Temperature affects gloomy scale (Melanaspis tenebricosa) abundance on urban trees

Outbreaks of arthropod pests are more frequent and severe on trees in urban areas than trees in rural or natural areas.  Our hypothesis is that high temperatures due to the urban heat island effect drive these outbreaks by increasing pest fecundity and abundance while reducing the abundance and efficacy of natural enemies.  Gloomy scales (Melanaspsis tenebricosa) frequently outbreak on urban maple trees, reducing tree health and aesthetic value.

Our overall objective is to understand how temperature affects pests, natural enemies, and plant damage to inform development of more effective and sustainable pest management strategies.  To achieve this, we used surface temperature maps to select trees in the hottest and coolest parts of Raleigh, NC.  We visited each tree to record scale abundance, parasitism, and natural enemy community structure.  As a result, we found that gloomy scales are thirty times more abundant in the hottest parts of Raleigh compared to the coolest parts.

Red maples are among the most widely produced and planted trees in the United States.  In addition, scale insects are one of the most common and damaging pests of maples.  Global temperatures are continually increasing and urban heat islands are expanding their effects further into rural areas.  Understanding how temperature affects pest outbreaks will facilitate development of sustainable management practices and may predict the consequences of global warming on trees in natural areas.