Temporal changes in distribution, prevalence and intensity of northern fowl mite (Ornithonyssus sylviarum) parasitism in commercial caged laying hens, with a comprehensive economic analysis of parasite impact.

Establishment and spread of Ornithonyssus sylviarum were documented through time on sentinel hens (50 per house of 28,000-30,000 hens) in the first egg production cycle of three large commercial flocks (12 houses) of white leghorn hens. Mites were controlled using acaricide, and the impacts of treatment on mite populations and economic performance were documented. Mite prevalence and intensity increased rapidly and in tandem for 4-8 weeks after infestation. Intensity declined due to immune system involvement, but prevalence remained high, and this would affect mite sampling plan use and development. Early treatment was more effective at controlling mites; 85% of light infestations were eliminated by a pesticide spray (Ravap), versus 24% of heavy infestations. Hens infested later developed lower peak mite intensities, and those mite populations declined more quickly than on hens infested earlier in life. Raw spatial association by distance indices (SADIE), incorporating both the intensity and distribution of mites within a house, were high from week-to-week within a hen house. Once adjusted spatially to reflect variable hen cohorts becoming infested asynchronously, this analysis showed the association index tended to rebound at intervals of 5-6 weeks after the hen immune system first suppressed them. Large, consistent mite differences in one flock (high vs. low infestation levels) showed the economic damage of mite parasitism (assessed by flock indexing) was very high in the initial stages of mite expansion. Unmitigated infestations overall reduced egg production (2.1-4.0%), individual egg weights (0.5-2.2%), and feed conversion efficiency (5.7%), causing a profit reduction of $0.07-0.10 per hen for a 10-week period. Asynchronous infestation patterns among pesticide-treated hens may have contributed to a lack of apparent flock-level economic effects later in the production cycle. Individual egg weights differed with mite loads periodically, but could be either higher or lower, depending on circumstances and interactions with hen weight. Individual hen weight gains were depressed by high/moderate mite loads, but the heavier hens in a flock harbored more mites. This led to compensatory weight gains after mites declined. Tradeoffs between resource allocation to body growth or production versus immune system function appeared to be operating during the early and most damaging mite infestation period, when high egg production was beginning and the hens were gaining weight. The results were related to other studies of mite impact on domestic hens and to wild bird-ectoparasite studies. Much of the mite economic damage probably is due to engaging and maintaining the immune response.

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% cypermethrin, 7.5% flucythrinate, 13.7% tetrachlorvinphos or 20.0% diazinon in protecting sheep against head strike by the sheep blowfly (Lucilia cuprina Wiedemann) was investigated in larval implant, fly cage and field studies. Tags impregnated with cypermethrin reduced the total number of egg masses deposited on the heads of sheep in fly cage studies over a 6 week period by 73.3% compared with no treatment. Tags impregnated 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 found on the majority of tagged sheep and no protection was provided against implants with first instar L. cuprina larvae by either cypermethrin 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 week period in field studies, 6.6% of rams treated with diazinon tags became struck compared with 30% treated by diazinon jetting, 35.7% treated with plastic tags not impregnated with insecticide and 24.2% of untreated rams. When the rams were exposed to high populations of L. cuprina in an exposure house from 13 to 18 weeks after treatment, 3.3% of rams 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 were not contacted by the tags. Tags impregnated with tetrachlorvinphos reduced the number of strikes in comparison with no treatment in larval implant and fly cage studies but the results were inconsistent and not as good as those from diazinon tags. It is concluded that well designed controlled release devices that reliably contact the wool on the heads of sheep at sites of flystrike risk and which are able to withstand damage from rams fighting may be able to give prolonged protection against head strike.

Effect of insecticidal ear tags on populations of lice (Damalinia ovis) infesting sheep.

Polymer matrix ear tags containing 13.7% w/w tetrachlorvinphos or 8.5% w/w cypermethrin were applied to Merino wethers infested with lice and carrying two months wool. The cypermethrin tags reduced louse numbers by a maximum of 89% in comparison to controls at 16 weeks after treatment and by 85% at the conclusion of the experiment 38 weeks after application. Lice were not eradicated from any sheep. The number of lice counted on sheep treated with tetrachlorvinphos-impregnated tags was not significantly different from controls.

Effectiveness of Ectiban, egg oil, Rabon, or Sevin for control of northern fowl mites on laying hens.

Two field trials were conducted on different ranches to compare acaricides for control of northern fowl mite (NFM) on White Leghorn hens. In Trial 1 Ectiban spray and dust treatments were compared to Rabon and Sevin spray-treatments; egg oil, Rabon, and Sevin sprays were tested in Trial 2. Concentration and rates of application followed label recommendations for the registered compounds. In Trial 1 Ectiban spray gave excellent NFM control; Ectiban dust, Rabon, and Sevin spray treatments resulted in poor NFM control. Egg oil and Rabon sprays gave effective NFM control in Trial 2. Sevin, as in Trial 1, gave poor NFM control. The failure of Sevin to control mites both times suggests the possibility of NFM resistance to this chemical.

Comparisons of permethrin formulations and application methods for northern fowl mite control on caged laying hens.

Formulations of permethrin (Ectiban), a synthetic pyrethroid, as an emulsifiable concentrate (EC), wettable powder (WP), and dust were nearly equally effective for 9 or more weeks for control of the northern fowl mite, Ornithonyssus sylviarum (Canestrini and Fanzago), on caged laying hens under environmentally controlled conditions. The permethrin was applied to the vent area as .05% active ingredient (AI) spray of the diluted EC or WP at 40 ml per bird, .1% AI mist of the diluted EC at 20 ml per bird, and 4.5 g per bird of the .25% AI dust. Dilute sprays of .05% permethrin prepared from the EC and WP and applied at 40 ml per bird were more effective in a commercial caged-laying hen house for northern fowl mite control than were .5% sprays of tetrachlorvinphos (Rabon), Ravap, and carbaryl (Sevin). Satisfactory mite control was obtained with .6% permethrin prepared from the EC and misted at the rate of 2.5 ml per bird. Low volume, high concentration misting of permethrin was a promising method for mite control with satisfactory control achieved with .2% AI at 5 ml per bird and .6% AI at 2.5 ml per bird.

Residues of stirofos (rabon) in eggs of laying hens treated for northern fowl mite control by dipping.

Laying hens were treated with a wettable powder formulation of stirofos [Rabon, 2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethylphosphate] by dipping in a .5 or 1.0% actual ingredient (AI) water suspension of a 50% wettable powder (WP) stirfos formulation. Stirofos residues were detected in eggs within 1 day after treatment and reached maximum levels 3 days after dipping (.021 and .035 ppm in the low- and high-dose birds, respectively). After that time, levels of residues in eggs declined rapidly and no sample contained detectable quantities (less than .004 ppm) of stirofos after 21 days. Dipping may be a practical control method for the northern fowl mite on chickens, because stirofos dips effectively control this mite on laying hens for at least 6 weeks and because resulting residues in eggs are well below established tolerances.

Comparative evaluation of four registered acaricides for field control of northern fowl mites on caged laying hens.

Carbaryl and tetrachlorvinphos provided longer lasting control of northern fowl mites, Ornithonyssus sylviarum (Canestrini and Fanzago), than did coumaphos or malathion when the materials were applied to caged laying hens as aqueous sprays. The average duration of residual control was ca. 5 weeks for carbaryl, 4.3 weeks for tetrachlorvinphos, 3.5 weeks for coumaphos, and 2 weeks for malathion. No presumptive evidence of northern fowl mite resistance to carbaryl or tetrachlorvinphos was encountered. In contrast, malathion often failed to produce satisfactory control, and difficulty with adequate dispersion of coumaphos wettable powder was noted.

Tetrachlorvinphos as an ineffective feed additive in control of gastrointestinal nematodes of beef cattle.

Tetrachlorvinphos was evaluated for anthelmintic efficacy as a feed additive against gastrointestinal nematodes of cattle. Tetrachlorvinphos was added to the mineral mixture of medicated cattle (n = 13) at the rate of 1.6 mg/day/kg of body weight for a 29-week period beginning May 2, 1975. Data suggest that the level of parasitism, as estimated by the number of nematode eggs per gram of feces, was not reduced by the addition of tetrachlorvinphos to the mineral mixture of medicated cattle. Results obtained from identification and quantification of nematodes recovered at necropsy from 6 medicated and 6 nonmedicated control heifers indicated that tetrachlorvinphos was ineffective as an anthelmintic against gastrointestinal nematodes of cattle.