Corethrella

When male túngara frogs call, not only do they risk being eaten by frog- eating bats, they also are in jeopardy of being parasitized by frog-biting midges (Diptera: Corethrella spp). Female midges use túngara frog mating calls to find and bite a calling male to obtain a blood meal to support egg production. These midges belong to a monogeneric family, Corethrellidae, of about 100 species of pantropical and subtropical flies (Borkent, 2008). Midges from this family look similar to mosquitoes, and given these similarities, these two groups were in the same family until the late 1980s when they were assigned to a separate family (Wood & Borkent, 1989). Corethrellidae is currently rec- ognized as the sister group to the phantom midges (Chaoboridae) and mosqui- toes (Culicidae).

Corethrella midges are eavesdroppers that specialize on frog mating calls and were first recognized by Sturgis McKeever (1977). Art Borkent (2008) reviewed the fossil, cladistic, and morphological evidence and suggests that midges and frogs have shared a long evolutionary history, probably at least since the Early Cretaceous. Midges are also vectors of disease. They transmit blood parasites to frogs (Johnsons et al., 1993). In túngara frogs, a new species of such blood parasites has been discovered, Trypanosoma tungarae (Pinto & Bernal, in press). Initial evidence suggests that frogs and frog-biting midges share a long evolutionary history with trypanosomes; their intricate associa- tions and interactions deserve further study.

Studies in Gamboa, Panama, revealed that at least seven species of frog- biting midges attack calling túngara frogs (Figure 5.7). Midges are abundant, and a calling túngara frog attracts an average of 142 midges in 30 minutes; on some nights, a single motivated male can attract over 500 midges in this period (Bernal et al., 2006). Once a female midge homes in on a calling male, she lands on his back and walks to the nostrils where, in this frog species, most of the midges take a blood meal. Males attract midges only while they are call- ing. Given that male túngara frogs call while floating in water, when a male stops calling, the midges do not remain in flight over the water but fly to nearby vegetation. Only those midges already on the frog continue attempting to obtain a blood meal. The midges’ dependence on the male frog’s call for localization creates bouts of midge attacks that parallel the call bouts of the male frog. [1]

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