Spatially Targeted Biological Control of Mile-a-Minute Weed Using Rhinoncomimus latipes (Coleoptera: Curculionidae) and an Unmanned Aircraft System.

Rhinoncomimus latipes Korotyaev is a specialist biocontrol agent of mile-a-minute weed, Persicaria perfoliata (L.) H. Gross (Caryophyllales: Polygonaceae). Currently, R. latipes is released by hand where the presence of the weed is readily detected. However, the hand-release method is not applicable to weed patches spread in hard-to-access areas. This study was conducted to develop a spatially targeted biocontrol strategy by using an unmanned aircraft system (UAS, a.k.a. drone) for the detection of P. perfoliata and aerial release of R. latipes. A ground survey was performed to locate P. perfoliata patches and then a rotary-wing UAS was flown at 15 different altitudes to determine the detectability of P. perfoliata patches. We developed an insect-release system including a pod that housed R. latipes for aerial release. The pod was 3D printed with biodegradable polyvinyl alcohol (PVA), and field tests were conducted to determine the ability of R. latipes to escape the pod and assess their post-release mortality and feeding ability. The results of this study showed that P. perfoliata patches were readily detectable on the aerial images taken at ≤15 m above the ground. More than 98% of R. latipes (n = 118) successfully escaped from the pod within 24 h after aerial deployment. There were no significant (P > 0.05) effects of PVA exposure on the mortality and feeding ability of R. latipes. These results indicate that aerial detection of P. perfoliata and deployment of R. latipes for spatially targeted biological control in hard-to-access areas can be accomplished using a rotary-wing UAS.