The Salicylic Acid-Mediated Release of Plant Volatiles Affects the Host Choice of \u3cem\u3eBemisia tabaci\u3c/em\u3e

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) causes serious crop losses worldwide by transmitting viruses. We have previously shown that salicylic acid (SA)-related plant defenses directly affect whiteflies. In this study, we applied exogenous SA to tomato plants in order to investigate the interaction between SA-induced plant volatiles and nonviruliferous B. tabaci B and Q or B- and Q-carrying tomato yellow leaf curl virus (TYLCV). The results showed that exogenous SA caused plants to repel nonviruliferous whiteflies, but the effect was reduced when the SA concentration was low and when the whiteflies were viruliferous. Exogenous SA increased the number and quantity of plant volatiles—especially the quantity of methyl salicylate and δ-limonene. In Y-tube olfactometer assays, methyl salicylate and δ-limonene repelled the whiteflies, but the repellency was reduced for viruliferous Q. We suggest that the release of plant volatiles as mediated by SA affects the interaction between whiteflies, plants, and viruses. Further studies are needed to determine why viruliferous Q is less sensitive than nonviruliferous Q to repellent plant volatiles

A male-produced aggregation-sex pheromone of the beetle Arhopalus rusticus (Coleoptera: Cerambycidae, Spondylinae) may be useful in managing this invasive species.

The longhorned beetle Arhopalus rusticus (Coleoptera: Cerambycidae, Spondylinae) is a common species in conifer forests of the Northern Hemisphere, but with global trade, it has invaded and become established in New Zealand, Australia, and South America. Arhopalus rusticus is a suspected vector of the phytopathogenic nematode, Bursaphelenchus xylophilus, the causative agent of pine wilt disease, which is a major threat to pine forests worldwide. Here, we report the identification of a volatile, male-produced aggregation-sex pheromone for this species. Headspace odours from males contained a major male-specific compound, identified as (2 S, 5E)-6,10-dimethyl-5,9-undecadien-2-ol (common name (S)-fuscumol), and a minor component (E)-6,10-dimethyl-5,9-undecadien-2-one (geranylacetone). Both compounds are known pheromone components for species in the same subfamily. In field trials in its native range in Slovenia, (S)-fuscumol was significantly more attractive to beetles of both sexes, than racemic fuscumol and a blend of host plant volatiles commonly used as an attractant for this species. Fuscumol-baited traps also caught significant numbers of another spondylidine species, Spondylis buprestoides (L.), and a rare click beetle, Stenagostus rufus (De Geer). The pheromone can be exploited as a cost-effective and environmentally safe tool for detection and monitoring of this invasive species at ports of entry, and for monitoring the beetle's distribution and population trends in both endemic and invasive populations

Host plant finding by Acraea acerata Hew. (Lepidoptera: Nymphalidae), the sweet potato butterfly: implications for pest management

Phytophagous insects such as Lepidopteran species utilise both olfactory and visual cues to locate their host-plants used as mating or oviposition sites, shelter or food. Larvae of Acraea aceratafeed on sweet potato plant leaves causing more that 50 % loss of sweet potato tuber yield in some East African countries. Attempting to elaborate a management strategy to control A. aceratasuitable to a tropical resource- poor farming system, it was essential to investigate how the butterfly finds its host- plants. The results of a wind tunnel bioassay using glass-screened, muslin-screened and non-screened sweet potato plants suggested that sweet potato plant volatiles play an important role in attracting A. aceratato its host-plant. This was supported by both the distance moved by female A. aceratatowards muslin-screened plants (olfactory cues) and the percentage of butterflies which landed on the screen. Visual stimuli seemed to have a negative effect. The attractiveness of sweet potato plant volatiles to A. aceratawas later confirmed by the use of volatiles collected by headspace entrainment from sweet potato plantsThe main components of sweet potato plant volatiles were tentatively identified by GC-MS (Gas Chromatography coupled with Mass Spectrometry) analysis and electrophysiological responses were recorded for some of them. Compared to ethylbenzene, 3-carene and (-) trans-caryophyllene, 3-hexen-l-ol,(Z), a general green leaf alcohol, elicited far more substantial EAG (electroantennogram) responses in A.acerata.This result suggested that A. aceratamight well respond to a specific blend of volatiles made up of the different chemical components of sweet potato plant volatiles instead of one or two specific chemical components.Considering the important role of sweet potato plant volatiles in attracting A. acerata,a number of plants reported to be repellent to herbivorous insects were mixed with sweet potato plants and screened for repelling/disorienting of female A. aceratain olfactometer and wind tunnel bioassays. Two plant mixtures with opposite effects on the response of A. aceratato their volatiles were identified: sweet potato + Desmodiumplant volatiles were found to be more attractive to the butterfly than sweet potato plant volatiles alone, and sweet potato + onion plant volatiles which reduced considerably the attractiveness of sweet potato plant volatiles to A. acerata.As the trichomes of Desmodiumplants were reported to trap insects, a ‘push-pull’ management strategy for A. aceratainvolving the two intercrops was suggested: the intercrop sweet potato + onion plants would ‘push’ away ovipositing A. aceratawhereas the intercrop sweet potato + Desmodiumplants would attract the butterflies which would be trapped by Desmodiumtrichomes. The results of a preliminary field experiment carried out in Uganda suggested that the intercrop sweet potato + onion plants had a negative effect on the number of egg batches laid by A. acerataon sweet potato plants. There is, therefore, a need for comprehensive field experimentation of the whole strategy to validate these laboratory and field experimental findings

Secondary Organic Aerosol Formation from Healthy and Aphid-Stressed Scots Pine Emissions.

One barrier to predicting biogenic secondary organic aerosol (SOA) formation in a changing climate can be attributed to the complex nature of plant volatile emissions. Plant volatile emissions are dynamic over space and time, and change in response to environmental stressors. This study investigated SOA production from emissions of healthy and aphid-stressed Scots pine saplings via dark ozonolysis and photooxidation chemistry. Laboratory experiments using a batch reaction chamber were used to investigate SOA production from different plant volatile mixtures. The volatile mixture from healthy plants included monoterpenes, aromatics, and a small amount of sesquiterpenes. The biggest change in the volatile mixture for aphid-stressed plants was a large increase (from 1.4 to 7.9 ppb) in sesquiterpenes-particularly acyclic sesquiterpenes, such as the farnesene isomers. Acyclic sesquiterpenes had different effects on SOA production depending on the chemical mechanism. Farnesenes suppressed SOA formation from ozonolysis with a 9.7-14.6% SOA mass yield from healthy plant emissions and a 6.9-10.4% SOA mass yield from aphid-stressed plant emissions. Ozonolysis of volatile mixtures containing more farnesenes promoted fragmentation reactions, which produced higher volatility oxidation products. In contrast, plant volatile mixtures containing more farnesenes did not appreciably change SOA production from photooxidation. SOA mass yields ranged from 10.8 to 23.2% from healthy plant emissions and 17.8-26.8% for aphid-stressed plant emissions. This study highlights the potential importance of acyclic terpene chemistry in a future climate regime with an increased presence of plant stress volatiles

Attractive plant volatiles as a control method against apple fruit moth (Argyresthia conjugella Zell.)?

Apple fruit moth, Argyresthia conjugella Zell. (Lepidoptera: Argyresthiidae), is the most important pest of apples in Scandinavia. In years when its primary host, rowan (Sorbus aucuparia L.), has little or no berries for egglaying, female A. conjugella fly into apple orchards to lay their eggs. In some years the entire apple crop can be destroyed. Volatiles from apples and rowan have been collected and identified. In GC-EAD tests females have responded to several compounds found in both rowan and apple. Some of these compounds were used in field trapping tests during 2002, and a mixture of two compounds trapped significantly more females and males compared to control traps. However, field trapping results from 2003 indicate that the two-compound blend seem to trap insects too late in the season to prevent egglaying in apples. Several new compounds were also tested in 2003, and some of these gave promising results. The results will be discussed in relation to use attractive plant volatiles as a control method against A. conjugella females

Odour perception in the codling moth Cydia pomonella L.

The codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae) is a renowned pest in apple, pear and walnut orchards, and its activities are in large guided by volatile odours as sensory cues. This thesis spans over a large part of the olfactory chain of events in the codling moth, from brain to behaviour. The main emphasis was placed on the detection of plant odours, and some of the works presented are novel to codling moth research. The volatiles emitted by host-plant species were analysed, revealing variations in the odour profiles both between species of host plants and at different phenological stages of a host plant, which indicates that females are flexible in their behavioural response to host odours. A first step was taken to map the antennal olfactory receptor neurons and their specificity, where several behaviourally active compounds were found to be detected by neurons housed in sensilla auricillica, one of the morphological types of sensilla found on the antenna of the moth. In a study of the antennal lobe, the primary integration centre for odour processing in the insect brain, we describe the three dimensional structure of the array of olfactory glomeruli of both sexes. Behavioural experiments show that both males and females are attracted to plant odours, and that host recognition in codling moths are encoded not by single compounds but by a blend of volatiles. Taken together, the results presented in this thesis provide new insights into moth olfaction and odour-dependent behaviour in general, and into that of the codling moth in particular