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Enhanced diazinon susceptibility in pyrethroid-resistant horn flies (Diptera: Muscidae): potential for insecticide resistance management.

Cilek JE, Knapp FW.

Department of Entomology, University of Kentucky, Lexington 40546.

Dose-mortality data from 40 horn fly, Haematobia irritans (L.), populations revealed that susceptibility to permethrin and diazinon was negatively correlated (i.e., as susceptibility to permethrin decreased, toxicity of diazinon increased). Permethrin-resistant horn fly populations exposed for 18 wk to cattle tagged with ear tags impregnated with 20% (AI) diazinon resulted in a 2- to 6-fold reduction in this resistance. These populations also had LC50s for diazinon that were two to five times lower than those of populations susceptible to permethrin. Frequency of homozygous permethrin-resistant individuals decreased as much as 57% after exposure to diazinon during this period.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8254132&dopt=Abstract permethrin Elimite



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Continuous, alternating, and mixed insecticides affect development of resistance in the horn fly (Diptera: Muscidae).

McKenzie CL, Byford RL.

Department of Entomology, New Mexico State University, Las Cruces 88003.

Susceptible populations of horn flies, Haematobia irritans (L.), were selected with six insecticide treatment regimens: continuous use of permethrin, diazinon, or ivermectin; permethrin/diazinon (1:2) mixture; permethrin-diazinon rotation; and permethrin-ivermectin rotation. Insecticide selection was applied as low-volume sprays on steers infested with horn flies housed in environmentally controlled rooms. During the study period, horn fly populations developed an apparent resistance to all insecticide treatment regimens. Selection with permethrin, diazinon, and ivermectin resulted in development of resistance in generations 21, 31, and 30, respectively. Selection with insecticide mixtures and rotations resulted in the delay of any apparent resistance development for an additional one to seven generations. The magnitude of this resistance ranged from 1,470-fold for the single continuous use of permethrin to < 3-fold for ivermectin in the permethrin-ivermectin rotation. Compared with single continuous insecticide selections, the onset and degree of resistance development was significantly reduced by alternating and mixing insecticides.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8376649&dopt=Abstract permethrin Elimite



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Locomotor and sensorimotor performance deficit in rats following exposure to pyridostigmine bromide, DEET, and permethrin, alone and in combination.

Abou-Donia MB, Goldstein LB, Jones KH, Abdel-Rahman AA, Damodaran TV, Dechkovskaia AM, Bullman SL, Amir BE, Khan WA.

Department of Pharmacology and Cancer Biology, Duke University Medical Center, North Carolina, USA. donia acpub.duke.edu

Since their return from Persian Gulf War (PGW), many veterans have complained of symptoms including muscle and joint pain, ataxia, chronic fatigue, headache, and difficulty with concentration. The causes of the symptoms remain unknown. Because these veterans were exposed to a combination of chemicals including pyridostigmine bromide (PB), DEET, and permethrin, we investigated the effects of these agents, alone and in combination, on the sensorimotor behavior and central cholinergic system of rats. Male Sprague-Dawley rats (200-250 gm) were treated with DEET (40 mg/kg, dermal) or permethrin (0.13 mg/kg, dermal), alone and in combination with PB (1.3 mg/kg, oral, last 15 days only), for 45 days. Sensorimotor ability was assessed by a battery of behavioral tests that included beam-walk score, beam-walk time, incline plane performance, and forepaw grip on days 30 and 45 following the treatment. On day 45 the animals were sacrificed, and plasma and CNS cholinesterase, and brain choline acetyl transferase, muscarinic and nicotinic acetylcholine receptors were evaluated. Animals treated with PB, alone or in combination with DEET and permethrin, showed a significant deficit in beam-walk score as well as beam-walk time as compared with controls. Treatment with either DEET or permethrin, alone or in combination with each other, did not have a significant effect on beam-walk score. All chemicals, alone or in combination, resulted in a significant impairment in incline plane testing on days 30 and 45 following treatment. Treatment with PB, DEET, or permethrin alone did not have any inhibitory effect on plasma or brain cholinesterase activities, except that PB alone caused moderate inhibition in midbrain acetylcholinesterase (AChE) activity. Treatment with permethrin alone caused significant increase in cortical and cerebellar AChE activity. A combination of DEET and permethrin or PB and DEET led to significant decrease in AChE activity in brainstem and midbrain and brainstem, respectively. A significant decrease in brainstem AChE activity was observed following combined exposure to PB and permethrin. Coexposure with PB, DEET, and permethrin resulted in significant inhibition in AChE in brainstem and midbrain. No effect was observed on choline acetyl transferase activity in brainstem or cortex, except combined exposure to PB, DEET, and permethrin caused a slight but significant increase in cortical choline acetyltransferase activity. Treatment with PB, DEET, and permethrin alone caused a significant increase in ligand binding for m2 muscarinic acetylcholine receptor (mAChR) in the cortex. Coexposure to PB, DEET, and permethrin did not have any effect over that of PB-induced increase in ligand binding. There was no significant change in ligand binding for nicotinic acetylcholine receptor (nAChR) associated with treatment with the chemical alone; a combination of PB and DEET or coexposure with PB, DEET, and permethrin caused a significant increase in nAChR ligand binding in the cortex. Thus, these results suggest that exposure to physiologically relevant doses of PB, DEET, and permethrin, alone or in combination, leads to neurobehavioral deficits and region-specific alterations in AChE and acetylcholine receptors.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11248143&dopt=Abstract permethrin Elimite



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Utility of a neurobehavioral screening battery for differentiating the effects of two pyrethroids, permethrin and cypermethrin.

McDaniel KL, Moser VC.

ManTech Environmental Technology Inc., Research Triangle Park, NC 27709.

The ability of a neurobehavioral screening battery to differentiate the effects of two pyrethroids, permethrin and cypermethrin, was assessed in this experiment. Although the structures of these pesticides differ only in the alpha-cyano group, the behavioral syndromes associated with the Type I and II pyrethroids are quite different. The tests included a functional observational battery which is a series of subjective and quantitative measures of neurological function and behavior, and an automated measure of motor activity. Our results verified previous reports in the literature describing these different syndromes, i.e., aggressive sparring behavior, fine to whole-body tremor, hyperthermia, and decreased motor activity for the Type I pyrethroid permethrin, and pawing, burrowing, salivation, whole body tremor to choreoathetosis, hypothermia, and lowered motor activity for the Type II pyrethroid cypermethrin. In addition, we report that permethrin produced decreased grip strengths, increased resistance to capture, increased reactivity to a click stimulus, and induced head and forelimb shaking and agitated behaviors, whereas cypermethrin produced pronounced neuromuscular weakness and equilibrium changes, retropulsion, lateral head movements, alterations in responses to various stimuli, and increased urination. Although there were similarities in some effects (e.g., decreased motor activity), the pesticides differed sufficiently in their overall behavioral profiles, and severity and time course of effects, to discriminate these two compounds. Thus, this type of screening approach is sensitive enough to differentiate these pyrethroids for hazard identification purposes.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8510610&dopt=Abstract permethrin Elimite



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Permethrin resistance in the head louse Pediculus capitis from Israel.

Mumcuoglu KY, Hemingway J, Miller J, Ioffe-Uspensky I, Klaus S, Ben-Ishai F, Galun R.

Department of Parasitology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.

Head lice, Pediculus capitis, were collected from children aged 3-12 years in Maale Adumin, a town near Jerusalem, after reports of control failure with the pyrethroid insecticide permethrin. A total of 1516 children were examined: living lice and eggs were found on 12.1% of the children; or another 22.8% of the children only nits were found. Twice as many girls as boys (8.1% v 4%) were infested with lice and or nits. Head lice collected from infested children were exposed to permethrin impregnated filter-papers. Log time probit mortality (ltp) regression lines were calculated for mortality data and compared to ltp lines for a similar collection of head lice made in 1989. The regression lines for the two years were significantly different, with a 4-fold decrease in susceptibility at the LT50 level between 1989 and 1994. The slopes of the lines also suggested that the 1994 population was more heterogenous in its response to permethrin than the 1989 population. In contrast, a laboratory population of body lice (Pediculus humanus) tested with the same batch of permethrin-impregnated papers showed a slight but non-significant increase in susceptibility between 1989 and 1994. The results suggest that resistance to pyrethroids has developed rapidly among head lice since permethrin was introduced in 1991 as a pediculicide in Israel.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8541597&dopt=Abstract permethrin Elimite