The Geography of Phytochemical Races

2.3 Europe 47
humulene [100], limonene [23], longifolene [101], myrcene [39], α-pinene [21],
ß- pinene [22], sabinene [92], and tricyclene [102]. Resin acids were determined to be
abietic [103] and other related diterpene acids.
Resin acids have been shown to be deterrents of insect herbivory in other species
[see Manninen et al. (1998) for leading references]. In the present study, activity was
highest in plant material from the southernmost provenance (Saaremaa) and decreased
toward the north. Absolute concentrations of two resin acids, sandaracopimaric and
dehydroabietic, correlated negatively with aphid performance, suggesting that they
may act as deterrents, whereas the other acids showed positive correlation suggesting
that they may in fact act as stimulants. Total terpene concentration increased toward
the north. Some interaction with insects was evident; the low terpene concentration in
seedlings from the southernmost provenance may be responsible for the lower preference
for these plants by aphids. In general, however, chemical factors appeared to be
much less signifi cant than other factors. Seedling size in particular is a better estimator
of susceptibility of Scots pine seedlings to both specialist and generalist insects.
2.3.11 Thymus (Lamiaceae)
Thymus caespitosus Brot. occurs on the northwestern Iberian Peninsula and on the
Madeiran and Azorean archipelagos. One of the Azores group is Sao Jorge, a small
island, located at ca. 38°40′N, 28°03′W, with an area of about 246 km 2 and a width
that does not exceed 10 km at any point (see Fig. 2.27 for location of Azores). The
island possesses a uniform climate and offers little in the way of environmental
extremes. It is thus of some interest that signifi cant quantitative chemical variation
Fig. 2.27 Map of Thymus sites on Sao Jorge, Azores