Fen valerate

The topical application of insecticides and/or repellents can reduce exposure. Suggested regimens include the application of 200 ml 0.5% fen-valerate alongjhe line of the back. Alternatively 1 litre 0.1% fenvalerate may be applied as a body spray. This should be repeated every 7 days, or following exposure to rain. Permethrin insecticidal repellents are also effective and are used as a pour on preparation (30-40 ml 4% permethrin). However, adverse skin reactions have been reported following application. Cypermethrin and permethrin are also used in plastic tags or strips that can be attached to the head collar, mane and tail. 

The insecticides and synergist used were technical grade fen valerate (98%, Shell), profenofos (99%, Ciba Geigy) and PBO (99%. Sigma). 

Larval bioassays to determine pyrethroid resistance status in the test insects were similar to those recommended by the Entomological Society of America (Anon.. 1970) Technical grade insecticide was dissolved in acetone and five serially diluted concentrations prepared- For each concentration, ien 3rd instar larvae (30-40 mg) were treated with l pL of solution applied by mieroappliea-tor or micro pipette to the dorsal thorax. Each test was replicated three times and every replicate included are tone-treated controls which confirmed no control mortality. Synergists PBO and profenofos were applied 30 minutes before the fen valerate at 10, and 0.1 pg per larva, respectively (Gunning er a/., 1991). After dosage, the larvae were held individually at 25 1DC with adequate food. Mortality was assessed 4ft hours after treatment. Larvae were considered dead if unable to move in a coordinated way when prodded with a blunt probe. The data were analysed by probil, and resistance factors calculated as the ratio of resistant LDW to susceptible LD. ... 

Bioassay data for the H. armi era strains arc shown in Tabic 13.1. Strains were 1U-, 30- and 60-fold resistant to fen valerate. Profenofos was ineffective as a pyrethroid synergist, but PBO rendered the 10-fold-resistant strain almost completely susceptible to fen valerate, In the more highly resistant populations (30-and 60-fold), PBO was much less effective. 

Daly and Fisk (1993) looked at pyrelhroid resistance in adult Hdkoverpa armigera in both laboratory and field-selected strains. PBQ synergized the effects of the synthetic pyre thro id fen valerate 1000-fold and eliminated resistance entirely. 

Various plants sprayed with 0.25 kg fen-valerate/ha all had measurable residues 7 days after application, and non-detectable residues 15-30 days after treatment. Washing plants in cold water to remove the pesticide was effective only on the initial day of application, removing 30-50%. Afterwards, only 3-13% could be removed by washing. Cooking removed 71-88% of the fenvalerate... 

Fen valerate is a highly active contact insecticide which is very useful because it controls some strains which are resistant to organochlorine, organophosphate and carbamate insecticides. It has the structure shown below. 

In the case of some a-alkylbenzyl alcohols like 383 and allethrobne there is a tendency in favour of the formation of the inactive racemate. Fen valeric acid chloride 384 and 3-phenoxy-a-methylbenzyl alcohol 383 produce a diastereomeric mixture, which contains twice as much inactive racemate [816] as racemate of the actual insecticide. Different kinds of reaction types produce different isomeric ratios ... 

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