il ' ii - Northern Research Station - USDA Forest Service

GENETIC AND ENVIRONMENTAL CONTRIBUTIONS TO VARIATION
- IN THE RESISTANCE OF PICEAABIES TO THE GALL-FORMING
ADELGID, ADELGES ABIETIS (HOMOPTERA: ADELGIDAE)
..
William J. Mattsonl, Jean Levieux2,and Dominique Piou 3
_North Central Forest Exper. Station, USDA Forest Service, Pesticide Res. Center, Michigan State University, East
Lansing, Mi: 48824
.2Department of Bietogy, University of Orleans, Orleans, France
3 Barres National Arboretum, 45290 Nogent sur Vernisson, France
Abstract.--Norway spruce, Picea abies, varies widely among individuals in its
susceptibility to the common gall-forming aphid, Adelges abietis (Homoptera:
Adelgidae), an Old World species which now has a circumtemperate, eircumboreal
distribution. We estimated the genetic and environmental contributions to this variation ,
in a polyclonal spruce plantation at the Barres National Aboretum in the southern Paris
basin of France. Aphids infested 98 percent of the clones, but infestation levels were
highly variable, ranging from an average of less than 1 to 95 galls/branch/ramet/clone.
Neither altitude nor forest region of clonal origin made a significant contribution to
. .variation in tree resistance. Instead, most of the variation was due to individual tree
genetics because broad sense heritability of resistance against A. abietis was estimated
to be 0.86. There was no consistent relationship between tree infestation by A. abietis,
and another common, co-occurring adelgid, A. laricis.
INTRODUCTION affected by the genetics of the tree can be inferred from
the fact that (a) progeny from different mother x father
The spruce gall adelgid, Adelges abietis, is one of about crosses exhibit different levels of infestation (Eidmann
52 species of primitive, aphid-like insects (Homoptera: and Eriksson 1978), (b) the distribution of insect galls
Ade!gida e) which attack conifers in the family Pinaceae per tree in plantations is not random and is highly
• (Carter 1971, Ghosh 1983). A. abietis is probably the consistent from year to year (Ewert 1967, Tjia and
• , best kn0wn and most widely distributed of these species. Houston 1975, Eidmann and Eriksson 1978, Mattson et
It has a nearly circumboreal and circumtemperate al. 1994), (c) putative resistant and susceptible trees
distribution on several species of spruce, Picea spp., on differ in their reactions to aphid stylets inserted into their
. which it completes its entire life cycle and forms bud cortex tissues (Thalenhorst 1972; Rohfritsch 1981,
characteristic pineapple-shaped galls (Rose and Lindquist 1988), and (d) and in their foliar phenolic profiles (Tjila
. 1985). North American spruces are recent hosts of A. and Houston 1975).
abietis (since thel 9th century); European and west Asian
spruces i such as Norway spruce, Picea abies, are Because so very little is known about the genetic bases of
believed to be its ancestral hosts '(Patch 1909). woody plant resistance to insects (Fritz and Simms
• 1992), we proposed to quantify the extent to which such
AS is typical for "intimate" plant-feeders such as aphids, tree-to-tree variation in aphid infestations is due to
scales, and gall-forming insects (Fritz and Price 1988, genetic or environmental factors. To make such esti-
Mattson etal. 1988), there is abundant, unequivocal mates we measured the broad sense heritability of tree
evidence showing that individual trees vary widely in resistance (H2), i.e., the proportion of the total phenotypic
, their susceptibility to A. abietis (Ewert 1967, Thalenhorst variation (Vp) (where Vp = Vg + Ve) in a trait that can be
1972, Tjia and Houston 1975, Eidmann and Eriksson attributed to total genetic variation (Vg) in the trait: H2=
i978, Rohfritsch 1981). That this variation is strongly Vg/Vp (Falconer 1989). We hypothesized that broad
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