Influence of groundcover substrate below urban trees on ant (Hymenoptera: Formicidae) establishment and mutualistic interactions with soft scales (Hemiptera: Coccidae)

Calico scale [Eulecanium cerasorum(Cockerell)] is a common pest of urban trees in the eastern United States. Several ant species (Hymenoptera: Formicidae) protect calico scales from natural enemies in tree canopies.  Ant-exclusion from trees can enhance scale biological control by preventing ant antagonism of scale natural enemies. Most urban trees are planted with a substrate below them such as gravel or wood mulch, and many of the ant species that protect scales in trees nest within this substrate. However, it is unclear how different substrates affect ant nesting behavior below scale infested trees. In this study we examined how the presence of wood mulch, gravel, or grass below scale-infested trees influenced ant establishment and natural enemy antagonism. We recorded calico scale nymph densities and parasitism rates on four randomly selected 30 cm twigs from the lower canopy of 40 honey locust (Gleditsia triacanthos) trees (15 with wood mulch, 13 with gravel, and 12 with grass), along with settled crawler densities and parasitism rates from two randomly selected leaves from the lower canopies. Ants specimens were collected, counted, and identified to species from tree trunks, branches and beneath trees using sticky bands, beat samples, sticky cards and vacuum samples. We counted ant mounds below trees, and quantified natural enemy abundance within each tree with a funnel beat sampler and sticky cards.  

The findings of this study will indicate how different substrates commonly used in landscaping influence ant establishment, natural enemy antagonism, and calico scale prevalence in urban trees.