(Continued from Part 3: the fungus amungus!)
I promised “beetles” for today’s final installment of my treasure hunt series. I have some bad news and some good news.
The bad news: the day I went walkabout on the lonely road, the temperature was well below zero, the snow cover was ample and Wiarton Willie was a few days shy of dropping the “6 more weeks of winter” bomb; active beetles were in pretty short supply.
The GOOD news: in keeping with the theme of “tracking” from Parts 1 and 2 , I still found ample trace material to satisfy my Coleopteran cravings.
An important part of any forest ecosystem is its wood-boring beetles. There are many families of beetles that use trees (living or dead) as a food source, including the longhorned beetles (Cerambycidae), metallic wood-boring beetles (Buprestidae), as well as several snout beetle (Curculionidae) sub-families: bark and ambrosia beetles (Scolytinae) pinhole bark borers (Platypodinae).
The larvae of these insects feed beneath the bark, happily chewing tunnels (or “galleries”) through the tissues responsible for moving water and nutrients throughout the tree. A heavy load of wood-boring larvae can kill a tree by effectively cutting off its circulation (called “girdling”, picture below). Boring beetles can also carry fungi, viruses and other pathogens into the tree, exacerbating the injury.
Girdled tree - damage is extensive enough to kill. Several types of wood-borers have been feeding at this site.
Signs of wood-borer activity can be seen on trees year-round. These include scars left on the bark from ovipositing (egg-laying) females, exit holes from newly-formed emerging adults, and larval galleries. The frass (wood-shaving-esque poop) of some larvae can be found in the forks of branches or at the base of a tree, although many species simply pack their galleries with excrement (below). Locating these signs on dead or dying trees is a fairly simple task, as the bark often sloughs off or cracks and exposes the beetle damage beneath.
Serpentine (S-shaped) larval galleries (typical of Buprestids), packed with frass.
Round exit hole (typical of Cerambycids) - note jagged edges created by chewing action of emerging adult beetle
D-shaped exit hole (typical of some Buprestids) from same tree. I observed woodpecker damage from a considerable distance; these exit holes are ~4mm in diameter and required a closeup inspection, but the woodpecker activity was a good first hint at their presence.
Bark beetle (Scolytinae) galleries-a female beetle deposits multiple eggs along the central chamber. Each "branch" stemming from it is formed by an individual larva.
Wood-boring beetles generally attack weak or dying trees. That said, some species do feed on healthy trees; these include serious forest pests such as the introduced Emerald Ash Borer (Agrilus planipennis) and Asian Long-horned Beetle (Anoplophora glabripennis), both of which are found in Ontario. Living trees with thick, rough bark often hide signs of their injuries for several years until the damage is extensive. This can make detection particularly challenging for monitoring programs. In younger trees, or species with smooth bark, it can be easier to detect recent borer damage.
For example, (TEXT OF SHAME removed and tossed away in SHAME). (Link to PHOTO OF SHAME here.) New, random pic of multiple galleries, exit holes, etc. created by ACTUAL beetles inserted in its place:
Sub-in for PHOTO OF SHAME: real beetle damage.
Wood-boring beetle larvae are an important food source for many animals, including other insects (such as parasitic wasps) and birds, especially woodpeckers. Woodpecker feeding damage can actually be an early indication of a beetle infestation in an otherwise healthy-looking tree, and is therefore often used in forest pest surveys.
Pileated Woodpecker damage. Note small beetle exit holes on exposed trunk below.
The large gouges and piles of wood chips left by the enthusiastic boring of the Pileated Woodpecker (above) are unmistakable. However, the tidier drill-holes of some smaller woodpeckers, such as the Yellow-bellied Sapsucker, can easily be confused for beetle entry or exit holes (below). The woodpecker damage can be recognized by the neat, evenly spaced rows of holes; beetles are not quite so organized.
Yellow-bellied sapsucker damage.
If you made it this far, thanks! I think I’ll be visiting the lonely road again in the near future to see what other goodies I can find. I’ve also decided to make more time to take advantage of the wild spaces near my home. I promise to share!
White Pine Insect Fauna Reference (no longer relevant due to SHAME, but still interesting):
Saunders, W.M. 1883. Insects injurious to the White Pine. Annual Report of the Entomological Society of Ontario. pp 52-59.