Silicon fertilisation affects morphological and immune defences of an insect pest and enhances plant compensatory growth

Herbivorous insects have evolved various anti-predator defences, including morphological, behavioural, and immune defences, which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against mandibulate insects. However, it remains uncertain how Si affects the anti-predator defences of insect herbivores and plant defences following herbivory. We grew the model grass, Brachypodium distachyon, hydroponically with (+Si) or without (–Si) Si and investigated the plant-mediated effects of Si on the anti-predator defences of the cotton bollworm, Helicoverpa armigera, integrating morphological (i.e. integument resistance and thickness), behavioural, and immune defences. We also examined the effects of Si on plant compensatory growth and leaf trichome production. Larval growth, leaf consumption, and integument resistance were lower when feeding on +Si plants compared to when feeding on –Si plants. Larval integument thickness, defensive behaviours, haemocyte density, and lysozyme-like activity in the haemolymph were unaffected by Si. Larvae fed on +Si plants had higher haemolymph phenoloxidase (PO) and total-PO activities than larvae fed on –Si plants, although this did not enhance the melanisation response of larvae. Furthermore, Si supplies increased plant compensation for herbivory and constitutive trichome production, whereas herbivory induced trichome production only on –Si plants. We provide the first evidence for plant-mediated effects of Si on anti-predator defences of an insect herbivore. We suggest that the lower integument resistance of larvae when feeding on Si-supplemented plants could contribute to their vulnerability to natural enemies and that high PO activity may impose fitness costs (e.g. delayed development).

Silicon Fertilisation Affects Morphological and Immune Defences of an Insect Pest and Enhances Plant Compensatory Growth

Insect herbivores employ various defences, including morphological, behavioural, and immune responses against their natural enemies (e.g., predators, parasitoids) which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against herbivores. However, it remains uncertain how Si affects pest defences to their enemies and plant defences following herbivore attack. We grew the model grass, Brachypodium distachyon, hydroponically with (+Si) or without (–Si) Si and investigated the impacts of Si on morphological (integument resistance and thickness), behavioural (flee, headrear, thrash, and regurgitation), and immune defences of the cotton bollworm, Helicoverpa armigera. We further examined the effects of Si on plant compensatory growth and leaf trichome production. Larval growth, leaf consumption, and integument resistance were lower when feeding on +Si plants compared to when feeding on –Si plants. Larval integument thickness, defensive behaviours, hemocyte density and lysozyme-like activity in the hemolymph were unaffected by Si. Larvae fed on +Si plants had higher hemolymph phenoloxidase (PO) and total-PO activities than larvae fed on –Si plants, although this did not enhance larval melanisation response. Furthermore, Si supply increased plant compensatory growth and constitutive trichome production whereas herbivory induced trichome production only on –Si plants. We provide the first evidence that Si fertilisation affects insect defences in addition to reducing their growth and feeding. Lower integument resistance might enhance larval vulnerability to parasitoids and pathogens and higher PO activities could impose fitness costs (e.g., delayed development), potentially increasing overall insect susceptibility to enemies.

Epichloë-endophytes increase constitutive and herbivore-induced silicon defences in grasses but do not directly increase grass resistance to a chewing insect herbivore

<p>Grasses accumulate large concentrations of silicon (Si) which alleviates a range of stresses including defence against herbivores. Likewise, grasses symbiotically associate with foliar <em>Epichloë-</em>fungal endophytes which provide herbivore defence, mainly via the production of alkaloids. Some <em>Epichloë</em>-endophytes increase foliar Si concentrations, particularly in tall fescue <em>(Festuca arundinacea</em>) but also in perennial ryegrass (<em>Lolium perenne</em>); it is unknown whether this impacts herbivores. Likewise, while Si is primarily a physical defence against herbivores, it can also affect defensive secondary metabolites; Si supply might therefore also affect alkaloids produced by <em>Epichloë</em>-endophytes, however, this remains untested. We grew tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of a chewing herbivore; <em>Helicoverpa armigera</em>. Grasses were associated with four different<em> Epichloë</em>-endophyte strains (tall fescue: AR584; perennial ryegrass: AR37, AR1, or wild type) or as <em>Epichloë</em>-free controls. Specifically, we assessed how Si supply and <em>Epichloë</em>-endophyte presence impacts plant growth and chemistry, and how their interaction with herbivory affects foliar Si concentrations and alkaloid production. Subsequently, their effects on <em>H. armigera</em> relative growth rates (RGR) were evaluated. In Fescue, the AR584-endophyte increased constitutive (herbivore-free) and induced (herbivore-inoculated) silicon concentrations when Si was supplied. In perennial ryegrass, AR37-endophyte increased constitutive and induced silicon concentration, meanwhile, AR1-endophyte increased constitutive levels only. Si supply and herbivory did not affect alkaloids produced by AR584- or AR1/Wt-endophyte in tall fescue and perennial ryegrass, respectively. However, Si suppressed herbivore-induced production of alkaloids in the AR37-endophyte perennial ryegrass association. Si was a more effective defence in tall fescue than perennial ryegrass, significantly reducing H. armigera RGR. Our results suggest that Si reduced herbivore performance to such an extent in tall fescue that it was operating at maximum effect and endophyte-mediated increases in Si concentration made no further difference. Si had a more modest impact on herbivores in perennial ryegrass, potentially linked to silicon decreasing herbivore feeding and thus, suppressing herbivore-induced alkaloids. We provide novel evidence that increased Si concentrations in some cases interact with endophyte-produced chemical defences, which could ultimately impact plant resistance to herbivores. <strong>  </strong></p>

The Imaging of Guard Cells of thioglucosidase (tgg) Mutants of Arabidopsis Further Links Plant Chemical Defence Systems with Physical Defence Barriers

The glucosinolate-myrosinase system is a well-known plant chemical defence system. Two functional myrosinase-encoding genes, THIOGLUCOSIDASE 1 (TGG1) and THIOGLUCOSIDASE 2 (TGG2), express in aerial tissues of Arabidopsis. TGG1 expresses in guard cells (GCs) and is also a highly abundant protein in GCs. Recently, by studying wild type (WT), tgg single, and double mutants, we showed a novel association between the glucosinolate-myrosinase system defence system, and a physical barrier, the cuticle. In the current study, using imaging techniques, we further analysed stomata and ultrastructure of GCs of WT, tgg1, tgg2 single, and tgg1 tgg2 double mutants. The tgg mutants showed distinctive features of GCs. The GCs of tgg1 and tgg1 tgg2 mutants showed vacuoles that had less electron-dense granular material. Both tgg single mutants had bigger stomata complexes. The WT and tgg mutants also showed variations for cell wall, chloroplasts, and starch grains of GCs. Abscisic acid (ABA)-treated stomata showed that the stomatal aperture was reduced in tgg1 single and tgg1 tgg2 double mutants. The data provides a basis to perform comprehensive further studies to find physiological and molecular mechanisms associated with ultrastructure differences in tgg mutants. We speculate that the absence of myrosinase alters the endogenous chemical composition, hence affecting the physical structure of plants and the plants’ physical defence barriers.

Physical Protection of Military Camps

One of the most important components of preparing and conducting military (convencional) and peace support operations is the support of the operations, and it’s effectiveness is highly affected by the distance of the supporting forces and equipments from the forces which are participating in the actual operation. In favor of the supporting forces, equipments and services’ effective availability, we can create military objects and camps outside the garrison’s area for the housing of the units providing the life – and working conditions for them. The defence level of a military camp depends on various factors, and that level can be different within the limits of the camp, and it has strong connections with the camp’s physical defence and it’s reinforcement. My aim is to provide a short overview about the opportunities of the military camp’s physical defences.

Anti-predator behavior

Insects have evolved a wide range of behavioral traits to avoid predation. Frequently, these behaviors are deployed to augment the effectiveness of a primary defence such as crypsis or mimicry, but they are also sometimes elicited as a secondary defence when a primary defence fails. Anti-predator behaviors in insects include adaptations to avoid being detected by predators, adaptations rendering the insect unattractive to consume, warning behaviors, and behaviors to enhance the effectiveness of mimicry. This chapter reviews many of these behavioral anti-predator adaptations, emphasizing when they are elicited and highlighting their adaptive significance. We argue that some of the inter-specific variation in behavioral defences can be explained in terms of defensive portfolios: if a physical defence is sufficient, then behaviour to augment or back-up this defence is unnecessary. As the use of comparative methods increases, researchers will be better placed to understand variation in the suites of defences that evolve.

Coat of many colours—DNA reveals polymorphism of mantle patterns and colouration in CaribbeanCyphomaRöding, 1798 (Gastropoda, Ovulidae)

The iconic gastropod genusCyphomais commonly observed in the Caribbean, where it lives in association with various octocorallian hosts. Each species in the genusCyphomahas a unique, characteristic mantle pattern and colouration, which separates the valid taxa. Because of its abundance and recognisabilityCyphoma gibbosumhas been used as a model organism in several studies concerning allelochemicals, reef degradation, and physical defence mechanisms. Molecular analyses based on four molecular markers (COI, 16S, H3 and 28S) for threeCyphomaspecies (C. gibbosum,C. mcgintyi,C. signatum) and an unidentified black morph, collected from three localities in the Caribbean, show that they represent morphological varieties of a single, genetically homogeneous species. This outcome is in agreement with previous anatomical studies. As a resultC. mcgintyiandC. signatumare synonymised withC. gibbosum, which is a key result for future work usingC. gibbosumas a model organism. The striking morphological differences in mantle pattern and colouration are hypothesised to be the result of one of three possible scenarios: rapid divergence, supergenes (including balanced polymorphism), or incipient speciation.