Systematics of Eucharitidae (Hymenoptera: Chalcidoidea)

University Of California-Riverside, Riverside CA

Investigators

Abstract

Eucharitidae are one of the most diverse parasitic groups attacking eusocial insects. All eucharitid larvae are specialized parasites of ant pupae. Females deposit their eggs in plant tissue, and the active first-instar larvae are responsible for gaining transport to the ant nest. They are most common in tropical regions, but a few species occur as far north as Alaska and the Yukon. Initial results from a phylogenetic analysis of the 53 genera using 75 morphological features of adults indicate a strong correlation between the relationships of Eucharitidae and their ant hosts: 1) parasitism of Myrmicinae appears correlated with use of a thrips intermediate host to gain access to the ant brood, 2) parasitism of Ponerinae is correlated with independent larvae, and 3) parasitism of Formicinae is associated with the attraction of ants to the egg mass. Preliminary results from data collected for the D2 and D3 expansion regions of 28S rDNA show a strong correspondence with results from morphology-based analyses, but not without critical areas of conflict that need to be resolved. If strongly corroborated, molecular analyses will be used to reevaluate morphological character state coding and also to imply transformation series so that a more resolved hypothesis can be proposed for all genera based on morphology alone. Preliminary analyses suggest that Gollumiella and Akapala are key elements for establishing the polarity of behavioral changes in Eucharitidae, and emphasis will be made on obtaining new collections and biological information for these genera. If use of a thrips intermediate host is shown to be an ancestral mode for Oraseminae and Eucharitinae, this would suggest the behavior as primitive for the family and might indicate how the initial host shift to ants may have occurred. In Trigonalyoidea and Elasmus (Chalcidoidea), adaptation to parasitism of eusocial hosts may have been accomplished through a host shift from ancestors that were hyperparasitic in lepidopteran hosts to the hymenopteran predators of those Lepidoptera. If adaptation through a prey item to the predator is true for each of these groups, this general hypothesis could be applied to other parasitoids of eusocial insects. In natural or agricultural systems, Chalcidoidea are one of the most important groups controlling insect populations. With only about 20,000 of the estimated 400,000 thousand species named, and far fewer with known biology, this is a relatively unknown group. Eucharitidae are unusual within this assemblage because the genera and species are well known and they have a relatively conservative biology that corresponds with the initial analyses of relationships. As well, they show a high degree of geographic endemism that corresponds with the breakup of the southern continents approximately 40 to 70 million years ago. By providing a robust phylogenetic hypothesis using multiple methods (molecular, morphological and behavioral), we can better understand the mechanism of host shifts and the correlated increase in taxonomic diversity. A resolved phylogeny and understanding of behavioral evolution for Eucharitidae would form a model system for future comparative studies across the superfamily.