Rose shoot sawfly
Hartigia trimaculata (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. Rose, blackberry. Reared from rose and blackberry,
and adults collected on raspberry and boysenberry; other Rubus species
probably serve as hosts (Champlain 1924, Ries 1937, Smith 1986).
Range. Distributed across southern Canada from New Brunswick
west; throughout the United States from Vermont south to Florida and Louisiana
and west to the Great Plains; and in a small area in the West around Caldwell
and Boise, Idaho (Smith 1986). Appears to be most common along Atlantic
Coast and north central United States.
Description
Adult. Elongate, slender, mostly black, wasplike sawfly (Ries
1937, Smith 1986). Head black with small, yellow spots around eye,
mandible, and molar areas. Mandibles bidentate, translucent, yellowish
with black tips and brown palpi. Antennae black with swollen beyond fourth
segment. Legs black and lightly marked with yellow on inner surface of
foretibia. Wings uniformly dark black infuscated with black veins.
Thorax black. Abdomen compressed, elongate, widened dorso-ventrally toward
apex, black with large, yellow spot laterally on fourth segment,and occasionally
a smaller spot on third or sixth segment. Saw sheath reaches only slightly
beyond tip of abdomen. Sheath narrow, not rounded
dorsally. Saw not distinctly widened at base. Females range from 12
to 14 mm long; males 10 to 17 mm long.
Larva. Pinkish white, cylindrical, somewhat S-shaped, with
slightly enlarged thorax, and abdomen terminating in short, horny projection or
prong (Middleton 1917, Smith 1986). Head pale with mandibles and other
mouthparts darkened. Thorax with three pairs of small teatlike, fleshy
legs. Fully-grown larvae are about 21 mm long.
Biology. Adults begin emerging in late April; numbers peak in
May, June, and July, and are all dead by early to mid-August (Champlain 1924,
Middlekauff 1969, Ries 1937, Smith 1986). Occasionally, the adult sawflies
can be observed flying and alighting on terminals and new shoots. Fenales
crawl downward from terminal tips along the shoot, stopping repeatedly to insert
their ovipositors into succulent tender tissue. The punctures are made at
short intervals along the stem. Several dozen punctures are often
clustered within a small area. To oviposit, females insert the eggs singly
deep in the shoot tissue. It seems likely that only one egg is laid in
most terminals. When two or more eggs are placed in a shoot, the one that
hatches first is the only one to survive. The larvae begin feeding in the
succulent terminals, which soon wilt and die; then they feed in the pith,
packing frass behind in their tunnels as they move down the stems. At
frequent intervals, the larvae girdle the insides of the stems apically to their
burrows, often causing the stems to break at that point. Fully grown
larvae make a partial opening in the stem to the outside in the fall, then spin cocoons at the basal ends of burrows and overwinter within. Pupation takes place during spring inside the
cocoons. This sawfly has one generation a year.
Injury and Damage. Although the blackish adults may be seen
flying and crawling about the succulent new growth of host plants, the earliest
indications of injury are wilting and dropping of tender terminals (Champlain
1924, Middlekauff 1969, Ries 1937, Smith 1986). Close examination reveals
ovipositor puncture marks along the shoots. Affected shoots promptly turn
brown and black and sometimes break. When infested shoots fail to break
early from the punctures, they frequently break at the girdled sites along the
stem. Infested shoots may continue to die back as the larvae burrow
further downward, repeatedly girdling the stem. Dissection reveals a
frass-packed gallery and slightly S-shaped larva. Emerging adults leave
circular exit holes in the stems. In the past, this borer has been an
economically important pest in Pennsylvania. Infested rosebushes produce
fewer flowers, and the loss of blackberry canes reduces fruit production.
Control. The infested terminal and shoot tips should be pruned
and destroyed as soon as wilting and dying are noticed (Champlain 1924).
When pruning is delayed, shoots must be cut lower to ensure that tunneling
larvae are removed. Chemical control occasionally may be needed locally
when high populations exist.
Larva(e) in rose. James Solomon,
USDA Forest Service. |
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