Astonishing Diversity Found Among Wasps That Prey on Caterpillars


A tiny wasp that lays its eggs in living caterpillars belongs to one of the most astoundingly diverse groups of insects on Earth.

“It’s been estimated to have [50,000] to 60,000 species, which is about the same as all vertebrates — all fish, birds, mammals, amphibians, reptiles — which is a lot,” says University of Illinois entomology professor James Whitfield, who led the taxonomic study.

Photo by Won Young Choi

Combining ecological and genetic data with painstaking detective work of taxonomy, the researchers nearly doubled the estimated number of species reported of six very species-rich genera of parasitoid wasps.

The subfamily to which these wasps belong, Microgastrinae, gets its name from its tiny abdomen, the researchers reported today. “The wasp itself is quite small, about the size of the lead at the tip of a pencil,” they said in a University of Illinois statement.

The findings were published on the Web site of the Proceedings of the National Academy of Sciences.

All of the 2,500 wasp specimens studied were reared from caterpillars collected in Area de Conservación Guanacaste (ACG), a biological reserve in northwestern Costa Rica. “A decades-long ecological inventory of the area conducted by University of Pennsylvania ecologists Daniel Janzen and Winnie Hallwachs revealed that the wasps are extraordinarily specific to the caterpillar hosts they attack,” the scientists said.

“More than 90 percent of the wasp species were found to target only one or a very few species of caterpillar, out of more than 3,500 caterpillar species sampled in ACG. More than 70 percent of the species first identified by the taxonomists were confirmed in the genetic analysis.”wasps.jpg

A subfamily of tiny wasps that prey on caterpillars is extraordinarily diverse, researchers say.

Image courtesy of Jim Whitfield

But DNA analysis also revealed that some wasps that looked alike and were once thought to belong to a single species were actually several different species, each of which preyed on only one or two species of caterpillar hosts.

“The most extreme case of overlooked diversity is the morphospecies Apanteles leucostigmus,” the authors wrote. Genetic analysis revealed that instead of being a single species that preyed on 32 different species of related caterpillars, as was previously thought, the wasps formerly classified as A. leucostigmus could be grouped into 36 provisional species, “each attacking one or a very few closely related species of caterpillars.”

“One of the messages of this paper is that you really need all of these different kinds of data in order to tell the species apart–that just using the morphology alone, or the genetic data or the ecological information alone, isn’t enough,” Whitfield said.

“This represents microgastrine wasps reared from approximately 3,500 caterpillar species in ACG,” said Josephine Rodriguez, a doctoral student and microgastrine expert in Whitfield’s lab. “Since there are an estimated 10,000 species of caterpillars there, including many unsampled ones that mine inside leaves or live in fungi, this is just the tip of the microgastrine iceberg.”

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