Search

Plant allelopathy offers hope as an additional means of weed control in modern agriculture. Its mechanisms and molecular basis are not yet well understood. Research on the chemical basis for allelopathy has often been hindered by the complexity of plant and soil matrices, making it difficult to track active compounds. Recent improvements in the cost and capabilities of bench-top chromatography–mass spectrometry instruments make these tools more powerful and more widely available to assist with molecular studies conducted in today's expanding field. Such instrumental techniques are herein recommended as economically efficient means of advancing the rigor of allelopathy research and assisting the development of a better understanding of the chemical basis for the allelopathy phenomenon.

Thiarubrine A, an antimicrobial and nematocidal 1,2-dithiin polyyne has been reported to be a constituent of Aspilia leaves swallowed whole by chimpanzees. Aspilia samples were analyzed for the presence of thiarubrine A and other sulfur-containing polyynes using high-performance liquid chromatography (HPLC) and an antifungal bioassay. Thiarubrines A, B, D, and E and their corresponding thiophenes were not present in the leaves of three Aspilia species including A. mossambicensis and A. rudis, which are swallowed by chimpanzees at Mahale Mountains National Park and Gombe National Park, Tanzania. Antifungal activity, indicative of the presence of thiarubrines, was not detected in Aspilia leaf samples. Small amounts of thiarubrines A and B, and thiophenes A and B were found in A. mossambicensis roots. Analysis of three North American taxa found high concentrations of thiarubrines and thiophenes in the roots of Eriophyllum lanatum and Chaenactis douglasii, and the roots and leaves of Ambrosia chamissonis.

Studies were conducted to determine the relative effectiveness of 5β-cholestane-3,24-dione (diketone) and 5β-cholestan-3-one (monoketone) in eliciting trail following from eastern tent caterpillars,Malacosoma americanum. In Y maze tests, trails prepared from the monoketone were followed preferentially over diketone trails, even when the diketone trail was several orders of magnitude stronger. Under field conditions, colonies readily abandoned well-developed trail systems in favor of artificial trails that were established with the monoketone. Other tests in which the caterpillars selected trails prepared from the monoketone (but not the diketone) more often than their own recruitment trails indicate that the monoketone constitutes the chemical basis of recruitment communication in this insect. The study also shows that tent caterpillars are highly sensitive to small differences in the amount of monoketone in a trail and can distinguish between new and aged trails prepared from the compound.

Human pheromones play a role in regulating relationships and apparently influence partner choice and mother-infant recognition. We analyzed the chemical content of volatiles from sweat patch samples from the para-axillary and nipple-areola regions of women during pregnancy and after childbirth. Solid phase microextraction was used to extract the volatile compounds, which were then characterized and quantified by gas chromatography-mass spectrometry. During pregnancy, women developed a distinctive pattern of five volatile compounds common to the para-axillary and nipple-areola regions (1-dodecanol, 1-1'-oxybis octane, isocurcumenol, alpha-hexyl-cinnamic aldehyde, and isopropyl myristate). These compounds were absent outside pregnancy and had slightly different patterns in samples from the two body areas. Differentiation of the volatile patterns among pregnant women may help newborns to distinguish their own mothers.

It is known that human individuals show different levels of attractiveness to mosquitoes. In this study, we investigated the chemical basis for low attractiveness. We recorded behaviors of Aedes aegypti toward the hands of human volunteers and toward the volatile chemicals produced by their bodies. Some individuals, and their corresponding volatiles, elicited low upwind flight, relative attraction, and probing activity. Analyzing the components by gas chromatography coupled to electrophysiological recordings from the antennae of Aedes aegypti, enabled the location of 33 physiologically relevant compounds. The results indicated that higher levels of specific compounds may be responsible for decreased "attractiveness." In behavioral experiments, five of the compounds caused a significant reduction in upwind flight of Aedes aegypti to attractive human hands. Thus, unattractiveness of individuals may result from a repellent, or attractant "masking," mechanism.

Interspecific responses among severalTrogoderma species have been correlated with their pheromone components. The most important component emitted by four of the species is (Z)- or (E)-14-methyl-8-hexadecenal, which is not detectable in extracts of macerated beetles. The response to macerated beetles is probably due to the corresponding alcohol and ester. The recency of common origin of seven species is discussed.

The responses of Colorado potato beetle,Leptinotarsa decemlineata (Say), to volatile components of tansy,Tanacetum vulgare L., were investigated in order to establish a chemical basis for observed reduction in beetle populations when potatoes,Solanum tuberosum L., were interplanted with tansy. Colorado potato beetles exhibited avoidance behavior to tansy oil, volatiles from intact tansy plants, a “hydrocarbon fraction” of tansy oil, obtained by fractionation on alumina, and five of the 13 known components of tansy oil that were tested. One constituent of tansy oil, α-pinene, attracted beetles.