CONTROLLED-RELEASE INSECTICIDE DEVICES FOR PROTECTION OF SHEEP AGAINST HEAD STRIKE CAUSED BY LUCILIA-CUPRINA

The effectiveness of polymer matrix tags containing (w/w) 8.5% cyperme thrin, 7.5% flucythrinate, 13.7% tetrachlorvinphos or 20.0% diazinon i n protecting sheep against head strike by the sheep blowfly (Lucilia c uprina Wiedemann) was investigated in larval implant, fly cage and fie ld studies. Tags impregnated with cypermethrin reduced the total numbe r of egg masses deposited on the heads of sheep in fly cage studies ov er a 6 week period by 7 3.3% compared with no treatment. Tags impregna ted with flucythrinate reduced the number of egg masses by 25.3% over 21 weeks but there were no significant differences (P < 0.05) between treated and untreated sheep at individual exposures. Egg masses were f ound on the majority of tagged sheep and no protection was provided ag ainst implants with first instar L. cuprina larvae by either cypermeth rin or flucythrinate tags. Tags impregnated with diazinon gave longer protection than treatment with a liquid formulation containing 400 ppm diazinon in larval implant, fly cage and field studies. Over a 12 wee k period in field studies, 6.6% of rams treated with diazinon tags bec ame struck compared with 30% treated by diazinon jetting, 35.7% treate d with plastic tags not impregnated with insecticide and 24.2% of untr eated rams. When the rams were exposed to high populations of L. cupri na in an exposure house from 13 to 18 weeks after treatment, 3.3% of r ams treated with diazinon tags, 57.1% treated by diazinon jetting, 43. 8% treated with plastic tags and 23.5% of untreated rams became struck . Most strikes in the diazinon tagged sheep occurred at sites which we re not contacted by the tags. Tags impregnated with tetrachlorvinphos reduced the number of strikes in comparison with no treatment in larva l implant and fly cage studies but the results were inconsistent and n ot as good as those from diazinon tags. It is concluded that well desi gned controlled release devices that reliably contact the wool on the heads of sheep at sites of flystrike risk and which are able to withst and damage from rams fighting may be able to give prolonged protection against head strike.