Bottom-Up Mechanisms Generate the Same Temporal Pattern of Attack by a Specialist and a Generalist Caterpillar on Short-Lived Plants

J Agronomy Crop Science

Oliveira

et al. 2019

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It was postulated that Si‐mediated plant resistance to herbivory changes with soil water status, increasing when plants are under drought stress. We subjected collard (Brassica oleracea) to such soil variables and assessed plant responses and effects on the leaf‐chewing larvae of Plutella xylostella and the sap‐sucking aphid Brevicoryne brassicae. Silicon accumulated in collard leaves independently of soil water conditions, but it influenced mainly drought‐stressed plants. Silicon suppressed harmful effects of drought on leaf and root length and raised leaf water content and stomatal size to the same conditions of well‐watered plants. Drought stress reduced hemicellulose and cellulose, but Si did not influence them or lignin. Combination of drought and Si increased total and soluble leaf nitrogen. Drought decreased total glucosinolates, but Si increased such defence metabolites to similar concentrations that were found in well‐watered plants. Nutritional changes mediated by drought and Si in fibre, leaf water content, soluble nitrogen and glucosinolates did not increase insect performance in any feeding guild. Instead, caterpillars performed worse in drought‐stressed or Si‐treated collards, mainly in plants under combined conditions. Silicon improved plant resistance to drought and herbivore stresses.

Section: Methodsmentioning

confidence: 99%

Combined effects of soil silicon and drought stress on host plant chemical and ultrastructural quality for leaf‐chewing and sap‐sucking insects

J Agronomy Crop Science

Oliveira

et al. 2019

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“…Brassica species in general use multiple defense mechanisms against insects, and glucosinolates (GLS) are thought to be their first line of defense (Ahuja et al 2010). GLS are found in higher concentrations in new foliage (Lambdon et al 2003;Campos et al 2016); however, DBM larvae can overcome this toxic barrier, and moths even rely on some GLS for host location and oviposition stimulation (Ratzka et al 2002;Sarfraz et al 2006;Hopkins et al 2009;Winde and Wittstock 2011). The aphid B. brassicae is also well adapted to circumvent and exploit the GLS.…”

Section: Methodsmentioning

confidence: 99%

Drought-induced acclimatization of a fast-growing plant decreases insect performance in leaf-chewing and sap-sucking guilds

Arthropod-Plant Interactions

Santos

et al. 2016

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An initial destabilization of functions triggered by drought stress in plants is followed by acclimatization and acquisition of tolerance; however, knowledge remains limited on drought-mediated changes in plant quality for herbivores. We tested whether a water-stressed fast-growing plant negatively affects host-specialist insects in both sap-sucking and leaf-chewing feeding guilds. Collards (Brassica oleracea var. acephala) were grown in wellwatered, slightly water-stressed and severely water-stressed conditions. Decreasing soil moisture adversely affected plant development, assessed as a reduction in leaf number and size, stomatal size and relative water content. Severely stressed plants had less fiber and glucosinolates; however, they showed more total nitrogen and lipids. Larval survival, pupal weight, reproductive rate (Ro) and rate of population growth (r) were lower when the leaf-chewing Plutella xylostella was reared with severely stressed collards. In multiple-choice tests, moths laid fewer eggs on leaf discs of collard that were exposed to drought. The fecundity of the sap-sucking Brevicoryne brassicae was higher and the development of alates was lower when insects were fed on plants kept in well-watered regime as compared to slight-stress and severe-stress. Despite higher nitrogen content and fewer glucosinolates, a higher level of leaf surface wax in severely stressed collards possibly decreased food quality for both herbivores. Thus, hostspecific herbivores of different guilds showed similar responses to drought-stressed, fast-growing plants. Waterstressed crops could discourage the attack of specialist insects, but the intensity of the stress that is required to achieve this effect will greatly reduce crop production, in terms of plant growth or foliage increment.

“…Generalist herbivores are usually more sensitive to plant defense compounds than specialist herbivores (Ali & Agrawal, ). Thus, specialists may perform better on the more nutritious host plants or plant tissues, independent of higher levels of chemical defenses (Campos et al., ; Valim et al., ). Therefore, different guilds and non‐adapted vs. highly host‐specific herbivores are supposed to respond differently to Si‐mediated modifications in plant nutrients and defense compounds.…”

Section: Introductionmentioning

confidence: 99%

Silicon‐mediated resistance against specialist insects in sap‐sucking and leaf‐chewing guilds in the Si non‐accumulator collard

Entomologia Exp Applicata

Campos

2017

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Soil amendment with Silicon (Si) can increase plant resistance against insect herbivores, but the underlying mechanisms remain unclear. The mechanical resistance hypothesis (MRH) states that Si accumulated in epidermal cells directly and passively protects against herbivores by creating a mechanical barrier. The physiological resistance hypothesis (PRH) states that Si enhances resistance by activating plant biochemical and physiological processes. We tested both hypotheses by manipulating Si fertilization of the Si non‐accumulator collard, Brassica oleracea L. cv. acephala (Brassicaceae). Then, we assessed functional and ultrastructural plant responses and the developmental and reproductive performance of the leaf‐chewing larvae of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), and the sap‐sucking cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae). There was a 20% increase in leaf Si content. Silicon deposition in epidermal cells was identified by confocal microscopy and directly coincided with lower performance of P. xylostella, but did not affect B. brassicae. On the other hand, we found no unequivocal evidence that Si‐mediated changes in primary and secondary metabolism improved plant resistance against the insects. Negative mechanical effects of Si on the insects may have masked beneficial effects of increased water, nitrogen, and mineral contents in Si‐treated collards. Silicon did not change leaf contents of hemicellulose, cellulose, and lignin. Although Si‐mediated increases in leaf glucosinolates (GLS) correlated with lower larval performance and higher oviposition preference of P. xylostella, both P. xylostella and B. brassicae are highly specialized in overcoming such secondary metabolites. Thus, mechanical resistance may have impaired P. xylostella, rather than the Si‐mediated increase in GLS. We suggest that the PRH may depend on the degree of insect feeding specialization, so that toxic Si‐mediated defenses may be more efficient against unadapted polyphagous herbivores. For them, a toxic barrier may be added to the mechanical resistance.