K.M.S. Sundaram

Azadirachtin biopesticide: A review of studies conducted on its analytical chemistry, environmental behaviour and biological effects

Abstract This paper provides a brief review of studies conducted in our laboratory on the analytical chemistry, environmental behaviour and biological effects of azadirachtin‐A, a neem‐based pesticide. Azadirachtin‐A (AZ‐A) was isolated from samples of neem seed kernels, leaves, bark, root and stem, obtained from Kanthayapalayam, South India. The extracts were subjected to column cleanup and AZ‐A concentration was quantified by using a high‐performance liquid chromatographic (HPLC) method. A flow diagram is given describing the procedures involved. AZ‐A was also isolated from four commercial formulations and from several forestry substrates, and its concentration in each sample was quantified by HPLC. To investigate the environmental behaviour of AZ‐A, five studies were conducted: (i) persistence of AZ‐A on balsam fir and red oak foliage, (ii) dissipation of AZ‐A in forest nursery soils, (iii) leaching in sandy loam forest soil, (iv) adsorption and desorption of AZ‐A in sandy loam soil, and (v) rate of hy...

Effects of pure and formulated azadirachtin, a neem‐based biopesticide, on the phytophagous spider mite, Tetranychus urticae koch

Abstract Pure azadirachtin‐A (AZ‐A) and four neem‐based formulations (RH, MO, PT and AT) containing the insecticide isomer were tested for their repellency, toxicity and oviposition deterrence against the phytophagous two‐spotted spider mite (Tetranychus urticae Koch). Mites were placed on treated and untreated aspen (Populus tremuloides Michx.) leaf discs and their fecundity, feeding rate and mortality were assessed. Results indicated that the effects of AZ‐A on T. urticae varied with formulation type and AZ‐A concentration. Significant reductions in feeding and oviposition, which correlated with AZ‐A concentrations, were recorded concomitantly with a significant increase in repellency. Leaf discs treated with increasing concentrations of the formulations showed increased mortality of T. urticae, reduction in the total number of eggs laid, reduced % of eggs hatched and reduced survival of emerged mites. The deterrent and biological effects decreased in the order AT>PT>MO>RH>AZ‐A.

Uptake, translocation, persistance and fate of azadirachtin in aspen plants (Populus tremuloides Michx.) and its effect on pestiferous two-spotted spider mite (Tetranychus urticae Koch)

Abstract A commercial neem formulation containing azadirachtin-A (AZ-A) was applied to the soil around the root system of potted aspen ( Populus tremuloides Michx.) plants. The uptake, translocation, persistence and dissipation of the chemical in the plants were studied. The effect of foliar residues of AZ-A on two-spotted spider mite ( Tetranychus urticae Koch) populations was also evaluated. The compound was taken up by the root system within 3 h and translocated in the stem and foliage within 3 days, confirming that AZ-A is systemic. The peak concentrations (μg/g, fresh weight) of AZ-A occurred at 10 days post-treatment, and were distributed in roots, stem and foliage in the ratio of 8.1:1.0:2.3, respectively. The rate of dissipation of AZ-A from the matrices was moderately rapid, and the residual concentrations on the last day of sampling (50 days post-treatment) in roots, stem and foliage were in the ratio 2.7:1.0:1.2, respectively. Control of mites by AZ-A residues in foliage was statistically significant, and the bioactivity declined within 30 days. The final residue of AZ-A in the soil after 50 days was about 25% of the initial value, with a half-life of dissipation of about 26 days.

Solubility products of six metal‐glyphosate complexes in water and forestry soils, and their influence on glyphosate toxicity to plants

Abstract The solubility products (Ksp) of 1:1 complexes of glyphosate, [N‐(phosphonomethyl)glycine], with Mg2+, Ca2+, Mn2+, Zn2+, Cu2+ and Fe3+, were determined in buffered (pH 7.0) distilled water, moist Ottawa sand, sandy loam and clay loam soils, each adjusted to 0.02 M with respect to KNO3. The Ksp values decreased in the order of Mg ≍ Ca > Mn > Zn > Cu > Fe, regardless of the medium in which they were determined. The constants measured in Ottawa sand were similar to those in water, but those in the forestry soils depended upon the type of metal ion involved. The values for the Mg, Ca, Mn and Zn complexes were about 2 to 3 times lower in sandy loam soil than those in water, but those in clay loam were about 3 to 10 times lower. The Ksp of the Cu and Fe complexes were similar to those in water regardless of the soil type used. In a bioassay experiment using tomato plants, immersed in the saturated solutions of the complexes or planted in the sand and soils containing saturated solutions of the complexe...

A Comparison of UV and Fluorescence Detectors in the Liquid Chromatographic Analysis of Glyphosate Deposits After Post-Column Derivatization

Abstract A sensitive and rapid liquid chromatographic method for the analysis of glyphosate using either post-column ninhydrin derivatization and UV detection (UV-D) or post-column reaction, fluorogenic labelling with o-phthalaldehyde in the presence of 2-mercaptoethanol and fluorescence detection (FD) is described. The sensitivity of the UV-D and two fluorescent detectors (HP-FD and Kratos-FD) were compared and evaluated to analyze glyphosate residues from glass fibre filter (GFF) discs used as deposit collectors in aerial application. The herbicide was extracted from the GFF discs using 30.0 mL of phosphate buffer adjusted to pH 2.1, derivatized and quantified. The method was tested initially, optimized and validated by using glyphosate standards. The average percent recoveries from fortified GFF samples were 93.7 (UV-D), 99.2 (HP-FD) and 94.9 (Kratos-FD). The corresponding standard deviation and coefficient of variation (percent) were 6.0 and 6.44; 1.6 and 1.67; and 4.4 and 4.59, respectively. The mini...

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg -1 , into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre -1 , into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0.05, 0.10, 0.26 and 0.5 mg litre -1 . This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study.

Foliar persistence and residual activity of tebufenozide against spruce budworm larvae

A field study was conducted to investigate the persistence of tebufenozide in white spruce foliage. An aqueous suspension concentrate formulation, RH-5992 2F, was sprayed over single trees at three dosage rates, 35, 70 and 140 g of the active ingredient (AI), in 2.0 litre ha -1 , using ground application equipment. Foliage was collected at different intervals of time up to 64 days after treatment and tebufenozide residues were measured by high-performance liquid chromatography. Foliage was also fed to laboratory-reared 4th- and 6th-instar spruce budworm (Choristoneura fumiferana Clemens). The data indicated that tebufenozide residues in foliage declined with time according to first-order kinetics. The average rate-constant and half-life of disappearance (DT 50 ) were 0.0340 and 20.45 days, respectively. Larval mortality declined gradually, corresponding to the residues, but was still appreciable (49 to 70%) when the larvae were fed with foliage collected 64 days after treatment. The amount of foliage consumed by the larvae decreased when foliar residues of tebufenozide increased, thus indicating anti-feedant activity of the chemical. The LD 50 values for both instars were similar and averaged c.25 ng per insect, but the LD 90 values were significantly lower for 4th-instar than for 6th-instar, at 63.6 and 96.1 ng per insect respectively. This implies that, theoretically, at a foliar concentration of 1.0 μg tebufenozide g -1 foliage (fresh wt), the spruce budworm larva needs to consume 65 to 100 mg of foliage in 10 days to cause mortality in about 90% of a population of the insect.

Persistence and fate of tebufenozide (RH‐5992) insecticide in terrestrial microcosms of a forest environment following spray application of two mimic® formulations

Abstract A terrestrial microcosm study was conducted to study the persistence and metabolic fate of tebufenozide in clay loam soil, forest litter, spruce needles and shoots after spray application of aqueous flowable (AF) and emulsion suspension (ES) formulation of tebufenozide, MIMIC®, at 35, 70 and 140 g active ingredient (A.l.)/ha. Soil, litter, spruce needles and shoots were collected at intervals of time up to 460 d post‐spray and analyzed by high‐performance liquid chromatography (HPLC) for the intact chemical. Droplet density, size spectra (DN.5 and Dv.5) and initial deposit data were gathered using collection units consisting of Kromekote® cards, glass fibre filters and glass plates. Droplet density, size spectra and deposition varied according to the formulation type sprayed. Deposit levels increased with dosage and the ES formulation usually gave higher deposition on the collectors compared to the AF formulation. Initial deposits (μg/g, fresh weight) were higher (ca. 150 %) on the spruce needles...

Formulation selection, and investigation of azadirachtin‐A persistence in some terrestrial and aquatic components of a forest environment

Five commercial formulations of azadirachtin-A (AZ-A) Margosan-O®, Azatin-EC®, Neem-EC®, RH-9999 and Neemix® 4.5, were investigated for their volatilization and washoff potential in laboratory studies. Prior to the investigation, RH-9999 (a wettable powder) was mixed with water to provide an end-use formulation containing 35.6 g AZ-A kg -1 , while the remaining four formulations were investigated without dilution. Volatilization and washoff of AZ-A occurred more from white spruce foliage than from wax-coated glass plates. Neem-EC provided the lowest amount of loss, whereas Margosan-O provided the highest. Physical properties and atomization behaviour of the five formulations indicated that Azatin-EC was highly viscous and caused phase separation in droplets collected on glass plates after atomization in a rotary atomizer. RH-9999, despite its low viscosity, caused phase separation in droplets because of the heterogeneity of the wettable powder formulation. Based on the minimum loss of AZ-A due to volatilization and washoff from spruce foliage, and on the minimum potential for phase separation in droplets after atomization in a rotary atomizer, Neem-EC was considered to be the most appropriate choice for use in field studies to investigate environmental persistence and fate of AZ-A in terrestrial and aquatic matrices of a forest ecosystem. The Neem-EC formulation was sprayed at 40 and 80 g AI ha -1 over single spruce trees and on litter and soil plots selected in a mixed-wood boreal forest in Ontario, Canada. In addition, outdoor aquaria containing stream water and sediment were also fortified with the formulation at 400 and 800 g AI ha -1 . Persistence of AZ-A was evaluated using one-year-old spruce needles, current-year shoots, spruce bark, litter, soil, stream water and sediment. The duration of persistence varied from 3 to 6 days in terrestrial matrices, whereas it ranged from 8 to 13 days in water, and 2 to 3 days in sediment. The half-life (DT 50 ) values ranged from 10.7 h (for soil) to 71.6 h (for spruce bark) at the lower dosage rate, and from 18.8 h (for litter) to 76.2 h (for bark) at the higher dosage rate. The DT 50 value for stream water was about 35 h regardless of the dosage rate applied. The data indicated that AZ-A was appreciably labile and short-lived in different forestry matrices, with low DT 50 values.

Photostabilization of the botanical insecticide azadirachtin in the presence of lecithin as UV protectant

Abstract The phytochemical insecticide, azadirachtin (AZ), undergoes UV‐induced photodegradation. Using the isomer AZ‐A as a standard, its photochemical stability was studied with and without adding lecithin surfactant as a UV protectant. Standard solutions of pure AZ‐A and Margosan‐O® were prepared in methanol‐hexane with (AZ‐A:lecithin, 1:2 by weight) and without lecithin, applied separately onto glass plates and maple (Acer L.) foliage and exposed to radiant energy under controlled conditions. Noticeable photostabilization of AZ‐A was achieved in the samples containing lecithin compared to AZ‐A samples without the lecithin additive. First‐order kinetic evaluation of the data showed that the DTy50 (half‐life) and C (rate constant) values for AZ‐A with and without lecithin on glass plates were 5.68 d and 0.122, and 5.42 d and 0.128, respectively. The corresponding values for the Margosan‐0 formulation were 7.37 d and 0.094, and 6.24 d and 0.111. The DT50 and C values for the pure AZ‐A on maple foliage wi...