Lesser peachtree borer
Synanthedon pictipes (Grote and Robinson)
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. Peach, plum, cherry, beach plum, black cherry.
Peach is the major cultivated plant host (Bobb 1969). Plum, cherry, and
other cultivated stone fruits are attacked as well (Engelhardt 1946).
Principal native wild plants attacked are cherry and plum, which may serve as an
infestation reservoir for spreading to cultivated plants (Beutenmuller
1901). Serviceberry and chestnut have also been mentioned as hosts (Beutenmuller
1901) but are questionable (Engelhardt 1946).
Range. Eastern half of Canada and the United States westward to
Minnesota in the north and eastern Texas in the south. Reported as far
west as the Rocky Mountains and Pacific Coast but doubtful (Engelhardt 1946).
Description
Adult. Black clearwing moth with a metallic sheen and whitish
yellowish markings on head, thorax, and narrow band on abdomen (Engelhardt
1946). Wings transparent and span 18 to 25 mm. Males and females
similar but male more slender with finely tufted antennae.
Egg. Small, about 0.4 by 0.6 mm, reddish brown and very hard;
chorion keeps shape after eclosion.
Larva. Newly hatched larvae small and difficult to see,
especially in bark crevices of trees (Bobb 1959). Twelve-day-old larvae
measure 2.5 to 5.0 mm long and reach 20 mm when grown (King 1914). Cocoons
are just beneath the bark or near debris around the wound (Bobb 1959).
Biology. Moths emerge over the entire growing season, peaking in
spring and early summer (Dupree 1972, King 1914, Rings 1960). Spring
broods emerge from early April until late July; summer broods emerge early July
through November (Bobb 1959). Females deposit eggs in broken bark, usually
near wounds on vigorous trees. Eggs are deposited singly, but several
female may lay large numbers of eggs in and around a wound. Eggs hatch in
about 20 days during early season but require as few as 8 days later in the
season (Bobb 1959). Larvae usually establish in bark cavities around wound
margins and may infest old uninjured trees that have rough bark. Cytospora
spp. cankers are particularly favorable for invasion (Swift 1986).
Numbers of larvae may increase rapidly in a wound and many may feed in a small
area. First-brood larvae develop in 40 to 50 days; second-brood larvae
overwinter and complete development in about 240 days (Bobb 1959). Larvae
overwinter in instars 2 through 6 (Dupree 1972). When development is
completed, larvae construct cocoons and pupate in 3 to 7 days. Depending
on the time of year, pupation requires 15 to 28 days. Two generations
develop each year in the South (Bobb 1959); one (and sometimes a partial second)
generation occurs in the North (King 1914).
Injury and Damage. Attacks are indicated by accumulation of
reddish frass, usually near wounds such as split limbs and crotches, pruning
scars, abrasions caused by machines, and winter injuries to bark (Bobb
1959). Cankers produced by the peach canker fungus are also
infested. Larvae prefer to feed on living tissue at the edge of such
injuries. Over several years, feeding can girdle the trunk or limb.
Larvae concentrate on trunks 30 to 60 cm above ground and rarely occur at
heights above 2.5 m (Rings 1960). A few larvae may be found below ground
in association with the peachtree borer (Bobb 1959). After becoming
established in a wound, larvae feed on cambium and inner bark but do not bore
into the wood. Larvae are often very active and, in large numbers, can
kill a tree or branch. Because this borer is not cannibalistic, many
survive in even small wounds, increasing the possibility of severe injury to the
tree (Bobb 1959). Pupal skins commonly protrude from the bark at infested
areas. Before the 1950's and 1960's, this moth was not considered a
problem in healthy, well-kept plantings (Bobb 1969). It was found mainly
in larger limbs where injuries provided favorable sites for attack.
However, in the past 20 to 30 years, it has gained greatly in importance by
attacking trunks from ground level to branch crotches. In Virginia, it
kills more peach trees than the peachtree borer (Bobb 1969). In Georgia,
up to 97% of the trees in some older orchards are infested (Dupree 1972).
Economic losses occur when trees die, lose scaffold branches, or are weakened by
the borers (Rings 1960). It seriously damages young trees in black cherry
seed orchards in Tennessee and North Carolina necessitating chemical control in
some areas.
Control. Cultural practices that minimize mechanical injuries
from cultivation, mowing, and harvesting reduced incidence. Diseases such
as peach canker and black knot, which result in rough, healed areas, create
infestation sites; the diseases should be controlled. Insect injury can be
minimized by properly pruning and shaping trees when limbs are small and heal
quickly (Rings 1960). Three hymenopterous paraites--Coccygomimus
annulipes (Brulle), Macrocentrus marginator (Nees) (Marsh 1979), and Venturia
nigricoxalis (Cushman) (Carlson 1979)--have been reported. It can be
effectively controlled by applying insecticides periodically during the season
to trunks and lower limbs (Bobb 1969, Rings 1960). Disruption of mating
communication with sex pheromone appears feasible.
Damage attack at old pruning scar in black cherry. James Solomon,
USDA Forest Service. |
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