UNH researchers connect structural differences in Nasonia wasps with evolution, behavior and disease

Tuesday, July 1, 2025
Holly Hoag looks at a Nasonia wasp through a microscope

Holly Hoag's undergraduate research on Nasonia wasp head structures led to the discovery of a new gland associated with courtship and mating.

What can a tiny wasp with a rather gruesome parasitic life cycle teach us about evolution, behavior and human developmental diseases? In a new paper, researchers led by and Holly Hoag at the 鶹app (UNH) suggest that it may be a lot.

Cover of Journal of Insect Science
The study was featured on the cover of
Journal of insect science.

The research team took a thorough three-dimensional look at four species of Nasonia wasps. , featured on the cover of Journal of Insect Science, describes subtle structural differences in the lower head regions between species that have important effects on courtship and mating behaviors. The findings yield insight for a much larger scope of development and disease research.

“Insects have very simple development pathways and tissues,” says Mikó. “They allow us to learn how genes contribute to basic differences in structures and behaviors in ways that are not possible in humans.”

Revealing the intricacies of the genetic interactions that lead to defects and differences in Nasonia therefore provides a key foundation for understanding them in other species, including humans. For example, Nasonia are an important model organism for craniofacial abnormalities, which are the most common human birth defects.

Courtship between parasites

Nasonia wasps lay their eggs in flies. To be more precise, females seek out the pupae — analogous to butterfly cocoons — of larval flies transforming into adults. After drilling a small hole though the tough outer layer, they inject venom and lay 20-40 small eggs. The venom stops development in the host flies, making them a better food source for the larval wasps once hatched. Thegrowing larva devour their hosts from within, then progress through their own pupal stage. The adult wasps eventually leave the host, but some species mate even before they emerge. The parasitism is so effective that Nasonia are employed as an important biocontrol for pest flies.

A wealth of resources at UNH

The newly renovated Spaulding Hall contains two extraordinary research resources. The herbarium is comprised of 235,000 plant specimens, while the insect collection houses a staggering 700,000 insects.

“The specimens have been collected over a period of 150 years, allowing us to study different insect species and figure out why they evolved the way they did,” says Mikó. “The collection also provides access to species that have since gone extinct.”

For Hoag, the collection that played a vital role in the Nasonia research also offered a rare opportunity for an undergraduate student: the ability to do original research that has led to a first-author paper. It was a long road — she began the project in the fall of 2020 — with many Zoom meetings along the way, but the work is providing tangible benefits.

“István is a wonderful mentor and has been very supportive of my interests,” she says. “Now I’ll be starting a Ph.D. program at UMass-Lowell this summer to study evolution and development in chameleons — moving up the food chain but continuing the path I began at UNH.”

Parasitic behavior aside, Nasonia are of particular interest to biologists. Their different species are quite closely related, providing an excellent model system for studying the evolution of species and the biological mechanisms driving specific behaviors.

Mikó, the collections manager of the UNH Collection of Insects and Other Arthropods, and Hoag, a 2021 UNH graduate who worked with Mikó for her senior capstone project, focused on the mating behavior of Nasonia males in conjunction with the structural features of their lower heads. Previous studies showed that differences in the lower head region of males can be used to distinguish between Nasonia species. Could those differences also be connected to variations in courtship behavior?

In general, male Nasonia are observed to initiate courtship with a sequence of “head-nods” and wing vibrations. There have also been indications that the male produces an aphrodisiac pheromone, though its composition and origin remain unknown. The female, in turn, chooses whether to signal receptivity and mate or to reject the male, ending the courtship process. The specifics of nodding intensity and duration and where courtship takes place, whether still within or outside of the host fly, depends on the Nasonia species.

The researchers used advanced three-dimensional microscopy technologies to examine the head regions in four Nasonia species — vitripennis Walker, longicornis Darling, giraulti Darling and oneida Raychoudhury et al. — to gain further insight.

Head shapes and aphrodisiacs

The research team found that the gena, the “cheek” area between the compound eye and mouth region, showed important differences between the males of different species. Also of note, they identified and characterized three glands in the head region that had not been previously described. Two of them showed no notable differences between species or sexes, but the other one, named the genomandibular gland, was either absent or so small that it was not measurable in females.

Istvan Miko and Holly Hoag
Istvan miko, holly hoag and the magnified head of a
nasonia wasp.

Accurately measuring such small structures usually requires expensive software packages to analyze the image data. Hoag used her ingenuity to create an effective, lower-cost option.

“I saw that dentists were using a free, open-source program to measure tooth volume,” says Hoag. “I was able to apply their workflow and use it for measuring the structures in Nasonia.”

Based on their findings, the researchers hypothesize that the genomandibular gland is in fact the source of the aphrodisiac pheromone. Further, they propose that the differences in courtship behaviors, lower head structures and gland size are connected and are associated with whether each species mates inside or outside of the fly host, or both. Further investigation of the specific differences between species of courtship behavior and pheromone production will yield increased knowledge of the relationship between evolution and development in the wasps as well as other species. Even humans.