Attracting lady beetles for Conservation Biocontrol of Crapemyrtle Bark Scale

Crapemyrtle bark scale (CMBS) poses a huge threat to the utility of crapemyrtle trees by reducing aesthetic value due to sooty mold growth and disrupting photosynthesis. Currently, most homeowners and nursery producers rely on chemical insecticides to manage CMBS populations, but these pesticides can negatively impact natural enemies, pollinators, and the environment at large. Different management approaches are being investigated to reduce the reliance on insecticides, particularly systemic insecticides to reduce CMBS populations and damage.

When insects feed on plants, the plants emit a blend of volatile odors; ‘smell’s that are released into the air. One function of these volatile odors is to attract predators to attack the herbivores. Multiple species of lady beetles present already in landscapes are attacking CMBS as predators and have the potential for biological control of CMBS. Unfortunately, lady beetles don’t arrive until populations of CMBS are large and causing damage. What if we could attract them to trees to attack these pests before CMBS causes damage? Synthetic lures that mimic those odors to recruit lady beetles are commercially-available but have not been evaluated for CMBS in urban landscapes.  Methyl salicylate (wintergreen oil) and limonene (orange oil) are two odors used in past research to recruit lady beetles to pest-infested field crops. Our objective was to evaluate methyl salicylate and limonene lures to attract lady beetles early to attack CMBS in landscapes.  These lures were placed into infested trees and evaluated on their ability to recruit lady beetles and to reduce populations of CMBS.

We compared the abundance of lady beetles on CMBS-infested trees baited with no lures, Methyl salicylate (M), Limonene (L), or a combination of Limonene and Methyl salicylate (L+M) over 10 days. Although there was no significant difference in the abundance of lady beetles on treated trees relative to the control trees, trees baited with both lures (L+M) had the highest average abundance of 42 lady beetles, whereas the control trees without lures had an average of 34 lady beetles. This spring, a trial baiting infested trees with these lures in urban landscapes was initiated in Alabama. This study builds upon earlier results and will determine the effectiveness of this approach.

We also wanted to know if these lady beetles would reduce CMBS populations on the trees.  To do this we marked two branches on each tree and recorded the mortality of scales over time. After 10 days, we observed an 80-95% reduction in CMBS on infested trees irrespective of treatment. This study demonstrates the potential of lady beetles as biocontrol agents of CMBS.  Although we don’t yet know the best method to recruit these beneficial insects, we do know they are attracted to infested trees and can reduce CMBS populations. Further studies using visual and volatile attractants to recruit lady beetles are currently ongoing in landscapes and our findings will be shared later.