Improving the Monitoring of the Walnut Husk Fly (Diptera: Tephritidae) Using Male-Produced Lactones.

It is important to monitor fruit flies (Diptera: Tephritidae) efficiently to implement sustainable means of control. Attractants are often used to increase the efficiency of sticky traps deployed in orchards to monitor Lepidopterans, but remains to be developed to monitor fruit flies. Rhagoletis completa Cresson (Diptera: Tephritidae) is an invasive species in the walnut orchards of Europe, and is commonly monitored with yellow sticky traps. In this study, we collected the volatile compounds released by male and female R. completa, and identified two lactones released exclusively by males. We then formulated both lactones in long-lasting volatile dispensers, and we quantified their release rate over a 26-d period. Finally, during the entire period when female flies are present in the field, we compared the efficiency of the conventional monitoring method using unbaited yellow sticky traps with yellow sticky traps associated with a dispenser releasing both male-produced lactones. These assays were conducted in 54 walnut orchards in France, in 2017. The number of fruit flies caught with sticky traps associated with lactones dispensers was increased by up to 10 times each week. Lactone-baited traps also allowed earlier detection in the season. These field results are promising for R. completa monitoring. A complete chiral identification of these lactones should be performed along with a clarification of their role in the sexual communication of R. completa.

Identification of walnut husk (Juglans regia L.) volatiles and the behavioural response of the invasive Walnut Husk Fly, Rhagoletis completa Cresson.

BACKGROUND: Several European countries are important walnut (Juglans regia L.) producers. However, these countries must contend with the recent introduction of the Walnut Husk Fly, Rhagoletis completa Cresson (Diptera, Tephritidae), which is causing severe economic losses, especially in organic production. Because most Tephritid fruit flies use kairomones in their search for host plants, we hypothesise that this highly specialist species orients toward the volatile blend released by walnut husks. RESULTS: We collected, identified, and quantified the volatile organic chemicals (VOCs) released by walnut husks from the most commonly cultivated variety in France (Franquette). Then, the behavioural response of R. completa toward synthetic odour blends was recorded in dual choice assays conducted in net cages. A total of 26 VOCs were identified, with α-pinene, ß-pinene, trans-linalool, eugenol, and tetradecane representing the major constituents. In the dual choice assay, male and female R. completa were strongly attracted to synthetic blend that included most of the identified husk VOCs. CONCLUSION: When searching for a host plant, R. completa use host fruit kairomones. The potential of these semiochemicals in monitoring and management of this quarantine pest is discussed. © 2017 Society of Chemical Industry.

Elevated Carbon Dioxide Concentration Reduces Alarm Signaling in Aphids.

Insects often rely on olfaction to communicate with conspecifics. While the chemical language of insects has been deciphered in recent decades, few studies have assessed how changes in atmospheric greenhouse gas concentrations might impact pheromonal communication in insects. Here, we hypothesize that changes in the concentration of atmospheric carbon dioxide affect the whole dynamics of alarm signaling in aphids, including: (1) the production of the active compound (E)-ß-farnesene (Eßf), (2) emission behavior when under attack, (3) perception by the olfactory apparatus, and (4) the escape response. We reared two strains of the pea aphid, Acyrthosiphon pisum, under ambient and elevated CO2 concentrations over several generations. We found that an increase in CO2 concentration reduced the production (i.e., individual content) and emission (released under predation events) of Eßf. While no difference in Eßf neuronal perception was observed, we found that an increase in CO2 strongly reduced the escape behavior expressed by an aphid colony following exposure to natural doses of alarm pheromone. In conclusion, our results confirm that changes to greenhouse gases impact chemical communication in the pea aphid, and could potentially have a cascade effect on interactions with higher trophic levels.

Aggregation behavior of Harmonia axyridis under non-wintering conditions.

The invasive multicolored Asian ladybeetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), aggregates inside dwellings during winter to avoid cold weather. This adaptive behavior disturbs homeowners, because of the large numbers of individuals that aggregate, which induces allergic reactions. The migratory flight patterns of this species have been well documented, with individuals preferentially moving toward prominent and high color contrast elements. However, the factors involved in the selection of aggregation sites by this species have yet to be elucidated. Here, we evaluated the influence of (i) the density of individuals and (ii) the type of available shelters on decisions by H. axyridis to settle and aggregate under shelters. A dual choice bioassay conducted in the laboratory demonstrated the presence of mutual attraction to conspecifics. We also found that individuals preferentially settled under red covered shelters compared to transparent shelters, and that the type of shelter outweighed the effect of social interactions among conspecifics. Moreover, this experiment was performed under non-wintering conditions, providing the first evidence that aggregative behavior in this species can also occur under those specific conditions.

First evidence of a volatile sex pheromone in lady beetles.

To date, volatile sex pheromones have not been identified in the Coccinellidae family; yet, various studies have suggested that such semiochemicals exist. Here, we collected volatile chemicals released by virgin females of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), which were either allowed or not allowed to feed on aphids. Virgin females in the presence of aphids, exhibited "calling behavior", which is commonly associated with the emission of a sex pheromone in several Coleoptera species. These calling females were found to release a blend of volatile compounds that is involved in the remote attraction (i.e., from a distance) of males. Gas Chromatography-Mass Spectrometry (GC-MS) analyses revealed that (-)-ß-caryophyllene was the major constituent of the volatile blend (ranging from 80 to 86%), with four other chemical components also being present; ß-elemene, methyl-eugenol, α-humulene, and α-bulnesene. In a second set of experiments, the emission of the five constituents identified from the blend was quantified daily over a 9-day period after exposure to aphids. We found that the quantity of all five chemicals significantly increased across the experimental period. Finally, we evaluated the activity of a synthetic blend of these chemicals by performing bioassays which demonstrated the same attractive effect in males only. The results confirm that female H. axyridis produce a volatile sex pheromone. These findings have potential in the development of more specific and efficient biological pest-control management methods aimed at manipulating the behavior of this invasive lady beetle.

Substrate marking by an invasive ladybeetle: seasonal changes in hydrocarbon composition and behavioral responses.

The multicolored Asian ladybeetle, Harmonia axyridis (Pallas), aggregates inside dwellings during the winter to survive the cold. Recent published reports have highlighted that overwintering individuals use hydrocarbon markings deposited on surfaces by conspecifics to orient toward aggregation sites. In the current study, monthly GC-MS analyses revealed seasonal modifications in the chemical profile of substrate markings deposited by moving individuals. The markings of overwintering ladybeetles contained larger proportions of heptacosadiene, nonacosadiene, hentriacontadienes, and methyl-nonacosanes, along with a lower proportion of heptacosene and nonacosene. This finding suggests the importance of the unsaturated and/or branched hydrocarbons in the H. axyridis aggregation process. Subsequently, we conducted behavioral assays to test whether (1) there is seasonal variation in the behavioral response of H. axyridis individuals toward substrate markings deposited by conspecifics in the same physiological state and (2) the observed behavioral modification is due to a change in ladybeetle sensitivity and/or a change in the chemical composition of the substrate marking. The results indicate that overwintering individuals exhibit a stronger "following" response toward conspecific substrate markings. This behavior is linked to both the physiological state of ladybeetles and the specific chemical profile of the marking biomolecules deposited under overwintering conditions.