Andrés Quiroz

Winter host component reduces colonization by bird-cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera, Aphididae), and other aphids in cereal fields.

Methyl salicylate, a volatile component ofPrunus padus, the winter host ofRhopalosiphum padi, was found to reduce colonization of the summer host by this aphid. The compound was identified by gas chromatographic analysis coupled with recordings from cells in the primary rhinarium on the sixth antennal segment of the aphid. Methyl salicylate eliminated the attractancy of oat leaves to spring migrants in olfactometer tests. In Sweden, this compound significantly decreased colonization of field grown cereals byR. padi and in the U.K., populations ofSitobion avenae andMetopolophium dirhodum were significantly lower on treated plots.

Semiochemicals mediating spacing behavior of bird cherry-oat aphid, Rhopalosiphum padi feeding on cereals.

Olfactometry using an apterous individual of Rhopalosiphum padi (L.) showed an arresting effect by volatiles from a wheat seedling and a repellent effect by volatiles from a wheat seedling infested with aphids at a high population density (ca. 9 aphids/cm2). Four compounds, 6-methyl-5-hepten-2-one, (−)- and (+)-6-methyl-5-hepten-2-ol, and 2-tridecanone, were identified by GC-MS in air entrainments from the wheat seedlings with high aphid density but not from the wheat seedlings alone. The mixture of the four compounds in the natural proportion counteracted the attractivity of the volatiles from the intact uninfested wheat seedling. The likely role of these compounds in the spacing behavior of this aphid species, when present in high densities on wheat, is discussed.

Insecticide resistance in the horn fly: alternative control strategies.

Abstract The horn fly, Haematobia irritans (Linnaeus 1758) (Diptera: Muscidae) is one of the most widespread and economically important pests of cattle. Although insecticides have been used for fly control, success has been limited because of the development of insecticide resistance in all countries where the horn fly is found. This problem, along with public pressure for insecticide‐free food and the prohibitive cost of developing new classes of compounds, has driven the investigation of alternative control methods that minimize or avoid the use of insecticides. This review provides details of the economic impact of horn flies, existing insecticides used for horn fly control and resistance mechanisms. Current research on new methods of horn fly control based on resistant cattle selection, semiochemicals, biological control and vaccines is also discussed.

Olfactometer-assessed responses of aphid Rhopalosiphum padi to wheat and oat volatiles

Volatiles from wheat and oat seedlings elicited attraction in apterae and alatae Rhopalosiphum padi. Cereal volatiles were identified by GC-MS and olfactometric tests were performed with each compound. Attraction of aphids was elicited by (E)-2-hexenyl acetate, (Z)-3-hexenol, (E)-2-hexenyl acetate, (E)-2-hexenol, (Z)-2-hexenol, n-heptanal, n-octanal, n-nonanal, n-decanal, benzaldehyde, and linalool. The difference between the sensory capacity of alatae and apterae is discussed in relation to migrations between hosts during their life cycle.

Variation in highbush blueberry floral volatile profiles as a function of pollination status, cultivar, time of day and flower part: implications for flower visitation by bees

BACKGROUND AND AIMS Studies of the effects of pollination on floral scent and bee visitation remain rare, particularly in agricultural crops. To fill this gap, the hypothesis that bee visitation to flowers decreases after pollination through reduced floral volatile emissions in highbush blueberries, Vaccinium corymbosum, was tested. Other sources of variation in floral emissions and the role of floral volatiles in bee attraction were also examined. METHODS Pollinator visitation to blueberry flowers was manipulated by bagging all flowers within a bush (pollinator excluded) or leaving them unbagged (open pollinated), and then the effect on floral volatile emissions and future bee visitation were measured. Floral volatiles were also measured from different blueberry cultivars, times of the day and flower parts, and a study was conducted to test the attraction of bees to floral volatiles. KEY RESULTS Open-pollinated blueberry flowers had 32 % lower volatile emissions than pollinator-excluded flowers. In particular, cinnamyl alcohol, a major component of the floral blend that is emitted exclusively from petals, was emitted in lower quantities from open-pollinated flowers. Although, no differences in cinnamyl alcohol emissions were detected among three blueberry cultivars or at different times of day, some components of the blueberry floral blend were emitted in higher amounts from certain cultivars and at mid-day. Field observations showed that more bees visited bushes with pollinator-excluded flowers. Also, more honey bees were caught in traps baited with a synthetic blueberry floral blend than in unbaited traps. CONCLUSIONS Greater volatile emissions may help guide bees to unpollinated flowers, and thus increase plant fitness and bee energetic return when foraging in blueberries. Furthermore, the variation in volatile emissions from blueberry flowers depending on pollination status, plant cultivar and time of day suggests an adaptive role of floral signals in increasing pollination of flowers.

Odour communication of Rhopalosiphum padi on grasses

There is ample field evidence on the mobility of apterous aphids, suggested as part of a spacing mechanism leading to better exploitation of the food resource (Hodgson, 1991). Thus, a considerable proportion of apterae of Sitobion avenae (Fabr.), Metopolophium dirhodum (Wlk.) and Rhopalosiphum padi (L.) were found walking on the ground in cereal fields (Sopp et al., 1987; Wiktelius, 1989). Although apterous aphids walking on the soil surface may also be the result of weather conditions, such as rain or wind (Araya & Fereres, 1991) or escape reactions after disturbance by predators (Nault & Phelan, 1984; Arakaki, 1989), adult apterous aphids ofR. padi (Wiktelius, 1989), S. avenae (Sopp et al., 1987), and Aphisfabae (Scop.) (Way & Banks, 1967) have been observed leaving the plants spontaneously. This emigration of apterae seemed to be induced by crowding. A spacing pheromone would contribute to resource management and can be active even at moderate population densities. In the present paper we report on the odour communication of alatae and apterae of R. padi on one of its summer hosts.

Antifungal activity of volatile metabolites emitted by mycelial cultures of saprophytic fungi

The antifungal activity of molecular identified Chilean saprobiontic fungi, Trichoderma viride, Schizophyllum commune and Trametes versicolor, on the fungal plant pathogens Botrytis cinerea and Fusarium oxysporum, and the saprotrophic mould Mucor miehei was investigated using two types of inhibition bioassay: (1) bi-compartmented Petri dishes and (2) two Erlenmeyer flasks connected by their upper parts. The chemical composition of volatile organic compounds (VOCs) released by saprobiontic fungi was also investigated using headspace solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC-MS) analysis. Of the saprobiontic fungi evaluated, one isolate of S. commune showed the highest inhibitory activity against B. cinerea and M. miehei, 86.0±5.4 and 99.5±0.5% respectively. The volatile profiles of fungal isolates were shown to contain a different class of compounds. The major components in the headspace of mycelial cultures were 6-pentyl-α -pyrone (T. viride), ethanol and β -bisabolol (S. commune), and a sesquiterpene alcohol (Tr. versicolor). This is the first study reported on the release of VOCs by Chilean native fungi and their antifungal activity wrt. plant pathogenic fungi.

Response of the Beetle Hylastinus obscurus Marsham (Coleoptera: Scolytidae) to Red Clover (Trifolium pratense L.) Volatiles in a Laboratory Olfactometer

Abstract The response of field-collected Hylastinus obscurus Marsham (Coleoptera: Scolytidae) to volatiles from Trifolium pratense L. of different ages was studied in a four-arm olfactometer. Volatiles from 1.5-, 2-, and 2.5-yr-old plants were more attractive than volatiles from 1-, 3-, and 3.5-yr-old plants. Two-year-old plants were preferred during winter, spring, and summer. One-year-old plants were not preferred in their early stages, but preference increased as they aged. Volatiles from 3-yr-old plants were never preferred. The essential oils obtained from 2-yr-old T. pratense elicited an attraction response from H. obscurus. Beetle response is discussed in relation to host-locating behavior.

Volatiles Released From Vaccinium corymbosum Were Attractive to Aegorhinus superciliosus (Coleoptera: Curculionidae) in an Olfactometric Bioassay

ABSTRACT The objective of this study was to evaluate the role of host volatiles in the relationship between a blueberry plant Vaccinium corymbosum L. and the raspberry weevil Aegorhinus superciliosus (Guérin) (Coleoptera: Curculionidae), the principal pest of blueberry in the south of Chile. Volatiles from the aerial part of different phenological stages of the host were collected on Porapak Q and analyzed by coupled gas chromatography-mass spectrometry (GC-MS). Several chemical groups were identified including green leaf volatiles, aromatic compounds, and terpenes. The olfactometric responses of A. superciliosus toward different odor sources were studied in a four-arm olfactometer. Blueberry shoots at the phenological stages of fruit set, and blue-pink fruit color elicited the greatest behavioral responses from weevils. Five compounds (2-nonanone, eucalyptol, R- and S-limonene, and 4-ethyl benzaldehyde) elicited an attractant behavioral response from A. superciliosus. The results suggest the host location behavior of A. superciliosus could be mediated by volatiles derived from V. corymbosum. This work has identified a number of compounds with which it is possible to develop a lure for the principal pest of blueberry in southern Chile.

Evidence of Contact Pheromone Use in Mating Behavior of the Raspberry Weevil (Coleoptera: Curculionidae)

ABSTRACT Numerous studies of insect species have shown that a subset of female cuticular hydrocarbons is used as short-range or contact pheromones. Here, we studied the possible use of contact pheromones in the mating behavior of the weevil Aegorhinus superciliosus, a native species of Chile. Males mounted females only after antennal contact with the females cuticle, and only 33% of the males attempted to mate with dead females washed with solvent. When a glass rod (dummy) was coated with female cuticular extracts, males exhibited behaviors similar to those observed with females. A preliminary gas chromatography-mass spectrometry (GC-MS) analysis of cuticular extracts indicated that males and females share a series of aliphatic hydrocarbons but that the relative abundance of some of these compounds differ between the sexes. These results suggest that cuticular lipids mediate mating behavior of the raspberry weevil and provide the first evidence of contact pheromones in curculionids.