Influence of tree growth rate, shoot size and foliar chemistry on the abundance and performance of a galling adelgid

Abstract

Summary 1.The abundance and performance of the Eastern Spruce Gall Adelgid, Adelges abietis, was evaluated on young, open-grown trees of White Spruce, Picea glauca, whose growth rates had been increased through fertilization or decreased through root-pruning. 2. In general, gall densities were highest on control trees and on mid-crown branches. Reduced galling success on fertilized trees was largely due to higher overwintering mortality of first-generation nymphs. Foliar magnesium, total tannin and total phenol contents were positively, and nitrogen and total monoterpene contents negatively, related to gall density and/or galling success. 3. Although short shoots were more abundant, shoot length was parabolically related to gall density. There was a non-significant parabolic trend between shoot size and galling success and volume. The number and average size of A. abietis females emerging from galls were positively related to gall volume, and realized fecundity was positively correlated to female size. Consequently, fitness was approximately twice as high for nymphs colonizing intermediate-sized than small or large shoots. 4. These results do not support the plant vigour or plant stress hypotheses. The results do, however, agree with predictions of the modified plant stress hypothesis for sucking insects. It is speculated that Adelges abietis lacks the necessary resources for successful gall formation on small shoots and is unable to produce a stimulus large enough to induce gall formation on large shoots. Key-words: Adelges abietis, insect-plant interactions, parabolic plant module size-galler abundance relationship, phenols, tanninsFunctional Ecology (1999) 13, [859][860][861][862][863][864][865][866][867] 859 DeBruyn 1994;Björkman 1997). Studies examining the relationship between insect performance and plant chemistry have also reported varying results (Tija & Houston 1975;Zucker 1982;Waring & Price 1990;Hartley & Lawton 1992;Waring & Cobb 1992;Bryant et al. 1993;Hartley & Jones 1997). Nevertheless, these studies generally found a positive relationship between insect performance and plant nitrogen content, and a negative relationship to secondary compounds (e.g. total phenols, tannins and monoterpenes).This study was carried out to determine the relationship between the abundance and performance of the shoot-galling Eastern Spruce Gall Adelgid Adelges abietis (L.) and the growth rate and foliar chemistry of White Spruce, Picea glauca (Moench) Voss. Tree growth and foliar chemistry were manipulated by fertilization and root pruning. We tested the predictions that gall abundance and galler performance would be higher on fast-growing trees (Plant Vigour hypothesis) with low C/N ratios than on slowgrowing trees with high C/N ratios, as well as the alternative prediction that gall abundance and galler performance would be highest on the slowest-growing, stressed trees (Plant Stress and Modified Plant Stress hypotheses). To obtain an estimate of fitness associated with the colonization of different-sized shoots we ...

Pattern of attack of a galling insect reveals an unexpected preference-performance linkage on medium-sized resources

“…However, these results are similar to those reported by Craig et al (1999), who reported that Eurosta solidaginis (Diptera, Tephritidae) survival was highest on ramets with intermediate growth rates of Solidago altissima (Asteraceae). Our results also support the parabolic curves relationship reported by Mckinnon et al (1999) who found that Adelges abietis (Linnaeus, 1758) (Hemiptera, Adelgidae) gall abundance and density were higher on intermediate-sized trees and shoots of the white spruce Picea glauca (Moench) Voss (Pinaceae). Additionally, they speculated that A. abietis lacks the necessary resources for successful gall formation on smaller shoots and that it is unable to produce a stimulus strong enough to induce gall formation on large shoots.…”

Morphogenesis of insect-induced plant galls: facts and questions

“…Larger galls also regulate the better survival rate of inducing insects (Abrahamson et al, 1989;Rehill and Schultz, 2001;Sopow and Quiring, 2001), because they have either more of or larger nutritive cells (Hartley, 1998). Alternatively, the optimal module-size hypothesis proposes that gall-inducing insect performance will be the greatest on intermediate-sized plant modules (McKinnon et al, 1999). This is based on the understanding that galls are induced by a dose-dependent stimulus from the insect (Sopow et al, 2003), and that a critical dose mass is necessary to induce a gall increase with module size (McKinnon et al, 1999).…”

“…Alternatively, the optimal module-size hypothesis proposes that gall-inducing insect performance will be the greatest on intermediate-sized plant modules (McKinnon et al, 1999). This is based on the understanding that galls are induced by a dose-dependent stimulus from the insect (Sopow et al, 2003), and that a critical dose mass is necessary to induce a gall increase with module size (McKinnon et al, 1999). The optimal module-size hypothesis proposes that galls are easily induced on smaller plant modules.…”

Variable Effects of Plant Module Size on Abundance and Performance of Galling Insects

“…Whereas all endoparasites must be extremely finetuned to the internal environment of their host, gallers must also "take over" the development of a plant part and induce it to make a foreign structure, the gall. The growth rate or size of the plant module could influence both gall induction success (Bjorkman 1998;McKinnon et al 1999;Sopow et al 2003) as well as the fitness of juveniles in the developing gall (Craig et al 1989). The size of any particular plant part, such as a leaf, bud or shoot, varies not only among plants but also within them.…”

“…Similarly, studies with other gall insects have also reported variations in the relationships between the size of plant modules galled and the abundance or performance of gallers. Positive, negative, and parabolic relationships between plant module size and galler abundance or performance have resulted in numerous hypotheses (e.g., Bjorkman 1998;Larsson 1989;Larson and Whitham 1997;McKinnon et al 1999;Price 1991;Sopow et al 2003) that will not be discussed here.…”