THE VIRGINIA PINE SAWFLY OUTBREAK 1955-1959 

No. 99 

1960 

A serious outbreak of the pine sawfly, Neodiprion 

pratti pratti (Dyar), now extends over a gross area of more 

than 14 million acres in Maryland, Virginia, and North 

Carolina. Since 1955, the approximate extent and severity 

of infestation have been determined from aerial and ground 

surveys by the U. S. Forest Service and state personnel. l 

Indications are that the outbreak will continue in 1960. 

This sawfly, commonly called the Virginia pine sawfly, 

recently was renamed by ~oss~ as a subspecies of the - N. 

pratti complex. Previously it was known as Neodiprion dyari 

Roh . 

The principal host trees are Virginia pine (Pinus 

virginiana Mill.), pitch pine (P. rigida Mill.), and shortleaf pine (P. echinata Mill.). In rare instances feeding on 

loblolly pine (P. taeda L.) has been observed. Where pitch 

pine is abundant in Maryland and northern Virginia, the sawfly favors this species for egg-laying; and adjacent Virginia pines may be only lightly infested. However, Virginia 

pine is the most generally abundant of the two hosts, and 

pure stands of it may be subjected to severe and repeated 

defoliations. Shortleaf pine appears to be the favored host 

in southern Virginia and North Carolina. 

This insect is a spring feeder and consumes only old 

foliage. Sometimes the tender bark on twigs is chewed when 

populations are high. The feeding may be masked within a 

few weeks after it is completed by the elongating shoots and 

new foliage. However, trees subjected to several years' de- 

'The data in this report were compiled from records of the U. S. Forest Service Northeastern and Southeastern Forest Experiment Stations and the Beltsville 

Forest Insect Laboratory, the Virginia Division of Forestry, and the North Carolina Forest Service. 

2~oss, H.H. The taxonomy and evolution of the sawfly genus Neodiprion. For- est Sci. 1: 196-209. 1955. 
Table 1.--Virginia pine sawfly defoliation 1955-59 (in thousand acres) 1 

.' 

'prom McIntyre, T., and Heller, R. C. The Virginia pine sawfly outbreak 1955-1959. U.S. Forest Service. (Processed, 

4 pp.). 1960. See also, the Virginia pine sawfly in 1959. A special cooperative report of the Beltsville Forest Insect 

Laboratory, North Carolina Forest Service, Virginia Division of Forestry, Northeastern Forest Experiment Station, and Southeastern Forest Experiment Station compiled by T. McIntyre and R. C. Heller. (Processed, 7 pp.). 1959. 

2 Includes all forest types and land areas where defoliation was recorded. 

3~ased on percent pine type from aerial survey or Forest Service inventory records. 

i .r. 

, Total 

GROSS ACREAGE^ 

1955 156 - - -- 170 - - -- - - - - -- 326 

1956 258 4 0 - - 86 - - - - - - -- - - 3 84 

1957 92 1 755 - - 929 4 1 - - -- -- - - 2,646 

1958 - - -- - - 2,625 333 5 0 100 - - -- 3,108 

1959 642 5,835 - - 817 5,141 365 142 1,341 4 8 14,331 

NET ACREAGE^ 

1955 15 - - -- 14 -- - - -- - - - - 29 

1956 19 4 -- 9 -- - - -- - - -- 32 

1957 129 106 -- 130 6 -- - - - - -- 371 

1958 -- -- -- 315 117 13 12 -- - - 457 

1959 77 992 - - 9 8 874 31 17 22 8 11 2,328 

t 

P3 

Year 

Light 

Maryland 

Moderate 

Maryland 

Heavy 

Virginia North 

Carolina Virginia North 

Carolina Maryland North 

Carolina Virginia 
I - - - - -7- - - - - - 

NORTH CAR LlNA 

1- --7- -- - 

NORTH CAR LlNA 

----- 7 ------ / 

NORTH CAR LlNA 

DEFOLIATION BY THE 

VIRGINIA PINE SWVFLY 

1955- 1959 

LIGHT DEFOLIATION 

MODERATE DEFOLIATION 

HEAVY DEFOLIATION 

m 

SCALE 

0 20 40 
foliation can be distinguished readily from uninfested trees 

during the summer monthsJ by the thinned-out or feathery appearance of their foliage. 

In the oldest areas of the outbreak (in Maryland) 

some mixed Virginia and pitch pine stands have withstood 3 

to 5 years of attack. Some scattered tree killing has occurred in these areas, however; and additional mortality in 

the Patuxent River drainage, where defoliation has been 

severe from the beginning of the outbreak, may be due in 

part to the sawfly. 

Life Cycle 

N. pratti pratti has just one generation a year. 

Egg-laying takes place in the fall, and the insect overwinters in the egg stage (egg surveys can be conducted from 

late fall to early spring to provide estimates of the potential degree of infestation). The eggs hatch and larval 

activity begins in April. The larvae generally canplete 

feeding by late May and drop to the ground where they form 

cocoons in the litter. The adults emerge in October and 

egg-laying is usually finished in early November. The various stages are probably a few days to a week earlier in 

North Carolina than in Maryland. 

.History Of The Outbreak 

The surveys each year were conducted within a few 

days after the cessation of larval feeding. Three broad 

classes of defoliation were distinguished: light - trace to 

25 percent of the total foliage consumes; moderate - 25 to 

75 percent; and heavy - over 75 percent. Some variation in 

the accuracy and consistency of observations no doubt occurred, because several agencies participated in the surveys 

over the 5-year period and both aerial and ground methods 

were used. However, the data given here are standardized so 

far as possible and are as accurate as the existing records 

permit. 

The estimated gross and net acreages defoliated each 

year according to the three categories are given in table 1. 

The rapid development of the outbreak is shown most graphically in the accompanying maps. From an initial gross area 

of infestation of 326,000 acres there has been an increase 

to over 14 million acres in 1959. More significantly, the 

net pine acreage defoliated has increased from an estimated 

29,000 acres in 1955 to over 2 million acres in 1959. 

--THOMAS McINTYRE 

Forest Entomologist 

Laurel (Md.) Research Center 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture