuals could be collected due to flight-proneness (of either host or midge). However, this appeared unrelated to any particular feeding site. Corethrella morphotypes were assigned based on morphological features, neglecting cryptic species diversity in C. ranapungens and C. amazonica/C. ramentum species groups (see Virgo et al. 2021). We took morphometric measurements for a subset of preserved midges (EtOH) using an Olympus SZX16 stereomicroscope, ColorviewIII camera and Cell^D software (Olympus Corporation, Tokio, Japan). We performed Fisher´s exact test on count data of frogs and midges to test for partitioning of hosts and feeding sites in Corethrella. We used Pearson correlation test to assess the effect of total midge catches on observed host and feeding site diversity. Statistical analyses were performed in R (R Core Team 2017). Results and Discussion We recorded feeding sites for 507 midges from 229 individual frogs (12 species of frogs; Table 1). Most midges were collected from the nostrils (54%), followed by the hindlegs (28%), the head and dorsum J Insect Behav Table 1  Distribution (total catch numbers) of frog-biting midges (Corethrella spp.) collected from frog hosts in La Gamba, Costa Rica. We categorized four distinct feeding sites: (1) Nostrils, (2) head/dorsum, (3) hindlegs, and (4) toes. *Data includes double counts for frogs attacked by multiple Corethrella spp. simultaneously; the number of individually sampled frogs was 229. Measurements (thorax + abdomen) of Corethrella spp. were taken under a dissecting microscope in EtOH on undissected specimens. The observed perch sites of calling male frogs are presented (a: aquatic, partly submerged; tg: terrestrial, ground level; te: terrestrial, elevated; **stream-associated breeder, sitting on streambed rocks) (13%), and the toes (5%). We found no significant correlation between the number of observed feeding sites per frog species and the total number of midge catches (r = 0.18, p = 0.57, t = 0.58, df = 10), or host individuals (r = 0.34, p = 0.29, t = 1.13, df = 10). The initial landing site often differed from the realized feeding site, which was then consecutively approached by walking (J. Virgo, pers. obs.). During this orientation we observed no probing with the proboscis; instead, midges (...truncated)