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Flat-Headed Wood Borer
Metallic
wood-boring beetles (or flat-headed borers)(Coleoptera:
Buprestidae)
Life
History & Ecology:
Coleoptera (beetles
and weevils) is the largest order in the class Insecta. As adults, most
beetles have a hard-bodied and boat shaped,with short antennae, a dense
exoskeleton that covers and protects most of their body surface. These
are beautiful beetles with distinctive metallic colors (green, blue,
bronze, copper). Larvae are cream-colored and legless with widened,
flattened body segments just behind the heads. Consequently, when these
larvae tunnel beneath bark or into the sapwood they produce oval or
flattened tunnels in
cross section. Galleries are often winding and packed with frass.
Tunneling activities can girdle trunks and branches. Many species of
flat-headed borers occur in the state. Most are secondary invaders.
The front wings, known as elytra, are just as hard as the rest of the
exoskeleton. They fold down over the abdomen and serve as protective
covers for the large, membranous hind wings. At rest, both elytra meet
along the middle of the back, forming a straight line that is probably
the most distinctive characteristics of the order. During flight, the
elytra are held out to the sides of the body where they provide a
certain amount of aerodynamic stability.
Both larvae and
adults have strong mandibulate mouthparts. As a group, they feed on a
wide variety of diets, inhabit all terrestrial and fresh-water
environments, and exhibit a number of different life styles. Many
species are herbivores -- variously adapted to feed on the roots, stems,
leaves, or reproductive structures of their host plants. Some species
live on fungi, others burrow into plant tissues, still others excavate
tunnels in wood or under bark. Many beetles are predators. They live
in the soil or on vegetation and attack a wide variety of invertebrate
hosts. Some beetles are scavengers, feeding primarily on carrion,
fecal material, decaying wood, or other dead organic matter. There are
even a few parasitic beetles -- some are internal parasites of other
insects, some invade the nests of ants or termites, and some are
external parasites of mammals.
Distinguishing Characteristics:
- Head sunk
deepy into
thorax
and eyes unusually large.
-
Antennae
usually short and saw-toothed.
- Tarsal formula 5-5-5.
- Many species metallic or bronzed particularly on ventral surface.
- Bullet shaped with tapering posterior end.
- 2-40mm in length.
Figure 2. Larvae of round-headed borer
(left) and
flat-headed borer (right with cross sections of tunnels (above).
Examples
of f lat-headed borers include the bronze birch borer (Agrilus anxius),
uncommon in Texas because of the lack of host trees; Agrilus
species found on oak and raspberry (A. bilineatus and A.
ruficollis, respectively); f lat-headed appletree borer (Chrysobothris
femorata) and a closely related species that attacks recently
transplanted or stressed shade, pecan and fruit trees.
Figure 3. Metallic
wood-boring beetles or flat-headed
borer adults: Agrillus bilineatus (left);
flat-headed
appletree borer (right).
Bark Beetles (Coleoptera: Scolytidae)
Beetles in this group tunnel below the bark of trees
and/or into the wood. Adult beetles are small and reddish-brown to black.
Larvae are cream-colored grubs without legs. One member of this group, the
European elm bark beetle (Scolytus multistriatus), is the carrier
of Dutch elm disease. It occurs in the Texas panhandle, but is
infrequently encountered in other parts of Texas.
Ecology:
There are around 15,00 known species of Buprestidae most of which
are tropical with only 120 or so occuring in Europe.
Eggs are laid in crevices on bark and upon hatching
the larvae bore under the bark or into the wood creating a winding series of
tunnels known as a gallery. The larvae then remain in these galleries until
pupation. The larvae of some species also tunnel in herbaceous plants and
some species induce gall formation. The larvae are given the common name of
'flat-headed borers' due to their large, flat expanded
thorax.
Biology
and Habits:
The
boat-shaped adult Buprestis lineata has a metallic sheen, hence it’s
often called the “metallic” wood borer. The elytra (wing covers) usually
have brightly colored (brick red to yellow) irregular markings and roughened
ridges. The adults usually measure ½ to ¾ inch in length.
Fertilized females deposit their eggs in the cracks and crevices in the bark
of tree trunks or limbs. The legless larvae, typically cream in color, have
well-developed, flattened plates on the upper and lower surfaces on the
prothorax. The abdominal segments are small. Larval development may take
two years or more.
Larvae bore under bark and then into sapwood, and can penetrate the
heartwood. Their feeding activity creates extremely flattened galleries
(tunnels) and frass consisting of fine sawdust-like borings and pellets.
Typically, galleries under bark edges cover the outer sapwood in a
serpentine design. The walls of the galleries are a scarred with fine,
transverse lines somewhat like, but more coarse than, those in old house
borer galleries. Frass from this feeding activity is salt-and-pepper
colored. This fine frass may remain packed in the galleries even after the
wood is processed.
Upon completion of its larval development, a larva
constructs an elongated pupal chamber near the surface of the wood. The
emerging adult cuts the characteristic flattened oval exit hole, up to ¼
inch long in diameter, to escape from the wood. Emerging adults can damage
uninfested materials, such as roofing, drywall and flooring that cover
infested lumber or logs. Attack in dry wood is uncommon.
Control
Infestations are rarely recognized until the adults emerge. Since
reinfestation is minimal, remedial treatments are not normally necessary.
For the most part, economic losses are incurred before the wood is graded
and built into a structure.
Additional damage to the structure may occur when the
galleries function as water channels, capturing rainwater and channeling it
inside the wood, creating a condition conducive for decay. Seal emergence
holes to prevent water damage to wooden members.
KEEP TREES
FREE OF DISEASES BY TAKING CARE OF THEM FROM THE START.
Trees give us
so much, oxygen, shade, beauty, shelter and value to our
homes, it makes good sense to do all
we can to protect our trees from harm.
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