Wireworms use barley root volatile chemicals to locate their host plant in soil

Poster (2011, July)

Wireworms (Coleoptera: Elateridae) are soil dwelling pests of many crops. Aldrin and lindane used to provide satisfactory treatment levels of infested lands. Their withdrawal from the market for ... [more ▼]

Wireworms (Coleoptera: Elateridae) are soil dwelling pests of many crops. Aldrin and lindane used to provide satisfactory treatment levels of infested lands. Their withdrawal from the market for environmental issues gave birth to new needs in terms of management. In order to enhance integrated management of this pest, we work on the chemical ecology of Agriotes sordidus Illiger. We focus on its interaction with barley roots, mediated by volatile organic compounds (VOCs). Our experimentations are based on behavioural responses of wireworms in olfactometric devices and their statistical relevance. [less ▲]

Assessment of aphid saliva role as plant defense elicitation by multiple approaches.

Poster (2011, July)

Carrion beetles visiting pig carcasses during early spring in urban, forest and agricultural biotopes of Western Europe

in Journal of Insect Science [=JIS] (2011), 11

Carrion beetles are important in terrestrial ecosystems, consuming dead mammals and promoting the recycling of organic matter into ecosystems. Most forensic studies are focused on succession of Diptera ... [more ▼]

Carrion beetles are important in terrestrial ecosystems, consuming dead mammals and promoting the recycling of organic matter into ecosystems. Most forensic studies are focused on succession of Diptera while neglecting Coleoptera. So far, little information is available on carrion beetles postmortem colonization and decomposition process in temperate biogeoclimatic countries. These beetles are however part of the entomofaunal colonization of a dead body. Forensic entomologists need databases concerning the distribution, ecology and phenology of necrophagous insects, including silphids. Forensic entomology uses pig carcasses to surrogate human decomposition and to investigate entomofaunal succession. However, few studies have been conducted in Europe on large carcasses. The work reported here monitored the presence of the carrion beetles (Coleoptera: Silphidae) on decaying pig carcasses in three selected biotopes (forest, crop field, urban site) at the beginning of spring. Seven species of Silphidae were recorded: Nicrophorus humator (Gleditsch), Nicrophorus vespillo (L.), Nicrophorus vespilloides (Herbst), Necrodes littoralis L., Oiceoptoma thoracica L., Thanatophilus sinuatus (Fabricius), Thanatophilus rugosus (L.). All of these species were caught in the forest biotope, and all but O. thoracica were caught in the agricultural biotope. No silphids were caught in the urban site [less ▲]

Microorganisms from Aphid Honeydew Attract and Enhance the Efficacy of Natural Enemies

in Nature Communications (2011), 2

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their ... [more ▼]

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their dispersal in natural environment. Here we report the first isolation of a bacterium from the pea aphid Acyrthosiphon pisum honeydew, Staphylococcus sciuri, which acts as a kairomone enhancing the efficiency of aphid natural enemies. Our findings represent the first case of a host-associated bacterium driving prey location and ovipositional preference for the natural enemy. We show that this bacterium has a key role in tritrophic interactions because it is the direct source of volatiles used to locate prey. Some specific semiochemicals produced by S. sciuri were also identified as significant attractants and ovipositional stimulants. The use of this host-associated bacterium could certainly provide a novel approach to control aphids in field and greenhouse systems. [less ▲]

Development of natural semiochemical slow-release formulations as biological control devices

in Ioannou, Efstathia; Roussis, Vassilios (Eds.) Trends in natural products research : a PSE young scientists' meeting, June 12-15, 2011, Kolymvari - Crete. Book of abstracts (2011, June 12)

Semiochemicals – informative molecules used in insect-insect or plant-insect interactions – have been widely considered within various integrated pest management (IPM) strategies. In the present work, two ... [more ▼]

Semiochemicals – informative molecules used in insect-insect or plant-insect interactions – have been widely considered within various integrated pest management (IPM) strategies. In the present work, two sesquiterpenoids, E-β-farnesene and E-β-caryophyllene, were formulated for their properties as aphid enemy attractants. E-β-farnesene, the alarm pheromone of many aphid species, was also identified as a kairomone by attracting aphid predators and parasitoids. E-β-caryophyllene was identified as a potential component of the aggregation pheromone of the Asian ladybird, Harmonia axyridis Pallas, another aphid predator. The two products were purified from essential oils of Matricaria chamomilla L. (Asteraceae) and Nepeta cataria L. (Lamiaceae), respectively. Natural and biodegradable formulations were then investigated in order to deliver these molecules on crop fields for a long period of time as biological control devices. Due to their sensitivity to oxidation, both sesquiterpenes needed to be protected from oxygen degradation. For this purpose, alginate – hydrophilic matrix with low oxygen permeability – was used as polymer for the formulations: the main objective was to deliver semiochemicals in the air in a controlled way. Consequently, a careful selection of alginates was realised. Formulated beads showed different structural and encapsulation properties depending on various formulation factors. Alginate formulations were characterised by texturometry and by confocal microscopy in order to observe the distribution of semiochemicals in alginate network. The last step of alginate bead characterisation consisted in studying release rate of semiochemicals in laboratory-controlled conditions by optimised volatile collection system and validated fast GC analytical procedures Finally, the efficiency of formulations as aphid predator (Syrphidae species) and parasitoid (Aphidius ervi) attractants was demonstrated by field trapping and olfactometry experiments. [less ▲]

Ant-aphid mutualism - How do ants locate aphid colonies?

Poster (2011, June)

That some ant species show mutualistic relationships with some aphid species is well known since several decades. Ants protect aphids against natural enemies and as a reward collect the sugar-rich aphid ... [more ▼]

That some ant species show mutualistic relationships with some aphid species is well known since several decades. Ants protect aphids against natural enemies and as a reward collect the sugar-rich aphid excretion called honeydew. However, very little information is available on possible semiochemicals involved in these interactions. This study aims to identify semiochemicals involved in the establishment of this relation, using both chemical and behavioral approaches. Preliminary choice tests confirmed that ant scouts are able to detect aphid colonies at a distance using volatile organic compounds (VOC). Those VOC influencing ant’s orientation may originate from different sources: the attacked plant, the honeydew produced by the aphids and the aphids themselves. VOC emission profiles of each of those potential sources have been established using gas chromatography. Y-olfactometer assay revealed that honeydew volatile compounds are the key element in this distant attraction. Moreover, based on these VOCs, ant scouts are able to discriminate between the honeydew produced by a myrmecophilous and a non myrmecophilous aphid species. Thus, more than just a sugar source, honeydew is an attractant for ant scouts towards myrmecophilous aphids. [less ▲]

Volatile organic compounds of the roots of barley and their role in the rhizosphere

Poster (2011, May 24)

Volatile organic compounds emitted by plants are known to intervene with various biotic environmental factors. Up to now, most of the studies have been focused on aerial volatiles and root liquid exudates ... [more ▼]

Volatile organic compounds emitted by plants are known to intervene with various biotic environmental factors. Up to now, most of the studies have been focused on aerial volatiles and root liquid exudates. Very few researches have been completed concerning belowground volatiles released into the rhizosphere despite their potential capacity to carry information between organisms. The Rhizovol project, started in autumn 2010, involves 5 different units of Gembloux Agro-Bio Tech collectively studying the production of belowground volatiles by barley roots underlying various biotic interactions in the rhizosphere. Some preliminary results of each partner of the project will be presented. To achieve this goal, analytical methods allowing the sampling, separation, identification and quantification of belowground volatile compounds have to be developed, taking into account their potential modifications in the rhizosphere once released by the roots. They enable the subsequent characterization and study of the interactions between barley and its rhizospheric partners chosen for this study. These interactions imply three types of organisms: beneficial organisms, pathogenic agents and plant and insect pests. Beneficial organisms can promote the growth of barley by the emission of volatiles; on the other hand barley can support their growth and metabolism. These phenomenons will be assessed by the study of 19 strains of plant growth-promoting bacteria (PGPR). Three pathogenic agents - two fungi (Fusarium culmorum and Cochliobolus sativus) and one virus (Barley yellow dwarf virus) - were chosen as they are known to cause various diseases on barley, especially on roots. The attractive or repellent effects of barley root volatiles on the pathogenic agents or their vectors, as well as the effect of volatiles on the diseases evolution will be evaluated. The project also includes several types of pests such as plants and insects. Plants can compete with barley for space and nutrients through volatile interactions. This will be assessed by the study of autotoxicity by barley itself and allelopathy with 8 weeds and a hemiparasitic plant (Rhinanthus minor). The effects of barley volatiles can also impact the severity of the attacks by insects. This part will be conducted with wireworms as they represent worldwide known pests, and aphids, through their viral vector role. Eventually, as soil characteristics can strongly influence the diffusion of volatile compounds, the diffusion behaviour of the identified volatile biomolecules through the soil will be modelled. Tritrophic interactions (e.g. insect-plant-pathogenic fungi) will be studied based on each bitrophic interaction results. Over-all, the Rhizovol project aims at improving the knowledge of interactions mediated by volatile compounds in the rhizosphere and at establishing new biocontrol methods that could contribute to integrated disease and pest management systems. [less ▲]

Impact of Harmonia axyridis (Coleoptera: Coccinellidae) on the survival rates of other aphidophagous species in semi-field conditions

in Communication in agricultural and applied biological sciences (2011, May 24), 76(2), 219-226

The multicoloured Asian ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae), previously introduced as a biological control agent against aphids, is now frequently considered as an intraguild ... [more ▼]

The multicoloured Asian ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae), previously introduced as a biological control agent against aphids, is now frequently considered as an intraguild predator, consuming other aphid natural enemies. Interactions between this exotic ladybird and other aphidophagous species present in Belgian agro-ecosystems such as Coccinella septempunctata, Episyrphus balteatus and Chrysoperla carnea are asymmetric to the benefit of H. axyridis. This study focuses on the survival rate of three aphidophagous species Harmonia axyridis (Ha), Coccinella septempunctata (C7) and Episyrphus balteatus (Eb) placed in cages in biological fields of potato and sugar beet. During June and July, hermetic cages were disposed on the crops with 10 larvae (second stage) of each aphidophagous. Four types of cages were observed (1) Ha+Eb+C7+ aphids, (2) Ha+Eb+C7, (3) Eb+C7+ aphids and (4) Eb+C7. Each combination was repeated three times. In sugar beet fields, E. balteatus was the species with the highest mortality rate. The two coccinellid species had a better survival rate than E. balteatus. All aphidophagous species had higher mortality rates in absence of aphids. In potato, when aphids were present in excess, the survival rates of all aphidophagous insects were lower than in sugar beet probably because A. fabae is less adapted to the potato morphology. Nevertheless, we have observed in potato no mortality of C. 7-punctata during all its development cycle. This suggests that (1) C. 7-punctata may use aphids as food sources more efficiently than H. axyridis and (2) that interactions between aphidophagous could be less frequent (difficulty of mobility). In potato and sugar beet, H. axyridis had the longest development cycle, being still at the larval stage when C. 7-punctata and E. balteatus reached the pupae stage. We can suppose that pupae of E. balteatus and C. 7-punctata were an alternative food (intraguild prey) to H. axyridis when aphids were lacking. Pupae are immobile and therefore more sensitive to the attack of predators. [less ▲]

Attraction of wireworms to root-emitted volatile organic compounds of barley

Conference (2011, May 24)

Wireworms, the belowground larvae of click beetles (Coleoptera: Elateridae), represent a threat for various crops, including cereals, potatoes and small fruits, in many countries. In order to promote the ... [more ▼]

Wireworms, the belowground larvae of click beetles (Coleoptera: Elateridae), represent a threat for various crops, including cereals, potatoes and small fruits, in many countries. In order to promote the development of bio-pesticides or the selection of resistant varieties, studies concerning the close relationship between wireworms and the roots they attack have to be conducted. Indeed, lacks of knowledge in the chemical ecology of these small but consequent pests baffle such achievements. Here, we studied the reactions of wireworms (Agriotes sordidus Illiger) facing root-emitted volatile organic compounds (VOCs) of barley. We first tested the ability of wireworms to orientate towards a blend of volatile compounds emitted by seven day’s old mashed roots of barley grown in vermiculite. We used a Y-shaped horizontal olfactometre, which inferior half was filled with compressed and humidified vermiculite. Wireworms were able to detect blends of volatiles emitted by mashed roots, and to orientate their foraging behaviour toward the emission source. Volatile compounds were identified from barley roots using SPME-GC-MS and several chemicals were identified. This study is part of a larger programme which purpose is the identification of VOCs emitted by the roots of barley and different actors of the rhizosphere, and to assess their semiochemical functions. [less ▲]

Predominant effects of host plant species on Aphis gossypii aphid and Episyrphus balteatus hoverfly in a tritrophic approach

Poster (2011, May 24)

The aphid Aphis gossypii Glover (Homoptera: Aphididae) is known as worldwide important pest. It causes serious injuries to crops, but is also able to feed on various cultivated and wild plants. Some ... [more ▼]

The aphid Aphis gossypii Glover (Homoptera: Aphididae) is known as worldwide important pest. It causes serious injuries to crops, but is also able to feed on various cultivated and wild plants. Some programs are developped to control this aphid. In many studies , hoverfy Episyrphus balteatus De Geer (Diptera : Syrphidae) is used as an efficient and aphid specific predator in biological control systems. In this work, we study cotton aphid choice plant discrimination, the effect of host plants on its developpment(fecondity and mortality), and the E.balteatus foraging and oviposition behavior according aphid host plants. Biologic parameters were observed using various plant combinations. E.balteatus behavioral observations were conducted using the Noldus Observer v.5.0. A.gossypii makes discriminant choice of his hosts, with better preference on Cucurbita pepo L. (Cucurbitaceae) and Capsicum annuum L. (Solanaceae). Dacryodes edulis (G. Don) H.J. Lam. (Burseraceae) and Vicia faba L. (Fabaceae) are the midle choice while Hibiscus sabdariffa L. (Malvaceae) is less chosen. A.gossypii develops easily on C.pepo, and weakly on C.anuum, H.sabdariffa,and V.faba. D. edulis induces very high mortality to A.gossypii. According to E. balteatus behavior, A. gossypii is more attractive when infesting C .pepo and V.faba, less on H. sabdariffa. While non infested , the hoverfly more attractive plant is V.faba. Our results highlited the importance of interactions between aphids and their host plants and the prey-host influence on a specific aphid predatory hoverfy. Suitable ways in correlation with this work are to investigated to complete this study and perform aphids biological control. [less ▲]