The role of larvae of black soldier fly and house fly and of feed substrate microbes in biotransformation of aflatoxin B1.

Over the past few years, there has been growing interest in the ability of insect larvae to convert various organic side-streams containing mycotoxins into insect biomass that can be used as animal feed. Various studies have examined the effects of exposure to aflatoxin B1 (AFB1) on a variety of insect species, including the larvae of the black soldier fly (BSFL; Hermetia illucens L.; Diptera: Stratiomyidae) and the housefly (HFL; Musca domestica L.; Diptera: Muscidae). Most of these studies demonstrated that AFB1 degradation takes place, either enzymatic and/or non-enzymatic. The possible role of feed substrate microorganisms (MOs) in this process has thus far not been investigated. The main objective of this study was therefore to investigate whether biotransformation of AFB1 occurred and whether it is caused by insect-enzymes and/or by microbial enzymes of MOs in the feed substrate. In order to investigate this, sterile and non-sterile feed substrates were spiked with AFB1 and incubated either with or without insect larvae (BSFL or HFL). The AFB1 concentration was determined via LC-MS/MS analyses and recorded over time. Approximately 50% of the initially present AFB1 was recovered in the treatment involving BSFL, which was comparable to the treatment without BSFL (60%). Similar patterns were observed for HFL. The molar mass balance of AFB1 for the sterile feed substrates with BSFL and HFL was 73% and 78%, respectively. We could not establish whether non-enzymatic degradation of AFB1 in the feed substrates occurred. The results showed that both BSFL and substrate-specific MOs play a role in the biotransformation of AFB1 as well as in conversion of AFB1 into aflatoxin P1 and aflatoxicol, respectively. In contrast, HFL did not seem to contribute to AFB1 degradation. The obtained results contribute to our understanding of aflatoxin metabolism by different insect species. This information is crucial for assessing the safety of feeding fly larvae with feed substrates contaminated with AFB1 with the purpose of subsequent use as animal feed.

Wave Turbulence on the Surface of a Fluid in a High-Gravity Environment.

We report on the observation of gravity-capillary wave turbulence on the surface of a fluid in a high-gravity environment. By using a large-diameter centrifuge, the effective gravity acceleration is tuned up to 20 times Earth's gravity. The transition frequency between the gravity and capillary regimes is thus increased up to one decade as predicted theoretically. A frequency power-law wave spectrum is observed in each regime and is found to be independent of the gravity level and of the wave steepness. While the timescale separation required by weak turbulence is well verified experimentally regardless of the gravity level, the nonlinear and dissipation timescales are found to be independent of the scale, as a result of the finite size effects of the system (large-scale container modes) that are not taken currently into account theoretically.

Assessing the efficacy of candidate mosquito repellents against the background of an attractive source that mimics a human host.

Mosquito repellents are used around the globe to protect against nuisance biting and disease-transmitting mosquitoes. Recently, there has been renewed interest in the development of repellents as tools to control the transmission of mosquito-borne diseases. We present a new bioassay for the accurate assessment of candidate repellent compounds, using a synthetic odour that mimics the odour blend released by human skin. Using DEET (N,N-diethyl-meta-toluamide) and PMD (p-menthane-3,8-diol) as reference compounds, nine candidate repellents were tested, of which five showed significant repellency to the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae). These included: 2-nonanone; 6-methyl-5-hepten-2-one; linalool; δ-decalactone, and δ-undecalactone. The lactones were also tested on the yellow fever mosquito Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae), against which they showed similar degrees of repellency. We conclude that the lactones are highly promising repellents, particularly because these compounds are pleasant-smelling, natural products that are also present in human food sources.

Behavioural responses of Anopheles gambiae sensu stricto to components of human breath, sweat and urine depend on mixture composition and concentration.

Host-seeking behaviour of the anthropophilic malaria vector Anopheles gambiae sensu stricto (Diptera: Culicidae) is mediated predominantly by olfactory cues. Several hundreds of odour components have been identified from human emanations, but only a few have been proven to act as attractants or synergists in the host-seeking behaviour of female An. gambiae. In previous work, aromatics, alcohols and ketones in human odours were found to elicit electrophysiological activity in antennal olfactory neurons of female An. gambiae. However, the behavioural effects of these compounds have not been investigated. In this study, behavioural responses of female An. gambiae to components of human breath, urine and sweat at a series of concentrations, or a single concentration in the case of acetone, were examined in combination with ammonia and L-lactic acid in a dual-choice olfactometer. The results showed that at specific concentrations 4-ethylphenol, indole, 3-methyl-1-butanol and two ketones inhibited the attractive effect of a mixture of ammonia and lactic acid. Acetone on its own was not attractive; however, when combined with lactic acid, the binary mixture was attractive. When combined with ammonia, acetone inhibited the attractiveness exerted by ammonia alone. Dodecanol and dimethyldisulphide did not affect the attraction exerted by ammonia and lactic acid at any of the concentrations tested. By contrast, a human-specific armpit odour, 7-octenoic acid, augmented the attraction exerted by the combination of ammonia and lactic acid at a specific dosage.

A systematic literature review on the effects of mycotoxin exposure on insects and on mycotoxin accumulation and biotransformation.

Novel protein sources for animal feed are needed, and the use of insects as feed ingredient is explored. The insect production sector offers opportunities for a circular and sustainable approach to feed production by upgrading waste or side streams into high-quality proteins. However, potential food or feed safety issues should be studied in advance. Mycotoxins, such as aflatoxin B1, are natural contaminants commonly found in agricultural crops and have proven to be detrimental to the agricultural industry, livestock, and human health. This systematic review aims to provide a comprehensive overview of the published evidence on effects of mycotoxin exposure on insect growth and survival, mycotoxin accumulation within the insect body, and metabolization of various mycotoxins by insects. The review includes 54 scientific articles published in the past 55 years, in total covering 32 insect species. The main findings are the following: (1) Insects of the order Coleoptera show lower mortality after exposure to aflatoxin B1 when compared to Lepidoptera and Diptera; (2) effects of mycotoxins on larval growth and survival are less detrimental in later larval stages; (3) accumulation of mycotoxins was low in most insect species; (4) mycotoxins are metabolized within the insect body, the degree of which depends on the particular mycotoxin and insect species; (5) cytochrome P450s are the main family of enzymes involved in biotransformation of mycotoxins in some insect species. Results of this review support an optimistic outlook for the use of mycotoxin-contaminated waste streams as substrate for insect rearing.

LEDs Make It Resilient: Effects on Plant Growth and Defense.

Light spectral composition influences plant growth and metabolism, and has important consequences for interactions with plant-feeding arthropods and their natural enemies. In greenhouse horticulture, light spectral composition can be precisely manipulated by light-emitting diodes (LEDs), and LEDs are already used to optimize crop production and quality. However, because light quality also modulates plant secondary metabolism and defense, it is important to understand the underlying mechanisms in the context of the growth-defense trade-off. We review the effects of the spectral composition of supplemental light currently used, or potentially used, in greenhouse horticulture on the mechanisms underlying plant growth and defense. This information is important for exploring opportunities to optimize crop performance and pest management, and thus for developing resilient crop-production systems.

An atomic force microscope operating at hypergravity for in situ measurement of cellular mechano-response.

We present a novel atomic force microscope (AFM) system, operational in liquid at variable gravity, dedicated to image cell shape changes of cells in vitro under hypergravity conditions. The hypergravity AFM is realized by mounting a stand-alone AFM into a large-diameter centrifuge. The balance between mechanical forces, both intra- and extracellular, determines both cell shape and integrity. Gravity seems to be an insignificant force at the level of a single cell, in contrast to the effect of gravity on a complete (multicellular) organism, where for instance bones and muscles are highly unloaded under near weightless (microgravity) conditions. However, past space flights and ground based cell biological studies, under both hypogravity and hypergravity conditions have shown changes in cell behaviour (signal transduction), cell architecture (cytoskeleton) and proliferation. Thus the role of direct or indirect gravity effects at the level of cells has remained unclear. Here we aim to address the role of gravity on cell shape. We concentrate on the validation of the novel AFM for use under hypergravity conditions. We find indications that a single cell exposed to 2 to 3 x g reduces some 30-50% in average height, as monitored with AFM. Indeed, in situ measurements of the effects of changing gravitational load on cell shape are well feasible by means of AFM in liquid. The combination provides a promising technique to measure, online, the temporal characteristics of the cellular mechano-response during exposure to inertial forces.

The threshold at which substrate nanogroove dimensions may influence fibroblast alignment and adhesion.

The differences in morphological behaviour between fibroblasts cultured on smooth and nanogrooved substrata (groove depth: 5-350 nm, width: 20-1000 nm) have been evaluated in vitro. The aim of the study was to clarify to what extent cell guidance occurs on increasingly smaller topographies. Pattern templates were made using electron beam lithography, and were subsequently replicated in polystyrene cell culture material using solvent casting. The replicates were investigated with atomic force microscopy (AFM). After seeding with fibroblasts, morphological characteristics were investigated using scanning electron microscopy (SEM) and light microscopy, in order to obtain qualitative and quantitative information on cell alignment. AFM revealed that the nanogroove/ridge widths were replicated perfectly, although at deeper levels the grooves became more concave. The smooth substrata had no distinguishable pattern other than a roughness amplitude of 1 nm. Interestingly, microscopy and image analysis showed that fibroblast after 4 h had adjusted their shape according to nanotopographical features down to cut-off values of 100 nm width and 75 nm depth. After 24 h culturing time, fibroblasts would even align themselves on groove depths as shallow as 35 nm. It appears depth is the most essential parameter in cellular alignment on groove patterns with a pitch ratio of 1:1. On the smooth substrata, cells always spread out in a random fashion. Analysis of variance (ANOVA) demonstrated that both main parameters, topography and culturing time, were significant. We conclude that fibroblast cells cultured on nanotopography experience a threshold feature size of 35 nm, below this value contact guidance does no longer exist.

Photoreceptor spectral sensitivity of the compound eyes of black soldier fly (Hermetia illucens) informing the design of LED-based illumination to enhance indoor reproduction.

Mating in the black soldier fly (BSF) is a visually mediated behaviour that under natural conditions occurs in full sunlight. Artificial light conditions promoting mating by BSF were designed based on the spectral characteristics of the compound eye retina. Electrophysiological measurements revealed that BSF ommatidia contained UV-, blue- and green-sensitive photoreceptor cells, allowing trichromatic vision. An illumination system for indoor breeding based on UV, blue and green LEDs was designed and its efficiency was compared with illumination by fluorescent tubes which have been successfully used to sustain a BSF colony for five years. Illumination by LEDs and the fluorescent tubes yielded equal numbers of egg clutches, however, the LED illumination resulted in significantly more larvae. The possibilities to optimize the current LED illumination system to better approximate the skylight illuminant and potentially optimize the larval yield are discussed.

Plant-mediated interactions between two herbivores differentially affect a subsequently arriving third herbivore in populations of wild cabbage.

Plants are part of biodiverse communities and frequently suffer from attack by multiple herbivorous insects. Plant responses to these herbivores are specific for insect feeding guilds: aphids and caterpillars induce different plant phenotypes. Moreover, plants respond differentially to single or dual herbivory, which may cascade into a chain of interactions in terms of resistance to other community members. Whether differential responses to single or dual herbivory have consequences for plant resistance to yet a third herbivore is unknown. We assessed the effects of single or dual herbivory by Brevicoryne brassicae aphids and/or Plutella xylostella caterpillars on resistance of plants from three natural populations of wild cabbage to feeding by caterpillars of Mamestra brassicae. We measured plant gene expression and phytohormone concentrations to illustrate mechanisms involved in induced responses. Performance of both B. brassicae and P. xylostella was reduced when feeding simultaneously with the other herbivore, compared to feeding alone. Gene expression and phytohormone concentrations in plants exposed to dual herbivory were different from those found in plants exposed to herbivory by either insect alone. Plants previously induced by both P. xylostella and B. brassicae negatively affected growth of the subsequently arriving M. brassicae. Furthermore, induced responses varied between wild cabbage populations. Feeding by multiple herbivores differentially activates plant defences, which has plant-mediated negative consequences for a subsequently arriving herbivore. Plant population-specific responses suggest that plant populations adapt to the specific communities of insect herbivores. Our study contributes to the understanding of plant defence plasticity in response to multiple insect attacks.

The effect of combined cyclic mechanical stretching and microgrooved surface topography on the behavior of fibroblasts.

Under the influence of mechanical stress, cultured fibroblasts have a tendency to orient themselves perpendicular to the stress direction. Similar cell alignment can be induced by guiding cells along topographical clues, like microgrooves. The aim of this study was to evaluate cell behavior on microgrooved substrates, exposed to cyclic stretching. We hypothesized that cellular shape is mainly determined by topographical clues. On basis of earlier studies, a 10-microm wide square groove, and a 40-microm wide V-shaped groove pattern were used. Smooth substrates served as controls. Onto all substrates fibroblasts were cultured and 1-Hz cyclic stretching was applied (0, 4, or 8%) for 3-24 h. Cells were prepared for scanning electron microscopy, immunostaining of filamentous actin, alignment measurements, and PCR (collagen-I, fibronectin, alpha1- and beta1-integrins). Results showed that cells aligned on all grooved surfaces, and fluorescence microscopy showed similar orientation of intracellular actin filaments. After 3 h of stretch, cellular orientation started to commence, and after 24 h the cells had aligned themselves almost entirely. Image analysis showed better orientation with increasing groove depth. Statistical testing proved that the parameters groove type, groove orientation, and time all were significant, but the variation of stretch force was not. Substrates with microgrooves perpendicular to the stretch direction elicit a better cell alignment. The expression of beta1-integrin and collagen-I was higher in the stretched samples. In conclusion, we can maintain our hypothesis, as microgrooved topography was most effective in applying strains relative to the long axis of the cell, and only secondary effects of stretch force were present.

Variation in plant-mediated interactions between rhizobacteria and caterpillars: potential role of soil composition.

Selected strains of non-pathogenic rhizobacteria can trigger induced systemic resistance (ISR) in plants against aboveground insect herbivores. However, the underlying mechanisms of plant-mediated interactions between rhizobacteria and herbivorous insects are still poorly understood. Using Arabidopsis thaliana Col-0-Pseudomonas fluorescens WCS417r as a model system, we investigated the performance and the molecular mechanisms underlying plant-mediated effects of rhizobacteria on the generalist caterpillar Mamestra brassicae and the specialist Pieris brassicae. Rhizobacteria colonisation of Arabidopsis roots resulted in decreased larval weight of M. brassicae, whereas no effect was observed on larval weight of P. brassicae. Using a jasmonic acid (JA)-impaired mutant (dde2-2), we confirmed the importance of JA in rhizobacteria-mediated ISR against M. brassicae. Interestingly, in some experiments we also observed rhizobacteria-induced systemic susceptibility to M. brassicae. The role of soil composition in the variable outcomes of microbe-plant-insect interactions was then assessed by comparing M. brassicae performance and gene transcription in plants grown in potting soil or a mixture of potting soil and sand in a 1:1 ratio. In a mixture of potting soil and sand, rhizobacteria treatment had a consistent negative effect on M. brassicae, whereas the effect was more variable in potting soil. Interestingly, at 24 h post-infestation (hpi) rhizobacteria treatment primed plants grown in a mixture of potting soil and sand for stronger expression of the JA- and ethylene-regulated genes PDF1.2 and HEL, respectively. Our study shows that soil composition can modulate rhizobacteria-plant-insect interactions, and is a factor that should be considered when studying these belowground-aboveground interactions.

Decreased mineralization and increased calcium release in isolated fetal mouse long bones under near weightlessness.

Mechanical loading plays an important role in the development and maintenance of skeletal tissues. Subnormal mechanical stress as a result of bed rest, immobilization, but also in spaceflight, results in a decreased bone mass and disuse osteoporosis, whereas supranormal loads upon extremities result in an increased bone mass. In this first in vitro experiment with complete fetal mouse cartilaginous long bones, cultured under microgravity conditions, we studied growth, glucose utilization, collagen synthesis, and mineral metabolism, during a 4-day culture period in space. There was no change in percent length increase and collagen synthesis under microgravity compared with in-flight 1x gravity. Glucose utilization and mineralization were decreased under microgravity. In addition, mineral resorption, as measured by 45Ca release, was increased. These data suggest that weightlessness has modulating effects on skeletal tissue cells. Loss of bone during spaceflight could be the result of both impaired mineralization as well as increased resorption.

Postoperative spiral computed tomography and magnetic resonance angiography after aneurysm clipping with titanium clips.

OBJECTIVE: To reduce morbidity and mortality after subarachnoid hemorrhage, it is imperative to evaluate the results of the surgical treatment of cerebral aneurysms. We investigated the usefulness of spiral computed tomography (CT) and magnetic resonance angiography as postoperative control examinations after cerebral aneurysms were clipped with titanium clips. METHODS: Eleven patients with 13 treated aneurysms were studied prospectively with postoperative digital subtraction angiography, spiral CT, and magnetic resonance angiography. The occlusion of the dome of the aneurysm, the presence of a remnant of the neck, the patency of the parent vessels and other major vessels, and the presence of vasospasm were investigated. RESULTS: The different parameters could all be well evaluated by postoperative spiral CT. The artifacts caused by the titanium clips, although relatively small compared with artifacts from other clips, precluded evaluating the dome and the neck of the aneurysm with magnetic resonance angiography. CONCLUSION: In our opinion, spiral CT promises to become a valuable aid in in the postoperative evaluation of clipped aneurysms, and we recommend its routine performance. Postoperative digital subtraction angiography remains the gold standard and has to be performed when spiral CT reveals abnormalities, when the neck of the aneurysm cannot be evaluated because the clip overlays it, or when, intraoperatively, imperfect clipping is suspected and intraoperative angiography cannot be performed.

Virtues and drawbacks of titanium alloy aneurysm clips.

This report describes the imaging characteristics of titanium alloy aneurysm clips and our clinical experience with these clips in more than 300 patients. Phantom and clinical investigations showed that clip artifacts on CT and MR are minor as compared to the cobalt alloy clips used previously. Spiral CT angiography (CTA) in combination with titanium alloy clips could be shown to be a feasible mode of postoperative control and can be used to determine completeness of aneurysm elimination, patency of adjacent arteries as well as vasospasm. In contrast, magnetic resonance angiography (MRA) proved to be unfeasible as a method of postoperative vascular imaging since the titanium clips still produce a shadow in the order of size of the entire aneurysm. Therefore, completeness of aneurysm elimination cannot be judged on magnetic resonance angiography. The clinical experience in more than 300 cases showed that the titanium alloy clips essentially performed well. However, the limits of elastic deformation appear to be somewhat inferior to cobalt alloy clips. The standard appliers do not open the blades of the titanium clips quite as far as with the comparable cobalt alloy clips and the corresponding appliers. Therefore the titanium aneurysm clips are not quite as well suited for large broad based aneurysms. Furthermore, the increased susceptibility of the new clips with regard to abuse suggests to follow the recommendations of the manufacturer not to recycle and re-sterilize clips that have been tried but not permanently implanted.

Microgravity and bone cell mechanosensitivity.

The capacity of bone tissue to alter its mass and structure in response to mechanical demands has long been recognized but the cellular mechanisms involved remained poorly understood. Bone not only develops as a structure designed specifically for mechanical tasks, but it can adapt during life toward more efficient mechanical performance. Mechanical adaptation of bone is a cellular process and needs a biological system that senses the mechanical loading. The loading information must then be communicated to the effector cells that form new bone or destroy old bone. The in vivo operating cell stress derived from bone loading is likely the flow of interstitial fluid along the surface of osteocytes and lining cells. The response of bone cells in culture to fluid flow includes prostaglandin (PG) synthesis and expression of prostaglandin G/H synthase inducible cyclooxygenase (COX-2). Cultured bone cells also rapidly produce nitric oxide (NO) in response to fluid flow as a result of activation of endothelial nitric oxide synthase (ecNOS), which enzyme also mediates the adaptive response of bone tissue to mechanical loading. Earlier studies have shown that the disruption of the actin-cytoskeleton abolishes the response to stress, suggesting that the cytoskeleton is involved in cellular mechanotransduction. Microgravity, or better near weightlessness, is associated with the loss of bone in astronauts, and has catabolic effects on mineral metabolism in bone organ cultures. This might be explained as resulting from an exceptional form of disuse under near weightlessness conditions. However, under near weightlessness conditions the assembly of cytoskeletal elements may be altered since it has been shown that the direction of the gravity vector determines microtubular pattern formation in vivo. We found earlier that the transduction of mechanical signals in bone cells also involves the cytoskeleton and is related to PGE2 production. Therefore it is possible that the mechanosensitivity of bone cells is altered under near weightlessness conditions, and that this abnormal mechanosensation contributes to disturbed bone metabolism observed in astronauts. In our current project for the International Space Station, we wish to test this hypothesis experimentally using an in vitro model. The specific aim of our research project is to test whether near weightlessness decreases the sensitivity of bone cells for mechanical stress through a decrease in early signaling molecules (NO, PGs) that are involved in the mechanical loading-induced osteogenic response. Bone cells are cultured with or without gravity prior to and during mechanical loading, using our modified in vitro oscillating fluid flow apparatus. In this "FlowSpace" project we are developing a cell culture module that is used to provide further insight in the mechanism of mechanotransduction in bone.

Development of tissue culture techniques and hardware to study mineralization under microgravity conditions.

To study the effects of weightlessness on mouse fetal long bone rudiment growth and mineralization we have developed a tissue culture system for the Biorack facility of Spacelab. The technique uses standard liquid tissue culture medium, supplemented with NA-beta-glycerophosphate, confined in gas permeable polyethylene bags mounted inside ESA Biorack Type I experiment containers. The containers can be flushed with an air/5% CO2 gas mixture necessary for the physiological bicarbonate buffer used. Small amounts of fluid can be introduced at the beginning (e.g. radioactive labels for incorporation studies) or at the end of the experiment (fixatives). A certain form of mechanical stimulation (continuous compression) can be used to counteract the, possibly, adverse effect of microgravity. Using 16 day old metatarsals the in vitro calcification process under microgravity conditions can be studied for a 4 day period.

Influence of nanostructural environment and fluid flow on osteoblast-like cell behavior: a model for cell-mechanics studies.

Introducing nanoroughness on various biomaterials has been shown to profoundly effect cell-material interactions. Similarly, physical forces act on a diverse array of cells and tissues. Particularly in bone, the tissue experiences compressive or tensile forces resulting in fluid shear stress. The current study aimed to develop an experimental setup for bone cell behavior, combining a nanometrically grooved substrate (200 nm wide, 50 nm deep) mimicking the collagen fibrils of the extracellular matrix, with mechanical stimulation by pulsatile fluid flow (PFF). MC3T3-E1 osteoblast-like cells were assessed for morphology, expression of genes involved in cell attachment and osteoblastogenesis and nitric oxide (NO) release. The results showed that both nanotexture and PFF did affect cellular morphology. Cells aligned on nanotexture substrate in a direction parallel to the groove orientation. PFF at a magnitude of 0.7 Pa was sufficient to induce alignment of cells on a smooth surface in a direction perpendicular to the applied flow. When environmental cues texture and flow were interacting, PFF of 1.4 Pa applied parallel to the nanogrooves initiated significant cellular realignment. PFF increased NO synthesis 15-fold in cells attached to both smooth and nanotextured substrates. Increased collagen and alkaline phosphatase mRNA expression was observed on the nanotextured substrate, but not on the smooth substrate. Furthermore, vinculin and bone sialoprotein were up-regulated after 1 h of PFF stimulation. In conclusion, the data show that interstitial fluid forces and structural cues mimicking extracellular matrix contribute to the final bone cell morphology and behavior, which might have potential application in tissue engineering.

Rhizobacteria modify plant-aphid interactions: a case of induced systemic susceptibility.

Beneficial microbes, such as plant growth-promoting rhizobacteria and mycorrhizal fungi, may have a plant-mediated effect on insects aboveground. The plant growth-promoting rhizobacterium Pseudomonas fluorescens can induce systemic resistance in Arabidopsis thaliana against several microbial pathogens and chewing insects. However, the plant-mediated effect of these beneficial microbes on phloem-feeding insects is not well understood. Using Arabidopsis as a model, we here report that P. fluorescens has a positive effect on the performance (weight gain and intrinsic rate of increase) of the generalist aphid Myzus persicae, while no effect was recorded on the crucifer specialist aphid Brevicoryne brassicae. Additionally, transcriptional analyses of selected marker genes revealed that in the plant-microbe interaction with M. persicae, rhizobacteria (i) prime the plant for enhanced expression of LOX2, a gene involved in the jasmonic acid (JA)-regulated defence pathway, and (ii) suppress the expression of ABA1, a gene involved in the abscisic acid (ABA) signalling pathway, at several time points. In contrast, almost no effect of the plant-microbe interaction with B. brassicae was found at the transcriptional level. This study presents the first data on rhizobacteria-induced systemic susceptibility to an herbivorous insect, supporting the pattern proposed for other belowground beneficial microbes and aboveground phloem feeders. Moreover, we provide further evidence that at the transcript level, soil-borne microbes modify plant-aphid interactions.

Herbivore-induced volatiles of cabbage (Brassica oleracea) prime defence responses in neighbouring intact plants.

When attacked by herbivores, plants release herbivore-induced plant volatiles (HIPV) that may function in direct defence by repelling herbivores or reducing their growth. Emission of HIPV may also contribute to indirect defence by attracting natural enemies of the herbivore. Here, cabbage (Brassica oleracea L.) plants (receiver plants) previously exposed to HIPV and subsequently induced through feeding by five Pieris brassicae L. caterpillars attracted more Cotesia glomerata L. parasitoids than control plants. HIPVs to which receiver plants had been exposed were emitted by B. oleracea infested with 50 P. brassicae caterpillars. Control plants had been exposed to volatiles from undamaged plants. In contrast, there were no differences in the attraction of wasps to receiver plants induced through feeding of one or ten larvae of P. brassicae compared to control plants. In addition, RT-PCR demonstrated higher levels of LIPOXYGENASE (BoLOX) transcripts in HIPV-exposed receiver plants. Exposure to HIPV from emitter plants significantly inhibited the growth rate of both P. brassicae and Mamestra brassicae caterpillars compared to growth rates of caterpillars feeding on control receiver plants. Our results demonstrate plant-plant signalling leading to priming of both indirect and direct defence in HIPV-exposed B. oleracea plants.