AN OLD TWIST ON A NEW PROBLEM: INFERRING THE PALEODISTRIBUTION OF THE PARASITE CAENOCHOLAX (STREPSIPTERA: MYRMECOLACIDAE) FROM A NEW FOSSIL DISCOVERY

Many studies have examined the phylogenetic position of insect order Strepsiptera, the “twisted-winged parasites,” but few have investigated the taxon’s unique life history traits, and none have focused on the order’s biogeography. We use new fossil evidence to consider the paleodistribution of parasitic Strepsiptera genus Caenocholax in relation to those of its host taxa. The two new fossil specimens we describe represent i) new species, ii) the northernmost New World record of genus Caenocholax, iii) the oldest record of family Myrmecolacidae, iv) the first record of order Strepsiptera from the Green River Formation, and v) the only preservation of fossil Strepsiptera adults as compression fossils in shale (all 25 previously described fossil Strepsiptera adults are preserved in amber). The two new specimens (YPM 389335 and YPM 320328) are deposited at the Yale Peabody Museum of Natural History, New Haven. Jim Barkley collected both fossils from the early Eocene Green River Formation of Rio Blanco Country, Colorado.

In Caenocholax, as in all Myrmecolacidae, females parasitize Orthopteroid insects, and larval males parasitize Formicidae. These two host taxa have been documented in the region of the Green River Formation both as living insects and as Eocene fossils. Contemporary Caenocholax occur only in the neotropics and southern United States, however, and are absent in Colorado. The Green River Formation during the Eocene was likely similar in climate to the modern neotropics. Although the occurrence of hosts is ultimately necessary for the occurrence of the parasite, Eocene and modern distributions of Caenocholax and of its host taxa suggest that environmental parameters relating to climate, rather than host availability, have strongly influenced the parasite’s distribution. Research on Orthopteroid and Formicidae fossils could provide insight into whether or not the change in distribution of parasitic Caenocholax has influenced the hosts’ distribution.