Drones target fruit tree pests in Hawaiʻi

The coconut rhinoceros beetle (CRB) is a major invasive pest that feeds on coconut palms, betelnut, Pandanus palms, banana, pineapple and sugarcane. In Hawaiʻi, with no natural enemies to this beetle, the damage to crops can be significant.

That’s where University of Hawaiʻi at Mānoa College of Tropical Agriculture and Human Resources Professor Dan Jenkins of the molecular biosciences and bioengineering department and his PhD student Mohsen Paryavi come in. Armed with a drone that looks like something borrowed from a Transformers movie set, the duo coordinated with Mike Melzer of the Department of Plant and Environmental Protection Sciences and his CRB Response team to combat the CRB.

Jenkins recently spent three days at the Hawaiʻi Country Club on Oʻahu, using the drone to shoot targeted aerial applications of an insecticide called Demon Max (cypermethrin) atop 53 coconut trees that showed signs of infestation.

Arising before dawn in order to avoid the stronger tradewinds later in the day, the team sent the drone up again and again, drenching each tree’s crown with a half-gallon of product diluted to 0.5% Demon Max.

″Most of the trees were defoliated enough that we really applied directly in the crown—in contrast to healthy trees where fronds grow straight up and occlude the crown,″ said Jenkins. ″At my discretion, I treated some highly defoliated trees with approximately half treatments.″

On the first day, 14 trees were treated and a total of 20 dying beetles were observed from the base of treated trees. On day two, 30 trees were treated and 59 dying beetles were collected at the base of treated trees. Mortalities from the previous day were cleaned up, out of concern of spreading them up the food chain. The collected beetles were placed in their own container in the quarantine facility for observation. On the last day, nine trees were treated, and 29 dying beetles were collected at the bases of these.

″One observation is that virtually all of the beetles we found were at the bases of trees that had no other vegetation or long grass at the base (approximately half of the trees), so I would think that we killed at least double what we were able to find,″ said Jenkins.

Jenkins added, ″Some trees had insect burrows/tunnels at the base of these trees and where they existed we collected a lot of beetles trying to dig further into them. We also found a lot of centipedes in this kind of habitat—possibly trying to predate on the beetles?″

For analysis and further study, Jenkins has created shapefiles showing the locations of treated trees, photos with GPS embedded in the metadata, and a 3- and 6-month timeline for revisiting the golf course.