Phototransformation of metoxuron [3‐(3‐chloro‐4‐methoxyphenyl)‐1,1‐dimethylurea] in aqueous solution

UV irradiation of metoxuron in aerated aqueous solution at 254 nm or between 300 and 450 nm led initially to an almost specific photohydrolysis of the C–Cl bond, resulting in the formation of 3‐(3‐hydroxy‐4‐methoxyphenyl)‐1,1‐dimethylurea (MX3) and hydrogen chloride. The quantum yield was determined to be 0.020 (±0.005) in solutions irradiated at 254 nm. Five minor photoproducts were also identified, in particular the dihydroxydimethoxybiphenyl derivatives resulting from the phototransformation of MX3. Irradiation increased the toxicity of an aqueous solution of metoxuron to the marine bacterium Vibrio fischeri. © 2001 Society of Chemical Industry     

Toxicity of δ‐phenothrin and resmethrin to non‐target insects

BACKGROUND: The susceptibility of adult house cricket, Acheta domesticus (L.), adult convergent lady beetle, Hippodamia convergens (Guérin‐Méneville), and larval fall armyworm, Spodoptera frugiperda (JE Smith), to resmethrin and δ‐phenothrin synergized with piperonyl butoxide (PBO) was evaluated in a laboratory bioassay procedure. RESULTS: The 1 day LC₅₀ values for resmethrin + PBO were 23.2, 32.08 and 307.18 ng cm^?2 for A. domesticus, H. convergens and S. frugiperda respectively. The 1 day LC₅₀ values for δ‐phenothrin + PBO were 26.9, 74.91 and 228.57 ng cm^?2 for A. domesticus, H. convergens and S. frugiperda respectively. The regression relationship between species mortality and concentration explained 51–81% of the variation for resmethrin + PBO and 72–97% of the variation for δ‐phenothrin + PBO. The LC₅₀ values decreased with time for these insecticides for all surrogate species. In terms of sensitivities among the insects to resmethrin + PBO and δ‐phenothrin + PBO, A. domesticus was most sensitive, followed by H. convergens and then S. frugiperda. CONCLUSION: The results indicate that resmethrin + PBO was generally more toxic than δ‐phenothrin + PBO. Based on the results, A. domesticus seems to be a good surrogate species for estimating potential non‐target terrestrial insect impacts from exposure to pyrethroids used in public health applications. Copyright © 2008 Society of Chemical Industry     

Synthesis and fungitoxic activity of 5‐aryl‐1‐formyl‐4,5‐dihydro‐3‐(2‐hydroxyphenyl)‐1H‐pyrazoles and their complexes

Cyclization of 3‐aryl‐1‐(2‐hydroxyphenyl)prop‐2‐en‐1‐ones with hydrazine hydrate in refluxing formic acid afforded the title ligands, 5‐aryl‐1‐formyl‐4,5‐dihydro‐3‐(2‐hydroxyphenyl)‐1H‐pyrazoles (HL¹–HL⁴, Ar = Ph, 4‐CH₃O‐C₆H₄‐, 2‐furyl, 2‐thienyl). Reaction of HL¹–HL⁴ with the divalent metal ions, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, afforded novel complexes of the type [ML₂] (M = metal ion; L = deprotonated ligand) which were characterized by elemental analyses, molecular weight determinations, molar conductances, magnetic moments and electronic and infrared spectral data. The ligands behaved as tridentate, coordinating through the phenolic oxygen after deprotonation, N‐2 of the pyrazole ring and oxygen of the 1‐formyl group. The ligands and their complexes were evaluated for growth‐inhibiting activity against four phytopathogenic fungi. Macrophomina phaseoli was generally most sensitive followed by Alternaria alternata and Colletotrichum falcatum while Fusarium oxysporum was least sensitive to the tested compounds. The ligand HL¹ and its complexes showed the best activity against the fungi tested. © 2000 Society of Chemical Industry     

Improvement of the desorption of the pesticide 2,4‐D via complexation with HP‐β‐cyclodextrin

Inclusion complex formation of 2,4‐dichlorophenoxyacetic acid (2,4‐D) with hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) has been proposed as a way of modifying the behaviour of the pesticide in the soil environment. The present study assesses the effect of complex formation on 2,4‐D physicochemical properties (aqueous solubility, crystallinity and dissolution rate) and its behaviour on soils. The solid complexes were prepared using different methods (spray drying, kneading and heating in a sealed container). To confirm the complex formation in the solid state differential scanning calorimetry, hot stage microscopy and x‐ray diffraction techniques were employed. Complex formation in solution was studied by phase solubility. The presence of HP‐β‐CD increased the 2,4‐D solubility nine times approximately. The apparent stability constant was determined as 98.6 M ⁻¹. The dissolution rates of the 2,4‐D/HP‐β‐CD complexes were examined and compared with that of the pure pesticide. The results indicated that the complex may have great utility as a rapid way of dissolving the pesticide. Batch experiments were performed to study the adsorption–desorption of 2,4‐D on soils and the influence of the HP‐β‐CD over these processes. The results showed that HP‐β‐CD could increase the desorption of 2,4‐D previously adsorbed on soils. © 2000 Society of Chemical Industry     

Callose and β‐1,3‐glucanase inhibit Phytophthora cinnamomi in a resistant avocado rootstock

Phytophthora root rot (PRR) of avocado, caused by Phytophthora cinnamomi, is a significant threat to sustainable production wherever the crop is grown. Resistant rootstocks in combination with phosphite applications are the most effective options for managing this disease. Recently, the mechanisms underpinning PRR resistance have been investigated by the avocado community. Here, biochemical assays and confocal and scanning electron microscopy were used to investigate early defence responses in PRR resistant and ‐susceptible avocado rootstocks. Zoospore germination and subsequent hyphal growth for the pathogen were significantly inhibited on the surface of resistant avocado roots. When penetration occurred in the resistant R0.06 rootstock, callose was deposited in the epidermal cells, parenchyma and cortex of roots. In addition, β‐1,3‐glucanase was released early (6 h post‐inoculation, hpi) in response to the pathogen, followed by a significant increase in catalase by 24 hpi. In contrast, susceptible R0.12 roots responded only with the deposition of lignin and phenolic compounds incapable of impeding pathogen colonization. In this study, PRR resistance was attributed to a timely multilayered response to infection by P. cinnamomi.     

Feeding‐deterrent activity of α‐asarone isomers against some stored Coleoptera

All isomers of α‐asarone [(E)‐4‐prop‐1‐enyl‐1,2,5‐trimethoxybenzene] were tested for their feeding deterrent activity against adults of Sitophilus granarius and Tribolium confusum and larvae of Trogoderma granarium and Tribolium confusum. (E)‐2‐prop‐1‐enyl‐1,3,5‐trimethoxybenzene exhibited the strongest deterrent activity against all the species tested. The total coefficients of deterrency for this compound were 140.6 and 169.7 for Tribolium confusum adults and larvae, respectively, and 144.9 and 104.6 for larvae of Trogoderma granarium and adults of Sitophilus granarius, respectively. © 2000 Society of Chemical Industry     

Competition between Solanum nigrum and pepper in the presence of Meloidogyne incognita

The influence of the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood on the competitive relationships between pepper (Capsicum annuum L.) and Solanum nigrum L. (black nightshade) was investigated in a glasshouse experiment. Seven competition treatments were set up: two intraspecific for the crop and the weed and five interspecific treatments in which the emergence of S. nigrum plants was progressively delayed with respect to that of the pepper. Nematodes reproduced in every inoculated plant and their multiplication rates were high in both pepper and S. nigrum. The parasite reduced all growth and yield parameters of the crop, but did less harm to the weed. The negative effect of S. nigrum on pepper peaked in the treatment in which the weed and pepper plants emerged together. S. nigrum was a stronger competitor than pepper under both nematode-infested and nematode-free conditions. The effect of nematodes on pepper yield was less than that of competition, but both appeared to be additive.     

Degradation of insecticide lindane (γ‐HCH) by white‐rot fungi Cyathus bulleri and Phanerochaete sordida

An Erratum for this article has been published in Pest Management Science 56(5) 493 (2000). The degradation of the insecticide lindane (γ‐hexachlorocyclohexane, γ‐HCH) by two white‐rot fungi, Cyathus bulleri and Phanerochaete sordida, was studied. C bulleri degraded lindane more efficiently than P sordida. Two degradative intermediates identified in P sordida culture were tetrachlorocyclohexene and tetrachlorocyclohexanol. However, tetrachlorocyclohexanol was the sole degradation product detected in cultures of C bulleri. The presence of lindane only inside the mycelial cells of both fungi eliminated any role of intracellular enzymes during initial steps of its degradation. The insecticide at 0.27 µM showed no adverse effect on fungal growth. © 2000 Society of Chemical Industry     

Synthesis and structure–activity relationship analysis of bicyclophosphorothionate blockers with selectivity for housefly γ‐aminobutyric acid receptor channels

BACKGROUND: Bicyclophosphorothionates (2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane‐1‐sulfides) are blockers (or non‐competitive antagonists) of γ‐aminobutyric acid (GABA) receptor channels. Twenty‐two bicyclophosphorothionates with different 3‐ and 4‐substituents were synthesised, and [³H]4′‐ethynyl‐4‐n‐propylbicycloorthobenzoate (EBOB) binding assays were performed to evaluate their affinities for housefly and rat GABA receptors. RESULTS: Introduction of an isopropyl group at the 3‐position enhanced the affinity of bicyclophosphorothionates for housefly GABA receptors and reduced the affinity towards rat GABA receptors. The 4‐isopentyl‐3‐isopropylbicyclophosphorothionate showed the highest affinity for housefly GABA receptors (IC₅₀ = 103 nM ) among the analogues tested, while the 4‐cyclohexylbicyclophosphorothionate showed the highest affinity for rat GABA receptors (IC₅₀ = 125 nM ). Among the bicyclophosphorothionates synthesised to date, the former analogue exhibited the highest selectivity for housefly GABA receptors, with an IC₅₀^rat/IC₅₀^fly ratio of approximately 97. Three‐dimensional GABA receptor models successfully explained the structure–activity relationships of the bicyclophosphorothionates. CONCLUSION: The results indicate that minor structural modifications of blockers can change their selectivity for insect versus mammalian GABA receptors. The substituent at the 3‐position of the bicyclophosphorothionates dictates selectivity for housefly versus rat GABA receptors. This information should prove useful for the design of safer insecticides and parasiticides. Copyright © 2010 Society of Chemical Industry