Ant-exclusion to promote biological control of soft scales (Hemiptera: Coccidae) on woody landscape plants

Ant-exclusion to facilitate biocontrol by endemic natural enemies was investigated for suppressing infestations of two coccids, calico scale, Eulecanium cerasorum (Cockerell), and magnolia scale, Neolecanium cornuparvum (Thro), in landscape settings. Application of sticky bands combined with basal trunk sprays resulted in 92-100% reduction in counts of honeydew-seeking ants, mainly Formica subsericea Say, ascending large, scale-infested sugar maple (Acer saccharum Marshall) trees. Ant-exclusion was associated with increased numbers of green lacewing, mainly Chrysoperla rufilabris (Burmeister), larvae and spiders on multiple sample dates, and 54 and 69% fewer surviving scale nymphs after the first and second growing seasons. Foliar sooty mold accumulation was also significantly reduced where ants were excluded. In feeding trials, C. rufilabris larvae collected from the tree canopies consumed large numbers of settled scale nymphs. On another site, ant-exclusion led to 82% reduction in magnolia scale densities on Magnolia stellata (Siebold & Zuccarini) Maximowicz, compared with controls, after 1 yr. Nine and 10 ant species were found tending calico and magnolia scales, respectively, at landscape sites in central Kentucky, and in situ observation trials showed that many of them aggressively attack approaching lacewing larvae. Our results suggest that where ants are closely associated with soft scales on woody landscape plants, ant-exclusion has potential as a sustainable pest management strategy.