View or print this publication - Northern Research Station - USDA ...

THE RESISTANCE OF SCOTCH PINE TO DEFOLIATORS
V.I. GRIMALSKY
Research Institute of Forestry, Gemol, Belorussia
SUMMARY
Scotch pine, Pinus sylvestris, is the most widely distributed tree species in Eurasia. It is often damaged by several
defoliating insects: Dendrolimus pini, Panolisflammea, Bupalus piniarius, and Diprion pini. The foci of mass outbreaks of
these insects typically occur in pure pine stands on poor, dry sandy soils, and on richer soils (loamy sands and sandy loams)
depleted by long agricultural use.
Chemical analyses of needles showed that N contents are always higher in pines growing outside (i.e., on richer,
moister soils) than inside the foci of mass outbreaks. With respect to sugars, no differences were found. Larvae on trees
enclosed in gauze bags, showed a high mortality of early instars (I-III) in stands on rich, moist soils. Young larvae cause
oleoresin droplets to fbrm where they chew into needles, the mechanism Ofpine resistance to them. Such exudations are
weak from trees on poor, dry soils. Therefore, larvae can feed on them without impediment, and their mortality is low.
To monitor this resistance, the ends of living needles (about 1/3 - 1/4 their length) on live trees, were cut. After 5
minutes the clipped needles were scored as follows: 0 - oleoresin does not exudate from the needle; 1 - a thin film of
oleoresin appears on the cut, or separate tiny droplets which do not converge to a single lens; 2 - a small oleoresin lens
appears (no more than 0.5-1.0 mm thick); 3 - a larger oleoresin lens appears. The following indices of July oleoresin exudation
intensity (I) and efficiency (E) were calculated:
I = (nl+2*n2+3*n3) / N E = (n2+n3) * 100 / N
where I is a mean index of oleoresin exudation; nl, n2, n3 are number of needles with scores of 1, 2, or 3; N = total number
of investigated needles (including those scored as 0); and E = oleoresin exudation efficiency.
The relationship between mortality (M) of larvae (I-III instars) and (I) was tested using regression: M = a*I - b,
where a and b are parameters specific for each insect species. Thus, for Dendrolimus pini, M = 65.0 1 - 34.4, for Acantholyda
stellata, M = 37.3 1- 8.3, for Diprion pini, M = 66.9 1- 51.2, and for Neodiprion sertifer, M = 42.4 1 - 29.9. The r2 values for
these regressions vary from 0.53 - 0.79.
One can calculate that Scotch pine is resistant to young larvae of Neodiprion sertifer beginning at I _>1.7 and E > 70.
For other defoliators, Scotch pine is resistant at I > 1.4 and E > 40. It should be noted that July oleoresin exudation intensity
must be determined no later than 3-4 days after heavy rains when the humus layer moisture is > 6-8%, and the moisture of the
lower layers (down to 50 cm depth) is _>3-4%, and air temperature, _>10 *C.
Oieoresin exudation intensity from the needles of several pine species show that they can be divided into three
groups: (1) low oleoresin exudation intensity (Pinus banksiana, P mugo, P maritima), (2) intermediate intensity (P
sylvestris, P. pallasiana, R nigra, P strobus), or (3) high intensity (P. sibirica, P. cembra, P. pithyusa).
The connection between the oleoresin exudation intensity of various pine species and their resistance to various
defoliators is not perfect. The resistance of pine species depends also upon terpene composition of oleoresin.
Mattson, W.J., NiemeRi, R, and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle. USDA
For. Serv. Gen. Tech. Rep. NC-183, N.C. For. Exp. Sta., St. Paul, MN 55108.
263