“It’s about the size of a mouse turd,” says Diana Six, Professor of Forest Entomology/Pathology at University of Montana, when describing the Mountain Pine Beetle.
Historically, the Mountain Pine Beetle contributed to a healthy forest by eliminating weakened trees, making room for new growth. Cold temperatures kept populations in check, only 20% of larvae would survive a winter.
If they are lucky or living at higher altitudes, Pine Beetles may live for up to two years; however, most beetles complete a life cycle within one year. They go through egg, larva and pupa stages beneath the bark of a tree. When summer temperatures warmed sufficiently, adults emerged in search of a new host. Females lead the charge, emitting pheromones that beckon males to follow.
Carrying a fungus in mouth pockets, it is released inside the tree when the beetles begin boring into it. The fungus grows, gathering nitrogen that supplies the beetles with needed food. A female will lay approximately 60 eggs. The fungus supplies nutrients to the growing offspring.
Fungus Kills the Tree
The fungus invades the sapwood, preventing the tree from using pitch to repel beetles. It also blocks water and nutrient transport inside the tree.
Pine Beetles are opportunists. When conditions are right, they colonize and reproduce. Now might be the beetle’s greatest moment in history.
Factors Contributing to Widespread Beetle Success:
- Managed forest landscapes – the practice of replanting only a single species
- Years of fire suppression procedures
- Climate change – low night temperatures at night don’t drop enough to kill larvae
- Forest trees weakened by years of drought 2014 – 2017
Mountain Pine Beetles have been devastating forests in Canada, trees at higher altitudes with no natural resistance. The insects aren’t picky when food source areas are depleted, they move on to another one. Ponderosa and other pines in Nevada County, stressed and weakened by drought, are feeling the bite.
Unfortunately, by the time tree needles turn red, the beetles have already settled in another host. A single besieged tree will nourish enough beetles to infect seven more. With numbers like that, they cut a wide swath through a forest quickly. Aside from keeping dead trees from becoming a hazard to humans or buildings, there is no effective method to halt or control the infestation…
Evidence of Infestation:
- Reddish dust and “boreholes”
- “Pitch tubes” resing globules the tree produced in an attempt to protect itself
- Leaves / needles turning yellow, then red
- Horizontal larvae egg galleries under the bark
- A blue-gray color in sapwood, caused by beetle introduced fungus
As disturbing as it is to see huge areas of forest turning red, a bright spot may be the survivors – genetic adaptors. These are trees that struggled in cooler, wetter conditions. The beetle blight is giving them an opportunity flourish. Mountain Pine Beetles don’t ‘see’ those trees as food.
It is too soon to tell the effects that these species will have on animal habitats, water retention, and snow packs.
“Insects are expected to be one of the first indicators of climate change in terrestrial ecosystems because they are cold blooded. Everything they do – everything – is dependent on temperature.” -Andrew Nikiforuk, author of Empire of the Beetle
Mercury News – Why tiny insects are tearing up Sierra forests
National Geographic 4/2015 – Pine Beetle Epidemic
Nature of Things with David Suzuki 8/2014 – The Beetles are Coming
University of Montana – Diana Six, Professor of Forest Entomology / Pathology
USDA – Bark Beetle Management
YubaNet – Tree Mortality in Nevada County 9/9/16
Wikipedia – Dendroctonus ponderosae
(beetle discussion with Diana Six 0-14:33)