How Aphids Choose Leaves: The Roles of Phenolics in Host Selection by a Galling Aphid

Abstract

The aphid Pemphigus betae does not induce galls at random on leaves of its host plant, Populus angustifolia (narrowleaf cottonwood). Probability of stem mother success in forming a gall, body mass of stem mother and progeny, number of progeny, development rate of progeny to maturity and numbers of embryos in mature progeny are all correlated positively with leaf size at maturity. Leaf size at maturity is predictable from leaf position in the shoot at bud burst (Whitham 1978, 1980). The major secondary compounds of the host plant are known phenol glycosides. Using the Folin Denis assay for total phenol determination, a strong inverse correlation has been established between the concentration of total phenols and suitability of a tree, leaf, or leaf section for galling at the time of bud burst, when the colonizing stem mothers are at the peak of their activity. Expanding leaves within the same shoot have different phenol concentrations; the potentially largest leaves have lower phenol levels. Leaves containing one or more incipient galls have lower phenols levels than leaves without galls. Phenol concentrations in leaves are not uniform; the existence of phenol gradients in leaves is demonstrated. In a comparison between two neighboring trees that are differentially infested with colonizing aphids, the tree with the higher aphid numbers per leaf has lower phenol levels in its leaves. These same leaves were shown to posses different average phenol gradients, suggesting that phenol gradients play a role in microhabitat selection. These findings are consistent with the known biology and territorial behavior of the aphid and provide a chemical basis for continuing studies on aphid habitat selection and fitness.

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

“…phenols, tannins and monoterpenes) within their host plants, especially for galling insects (Mitchell & Paul 1974;Tija & Houston 1975;Zucker 1982;Haukioja, Niemelä & Sirén 1985;Waring & Price 1990;Bryant et al 1993). The only support the present study gives to the prediction that insect performance is inversely correlated to the foliar content of secondary chemicals is that (1) the total monoterpene content of spring foliage was negatively correlated to the number of galls per shoot on whorl 5 in 1994 and (2) the Mg content of foliage was positively correlated to gall density on whorls 2, 4 and 6 and to galling success on whorl 5.…”

“…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.…”

“…However, a few studies on galling insects have reported a negative or lack of relationship between insect performance and plant growth (Carrow & Graham 1968 Influence of tree growth rate, shoot size and foliar chemistry on the abundance and performance of a galling adelgid 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.…”

RESISTANCE OF EUCALYPTUS MARGINATA TO PERTHIDA GLYPHOPA (LEPIDOPTERA: INCURVARIIDAE)

“…This is indicated by the near absence of eggs in tree 12 of Gold Gully, which through the lack of tannins either fails to attract or repels the females. In contrast, aphids associated with cottonwood (Populus angustifolia James), seek individuals with a lower content of tannins (Zucker 1982). Differences in tannin concentration may also exist in jarrah.…”

Leaves Material Decomposition from Leguminous Trees in an Enriched Fallow

“…Also, polyphenol can serve as a carbon substrate for decomposers (Mafongoya et al 1998) but in general they inhibit the growth or function of decomposers and the other organisms (Swift et al 1981, Zucker 1982. Defense compounds, including phenolics and terpenoids can also influence rates of litter decomposition, by means of direct inhibitor effects on saprophytic organisms (Palm and Sanchez 1991).…”