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     

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.     

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     

Role of the α subunit of nicotonic acetylcholine receptor in the selective action of imidacloprid

Examination of agonist interactions of imidacloprid on recombinant chicken α4β2 and Drosophila SAD/Chicken β2 hybrid receptors, expressed in Xenopus oocytes by nuclear injection of the cDNAs, indicates that imidacloprid is a partial agonist. Replacement of the α4 subunit for the Drosophila SAD subunit lowered the imidacloprid EC₅₀ 37-fold, whereas EC₅₀s for other agonists increased 4-50 fold, suggesting that the α subunit contributes to the high affinity of insect nicotonic receptors for imidacloprid. ©1999 Society of Chemical Industry     

Recovery of solubilized δ‐endotoxin from Bacillus thuringiensis subsp kurstaki fermentation broth

Insecticidal δ‐endotoxin proteins, degraded from parasporal crystals by protease, were recovered by a simple procedure using heat treatment, solubilization, and ultrafiltration of a fermentation broth of Bacillus thuringiensis subsp kurstaki HD‐1. A 68 kDa insecticidal protein was obtained and characterized by SDS‐PAGE. The procedure described gave a nearly quantitative recovery of toxicity. Furthermore, bioassay results on larvae of the diamondback moth (Plutella xylostella) showed that the 68 kDa δ‐endotoxin fraction (P1) was the principal insecticidal component to this target insect. A similar molecular mass polypeptide P2 (65 kDa) which was solubilized together with P1 from the parasporal crystals, gave relatively low mortality. © 2000 Society of Chemical Industry