Wednesday, February 25, 2015

Bugs that cost the US billions

Just completed a lecture on Pennsylvania forests today. I was surprised and I think the students were surprised to hear that PA is gaining forests and the state is now well over 60% forest.

Wilkes property in the Poconos

Yet there are threats to PA forests - not in losing forests per se but our forests are changing - and fast. The forests we had a few decades ago are not the forests we have now or will have a few decades from now.

Some perspective: if we look at Eastern Deciduous Forests on geological time scales, even recently, they have changed dramatically. During the Pleistocene, Pennsylvania would have been covered in boreal forests (spruces, birches, alders) or ice sheets across the northern half. But for the last few thousand years, the forests have been relatively stable (Askins, 2014).  Forest change naturally - even dramatically but recently the change has been rapid. Invasive insects and fungi have altered the composition of PA forests. Examples I gave today were chestnut blight (Cryphonectria parasitica) that obliterated native American chestnut (Castenea dentata) trees across the northeast US and Dutch elm disease, caused by the fungi Ophiostoma ulmi and O. novo-ulmi. More recently the woolly adelgid has been killing hemlocks and the emerald ash borer is picking up steam. There are native pests as well, such as the forest tent caterpillar (Malacosoma disstria), which is more damaging than the invasive gypsy moth (Lymatria dispar). 

Dead barkless American elm tree

I just came across this 2011 PLoS paper by Aukema and colleagues. There are 455 invasive plant-eating insects in the US and they looked at the 62 species that have economic impacts. I dig their quantitative approach using Bayesian analysis but I was floored by this statement "We considered 39 parametric families of curves [19], and reduced these to four non-redundant families with appropriate theoretic properties: the gamma, Weibull, power function and log-normal distributions."  I think I know eight or nine parametric families but there are more than thirty-nine? Jeesh. They also predicted the probability of new expensive pest invaders. Here were the major findings:

  • borers cost the most with $1.7 billion per year in local costs, $92 million in federal costs, $830 million lost in property value, and $760 million in household costs per year... PER YEAR!!
  • lots of sap feeders but they were not as costly ($14 million per yer)
  • foliage eaters cost the most for federal costs at $110 million per year
  • there's a 32% chance a more expensive wood borer than the emerald wood borer will be established in ten years
I added up all the costs (federal, local, household, lost timber, property value loss) and this amounted to just under $5 billion per year. And we will be getting more. 

Good to get a post out. 


Askins, R. A., 2014. Saving the world's deciduous forests: ecological perspectives from East Asia, North America, and Europe. Yale University Press.


  1. I am surprised not to see you reference Lumbricus, perhaps that most profoundly transformative North American invasive!

  2. Hey, that's a great idea for its own post. I was completely floored years ago when I heard a talk from Wisconsin that showed worms were more important than deer for forests dynamics. Thanks!