A drone-applied entomopathogen for targeting click beetles in refugia
Kabaluk, T. 2022. A drone-applied entomopathogen for targeting click beetles in refugia. Western Forum on Pest Management. October 26-28, Grand Prairie, AB.
Plain language summary
Wireworms are serious agricultural pests that are present in the soil, eating the underground parts of crops. They are difficult to control, but there may be value in controlling their adult stage: click beetles. These beetles reside in refugia - the semi-natural crop margins - and can move into the cropped are an lay eggs and sustain the wireworms. Refugia cannot be accessed with conventional farm equipment, so we conducted a field trial to see if applying the biological pesticide Metarhizium brunneum, using a drone - which would be able to access the refugia. We found that beetles receiving a M. brunneum spray from a drone would get infected and die. Furthermore, the beetles even acquired M. brunneum's lethal spores from the grass which also received the spray. Applying a pheromone (chemical which beetles use to attract each other) increased the dose of spores received by the beetles. This was likely because beetles were more active, picking up more spores from the grass.
An aqueous suspension of Metarhizium brunneum applied at a rate of 10^13 conidia/ha using a drone killed click beetles (Agriotes obscurus) in perennial ryegrass (Lolium perenne) serving as a surrogate for refugia habitat. A pre-spray application of pheromone granules in one treatment that served to agitate beetles and better expose them to spray droplets, increased beetle mortality and conidia dose. Environmental transmission of the entomopathogen was demonstrated by virtue of greater mortality and conidia acquisition of beetles released into sprayed areas 3 and 6 hours post application. This study proved the concept that a drone can be an effective vehicle for targeting pests with entomopathogens in areas not accessible by conventional farm equipment, and that pheromones can increase conidia acquisition and beetle mortality. The study also showed that click beetles can acquire a lethal dose of conidia from the environment up to 6 hours after spraying an aqueous suspension. Targeting click beetles in refugia may limit their invasion of farm fields since these beetles typically increase, sustain, or re-populate larvae in the field.