The potential of host-specific volatiles from Tribolium confusum larval faeces for luring the ectoparasitoid Holepyris sylvanidis: Presentation

The ectoparasitoid Holepyris sylvanidis (Bethylidae) attacks larvae of different stored product pest beetles. Previous studies on the olfactory host search of H. sylvanidis revealed that female parasitoids are strongly attracted to volatiles released from Tribolium confusum larval faeces, in particular to (E)-2-nonenal and 1-pentadecene. We suggested that these host-specific key compounds may serve the parasitoid as long-range attractants for host location. In this context, we propose that the attractive volatile blend could be used to establish a new approach within the biological control of stored product pests by guiding the parasitoid to its host and thus, increasing the host finding success. We investigated the potential of the identified host-indicating volatile cues to attract H. sylvanidis from a distance by offering the two key compounds to female parasitoids. Their walking behaviour and the covered distance were analysed on a Kramer sphere. Moreover, in semi-field trials both attractive volatiles were loaded onto rubber septa which were placed next to 4th instars of T. confusum at 1.5 m distance from the parasitoids. We studied the host finding success of H. sylvanidis by (i) measuring the mean time to locate and parasitise T. confusum larvae and (ii) counting the number of parasitised and unparasitised host larvae as well as the number of newly hatched parasitoids compared to the control without additional olfactory cues. First results showed that H. sylvanidis females can locate the provided host larvae from a distance. Parasitistion of host larvae started four days after the release of parasitoids. No effect of the additionally offered hostspecific key volatiles ((E)-2-nonenal and 1-pentadecene) on the parasitoid´s host finding success was observed at the given conditions and used amounts of compounds. Further studies are required to determine the right odour blend and concentrations for attraction of parasitoids over a distance and finally to show that the addition of host-derived kairomones may support the host finding success of H. sylvanidis.The ectoparasitoid Holepyris sylvanidis (Bethylidae) attacks larvae of different stored product pest beetles. Previous studies on the olfactory host search of H. sylvanidis revealed that female parasitoids are strongly attracted to volatiles released from Tribolium confusum larval faeces, in particular to (E)-2-nonenal and 1-pentadecene. We suggested that these host-specific key compounds may serve the parasitoid as long-range attractants for host location. In this context, we propose that the attractive volatile blend could be used to establish a new approach within the biological control of stored product pests by guiding the parasitoid to its host and thus, increasing the host finding success. We investigated the potential of the identified host-indicating volatile cues to attract H. sylvanidis from a distance by offering the two key compounds to female parasitoids. Their walking behaviour and the covered distance were analysed on a Kramer sphere. Moreover, in semi-field trials both attractive volatiles were loaded onto rubber septa which were placed next to 4th instars of T. confusum at 1.5 m distance from the parasitoids. We studied the host finding success of H. sylvanidis by (i) measuring the mean time to locate and parasitise T. confusum larvae and (ii) counting the number of parasitised and unparasitised host larvae as well as the number of newly hatched parasitoids compared to the control without additional olfactory cues. First results showed that H. sylvanidis females can locate the provided host larvae from a distance. Parasitistion of host larvae started four days after the release of parasitoids. No effect of the additionally offered hostspecific key volatiles ((E)-2-nonenal and 1-pentadecene) on the parasitoid´s host finding success was observed at the given conditions and used amounts of compounds. Further studies are required to determine the right odour blend and concentrations for attraction of parasitoids over a distance and finally to show that the addition of host-derived kairomones may support the host finding success of H. sylvanidis

Early detection of stored-product pest insects in grain storage and in the field in Germany

Eine erfolgreiche Früherkennung von Vorratsschädlingen beginnt schon im Freiland und stellt einen zukünftigen und wichtigen Weg des Pflanzenschutzes gegen Schadinsekten dar. Derzeit gibt es allerdings nur wenige Zahlen über das Vorkommen und die Verbreitung von vorratsschädlichen Insekten in Deutschland und über die von ihnen verursachten Schäden an pflanzlichen Nachernteprodukten. Sowohl einheimische/bereits etablierte Arten als auch neue Arten, die durch Handel und Tourismus eingeschleppt werden oder aufgrund der Erwärmung in Folge des Klimawandels auf natürliche Weise einwandern, stellen eine Bedrohung dar. Ziel dieser Pilotstudie war es, Konzepte und Methoden zur Erhebung von Daten über das Auftreten vorratsschädlicher Insekten in Deutschland zu testen. Zu diesem Zweck wurde von 2020 bis 2022 ein Monitoring auf vier landwirtschaftlichen Betrieben, davon drei Ökobetriebe, durchgeführt. Innerhalb und außerhalb der Getreideläger wurden verschiedene mit Lockstoffen versehene Fallen aufgestellt, die monatlich kontrolliert und im Labor ausgewertet wurden. Die Ergebnisse zeigen, dass neben einer großen Anzahl typischer Vorratsschädlinge innerhalb der Läger (z. B. Getreideplattkäfer Oryzaephilus surinamensis oder Dörrobstmotte Plodia interpunctella), einige Insekten auch in den Fallen auf den an die Läger angrenzenden Getreideanbauflächen gefangen wurden. Darunter waren verschiedene Mottenarten und der Getreidekapuziner Rhyzopertha dominica. Die hier gewonnenen Erkenntnisse bilden die Grundlage für das im Rahmen des Klimaschutz-Sofortprogramms 2022 vom Bundesministerium für Ernährung und Landwirtschaft (BMEL) finanzierte und im November 2022 gestartete dreijährige Forschungsvorhaben AVoiD (Abwehr von Vorratsschädlingen in Deutschland). Dabei werden die hier publizierten Erfahrungen in einem entsprechenden Monitoring von Vorratsschädlingen an bundesweit verteilten Standorten umgesetzt.A successful early detection of storage pests already begins in the field and represents a future and important way of plant protection against insect pests. Currently, however, there are few data on the occurrence and distribution of stored-product pest insects in Germany and on the damage they cause to postharvest plant products. Not only established, but also species newly introduced by trade and tourism or expanding naturally due to warming in the course of climate change pose a threat. The objective of this pilot study was to test concepts and methods for collecting data on the incidence of stored-product pests. To this end, a monitoring was carried out from 2020-22 on four farms, three of which were organic. Various semiochemical-baited traps were set up inside and outside grain stores, which were checked monthly and evaluated in the laboratory. The results show that in addition to a large number of pest species inside storages (e.g. sawtoothed grain beetle Oryzaephilus surinamensis or Indianmeal moth Plodia interpunctella), some insects, including different moth species and the lesser grain borer Rhyzopertha dominica, were caught in traps outside, near the adjacent grain fields. The findings obtained here form the basis for the three-year research project AVoiD (Abwehr von Vorratsschädlingen in Deutschland – preventing stored product pests in Germany), which is funded by the Federal Ministry of Food and Agriculture (BMEL) as part of the German Climate Protection Programme 2022 and started in November 2022. In this project, among other things, locations throughout Germany will be sampled and the knowledge published here implemented

Kairomone-induced changes in foraging activity of the larval ectoparasitoid Holepyris sylvanidis are linked with an increased number of male parasitoid offspring

Interactions between stored product pest insects and their parasitoids are well known to be mediated by infochemicals. However, little knowledge is available about the extent to which parasitoid responses to host kairomones improve host search and parasitization success. Here, we tested whether the release of host-specific kairomones of the confused flour beetle, Tribolium confusum, improves host finding of the larval ectoparasitoid Holepyris sylvanidis. Previous studies revealed that volatiles from host larval feces [i.e., (E)-2-nonenal and 1-pentadecene] attract the parasitoid. To determine the most attractive concentration of these two key components, we conduced Y-tube olfactometer bioassays. Most female parasitoids were attracted to a mixture of (E)-2-nonenal and 1-pentadecene at the lowest concentration, while the highest concentration was repellent. Volatiles from host adults (methyl-p-benzoquinone and 4,8-dimethyldecanal) did not attract the parasitoid females at any of the concentrations tested. In flight cage experiments, we analyzed the host finding success of H. sylvanidis by offering host larvae in a Petri dish for 3 days (i) with additionally applied host larval kairomones in the most attractive concentration (test) or (ii) without additional kairomones (control). In test cages, the parasitoids removed a significantly higher number of paralyzed host larvae from the initial population within 48 h than in control cages. After 72 h, significantly more host larvae were parasitized in test cages than in the control. The offspring of parasitoids in test cages differed from the one in control cages by total numbers and especially the number of males. Significantly more parasitoids emerged from the parasitized host larvae in test cages, with enhanced male offspring. Our study demonstrates that the parasitoid’s response to host-associated volatiles can improve parasitization success but also affects the number of males in the parasitoids’ progeny

Cuticular Hydrocarbon Trails Released by Host Larvae Lose their Kairomonal Activity for Parasitoids by Solidification

Successful host search by parasitic wasps is often mediated by host-associated chemical cues. The ectoparasitoid Holepyris sylvanidis is known to follow chemical trails released by host larvae of the confused flour beetle, Tribolium confusum, for short-range host location. Although the hexane-extractable trails consist of stable, long-chain cuticular hydrocarbons (CHCs) with low volatility, the kairomonal activity of a trail is lost two days after release. Here, we studied whether this loss of kairomonal activity is due to changes in the chemical trail composition induced by microbial activity. We chemically analyzed trails consisting of hexane extracts of T. confusum larvae after different time intervals past deposition under sterile and non-sterile conditions. GC-MS analyses revealed that the qualitative and quantitative pattern of the long-chain CHCs of larval trails did not significantly change over time, neither under non-sterile nor sterile conditions. Hence, our results show that the loss of kairomonal activity of host trails is not due to microbially induced changes of the CHC pattern of a trail. Interestingly, the kairomonal activity of trails consisting of host larval CHC extracts was recoverable after two days by applying hexane to them. After hexane evaporation, the parasitoids followed the reactivated host trails as they followed freshly laid ones. Cryo-scanning electron microscopy showed that the trails gradually formed filament-shaped microstructures within two days. This self-assemblage of CHCs was reversible by hexane application. Our study suggests that the long-chain CHCs of a host trail slowly undergo solidification by a self-assembling process, which reduces the accessibility of CHCs to the parasitoid’s receptors as such that the trail is no longer eliciting trail-following behavior

Innovative stored plant products in Germany and the potential threat by native and invasive pest insects: Presentation

Climate change, economic-political developments as well as new trends in diet and in bio-economy considerably influence the assortment of cultivated plants in Germany and thereby, determine the plant products which have to be stored after harvest. In the light of the International Year of Pulses 2016 and also, as a result of the European Soya Declaration, the acreage cultivated with new plants such as pulses, stress tolerant wheat varieties and also oil seed rape expanded worldwide. Due to increasing stocks of novel commodities, the emergence of economically important insects infesting stored products and the possible risk caused by native and invasive pest species have to be generally considered during storage. In this overall context, we studied the capacity of various stored-product pest insects to infest two important pulses. In laboratory tests different varieties of soy and lupine have been offered as whole seeds, grist and flour to selected moth and beetle species common in Germany. Over 14 weeks we examined the developmental time from egg to eclosion as well as the number of adults in the F1 generation compared to control insects reared on their standard feeding substrate. First findings under laboratory conditions (20-25 °C, 65-70 % RH) indicate that these innovative stored products, and in particular its simply processed plant products are highly susceptible to moths (i.a. Ephestia elutella, Plodia interpunctella) and to a much lesser extent also to some beetle species (i.a. Callosobruchus chinensis, Tribolium confusum), but the usally recommended optimal storage conditions (T = 16 °C, RH = 65%) can prevent a loss of volume and quality.Climate change, economic-political developments as well as new trends in diet and in bio-economy considerably influence the assortment of cultivated plants in Germany and thereby, determine the plant products which have to be stored after harvest. In the light of the International Year of Pulses 2016 and also, as a result of the European Soya Declaration, the acreage cultivated with new plants such as pulses, stress tolerant wheat varieties and also oil seed rape expanded worldwide. Due to increasing stocks of novel commodities, the emergence of economically important insects infesting stored products and the possible risk caused by native and invasive pest species have to be generally considered during storage. In this overall context, we studied the capacity of various stored-product pest insects to infest two important pulses. In laboratory tests different varieties of soy and lupine have been offered as whole seeds, grist and flour to selected moth and beetle species common in Germany. Over 14 weeks we examined the developmental time from egg to eclosion as well as the number of adults in the F1 generation compared to control insects reared on their standard feeding substrate. First findings under laboratory conditions (20-25 °C, 65-70 % RH) indicate that these innovative stored products, and in particular its simply processed plant products are highly susceptible to moths (i.a. Ephestia elutella, Plodia interpunctella) and to a much lesser extent also to some beetle species (i.a. Callosobruchus chinensis, Tribolium confusum), but the usally recommended optimal storage conditions (T = 16 °C, RH = 65%) can prevent a loss of volume and quality

The Importance of Methyl-Branched Cuticular Hydrocarbons for Successful Host Recognition by the Larval Ectoparasitoid Holepyris sylvanidis

Cuticular hydrocarbons (CHCs) of host insects are used by many parasitic wasps as contact kairomones for host location and recognition. As the chemical composition of CHCs varies from species to species, the CHC pattern represents a reliable indicator for parasitoids to discriminate host from non-host species. Holepyris sylvanidis is an ectoparasitoid of beetle larvae infesting stored products. Previous studies demonstrated that the larval CHC profile of the confused flour beetle, Tribolium confusum, comprises long chain linear and methyl-branched alkanes (methyl alkanes), which elicit trail following and host recognition in H. sylvanidis. Here we addressed the question, whether different behavioral responses of this parasitoid species to larvae of other beetle species are due to differences in the larval CHC pattern. Our study revealed that H. sylvanidis recognizes and accepts larvae of T. confusum, T. castaneum and T. destructor as hosts, whereas larvae of Oryzaephilus surinamensis were rejected. However, the latter species became attractive after applying a sample of T. confusum larval CHCs to solvent extracted larvae. Chemical analyses of the larval extracts revealed that CHC profiles of the Tribolium species were similar in their composition, while that of O. surinamensis differed qualitatively and quantitatively, i.e. methyl alkanes were present as minor components on the cuticle of all Tribolium larvae, but were absent in the O. surinamensis CHC profile. Furthermore, the parasitoid successfully recognized solvent extracted T. confusum larvae as hosts after they had been treated with a fraction of methyl alkanes. Our results show that methyl alkanes are needed for host recognition by H. sylvanidis

Electrophysiological and behavioral responses of the black-banded oak borer Coroebus florentinus to conspecific insect and host plant volatiles

Aspects of the chemical ecology of the black-banded oak borer, (BBOB) Coroebus florentinus (Coleoptera: Buprestidae), were studied. Odors produced by males and females were similar, both qualitatively and quantitatively. Nonanal, decanal, and geranylacetone, identified in the headspace of both sexes, elicited strong electroantennographic responses from male antennae, but not from female antennae. In dual-choice olfactometer experiments, a blend of these three compounds was attractive to both sexes; males responded to decanal alone, while females responded to geranylacetone alone, suggesting that these compounds are responsible for activity of the blend to the respective sexes. Antennae of both sexes responded electroantennographically to the green leaf volatiles (E)-2-hexenal, (E)-2-hexenol, 1-hexanol, (Z)-3-hexenyl acetate, and n-hexyl acetate, all identified from the host plant Quercus suber. In behavioral experiments, only females were attracted to host-plant odors, and in tests with synthetic compounds, females were attracted to (E)-2-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate. It is likely that these compounds play a role in foraging and/or oviposition behavior of BBOB females