Biological control is a sustainable method of weed management because agents can establish persistent and self-dispersing populations on a landscape scale. Strategic releases are often conducted to accelerate the widespread dispersal and establishment of agents. Drones (unmanned aerial systems, UAS) could facilitate these releases, particularly in remote areas that are difficult or dangerous for humans to access. Lygodium microphyllum (Lygodiaceae), Old World climbing fern, is a damaging weed that outcompetes native plants in many habitat types in Florida. This weed often occurs in remote conservation areas accessible only by helicopter, airboat, or swamp buggy. Although the biological control agent Neomusotima conspurcatalis (Lepidoptera: Crambidae) is established and dispersing in Florida, populations are patchy and additional releases are needed, particularly in conservation areas where human access is limited. We conducted the first releases of N. conspurcatalis using a drone to test agent survival and larval transfer to field populations of L. microphyllum. In the survival experiment, 85% of individuals were recovered from the flight, flight with impact, and control treatments with no treatment differences. In the larval transfer experiment, significantly more larvae and pupae were recovered four days post-release from the drone releases than hand releases. Drone releases of N. conspurcatalis could improve the establishment and potential impact of this agent on a landscape scale. In general, drone releases in L. microphyllum and other biological control systems could help to mitigate limits of agent dispersal.

The successful establishment or failure of a new population is often attributed to propagule pressure, the combination of the number of independent introduction events, and the number of individuals released at each event. The design of optimal release strategies for biological control agents benefits from an understanding of the impact of propagule pressure on the species being released. The dispersal rate of individuals from nascent population foci can also affect establishment success. We assessed the minimum threshold for establishment and measured dispersal of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent for Dioscorea bulbifera (Dioscoreales), air potato. Replicated releases of 10, 50, and 100 adults of L. cheni were conducted on the east and west coasts of south Florida. Dispersal was measured from 19 of these sites plus 19 additional release locations in south and central Florida. Lilioceris cheni established populations from all three release sizes with no apparent influence of site location. Releases of 10, 50, and 100 adults resulted in 50%, 67%, and 85% establishment, respectively. Beetles dispersed an average of 1.41 ± 0.515 km/yr. Dispersal distance was significantly affected by the time since release but not the number of individuals released. Our results suggest that future releases of 100 individuals could be spaced several kilometres apart on the landscape to facilitate rapid colonisation of D. bulbifera infestations.