Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. ...Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas.
We report here a first survey of insect orientation to fungal cultures and fungal volatiles from a community ecology perspective. We tested whether volatiles from a ubiquitous yeast-like fungus ...(Aureobasidium pullulans) are broadly attractive to insects in an agricultural landscape. We evaluated insect attraction to fungal cultures and synthetic compounds identified in fungal headspace (2-methyl-1-butanol, 3-methyl-1-butanol, 2-phenylethanol) in a spearmint (Mentha spicata L.) plantation. Three findings emerged: (1) 1,315 insects representing seven orders and 39 species oriented to traps, but 65 % of trapped insects were Dipterans, of which 80 % were hoverflies (Diptera: Syrphidae); (2) traps baited with A. pullulans caught 481 % more insects than unbaited control traps on average, and contained more diverse (Shannon’s H index) and species rich assemblages than control traps, traps baited with Penicillium expansum, or uninoculated media; and (3) insects oriented in greatest abundance to a 1:1:1 blend of A. pullulans volatiles, but mean diversity scores were highest for traps baited with only 2-phenylethanol or 2-methyl-1-butanol. Our results show that individual components of fungal headspace are not equivalent in terms of the abundance and diversity of insects that orient to them. The low abundance of insects captured with P. expansum suggests that insect assemblages do not haphazardly orient to fungal volatiles. We conclude that volatiles from a common fungal species (A. pullulans) are attractive to a variety of insect taxa in an agricultural system, and that insect orientation to fungal volatiles may be a common ecological phenomenon.
Flavonoids are biologically active low molecular weight secondary metabolites that are produced by plants, with over 10,000 structural variants now reported. Due to their physical and biochemical ...properties, they interact with many diverse targets in subcellular locations to elicit various activities in microbes, plants, and animals. In plants, flavonoids play important roles in transport of auxin, root and shoot development, pollination, modulation of reactive oxygen species, and signalling of symbiotic bacteria in the legume
Rhizobium
symbiosis. In addition, they possess antibacterial, antifungal, antiviral, and anticancer activities. In the plant, flavonoids are transported within and between plant tissues and cells, and are specifically released into the rhizosphere by roots where they are involved in plant/plant interactions or allelopathy. Released by root exudation or tissue degradation over time, both aglycones and glycosides of flavonoids are found in soil solutions and root exudates. Although the relative role of flavonoids in allelopathic interference has been less well-characterized than that of some secondary metabolites, we present classic examples of their involvement in autotoxicity and allelopathy. We also describe their activity and fate in the soil rhizosphere in selected examples involving pasture legumes, cereal crops, and ferns. Potential research directions for further elucidation of the specific role of flavonoids in soil rhizosphere interactions are considered.
The vast spectrum of inducible plant defenses can have direct negative effects on herbivores, or indirect effects, for instance in the form of herbivore-induced plant volatiles (HIPVs) that attract ...natural enemies. Various arthropods have evolved ways to suppress plant defenses. To test whether this is the case for caterpillar-induced HIPVs, we compared the volatile induction by
Spodoptera frugiperda
(Lepidoptera: Noctuidae), which is particularly well adapted to feed on maize (
Zea mays
), with the induction by three more generalist noctuid larvae. We tested the hypothesis that
S. frugiperda
suppresses HIPV emissions in maize, and thereby reduces attractiveness to natural enemies. HIPV emissions triggered by
S. frugiperda
when feeding on maize were indeed found to be significantly weaker than by
Spodoptera littoralis
,
Spodoptera exigua
, and
Helicoverpa armigera
. The suppression seems specific for maize, as we found no evidence for this when
S. frugiperda
caterpillars fed on cotton (
Gossypium herbaceum
). Artificially damaged maize plants treated with larval regurgitant revealed that HIPV suppression may be related to factors in the caterpillars’ oral secretions. We also found evidence that differential physical damage that the caterpillars inflict on maize leaves may play a role. The suppressed induction of HIPVs had no apparent consequences for the attraction of a common parasitoid of
S. frugiperda
,
Cotesia marginiventris
(Hymenoptera: Braconidae). Nevertheless, the ability to manipulate the defenses of its main host plant may have contributed to the success of
S. frugiperda
as a major pest of maize, especially in Africa and Asia, which it has recently invaded.
Soil is one of the major habitats of bacteria and fungi. In this arena their interactions are part of a communication network that keeps microhabitats in balance. Prominent mediator molecules of ...these inter- and intraorganismic relationships are inorganic and organic microbial volatile compounds (mVOCs). In this review the state of the art regarding the wealth of mVOC emission is presented. To date, ca. 300 bacteria and fungi were described as VOC producers and approximately 800 mVOCs were compiled in DOVE-MO (database of volatiles emitted by microorganisms). Furthermore, this paper summarizes morphological and phenotypical alterations and reactions that occur in the organisms due to the presence of mVOCs. These effects might provide clues for elucidating the biological and ecological significance of mVOC emissions and will help to unravel the entirety of belowground‚ volatile-wired’ interactions.
It has been demonstrated that Drosophila suzukii is capable of attacking ripening fruit, making it a unique species within a fly family named for their attraction towards the fermentation products ...associated with rotten fruits, vinegar, and yeast. It also has been hypothesized that D. suzukii is more attracted to the volatiles associated with the earlier ripening stages of fruit development, and in turn, that D. suzukii is less attracted to fermented food resources, especially when compared with D. melanogaster. Here, we demonstrate that D. suzukii and its close relative D. biarmipes are in fact more sensitive to volatiles associated with the fruit-ripening process; however, in choice-assays, both spotted-wing species are more attracted to fermented fruit than to earlier stages of fruit development, which is similar to the behavioral preferences of D. melanogaster, and thus, fruit developmental stage alone does not explain the ecological niche observed for D. suzukii. In contrast, we show that both D. suzukii and D. biarmipes are more attracted to leaf odors than D. melanogaster in behavioral trials. For D. suzukii, this differential behavioral preference towards leaves appears to be linked to β-cyclocitral, a volatile isoprenoid that we show is most likely a novel ligand for the “ab3A” neuron. In addition, this compound is not detected by either of the other two tested fly species.
The glasshouse whitefly (
Trialeurodes vaporariorum
Westwood) is a polyphagous arthropod pest that is of particular detriment to glasshouse grown tomato (
Solanum lycopersicum
) across temperate ...regions of the world. Control of whiteflies with synthetic pesticides has resulted in the evolution of resistant genotypes and a reduction in natural enemies, thus highlighting the need for environmentally sound control strategies. Volatile organic compounds (VOCs) offer an environmentally benign alternative to synthetic chemical sprays and this study explored the use of VOCs as insect repellents and plant defence elicitors to control whiteflies on tomato in a commercial glasshouse setting. Limonene in the form of a volatile dispenser system was found to successfully repel whitefly from the target crop and increased fruit yield by 32% during a heavy whitefly infestation. Analysis of tomato herbivore induced plant volatiles (HIPVs) led us to select methyl salicylate (MeSA) as the plant elicitor and application of MeSA to un-infested tomato plants was found to successfully reduce whitefly population development and increase yield by 11%, although this difference was marginally statistically significant. Combination of these two methods was also effective but whitefly abundance in combined plots was similar to the standalone limonene treatment across the course of the experiment. All of the VOC based control methods we used had a negative impact on whitefly performance, with more pronounced effects during the first few weeks of infestation. In subsequent laboratory experiments, we found elevated peroxidase (POD) activity and a significant increase in TPX1 and PR1 transcripts in MeSA treated plants. This led us to deduce that MeSA immediately induced plant defences, rather than priming them. We did however see evidence for residual priming, as plants treated with MeSA and infested with whiteflies produced significantly higher levels of POD activity than whitefly infestation alone. Despite the fact that our treatments failed to synergise, our methods can be optimised further, and the effectiveness of the standalone treatments is promising for future studies. In particular, our repellent limonene dispensers were extremely effective at deterring whiteflies and offer a low economic cost and easy to implement whitefly control option. The methods we have used here could be incorporated into current integrated pest management (IPM) systems, a sustainable approach to pest control which will be central to our efforts to manage whitefly populations under glass in the future.
Mosquito Attractants Dormont, Laurent; Mulatier, Margaux; Carrasco, David ...
Journal of chemical ecology,
05/2021, Volume:
47, Issue:
4-5
Journal Article
Peer reviewed
Vector control and personal protection against anthropophilic mosquitoes mainly rely on the use of insecticides and repellents. The search for mosquito-attractive semiochemicals has been the subject ...of intense studies for decades, and new compounds or odor blends are regularly proposed as lures for odor-baited traps. We present a comprehensive and up-to-date review of all the studies that have evaluated the attractiveness of volatiles to mosquitoes, including individual chemical compounds, synthetic blends of compounds, or natural host or plant odors. A total of 388 studies were analysed, and our survey highlights the existence of 105 attractants (77 volatile compounds, 17 organism odors, and 11 synthetic blends) that have been proved effective in attracting one or several mosquito species. The exhaustive list of these attractants is presented in various tables, while the most common mosquito attractants - for which effective attractiveness has been demonstrated in numerous studies – are discussed throughout the text. The increasing knowledge on compounds attractive to mosquitoes may now serve as the basis for complementary vector control strategies, such as those involving lure-and-kill traps, or the development of mass trapping. This review also points out the necessity of further improving the search for new volatile attractants, such as new compound blends in specific ratios, considering that mosquito attraction to odors may vary over the life of the mosquito or among species. Finally, the use of mosquito attractants will undoubtedly have an increasingly important role to play in future integrated vector management programs.
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