Southern pine beetles (Dendroctonus frontalis Zimmermann) and symbiotic fungi are associated with mass mortality in stands of Caribbean pine (Pinus caribaea Morelet). This study provides a 12.7-year assessment of semiochemical mediation between southern pine beetle and Caribbean pine in relation to concentrations of 4-allylanisole (estragole, methyl chavicol) and monoterpenes measured by gas chromatography–mass spectrometry in different seasons in premontane and coastal pine stands of Belize and Guatemala. Individual trees and stands with >2.5% (relative mass %) of 4-allylanisole in the xylem oleoresin exhibited significantly less beetle-induced mortality than those with <2.5%. Changes in relative levels of 4-allylanisole and monoterpenes during this study are consistent with seasonal temperature and cumulative water deficit effects and suggest bark beetle attack of P. caribaea may intensify in the future.

Monoterpenes, the major constituents of essential oils, are known for theirdiverse biological activities. This study was conducted to assess theherbicidal effect of six monoterpenes viz. (R)-carvone,1,8-cineole, cuminaldehyde, (S)-fenchone, geraniol, (S)-limonene, and (R)-linalool onbarnyardgrass under laboratory and glasshouse conditions with a view toexplore the possibility of their utilization for future weed management. Theeffect of monoterpenes on chlorophyll contents and total phenolic compoundswas also evaluated. The inhibitory effects of monoterpenes on seedgermination and seedling growth were tested at concentrations of 1, 2, 4, 6,and 8 mM. The results showed that geraniol and (R)-carvonecaused greatest reduction of seed germination with complete inhibition atthe concentrations > 2 mM. Similarly, these two compounds were the mostpotent inhibiters for root and shoot growth. In general, monoterpenes wereless effective against seed germination than seedling growth. Furthermore,the inhibition of root growth by all compounds was greater than that ofshoot growth. In foliar application treatments under glasshouse conditions,the monoterpenes reduced the fresh and dry weights, and shoot length oftwo-leaf stage barnyardgrass at concentrations of 1 and 2%. In addition, thetested monoterpenes caused phytotoxicity symptoms, mainly chlorosis andnecrosis, followed by weed death. Complete weed control was observed in thetreatments with 1 and 2% of geraniol, and 2% of cuminaldehyde. Further, areduction of chlorophyll contents and total phenolic compounds ofbarnyardgrass leaves was noticed, indicating that the monoterpenes causeadverse effect on photosynthesis and weed metabolism. Based on the resultsof this study, it can be concluded that the monoterpenes, particularlygeraniol, (R)-carvone, and cuminaldehyde, can be used aspotential natural herbicides.

Pinus halepensis and P. brutia hybridize extensively.The analysis of monoterpenoid and morphological variability of 122 pine treesat five sites showed that the within-site heterogeneity is high while theentire provenance diversity is comparable with that of a circum-Mediterraneanscale. Four morphotypes and four chemotypes were recognized. The congruencebetween morphological and monoterpenoid classification of pines was high (coefficientof contingency 89%) while thirteen family groups of genetically closelyrelated trees were found by means of a specifically designed sampling schemeof continuous classification – identification and re-sampling. Putativehybrids contributed substantially to the observed diversity and there is considerableheterogeneity between sites. Low-altitude sites, presumably susceptible tosea-level fluctuations, alluvial deposition and human influence, are in generalmore diverse at both levels of genetic complexity than inland sites. The hybridphenotypes were not merely intermediate forms of parental taxa, and in a multivariatesense they are located on a parabola in the space of morphological properties.The arrangement of hybrids in the monoterpenoid space did not reveal any clear-cutpattern except that three major composite axes can summarize 98.9%of the entire monoterpenoid variation. The observed pattern of variation wasinterpreted as a result of waves of introgressive influence of eastern P. brutia population on P. halepensis, which was caused by marinetransgressions in Pliocene and eustatic sea-level fluctuations in Pleistocene.The human influence on this introgression accelerated the process, and amplifiedthe resulted pattern, although it blurred in many instances the biogeographicroutes of germplasm mixing. Its bearing on the evolution of pines is discussed,and it was found that the ‘Eocene refugia hypothesis’ of C.I.Millar holds by analogy also in central Aegean pines.

We tested if fumigation with exogenous monoterpenes might induce thermotolerance in leaves of an oak species (Quercus suber) which does not form and emit isoprenoids. To understand if exogenous monoterpene fumigation results in internal accumulation of monoterpenes, a physical method of monoterpene extraction was used. The internal content of monoterpenes increased in concert with increasing fumigation doses. This unambiguously demonstrated acquisition of exogenous monoterpenes. We exposed fumigated Q. suber leaves to two cycles of increasing temperatures from 35 to 55°C at 5°C steps. When leaves were exposed to a low dose of exogenous monoterpenes, yielding an internal content similar to that endogenously formed in the leaves of the monoterpene-emitter Q. ilex, no clear improvement in thermotolerance was found. When leaves were exposed to a high dose of exogenous monoterpenes, yielding an internal content of about five fold the endogenous pool of Q. ilex, but comparable with the expected content following stress-induced stomatal closure, photosynthesis inhibition at high temperatures was attenuated. This effect was observed only at temperatures <45°C during the first cycle, but at all temperatures between 35 and 55°C when plants were exposed to two cycles of high temperatures. Monoterpenes were still found in the leaves of Q. suber 12 h after ending the fumigation. Monoterpenes were also found in non-fumigated leaves distant up to 45 cm from the fumigated leaves. If monoterpenes make the photosynthetic apparatus more resistant to high temperatures, the effect might not be limited to the fumigated leaves and might be persistent after fumigation.