Biochemical mode of action of the acaricide fenazaflor

Abstract

The active ingredient of 'Lovozal' (fenazaflor) is hydrolysed in solution to 5,6-dichloro-2-trifluoromethylbenzimidazole (DTFB). Rat liver mitochondria were uncoupled by fenazaflor after a lag phase, while uncoupling by DTFB was immediate, and a similar situation occurred with mitochondria isolated from Tetranychus telarius L. (This is the first report of isolation of mite mitochondria.) Since both compounds ultimately have the same uncoupling activity, it is likely that fenazaflor exerts its effect only after hydrolysis to DTFB. Living mites showed a stimulation of respiration of 70% on addition of either fenazaflor or DTFB before death occurred, suggesting that the acaricidal effect of fenazaflor is due to uncoupling of oxidative phosphorylation after hydrolysis to DTFB.

Discriminating Toxicant Classes by Mode of Action: 2. Physico-Chemical Descriptors

“…The descriptor pro®le of class 3 chemicals (uncouplers of oxidative phosphorylation) is dominated by electronic charge parameters with major contributions of steric bulk. Most of them are hydrophobic weak acids that have protonophoric activities, i.e., they are able to transport H through the mitochondrial membranes [35,36]. For induction of uncoupling, an acid dissociable group, a bulky hydrophobic moiety and strongly electron withdrawing group(s) are required, such as derivatives of phenols, benzimidazoles, N-phenylanthranilates, salicylanilides, phenylhydrazones, salicylic acids, coumarins and aromatic amines.…”

“…The principal patterns are alike, although the steric properties of class 4 compounds are more pronounced relative to log K OW and the values of electronic charge distribution descriptors are lower except DIPOL. Comparison of target sites reveals similar structural requirements for inhibitors of photosynthesis and uncouplers of oxidative phosphorylation [35,38,39]. The herbicide binding niche on the D-1 quinone-binding protein of photosystem II (PS II: a 32 Kdalton protein in thylakoid membranes) reveals two interaction sites ± histidine-215 and serine-264.…”

“…For toxicities of class 4 chemicals, like those of class 3, the electronic and steric properties are of major relevance, the mean values being very close for many descriptors of the two classes. The functional similarity gives rise to`inhibitory uncouplers' [35], i.e., compounds which affect electron transport and phosphorylation in both mitochondria and chloroplasts. The inevitable overlap in class domains can partly be resolved from (eco)toxicological studies, e.g., different effect-concentrations in vitro at the isolated targets [7,40] or different symptoms in vivo at different concentrations, and to some extent (75% correct classi®cation) from physico-chemical descriptors (log K OW (class 3: mean log K OW 2.96, class 4: mean log K OW 2.51), V (class 3: mean V 10.74, class 4: mean V 8.48)).…”

Heterogeneity in the sensitivity of microtubules of Giardia lamblia to the herbicide oryzalin

“…Therefore, it is important to explore the potential effect of other drugs. Dinitroaniline herbicides such as oryzalin, which was shown to cause disruption of plant cell microtubules (Corbett et al 1984), disrupt the microtubules of several protozoa including Tetrahymena (Stargell et al 1992) and protozoan parasites such as Trypanosoma spp. (Traub-Cseko et al 2001), Leishmania spp.…”

Evaluation of four fresh-water unicellular cyanobacteria as potential hosts for mosquitocidal toxins

“…To investigate whether the four cyanobacterial strains could resist existing larvicides, some commercial chemical and biological larvicides were tested at the concentrations Table 1 Tolerance of cyanobacteria to temperature, salinity, and biological and chemical larvicides Chemspray respectively, are organophosphorous insecticides known to inhibit the acetylcholinesterase of susceptible mamalian cells (Corbett et al, 1984). Thiery et al (1991) reported that chemical larvicides did not affect the growth of some strains of cyanobacteria isolated from the French Mediterinean Coast.…”