Tiny parasitoid flies show how early-life competition shapes adult success

In a new study published and featured in the Annals of the Entomological Society of America, researchers have discovered that the developmental struggles of young parasitoid flies can have lasting effects that echo into adulthood. Led by a team from St. Olaf College in collaboration with others from the University of Strathclyde and the University of Toronto,  the study shows that when larvae of the acoustic parasitoid fly Ormia ochracea compete for resources inside a single cricket host, the consequences include reduced survival, smaller pupae, and ultimately smaller adult flies.

These flies are no ordinary insects. Ormia ochracea is known for its remarkable ability to track sound. The females eavesdrop on the mating songs of crickets, using them to locate and infest hosts where their larvae develop internally.

“Our research shows that the number of larvae sharing a host can dramatically influence not just whether the flies survive to adulthood, but how big and possibly how fecund they become,” says co-lead author Jimena A. Dominguez, a post-baccalaureate research associate at St. Olaf. 

“It’s like the insect version of childhood nutrition. Limited resources during development can lead to stunted growth that persists for life,” added co-lead author Brendan Latham, a doctoral researcher at the University of Strathclyde. 

Using a combination of experimental parasitizations, morphometric measurements, and statistical models, the team examined how larval crowding affected survival rates, pupal size, and adult body size. They found that fewer flies survived to adulthood when two larvae shared a single host cricket, and those that did were noticeably smaller. The study also revealed that pupal size — a stage between larva and adult — was a powerful predictor of adult body size.

“These findings give us a window into how early competition and nutritional stress shape life history in parasitic insects,” says senior author Norman Lee, an associate professor of biology and director of the neuroscience program at St. Olaf. “It’s not just about who survives, it’s about how early experiences shape the adults these animals become.”

The study offers new insights into how developmental constraints can affect behavior, reproduction, and ecological success, not only in flies, but potentially in other parasitoids. The collaborative research team also underscores the value of hands-on research experiences for undergraduate students, which will serve as the future of our STEM workforce. This work was made possible through a federally funded NSF CAREER grant that provides critical opportunities for students to engage in real-world scientific discovery. 

“In a time of increasing challenges to higher education and research support, this study serves as a reminder of the broad societal benefits that come from sustained investment in scientific research and training” Lee said.“Supporting science means supporting innovation, education, and the next generation of problem-solvers.”

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