Peachtree borer
Synanthedon exitiosa (Say)
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. The commercial fruit trees--peach, plum, (including prune
varieties), nectarine, cherry, apricot, and almond--as well as black
cherry. Original host plants were wild cherry and wild plum until early
settlers introduced the peach (Gossard and King 1918, Snapp and Thomson
1943). Now it is a major pest of both fruit-bearing and flowering
varieties of the genus Prunus (Russell and Stanley 1969). Although this
borer attacks several kinds of fruit and ornamental trees and shrubs, the peach
tree is its most common host (Russell and Stanley 1969).
Range. A native of the United States found in most peach-growing
areas of the United States. Occurs mainly east of the Rocky Mountains from
Canada to the Gulf of Mexico, where it is more important as an economic pest
than it is in the Rocky Mountain and Pacific Coast regions (Snapp and Thomson
1943).
Description
Adult. Bluish black clearwing moth with wingspan of 27 to 38 mm
and body length of 17 to 23 mm. Body scales of males bright steel blue;
pale yellow to white narrow banding around abdomen; forewings and hindwings
clear. In females, front wings, legs, and body, except for broad band of
orange to reddish scales on fourth abdominal segment, covered with dark
steel-blue scales; hindwings of females clear. Several color forms with
variations in wing scaling and abdominal banding exist over its range (Engelhardt
1946).
Egg. Dark to light brown, somewhat flattened, depressed or
concave on one side, with one end slightly broader than other. Eggs mesure
about 0.7 mm long, 0.5 mm wide, and 0.3 mm thick (Snapp and Thompson 1943).
Larva. Young larva, grayish white with brown head; older larva,
white or cream colored with dark brown head and sclerotized area dorsally on
prothorax and another on last segment of abdomen. Young larvae 1.5 to 1.7
mm long; mature larvae 32 to 38 mm long.
Pupa. White when first formed but soon changing to bright
brown; 19 to 24 mm long (Snapp and Thompson 1943). Protected inside frass-
or soil-coated cocoons, from which they exit for moth emergence.
Biology. Adults emerge in May to October, with peaks in early
and late summer. Moths mate soon after emergence and live on a few
days. Adult have not been observed to feed in the field (Russell and
Stanley 1969). Oviposition typically begins the day of emergence but
occasionally does not start until the second day. Females typically
deposit from 200 to 800 eggs, but a few lay more than 1,200 eggs. Eggs are
usually deposited singly in small groups, mostly on host trees adjacent to or
near the emergence site. Sometimes, eggs are laid on all parts of a tree
and occasionally on weeds, grass, debris, and bare soil around the trunk.
Most eggs, however, are laid on the lower 15 cm of the trunk and on the soil
nearby (Snapp and Thomson 1943). At 27o C, eggs hatch in about
a week. Newly hatched larvae move to the base of trees, usually near the
soil line, where they chew through the bark to the cambium. Wounds or
breaks in the bark are not needed for entry (Russell and Stanley 1969).
The peachtree borer usually has one generation per year (King and Morris 1956,
Russell and Stanley 1969) but sometimes it has two generations (Snapp and
Thomson 1943). After overwintering, larvae usually build cocoons beneath
the bark, on the trunk just below the groundline, or at the soil surface under
gum exudates. Pupation occurs inside cocoons and lasts about 3 weeks
(Russell and Stanley 1969).
Injury and Damage. Large masses of gum exudate, particles of
bark, and frass at the base of a tree are evidence of infestation. Damage
results from larvae feeding on the cambium and inner bark of the lower trunk,
usually just below the soil but sometimes just above ground. Feeding also
may injure the larger roots (Snapp and Thompson 1943). Larvae usually
attack only after trees are about 50 mm or greater in diameter (Dorn and
Auchmoody 1974). They sometimes girdle young trees (and less commonly
girdle older trees) and damage is often severe. In some areas, only one or
two borers inhabit an infested tree; in other areas, many borers may be in a
tree. Trees with old damage are more susceptible and repeated attacks and
to invasion by fungi (Russell and Stanley 1969). Occasionally the
peachtree borer has killed young black cherry trees in seed orchards in the
Allegheny and Monongahela National Forests (Dorn and Auchmoody 1974). More
recently this borer has injured trees in black cherry seed orchards in North
Carolina. It also causes minor defects in sawtimber trees.
Control. Natural enemies include the egg parasite Telenomus
quaintancei Girault (Muesebeck 1979) and the following larval hymenopterous
parasites--Macrocentrus marginator (Nees), Microbracon sanninoideae (Gahan)
(Marsh 1979), Cryptus rufovinctus Pratt, Phaeogenes ater Cresson (Carlson
1979),
Hyssopus sanninoideae (Girault), Syntomosphyrum clisiocampae (Ashmead), and
Venturia nigricoxalis (Cushman) (Burks 1979)--and the pupal dipterous parasite
Anthrax lateralis Say (Arnaud 1978). Important predators are field mice
and rate, which sometimes greately reduce populations by destroying pupae.
Other predators include ants, chrysopid larvae, spiders, moles, and skunks (Snapp
and Thompson 1943). Several insecticides effectively reduce populations
(Dorn and Auchmoody 1974, Russell and Stanley 1969, Wylie 1968).
Disruption of mating communication with synthetic pheromone has been very
effective in field trials.
Damage at the base of young peach tree. James Solomon,
USDA Forest Service. |
Damage to 1 year old tree in Thomason, Georgia. H C Ellis,
The University of Georgia. |
Adult(s) female on right, male on left. H C Ellis,
The University of Georgia. |
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