Journal of Chemical Ecology

Osier, Tod; Lindroth, Richard

doi: 10.1023/A:1010352307301pmid: 11504029

Genetic and environmental variability, and their interactions, influence phytochemical composition and, in turn, herbivore performance. We evaluated the independent and interactive effects of plant genotype, nutrient availability, and defoliation on the foliar chemistry of quaking aspen (Populus tremuloides) and consequences for performance of gypsy moths (Lymantria dispar). Saplings of four genotypes were grown under two conditions of nutrient availability and subjected to three levels of artificial defoliation. Concentrations of all secondary and primary metabolites evaluated responded to at least one or more of the experimental treatments. Of the secondary metabolites, phenolic glycosides were affected strongly by genotype, less so by nutrient availability, and not induced by defoliation. Condensed tannins were strongly dependent upon genotype, soil nutrient availability, and their interaction, and, in contrast to phenolic glycosides, were induced by artificial defoliation. Of the primary metabolites, foliar nitrogen was affected by genotype and soil nutrient availability. Starch concentrations were affected by genotype, nutrient availability, defoliation and interactions among these factors. Foliar water content responded to genotype, nutrient availability, and defoliation, and the effect of nutrient availability depended on genotype. Herbivore performance on these plants was strongly influenced by plant genotype and soil nutrient availability, but much less so by defoliation. Although several of the compound types (condensed tannins, starch, and water) responded to defoliation, quantitative variation in these compounds did not contribute to substantive changes in herbivore performance. Rather, the primary source of variation in insect performance was due to plant genotype (phenolic glycoside levels), while nutrient availability (foliar nitrogen levels) was of secondary importance. These results suggest that genetic variation in aspen plays a major role in determining patterns of insect performance, whereas environmental variation, such as was tested, here is of negligible importance.

Jojola-Elverum, S.; Shivik, J.; Clark, L.

doi: 10.1023/A:1010357024140pmid: 11504030

Brown treesnakes are an invasive species to the island of Guam that have caused extensive ecological and economic damage. Efforts to control the snake population have included trapping using live mouse lures, but for logistical and economic reasons a synthetic lure is needed. When searching for live food, brown treesnakes use both visual and odor cues. However, when searching for carrion, odor cues are sufficient. Attempts to develop synthetic lures based on chemical reconstruction of the complex carrion odor have not succeeded. We provide evidence that a microbial–substrate interaction is important for bait take by brown treesnakes. Microbial cultures taken from mouse carrion indicate that Enterobacter agglomerans is the predominant bacterium, and field tests suggest that this organism may be important to odor production that attracts brown treesnakes. This information may prove useful in the development of microbial-based biological reactors that could be formulated to produce a continuous stream of odor of sufficient complexity so as to be attractive to foraging snakes.

Maerz, John; Panebianco, Nova; Madison, Dale

doi: 10.1023/A:1010309108210pmid: 11504031

Red-backed salamanders, Plethodon cinereus, show a variety of alarm responses to chemical cues from eastern garter snakes, Thamnophis sirtalis. We measured the foraging activity of red-backed salamanders exposed to water soiled by a garter snake (fed P. cinereus) or to unsoiled water. Salamanders exposed to snake-soiled water showed less foraging activity than salamanders exposed to unsoiled water; therefore, predators could have nonlethal effects on salamander populations. Our results also show additional factors influenced salamander foraging activity. Salamander foraging activity and responsiveness to chemical cues do not appear to have been affected by sex or food deprivation. Salamander foraging activity does appear to have been influenced by activity biorhythms. Foraging activity of animals in both treatments showed a bimodal periodicity that is consistent with natural activity patterns controlled by internal biorhythms. Exposure to snake-soiled water significantly reduced foraging activity during periods of peak foraging activity, but had a subtler effect0 on foraging activity during natural lulls in activity. We suggest that both activity biorhythms and exposure to chemical cues are important factors affecting salamander foraging behavior.

Yasui, Hiroe

doi: 10.1023/A:1010361125048pmid: 11504032

A predatory stink bug, Eocanthecona furcellata, died after feeding on Milionia basalis larvae. The compounds toxic to E. furcellata were isolated from the hemolymph of M. basalis larvae and identified as inumakilactone A, nagilactone C, and nagilactone C glucoside. The concentrations of inumakilactone A, nagilactone C, and nagilactone C glucoside in the hemolymph of the final instar larvae were 130, 50, and 770 μg/ml, respectively. Nagilactone C showed the highest insecticidal activity against second-instar nymphs of E. furcellata, while nagilactone C glucoside showed the lowest, one twentieth of that of nagilactone C. When mixed compounds were given at the same concentrations as those in hemolymph of M. basalis, all nymphs of E. furcellata died with in three days. Inumakilactone A and nagilactone C were found to be in the leaves of podocarp, Podocarpus macrophyllus, the only host plant of M. basalis, at concentrations of 13 and 175 μg/g fresh weight, respectively. However, no nagilactone C glucoside was detected in the leaves of this species. These results suggested that M. basalis may transform nagilactone C to its glucoside.

Krips, O.; Willems, P.; Gols, R.; Posthumus, M.; Gort, G.; Dicke, M.

doi: 10.1023/A:1010313209119pmid: 11504033

We investigated whether volatiles produced by spider mite-damaged plants of four gerbera cultivars differ in attractiveness to Phytoseiulus persimilis, a specialist predator of spider mites, and how the mite-induced odor blends differ in chemical composition. The gerbera cultivars differed in resistance, as expressed in terms of spider mite intrinsic rate of population increase (r m). In order of increasing resistance these were Sirtaki, Rondena, Fame, and Bianca. To correct for differences in damage inflicted on the cultivars, we developed a method to compare the attractiveness of the blends, based on the assumption that a larger amount of spider mite damage leads to higher attraction of P. persimilis. Spider mite-induced volatiles of cultivars Rondena and Bianca were preferred over those of cultivar Sirtaki. Spider mite-induced volatiles of cultivars Sirtaki and Fame did not differ in attractiveness to P. persimilis. Sirtaki plants had a lower relative production of terpenes than the other three cultivars. This was attributed to a low production of cis-α-bergamotene, trans-α-bergamotene, trans-β-bergamotene, and (E)-β-farnesene. The emission of (E)-β-ocimene and linalool was lower in Sirtaki and Fame leaves than in Bianca and Rondena. The importance of these chemical differences in the differential attraction of predatory mites is discussed.

Hammack, Leslie

doi: 10.1023/A:1010365225957pmid: 11504034

Synthetic maize volatiles and analogs dispensed singly and blended were tested for attractiveness to western (WCR, Diabrotica virgifera virgifera) and northern corn rootworm beetles (NCR, D. barberi) in maize fields. Newly identified attractants included syn-benzaldoxime, especially for NCR, and β-caryophyllene for WCR females. (±)-Linalool was more effective than was (−)-linalool. Myrcene, (+)-β-pinene, and (−)-β-pinene were unattractive. Adding methyl salicylate to (±)-linalool, (+)-α-terpineol, or β-ionone appeared to synergistically increase capture of WCR females, but dispensing the terpenes in binary blends did not. Dose–response data for methyl salicylate, (±)-linalool, and a blend of both compounds confirmed the synergy. β-Caryophyllene, but not (−)-α-pinene, added to the latter blend produced a further synergistic increase in WCR female capture that did not vary with sesquiterpene dose from 1.0 to 100 mg. Indole addition to the same blend caused an increase in WCR female captures indicative of synergy, assuming that each did not individually lure different segments of the WCR female population. The green leaf volatiles (Z)-3-hexenyl acetate and (Z)-3-hexen-1-ol were unattractive alone and had no influence on efficacy of traps baited with 3.3 mg each of (±)-linalool, methyl salicylate, and β-caryophyllene. The latter mixture captured about half as many WCR females as did 10 mg of 4-methoxycinnamaldehyde, a potent WCR attractant standard. Substituting β-ionone for (±)-linalool yielded a ternary blend that captured more beetles than did the aldehyde and was unaffected by aldehyde addition. Olive oil, which has been used to sustain attractant volatilization, did not affect captures. The results show that the blending of maize volatiles has the potential to greatly improve efficacy of lures having promising applications in corn rootworm population management.

Hillbur, Ylva; Bengtsson, Marie; Löfqvist, Jan; Biddle, Anthony; Pillon, Olivier; Plass, Ernst; Francke, Wittko; Hallberg, Eric

doi: 10.1023/A:1010317310027pmid: 11504035

The sex pheromone of the pea midge consists of 2-acetoxytridecane, (2S,11S)-diacetoxytridecane and (2S,12S)-diacetoxytridecane. The responses of male pea midges to the corresponding stereoisomers of (2S,11S)-diacetoxytridecane and (2S,12S)-diacetoxytridecane were tested in field trapping experiments and by electroantennographic recordings. When added at 20% of the pheromone component to the sex pheromone blend, the (2S,11R)- and (2R,11S)-stereoisomers of (2S,11S)-diacetoxytridecane, were shown to have a strong inhibitory effect on male attraction in the field. At the same dose, (2R,11R)-diacetoxytridecane, (2R,12R)-diacetoxytridecane, and meso-2,12-diacetoxytridecane, did not have a significant effect on male behavior. It was also shown that substitution of either (2S,11S)-diacetoxytridecane or (2S,12S)-diacetoxytridecane with the related stereoisomers reduced trap catches to the level of blank traps. The electroantennographic recordings showed similar dose–response curves for the pheromone components and the stereoisomers shown to have an inhibitory effect. It seems likely that male antennae have receptors for both pheromone components and for inhibitory stereoisomers. Scanning electron microscopy and transmission electron microscopy of the antennae revealed three types of sensilla involved in chemoreception: sensilla circumfila, sensilla trichodea, and sensilla coeloconica. The sensilla circumfila and trichodea are both innervated by two sensory cells, whereas the sensilla coeloconica are innervated by four to five cells.

Mcelfresh, J.; Hammond, Abner; Millar, Jocelyn

doi: 10.1023/A:1010369326866pmid: 11504036

The sex attractant pheromone blend of Hemileuca maia (Lepidoptera: Saturniidae) from the vicinity of Baton Rouge, Louisiana, has been identified. The major component of the blend is (E10,Z12)-hexadeca-10,12-dienal (E10,Z12–16:Ald), in combination with the minor components (E10,Z12)-hexadeca-10,12-dien-1-ol (E10,Z12–16:OH), and (E10,Z12)-hexadeca-10,12-dien-1-yl acetate (E10,Z12–16:Ac). Ratios of the compounds in extracts of female pheromone glands varied around a mean of 100:7.4:6.3. None of the three components were attractive to male moths when tested as single components. Several other compounds were tentatively identified from female pheromone gland extracts, including E10,E12–16:Ald, E10,E12–16:OH, and E10,E12–16:Ac, but addition of these components, either alone or in combination, at biologically relevant rates, did not significantly increase the attractiveness of lures. The saturated analogs, hexadecanal, hexadecanol, and hexadecyl acetate, also were identified in gland extracts, but had no apparent effect as pheromone components.

Malual, Atem; Hassanali, Ahmed; Torto, Baldwyn; Assad, Yousif; Njagi, Peter

doi: 10.1023/A:1010321410936pmid: 11504037

We examined aggregative behavior of hatchlings of the desert locust Schistocerca gregaria emerging from solitaria egg pods that had been incubated in sand previously used for consecutive ovipositions by gregarious females. Hatchlings derived from such eggs were significantly more gregarious than those derived from pods laid in clean sand. The gregarizing effect of the sand-associated factor originating from 3, 5, or 10 ovipositions by gregarious females increased in a dose-dependent fashion. Washing the sand with organic solvents following such ovipositions, or flushing it with nitrogen gas, led to substantial loss of its gregarizing effect, showing that the active signal is volatile and of medium polarity. The gregarizing activity of the exposed sand correlated with the presence of C-8 unsaturated ketones, (Z)-6-octen-3-one and (E,E)-3,5-octadiene-2-one and its E,Z isomer, previously shown by us to form part of the releaser pheromone system that mediates group oviposition in S. gregaria. These ketones were present in relatively large amounts in the eggs obtained from egg pods of gregarious females and were also detected in the extracts of accessory glands of gregarious females, a candidate source of the gregarization factor. It is proposed that the pheromone is secreted at the onset of oviposition. This would account for its distribution predominantly within the eggs and surrounding sand at the site of oviposition. The study sheds new light on the pheromonal mechanism associated with transgenerational transmission of gregarious characters in crowded S. gregaria populations and provides yet another case in this insect of dual releaser and primer roles played by the same pheromone blend.

Clarke, S.; Dani, F.; Jones, G.; Morgan, E.; Schmidt, J.

doi: 10.1023/A:1010373427774pmid: 11504038

The males of the decorator wasps Eucerceris have been observed to display abdomen-dragging behavior on plants surrounding their nest. It is thought that this applies a territorial-marking sex pheromone that serve to alert females to the males' territory for courtship and mating. The extracts of three species E. rubripes, E. conata, and E. tricolor have been analyzed by GC-MS. The gas chromatograms revealed the presence, in large quantities, of one common volatile compound in the male head extracts. By analogy with the closely related bee wolves Philanthus, we believe the pheromone is produced in the mandibular glands. Utilizing mass spectrometry, microreactions, FT-IR, and 1H and 13C NMR spectroscopy the structure of the pheromone was proposed to be (Z)-3-hexenyl 3-hydroxybutanoate, which was confirmed by synthesis. The absolute configuration of the chiral center was determined to be R for the three species by preparing the Mosher esters of the insect samples and comparing their GC retention times with a synthetic sample of known absolute configuration. In addition 2- and 3-hexenoic acid and some aromatic compounds were also found in varying quantities in both males and females along with hydrocarbons and fatty acids, although no species-specific profiles emerged.