Paper: In a first for the state, UH Hilo researchers use drones to deliver biocontrol to fight strawberry guava in native forests; method found fast and successful

Posted on July 31, 2025November 4, 2025 by Staff

The research team found drone-based aerial deployment of a biocontrol was nearly five times faster than the current ground-based approach in native forests invaded by strawberry guava.

Olivia and Ryan in hard hats and communication gear with helicopter in background. — Researchers (from left) Olivia Jarvis and Ryan Perroy join research team for a day of aerial field work. (Photo: Spatial Data Analysis and Visualization Lab/UH Hilo)

By Susan Enright/UH Hilo Stories.

A research team based at the University of Hawaiʻi at Hilo has published a paper on their release of a biocontrol via drones and helicopter to address invasive strawberry guava that is choking native forests.

Study: Scaling up the deployment of Psidium cattleyanum biocontrol in a Tropical Forest (Journal of Economic Entomology, June 2025)
Update, new story on the study: “Drones Prove Optimal in Spreading Gall Insects to Control Invasive Trees in Hawaiʻi” (Entomology Today, Aug. 6, 2025)

“To our knowledge, this is the first time biocontrol has been released via drone in the state,” says Ryan Perroy, a professor of geography and environmental science who headed the project. Professor Perroy’s areas of expertise and research are in remote sensing, high-resolution mapping, geospatial data analysis, and aerial robotics (learn more).

Co-authors of the paper are UH Hilo Assistant Professor of Aeronautical Science Roberto Rodriguez III and alumni Olivia Jarvis who graduated from the tropical conservation and environmental science graduate program and is now an employee at Perroy’s Spatial Data Analysis and Visualization Lab, and U.S. Forest Service collaborator M Tracy Johnson.

Aerial photos and island map show areas studied. — Fig. 1. Study site locations on Hawaiʻi Island. (A) Long-term photo monitoring Site A within the Upper Waiākea Forest Reserve. (B) Pole vs. drone deployment experimental trial Site B within the Olaʻa Forest Reserve. (C) High-capacity *T. ovatus* release trial Site C via helicopter and drone. (D) Map of site locations on Hawaiʻi Island. (Image from study)

The authors of the paper published last month note it can be challenging to deploy and monitor biocontrol for invasive species, particularly in remote forest settings. They note one of the most abundant and disruptive invasive tree species in Hawaiʻi and across the Pacific is strawberry guava (Psidium cattleyanum Sabine) that takes over native vegetation and negatively impacts forest structure and ecosystem services.

Working with a Brazilian leaf-galling insect, Tectococcus ovatus Hempel (Homoptera: Eriococcidae), an approved biocontrol for strawberry guava whose use has been previously limited to ground-base dispersal, the research team’s aim was to develop and test aerial methods of deploying T. ovatus within the larger goal of landscape-scale deployment.

Images of biocontrol insects, helicopter and drones used in study. — Fig. 2. (A) *T. ovatus*-galled *Psidium cattleyanum* Sabine (strawberry guava) leaves with mature galls tied to one end of a bola. (B) Bola with *T. ovatus*-galled leaves and biodegradable flagging for increased visibility. (C) Mature gall of *T. ovatus* split open to reveal numerous eggs (yellow) and nymphal crawlers (pinkish) (photo: JB Friday). (D) Photo of the extendable pole used to deploy *T. ovatus* bolas via the ground-based method. (E) Drone photo of the extendable pole set for placement; target tree is on the left side of the photograph. (F) Photograph of the 4-unit bolas deployment system on the ground. (G) Drone in the air, red circle shows bola in mid-drop. (Image from study)

“We also investigated using very high-resolution aerial imagery to detect T. ovatus galls on infected leaves to monitor post-deployment inoculation success and quantify spread,” write the authors. “We found drone-based aerial deployment using a small 4-unit system was nearly 5 times faster than a ground-based approach in a heavily invaded lowland tropical forest setting and produced a statistically larger inoculation success rate one year after deployment, likely due to more central and higher placement within the targeted canopies.”

The team found aerial imagery to be a useful tool to determine inoculation success and quantify spatiotemporal spread.

“We also found that larger-capacity drone platforms and conventional helicopters can successfully deploy T. ovatus onto individual targeted tree canopies and that landscape-scale deployment operations are feasible using these methods,” the researchers write in their paper. “Our findings are relevant to others working to deploy and monitor biocontrol in forested ecosystems worldwide.”