Assessment of the efficacy of Piper methysticum (Micrembryeae: Piperaceae) as a bioinsecticide, and/or spinosad combined with attractive plant volatiles for a novel lure and kill strategy against Bactrocera tryoni (Diptera: Tephritidae) in laboratory.

The Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is a crop pest of global economic importance because of its wide range of hosts and its invasiveness capacities. To develop a novel integrated and sustainable crop protection, we have investigated the insecticidal properties of different varieties of kava (Piper methysticum [Frost]) extracted by two methods and the attractive effects of six plant volatiles identified from B. tryoni host plants to female, mated or not. We did not identify any significant insecticidal effect of the traditional Pacific kava plant at the tested concentrations. Among mated females, ethyl acetate compared to the no odor control elicited the highest attraction (87%, of which 60% for this odor), while ethyl butyrate was preferred compared with ethyl acetate in dual choice assays. Flies' preferences for specific odors depended on their mating status and the odor landscape they were confronted with. Combination with the commercial ingestion insecticide (Success 4: spinosad, 480 g/l, Dow AgroSciences, Valbonne, France) with the plant volatiles were tested to detect an increase in mortality related to the addition of an attractant. The 2-heptanone slightly showed a tend to increase the attractiveness of mated females within 4-6 h to the food bait, but the results were not statistically significant after 8 h. Further tests should be performed with other concentrations or mixtures of the identified host plant volatiles to develop a strong lure and kill strategy.

Electrophysiological and Behavioral Responses of Virgin Female Bactrocera tryoni to Microbial Volatiles from Enterobacteriaceae.

The Queensland fruit fly (Bactrocera tryoni) is a major polyphagous pest widespread in Australia and several Pacific Islands. Bacteria present on the host plant phyllosphere supply proteins, essential for egg development and female sexual maturity. We investigated the role of microbial volatile organic compounds (MVOCs) emitted by Enterobacteriaceae commonly found on the host plant and in the fly gut in attracting virgin females. Bacteria were cultured on artificial media and natural fruits, at various pH, and MVOCs were collected using different headspace volatile absorbent materials. The olfactory responses of virgin females to bacterial MVOCs were assessed via electrophysiology and behavioral assays. The production of MVOCs was strongly influenced qualitatively by the bacterial strain and the type of media, and it semi-quantitatively varied with pH and time. MVOCs emitted by Klebsiella oxytoca invoked the strongest antennal response and were the most attractive. Among the identified compounds triggering an olfactory response, D-limonene and 2-nonanone were both significantly behaviorally attractive, whereas phenol, nonanal, isoamyl alcohol, and some pyrazines appeared to be repulsive. This study deepens our understanding of the chemical ecology between fruit flies and their bacterial symbionts and paves the way for novel synthetic lures based on specifically MVOCs targeting virgin females.

The Scent of Individual Foraging Bees.

Honey bees (Apis mellifera) forage by using their sense of smell and returning to floral odours that they have previously learned to associate with high-quality food rewards. Foraging bees communicate with other bees in the hive about food sources by exchanging chemical and locational information. It is well established that bees transfer non-volatile information regarding taste and quality of nectar via trophallaxis and communicate location information via directional dances. But to our knowledge, volatiles carried by returning forager bees on their bodies has not been explored as another source of chemical information. We investigated the cuticular-adsorbed odours of bees when foraging on three different crops and compared their odours with the crops' flower headspace. We found that cuticular extracts were in majority correlated with the flower headspace where bees were foraging, specific to the crop and field. Our results support the hypothesis that the scent of returning forager bees can be communicated to hivemates and is associated with information about current floral resources. Some of the floral volatiles that we identified in bee extracts had been previously found to be key compounds learned from the crop, thus supporting a mechanism for the selection of decisive compounds.

Electrophysiological and Behavioral Responses of Queensland Fruit Fly Females to Fruit Odors.

Females of the Queensland fruit fly (QFF), Bactrocera tryoni, are amongst the most damaging pests of horticulture in Australia and neighboring countries. Females can lay eggs into more than a hundred species of fruits and vegetables, resulting in large crop losses. Sexually mature males can be managed sustainably with traps baited with long-lasting synthetic lures, and sexually immature males and females can be attracted and killed by short-lived protein baits applied directly on surfaces, with a low success rate (< 20%). No long-lasting attractants for virgin or mated females exist. With the aim of developing a female attractant for surveillance, we collected and analyzed the odors of four ripe host fruits: orange, cherry guava, banana and feijoa. Virgin and mated female QFF were tested with gas-chromatography coupled with electro-antennographic detection to identify electrophysiologically (EAD)-active compounds. We detected 41 EAD-active compounds, with seven found common for more than one fruit. Overall, mated females responded more often and with higher intensity than virgin females. In particular, five compounds present either in cherry guava or feijoa triggered a significantly higher EAD response from mated females than from virgins. Twenty-six EAD-active compounds were selected and tested individually in a Y-tube olfactometer to measure attraction of both virgin and mated females. Behavioral responses differed significantly amongst the compounds, but not strongly between virgin and mated females. We did not find any correlation between electrophysiological and behavioral responses. Further field testing with behaviorally-active compounds is needed for the development of a new QFF female lure.

Selection of key floral scent compounds from fruit and vegetable crops by honey bees depends on sensory capacity and experience.

Flowers have complex odours often comprising hundreds of volatile compounds. Floral scents are species-specific, and vary also among populations, varieties, sexes or lines, as well as with phenology. Honey bees, Apis mellifera, generally associate only a few key compounds among the complex floral scent with the food reward which guides their foraging choices. How these key compounds are selected remains partially unexplained, despite their crucial role in influencing foraging. Using electrophysiological techniques and behavioural assays, we identified the key bioactive compounds that bees detected with their antennae and that were associated with appetitive responses from four fruit crops and three vegetable crops. Three quantities of identified key volatile compounds were assayed with the two methods in each of four different seasons with experienced foragers. Whether the selection of these key compounds is determined by the sensory capability of the bee or influenced by its foraging experience was assessed by comparing experienced and naïve bees. Our results showed that experienced foragers were electrophysiologically-sensitive to a specific set of key compounds for each crop, independent of variation in quantity among several varieties. Experienced foragers responded to these compounds in all seasons, with increased electrophysiological amplitude with increasing quantities. Behavioural appetitive responses varied amongst compounds and seasons, revealing preferences based on associative learning. Naïve bees that were exposed to compounds and subsequently learned them, tended to be overall more sensitive. We discuss our results based on the identity of each bioactive compound and their presence in nature. Preferences for specific floral compounds based on sensory biases exist and associative learning may reinforce behavioural attraction depending on foraging experience in each season.

Odorant-Based Detection and Discrimination of Two Economic Pests in Export Apples.

Detection of pest infestations in fresh produce traded internationally could offer improved prospects for reducing the movement of unwanted pests. Because immature stages of some pests can be difficult to find visually, other cues such as herbivore-induced volatiles that can potentially be detected at the early stages of infestation are worth investigating. In this study, we artificially infested postharvested apples (Malus × domestica 'Royal Gala') with two economic apple pests, the specialist codling moth (CM, Cydia pomonella Linnaeus, Lepidoptera: Tortricidae) and the generalist Queensland fruit fly (QFF, Bactrocera tryoni, Froggatt, Diptera: Tephritidae) and collected volatile organic compounds (VOCs) over time (days 0, 6, and 14-15). In both infestation experiments, we found a strong and significant interaction between time and treatment. Apples infested with the QFF emitted lower total amounts of VOCs than uninfested apples, whereas apples infested with the CM released similar total amounts of VOCs. Apples infested with CM had increases in several hexyl and butyl esters, which were particularly noticeable after 15 d. In contrast, changes in ethyl esters were characteristics of QFF infestation and could be detected from day 6. Our multilevel and multivariate statistical analysis identified specific volatile biomarkers for each species at each sampling time that can be used to design a new tool for remote detection and surveillance of these invasive pests in harvested apples. Nevertheless, other information such as the cultivar as well as the storage condition needs to be taken into consideration to increase accuracy of future odorant-based sensors for pest identification.

The importance of key floral bioactive compounds to honey bees for the detection and attraction of hybrid vegetable crops and increased seed yield.

BACKGROUND: Crop breeding programmes generally select for traits for improved yield and human consumption preferences. Yet, they often overlook one fundamental trait essential for insect-pollinated crops: pollinator attraction. This is even more critical for hybrid plants that rely on cross-pollination between the male-fertile line and the male-sterile line to set seeds. This study investigated the role of floral odours for honey bee pollination that could explain the poor seed yield in hybrid crops. RESULTS: The key floral bioactive compounds that honey bees detect were identified for three vegetable hybrid crops. It was found that 30% of the variation in bioactive compound quantities was explained by variety. Differences in quantities of the bioactive compounds triggered different degrees of olfactory response and were also associated with varied appetitive response. Correlating the abundance of each bioactive compound with seed yield, it was found that aldehydes such as nonanal and decanal can have a strong negative influence on seed yield with increasing quantity. CONCLUSION: Using these methodologies to identify relevant bioactive compounds associated with honey bee pollination, plant breeding programmes should also consider selecting for floral traits attractive to honey bees to improve crop pollination for enhanced seed yield. © 2018 Society of Chemical Industry.

Possible mechanisms of pollination failure in hybrid carrot seed and implications for industry in a changing climate.

Approximately one-third of our food globally comes from insect-pollinated crops. The dependence on pollinators has been linked to yield instability, which could potentially become worse in a changing climate. Insect-pollinated crops produced via hybrid breeding (20% of fruit and vegetable production globally) are especially at risk as they are even more reliant on pollinators than open-pollinated plants. We already observe a wide range of fruit and seed yields between different cultivars of the same crop species, and it is unknown how existing variation will be affected in a changing climate. In this study, we examined how three hybrid carrot varieties with differential performance in the field responded to three temperature regimes (cooler than the historical average, average, and warmer that the historical average). We tested how temperature affected the plants' ability to set seed (seed set, pollen viability) as well as attract pollinators (nectar composition, floral volatiles). We found that there were significant intrinsic differences in nectar phenolics, pollen viability, and seed set between the carrot varieties, and that higher temperatures did not exaggerate those differences. However, elevated temperature did negatively affect several characteristics relating to the attraction and reward of pollinators (lower volatile production and higher nectar sugar concentration) across all varieties, which may decrease the attractiveness of this already pollinator-limited crop. Given existing predictions of lower pollinator populations in a warmer climate, reduced attractiveness would add yet another challenge to future food production.

Kiwifruit Flower Odor Perception and Recognition by Honey Bees, Apis mellifera.

Volatile organic compounds (VOCs) from male and female kiwifruit (Actinidia deliciosa 'Hayward') flowers were collected by dynamic headspace sampling. Honey bee (Apis mellifera) perception of the flower VOCs was tested using gas chromatography coupled to electroantennogram detection. Honey bees consistently responded to six compounds present in the headspace of female kiwifruit flowers and five compounds in the headspace of male flowers. Analysis of the floral volatiles by gas chromatography-mass spectrometry and microscale chemical derivatization showed the compounds to be nonanal, 2-phenylethanol, 4-oxoisophorone, (3E,6E)-α-farnesene, (6Z,9Z)-heptadecadiene, and (8Z)-heptadecene. Bees were then trained via olfactory conditioning of the proboscis extension response (PER) to synthetic mixtures of these compounds using the ratios present in each flower type. Honey bees trained to the synthetic mixtures showed a high response to the natural floral extracts, indicating that these may be the key compounds for honey bee perception of kiwifruit flower odor.

Influence of the pathogen Candidatus Liberibacter solanacearum on tomato host plant volatiles and psyllid vector settlement.

Candidatus Liberibacter solanacearum (CLso) is an unculturable bacterium vectored by the tomato potato psyllid (TPP) Bactericera cockerelli and has been associated with Zebra chip disease in potato and with other economically relevant symptoms observed in solanaceous crops. By altering their host and vector's biological system, pathogens are able to induce changes that benefit them by increasing their transmission rate. Understanding these changes can enable better targeting of mechanisms to control pathogen outbreaks. Here, we explored how the CLso infectious status affects the volatile organic compounds (VOCs) of the tomato plant, and whether the CLso infectious status of TPP influences host plant settlement. These chemical and behavioral changes can ultimately affect the rate of encounter between the host and the vector. Results from headspace volatile collection of tomato plants showed that CLso infected tomato plants emitted a qualitatively and quantitatively different blend of VOCs compared to sham-infected plants. By a factorial experiment, we showed that CLso negative (CLso-) TPP preferred to settle 70 % more often on infected tomato plants, while CLso positive (CLso+) TPP were found 68 % more often on sham-infected tomato plants. These results provide new evidence in favor of both host and vector manipulation by CLso.

An offspring signal of quality affects the timing of future parental reproduction.

Solicitation signals by offspring are well known to influence parental behaviour, and it is commonly assumed that this behavioural effect translates into an effect on residual reproduction of parents. However, this equivalence assumption concerning behavioural and reproductive effects caused by offspring signals remains largely untested. Here, we tested the effect of a chemical offspring signal of quality on the relative timing and amount of future reproduction in the European earwig (Forficula auricularia). We manipulated the nutritional condition of earwig nymphs and exposed females to their extract, or to solvent as a control. There were no significant main effects of exposure treatment on 2nd clutch production, but exposure to extracts of well-fed nymphs induced predictable timing of the 2nd relative to the 1st clutch. This result demonstrates for the first time that an offspring signal per se, in the absence of any maternal behaviour, affects maternal reproductive timing, possibly through an effect on maternal reproductive physiology.

A chemical signal of offspring quality affects maternal care in a social insect.

Begging signals of offspring are condition-dependent cues that are usually predicted to display information about the short-term need (i.e. hunger) to which parents respond by allocating more food. However, recent models and experiments have revealed that parents, depending on the species and context, may respond to signals of quality (i.e. offspring reproductive value) rather than need. Despite the critical importance of this distinction for life history and conflict resolution theory, there is still limited knowledge of alternative functions of offspring signals. In this study, we investigated the communication between offspring and caring females of the common earwig, Forficula auricularia, hypothesizing that offspring chemical cues display information about nutritional condition to which females respond in terms of maternal food provisioning. Consistent with the prediction for a signal of quality we found that mothers exposed to chemical cues from well-fed nymphs foraged significantly more and allocated food to more nymphs compared with females exposed to solvent (control) or chemical cues from poorly fed nymphs. Chemical analysis revealed significant differences in the relative quantities of specific cuticular hydrocarbon compounds between treatments. To our knowledge, this study demonstrates for the first time that an offspring chemical signal reflects nutritional quality and influences maternal care.

Sexual isolation and cuticular hydrocarbon differences between Drosophila santomea and Drosophila yakuba.

Drosophila santomea and Drosophila yakuba are two sister species inhabiting Saõ Tomé island. Previous studies showed that both species display strong reproductive isolation, although they can produce a few viable hybrids. Our study tried to understand the mechanism of this ethological isolation between two allopatric strains. A strong sexual isolation was confirmed, with a marked asymmetry. Comparisons of latency times to either courtship or copulation suggest that males do not discriminate females, whereas D. yakuba females, but not D. santomea females, accept their homospecifics more quickly. Cuticular hydrocarbon compositions of both species and sexes were also established with gas chromatography (GC) and GC/mass spectrometry analysis. All have (Z)-7-tricosene as their major compound. There are several quantitative differences between species for few minor compounds. The largest difference concerns n-heneicosane, which is more abundant in D. santomea than in D. yakuba flies (up to seven times more between males). A similar quantitative difference was also found in a pair of sympatric strains. Furthermore, D. yakuba males artificially perfumed with n-heneicosane were discriminated negatively by D. yakuba females, suggesting a role for this compound in the sexual isolation between these two species.