Pacific flatheaded borer
Chrysobothris mali Horn
From: Solomon, J.D. 1995. Guide to insect borers of North
American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC:
U.S. Department of Agriculture, Forest Service. 735 p.
Hosts. Alder, birch, ash, ceanothus, oak, boxelder, mahogany,
maple, poplar, sycamore, willow, apple, pear, beech, elm, cotoneaster, peach,
plum, avocado, loquat, cherry, currant, fig, apricot. At least 70 species
belonging to 40 genera in 21 plant families have been reported as hosts (Burke
and Boving 1929). Sycamore, mahogany, ceanothus, and fruit and nut trees
seem particularly susceptible (Davis and others1968, Essig 1929)
Range. Widely distributed throughout western North America west
of the Rocky Mountains from California to British Columbia and Manitoba (Burke
and Boving 1929, Fisher 1942). Its economic effect are particularly felt
in California.
Description
Adult. Dark bronze to reddish copper beetle with distinct copper
spots on the elytra; 6 to 11 mm long.
Egg. About 1 mm in diameter, subcircular or disk-like, and
yellowish white (Brown and Eads 1965a). Form of egg varies with the
crevice or depression in which they are laid (Burke and Boving 1929).
Larva. Varies from yellowish white to yellow and 15 to 18 mm
long when mature. Thoracic segments--not head, as name implies--greatly
enlarged and flattened. Abdomen bent back, making larva look like hook
when exposed in feeding burrow.
Pupa. Translucent white when first formed, dark bronze near
adult emergence, and 6 to 11 mm long (Brown and Eads 1965a).
Biology. Adults emerge from April through August
but mostly in June and July. Soon after emergence, mating and egg-laying
begin (Brown and Eads 1965a). Eggs are deposited singly but may be laid
close enough together to form clusters. The eggs are usually deposited in
bark crevices or depressions (Burke and Boving 1929). During eclosion,
larva bore through the bottoms of their egg shells directly into the bark.
Most larvae reach maturity by September or October, construct pupal chambers in
the heartwood, and then molt into the last larval instar. Borers
overwinter as prepupae. Pupation occurs mid-March into June, with most
larva pupating between mid-April and mid-May. Adult emerge in the pupal
cells and chew their way to the outside. Usually, there is one generation
per year, but the life cycle may be longer at higher elevations and in its
northern range (Brown and Eads 1965a).
Injury and Damage. The first evidence of feeding is usually dark
wet spots on the bark, which may later crack slightly and expose borings (Burke
and Boving 1929). Some tree species, especially those in the genus Prunus,
show a slight flow of gum from the affected area. Little (sometimes no)
frass is ejected to the outside, but as they burrow, larvae pack it behind them
within mines. The area around and over the wound often becomes
roughened. Feeding burrows are winding, shallow mines in the inner bark
and outer wood of the tree. Mines, oval in cross section, sometimes spiral
and girdle branches or the trunks of small trees. Mines end in the outer
wood in pupal cells that open to the surface through oval exit holes.
Usually, bark over the tunnel cracks and peels, but thick bark may not
crack. Either a ridge or a depression may occur in the bark over a
tunnel. After larvae mine extensively, the bark often loosens and drops
away, leaving ugly cankerlike spots. Larval feeding may occur in any part
of the bark from the roots to the tree top; however, feeding typically occurs in
the main trunk, especially in smaller trees. The extent of damage to
the tree is related to the location in the tree of feeding sites and often to
whether or not the borers encircle and girdle the branch or trunk. This
borer is considered one of the most damaging pests of newly planted deciduous
trees. It is an important pest in nurseries, where trees may be killed or
so severly injured that their value is disminished. Also, shade, fruit,
and nut trees may be killed or disfigured. In native forests, branch
mortality is common, but the insect rarely kills an entire tree (Burke and
Boving 1929).
Control. Five species of larval parasites have been found--two
braconids, one chalcid, one ichneumonid, and one tetrastichid (Burke and Boving
1929). The chalcid Trigonura californica Rohwer is the most important
parasite, being found in 29 of 151 infestations studied. A chalcid egg
parasite has also been found, but little is known of its effectiveness. A
mite--Pediculoides ventricosus Newport--the most important predator, was
reported to destroy a high proportion of the developing brood in heavily
infested plants in California. Field observations suggest that birds remove
immature stages of the borer from infested trees. Control can be enhanced
by cultural practices that encourage vigorous, healthy plants. Young
transplanted trees can be protected by mechanical covers over the trunks.
Mechanically removing larvae is an effective control for valuable trees.
Sanitation practices include removing weakened, injured, dying, and dead trees
from the area. Chemical controls are sometimes needed to protect valuable
plantings (Davis and others 1968).
Damage. James Solomon,
USDA Forest Service. |
Damage. James Solomon,
USDA Forest Service. |
[ Contents ]
[ Previous ]
[ Next ]
[ Home ]
|
