RIVERSIDE, Calif. — An entomologist at the University of California, Riverside has received a three-year $566,000 grant from the National Science Foundation to study a group of wasps that specialize as parasitoids of ants.
John Heraty, a professor of entomology and the principal investigator of the grant, will study the eucharitid wasp genus Orasema, a specialized group of ant parasitoids (parasites that kill their host) known to attack some of the most pestiferous and invasive ants, including fire ants and the big-headed ant.
More than 200 species, most new to science, are expected to be described as part of the study, which uses both morphological and molecular approaches to understand relationships and species boundaries.
Ants are one of the most successful insect groups on the planet. Their often large, complex societies are built around feeding and nurturing the egg-laying queen and protecting their brood from a tremendous array of natural enemies.
Few insects have been able to broach these formidable defenses. Eucharitid wasps are an exception. The family is a diverse group of more than 700 species that is the only insect family known to specialize as parasitoids of the ant brood. Adult wasps circumvent host defenses by depositing their eggs away from the host into plant tissue. It is the active, minute (less than 0.1 mm) larvae of the wasp that must gain access to the ant nest, either by attaching directly to the host ants or indirectly by being carried by the ants along with their food source, such as plant nectar or insect prey. Once in the nest, the wasps feed first on the host larva and then finish their development on the host pupa.
Earlier this year, UC Riverside researchers, including Heraty, published the first large-scale study in the Proceedings of the Royal Society, B of the shared evolutionary histories of both the ants and their parasitoids. While the ants first evolved and diversified during the Cretaceous period (110-120 million years ago), their eucharitid parasitoids radiated much later during the Eocene, about 40 million years ago.
"After a few critical host shifts early in their evolution, eucharitids tended to maintain their host affinity even after multiple dispersals between the Eastern and Western Hemispheres," Heraty said.
He explained that two major groups, including Orasema, potentially underwent a single radiation from Asia into North America and ultimately the tropics of South America approximately 20 million years ago.
"This radiation was followed by several important host shifts to novel ant genera, extreme diversification of species, and colonization of both desert and tropical forests," Heraty said. "Researchers hope that by thoroughly understanding the pattern of host ant and host plant associations, the biology and radiation of morphologically cryptic species, and within-nest biology, that they can better understand how these wasps can be used as effective biological control agents of pest ants."
Heraty received his doctoral degree in entomology from Texas A&M University, and was a postdoctoral researcher at the Canadian National Insect Collection and the Smithsonian Institution. He has spent more than 30 years researching Eucharitidae and other members of the parasitic wasp superfamily Chalcidoidea, which have more than 500,000 estimated species and may be the most diverse group of organisms on the planet.
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