Resistance to 16 diverse species of herbivorous insects within a population of goldenrod, Solidago altissima: genetic variation and heritability.

Genetic variation in resistance to 16 species of herbivorous insects was studied in 18 clones of Solidago altissima growing in an old field near Ithaca, New York, USA. Resistance to each insect, defined as the abundance of a species attacking a particular host genotype relative to other genotypes, was measured in both the natural stand and in two experimental gardens. The heritability of resistance was estimated by parent-offspring regression and sibcorrelation. The primary result was that clones differed in resistance to 15 of 16 insect species. The resistance of genotypes to these insect species remained relatively constant over the four years of the study. However, for only 10 of these resistances were the heritability estimates significantly different from zero. Thus the common assumption of plant-insect studies - that phenotypic variation in insect abundance is closely correlated with underlying genetic variation - is only conditionally true. There is heritable variation in resistance to many insects, but not all. The insects for which we observed heritable variation in plant resistance represent five different orders and several functional groups, including leaf chewers, phloem and xylem feeders, and gall formers. There was no apparent pattern between the degree of heritability of plant resistance and the destructiveness, feeding method, breadth of host range, or taxonomic group of the insects. The lack of marked heritable variation in resistance to some insects may be the result of (a) reduced variation caused by strong selection during prolonged or repeated insect outbreaks, and (b) genotype-environment interactions that obscure differences among genotypes.