Silicon enhances natural enemy attraction and biological control through induced plant defences

Abstract

Silicon (Si) is known to have a role in constitutive plant defence against arthropod pests, and recent work has illustrated involvement in induced plant defences. The present tri-trophic study tested the hypothesis that Si increases natural enemy attraction to pest-infested plants and improves biological control. Cucumber plants treated with potassium silicate (Si+) and untreated control plants (Si-) were maintained in separately vented glasshouse compartments. Y-tube olfactometer studies showed that adult Dicranolaius bellulus were significantly more attracted to Si+ plants upon which Helicoverpa armigera larvae had fed compared with Si-, pest-infested plants. Predators were not significantly more attracted to Si+ plants when comparing uninfested cucumbers. In a field experiment, we placed H. armigera-infested and uninfested Si+ and Si- cucumber plants in a lucerne stand. Removal rates of H. armigera egg baits showed predation was greater for Si+ infested plants than for other treatments. Results suggest that Si applied to plants with a subsequent pest infestation increases the plants' attractiveness to natural enemies; an effect that was reflected in elevated biological control in the field.

Priming of jasmonate-mediated antiherbivore defense responses in rice by silicon

“…Si deposition, occurring mainly as opaline phytoliths, is associated with increased rigidity and abrasiveness of plant tissues, thereby reducing their digestibility to herbivores. Recent studies also have shown that Si treatment induces the activities of plant defensive enzymes (9, 10) and leads to increased accumulation of defensive compounds such as phenolics, phytoalexins, and momilactones (11)(12)(13) and to increased release of plant volatiles that attract natural enemies of herbivorous insects (6). Furthermore, transcriptome analyses in Si-pretreated Arabidopsis thaliana plants inoculated with powdery mildew suggest that Si attenuates the decrease in primary metabolism associated with pathogen infection, leading to an overall more efficient defense response (4).…”

The Effects of Silica Fertilizer as an Anti-Herbivore Defense in Cucumber

“…We found no such difference, suggesting that the toughness or brittleness of leaf trichomes was not different between Si+ and Si-plants. Kvedaras et al (2010) concluded that plants with high amounts of silica being consumed by herbivores can attract herbivore predatory insects. The authors from the study hypothesized that it may be the presence of particular volatiles that were responsible for triggering the attraction, and that the observed increase in number of herbivore predators attracted to the silicatreated plants may indicate plant signaling driven by production of particular volatiles.…”

“…In cucumbers, we found one difference between Si+ and Si-plants in production of volatiles, an increase in Indole. Although, our volatile extraction was conducted on harvested plants that had not experienced herbivory, while the Kvedaras et al (2010) study used plants that were currently undergoing herbivore damage, the constitutive increase in Indole indicates that Si+ plants are more primed for herbivore defense, and able to communicate attack to surrounding plants (Erb et al 2015). This, along with the potential greater sensitivity of the JA pathway through silicon, could indicate that along with increased physical defenses the volatiles also helped deter the mobile piercing sucking herbivores (Pare & Tumlinson 1999, Reynolds et al 2016).…”

“…Silicon may also play a role in the production of volatile organic compounds, also used for plant defense, by potentially inducing plant signaling to herbivore predators (Kvedaras et al 2010). In certain systems silicon increases induced plant defenses through the jasmonic acid (JA) pathway (Reynolds et al 2016;Kvedaras et al 2010;Pare & Tumlinson 1999).…”

“…In certain systems silicon increases induced plant defenses through the jasmonic acid (JA) pathway (Reynolds et al 2016;Kvedaras et al 2010;Pare & Tumlinson 1999). This pathway increases both direct defenses through plant secondary metabolites as well as volatile attraction of predators and parasitoids (Pare & Tumlinson 1999).…”