We investigated the effects of two commercial diatomaceous earth based insecticides (DE), Protect-It Ò and SilicoSec Ò , the nano-structured silica product AL06, developed by the section for Urban Plant Ecophysiology at Humboldt University Berlin, and the monoterpenoids, eugenol, and cinnamaldehyde on two stored product pests, Callosobruchus maculatus and Sitophilus oryzae. ProtectIt Ò was more effective than SilicoSec Ò against C. maculatus while the reverse was true for S. oryzae. Generally C. maculatus was more sensitive towards DE and silica treatment than S. oryzae. Mortality rate of both pest species increased when DE's were applied to food commodities previously treated with a monoterpenoid. In admixture experiments, the toxicity of SilicoSec Ò ? cinnamaldehyde (LD 50 = 42.73 ppm), SilicoSec Ò ? eugenol (LD 50 = 24.30 ppm), and Protect-It Ò ? eugenol (LD 50 = 2.60 ppm) was increased over DE alone against S. oryzae. Both substances showed a synergistic effect considering their co-toxicity coefficient relative to the LD 50 -value. In contrast, we could not find any synergistic effects in experiments with C. maculatus. Here only Protect-It Ò ? cinnamaldehyde (LD 50 = 20.84 ppm) showed an additive effect while all other combinations of monoterpenoid and DE indicated antagonistic effects. In addition to contact insecticidal effects both monoterpenoids showed a strong fumigant action. The presented results indicate that the natural product DE has great potential to replace synthetic pesticides commonly used in stored product pest management. Efficacy of DE can be improved by adding certain monoterpenoids against certain insect pests.
Silica-based substances have increased in popularity in recent years as alternative insecticides in horticultural crop protection. However, no research has been conducted into the influence of silica on plant biochemistry. Formulations (Fossil Shield 90.0s, AE R974, AL-06-109, Surround) were applied electrostatically on pak choi. Plants were harvested on two dates to measure immediate (first) and decelerated (second) influence, as well as recovery following the removal of silica formulations. The predominant individual glucosinolate (GS) in pak choi Black Behi was 1-methoxy-3-indolylmethyl GS. A significant increase in total glucosinolate contents in all treatments was measured from the first to second harvest. During the first harvest, no changes in glucosinolate levels in plants were found in any of the treatments. After a 48 h recovery period, two substances showed decreased amounts for indole GS compared to the control. Flavonoids (kaempferol and isorhamnetin) decreased from the first to second harvest. Kaempferol in particular decreased in treated plants from the first to second harvest date. The shading of leaves by silica mainly caused the decrease in secondary metabolites in treated plants. Treatments with silica formulations as an alternative insecticide cause shifts in the composition and contents of bioactive secondary metabolites in Brassica rapa spp. chinensis plants and should, therefore, be used with care to control insects.
Zusammenfassung Amorphe silikathaltige Stäube, in ihrer natürlich vorkommenden Form als Diatomeenerden oder synthetisch produziert, werden im Vorratsschutz und in der Tierhaltung seit Jahren zur Bekämpfung von Schadinsekten und Parasiten eingesetzt. Neue Formulierungen lassen auch einen möglichen Einsatz gegen Schädlinge im Gartenbau erwarten. Um Schädlinge auch an Blattunterseiten zu bekämpfen, wurde versucht, ein natürliches Silikat elektrostatisch auf Blätter von Brassica chinensis zu applizieren. Dabei ließen sich siliziumdioxidhaltige Stäube nicht mit Tribo-Sprühgeräten aufladen und es musste auf Korona-Sprühgeräte zurückgegriffen werden. Mit diesen gelang es, gleichmäßige Schichten einer Diatomeenerde auf Blätter zu applizieren und die Schichtdicke zwischen 25-125 µm zu variieren. Die insektizide Wirkung im Petrischalenversuch mit je 20 Kornkäfern (Sitophilus granarius (L.)) unterschied sich dabei nicht für Schichtdicken von 50-100 µm und 100-125 µm. Eine Silikatschichtdicke von 25-50 µm führte zu einer niedrigeren Mortalitätsrate. Die Applikationen führten bereits innerhalb von zwei Stunden zu einer Reduktion der Kohlenstoffdioxidabsorption von 45%. Dieser Wert schwankte über einen Zeitraum von C. Ulrichs (u) · T. Mucha-Pelzer · I. Mewis sieben Tagen zwischen 45 und 73%. Auch nach einem Entfernen des Staubes blieb die Kohlenstoffdioxidabsorption der Pflanze um 19-28% reduziert. Dieses spricht für ein Eindringen der Silikatpartikel in die Stomata, wo diese zu Verstopfungen führen bzw. eine reduzierte Transpiration sowie Fotosyntheseleistung bewirken.Schlüsselwörter Silikate · Diatomeenerde · Sitophilus granaries · Elektrostatische Applikation Plant protection with silica particles: Electrostatic application and impact of particle layer density on the insecticidal efficacy Abstract Natural occurring amorphous silica is ubiquitous on the earth in soils and sediments. Both, natural derived silica and synthetically produced amorphous silica are used against stored product pests and parasites in animal houses. New formulations, active even under higher relative humidity's can be possible used against horticultural arthropod pests. Since many horticultural pests hide on the undersides of leaves and silica is a physical contact insecticide, an appropriate application method is needed. This paper reviews electrostatic application of natural derived amorphous silica to Brassica chinensis leaves. Due to the inherent high volume resistivity of silica powder, induction charging was ineffective for electrostatic powder coating. Corona charging involves a reliable current source, but typically is inefficient in charging the powder particles and creates a high density of free ions between the gun and grounded substrate as well as within the coating layer. These factors resulted in poor coating quality and inefficient particle deposition. The best leave coating was archived using tribo charging. Here we have been able to apply 1 3 30 Gesunde Pflanzen (2008) 60:29-34 coatings with different thickness. While a silica coat...
Problem statement: One focus in recent atmospheric pollution research is on fine Particle Matter (PM), especially as result of increasing traffic and anthropogenic activity in urban areas. Here, the impact on animal and human health has been in the center of many studies. Despite the fact that PM depositions can affect plants on the long term, there are only few studies about the impact on plants conducted. Approach: Therefore we studied the impact of PM on plants, using naturally occurring silica dusts (diatomaceous earth) and hard Coal Fly Ash (CFA) from burning processes. Dusts were applied onto Brassica chinensis L. using a simple duster (covering upper leaf surfaces) or electrostatically (covering leaf upper and -underside). Results: Main components of the tested CFA are SO 4 2-, K, Ca and NH 4+ . The pH value of eluates was found to be around 9.5 in CFA and 5.7 in silica. B. chinensis was insensitive towards the high pH and showed no growth reduction when grown in silica or CFA substrate. PM deposition on leaf surfaces results through shading in a reduced photosynthetic activity. The reduction is relatively higher at higher light intensities. Photosynthesis stays reduced after removal of silica PM from leaf surfaces. We assume that stomata get cloaked by small particles and that silica absorbs lipids from the epicuticle resulting in a general stress reaction. Smaller sized silica particles resulted in a higher reduction of CO 2 -absorption. Next to particle size is the photosynthesis negatively correlated with exposure time for silica PM. The chlorophyll fluorescence data indicate that dust-covered leaves exhibited significantly lower quantum yield of PS II and a reduced quantum efficiency of PS II and therefore supported the gas exchange data. Conclusion: Reduced photosynthetic performance would be expected to reduce growth and productivity of B. chinensis. In contrast to silica hard coal fly ash showed only a reduction of photosynthesis through shading but did not have any long time effects after washing them off.
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