Delbert D. Oehler

Moxidectin: pharmacokinetics and activity against horn flies (Diptera: Muscidae) and trichostrongyle nematode egg production.

The concentration of moxidectin, a macrocyclic lactone endectocide, in the blood serum of cattle resulting from single and daily subcutaneous injections and oral dosing was determined as a function of time. When given as a single subcutaneous (SC) injection, the drug peaked between 4 and 6 h post-treatment. As a single oral dose, the peak serum level occurred at 1 day post-treatment. Daily SC injections and oral doses resulted in a gradual increase in blood serum level over the 21 days of treatment but did not reach a plateau during this time. Horn flies, Haematobia irritans (Linnaeus), feeding on the blood of treated cattle drawn on Day 21 of daily treatment showed a decline in survival and egg production, but a negligible effect on egg hatching. Dose-mortality data on adult horn flies showed an LC-50 and LC-90 value of 10 ppb and 19 ppb in the blood, respectively. Moxidectin was also found to have larvicidal activity against the immature stages of the horn fly in the manure of treated cattle. Moxidectin administered at 100, 50 and 25 micrograms kg-1 as a daily oral medication was 100% effective in eliminating trichostrongyle egg counts by Day 3 of the treatment. Counts remained negative to the end of the trial.

The Ivomec SR Bolus for Control of Boophilus annulatus (Acari: Ixodidae) on Cattle in South Texas

Abstract When Hereford heifers infested with Boophilus annulatus (Say) were treated with a single Ivomec SR Bolus, the concentration of ivermectin in the serum of the treated cattle reached a maximum of 8.8 ± 0.9 ppb at 2 wk posttreatment. The single bolus treatment resulted in 84.4% control of standard engorging B. annulatus females on treated cattle over the 20-wk trial. Although fewer engorged ticks were collected from the sentinel heifers exposed in the treated pasture than those in the control pasture at weeks 4, 10, and 16 posttreatment, none of the differences was statistically significant. Each exposure of sentinel cattle found free-living ticks in both the treated and control pastures, indicating the infestation was not eliminated by the treatment. When the trial was repeated using two Ivomec SR Boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 ± 3.9 ppb at week 13 posttreatment. The use of two boluses/heifer resulted in 99.6% control of standard engorging B. annulatus females over the 20-wk trial. No ticks were found on sentinels placed in the treated pasture after week 9 posttreatment, an indication that the treatment had eliminated the free-living population in the treated pasture. From these studies, we conclude that a single Ivomec SR Bolus is incapable of sufficient control of B. annulatus to meet the rigid requirements of the Cattle Fever Tick Eradication Program in South Texas. Although two boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, the treatment would not be sufficiently efficacious for mature cattle (>400 kg) for it to be useful in the program.

Efficacy of the Ivomec SR Bolus for Control of Horn Flies (Diptera: Muscidae) on Cattle in South Texas

The concentration of ivermectin in the serum of Hereford heifers treated with a single Ivomec SR bolus reached a maximum of 8.8 +/- 0.9 ppb at 2 wk post-treatment. The single bolus treatment resulted in <10% mortality of adult horn flies feeding on the blood of the treated animals over the 21-wk trial. Bioassays of the manure from treated cattle showed complete inhibition of development of immature horn flies through week 19 post-treatment. When the trial was repeated using two Ivomec SR boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 post-treatment. During the first 17 wk of treatment, the use of two boluses/heifer resulted in 96.2 and 81.2% mortality of adult male and female horn flies feeding on the blood of treated animals, respectively. From these studies, we conclude that a single Ivomec SR bolus used as an anthelmintic treatment can be expected to provide significant control of immature horn flies developing in the manure, but not of adults feeding on the treated cattle.

A reservoir neckband system for delivery of organophosphorus insecticides to cattle

Abstract Because of the problem of pyrethroid resistance in the horn fly, alternatives to the controlled-release insecticidal ear tags are being explored. In laboratory studies, the rate of 5 selected organophosphorus insecticides from polymeric reservoirs of 10 different compositions was determined. Based on the results of the laboratory studies, chlorfenvinphos, diazinon, and crotoxyphos were loaded into thin-walled poly(vinyl chloride) reservoirs and fabricated into neckbands for cattle. In field trials, reservoir neckbands containing chlorfenvinphos, diazinon and crotoxyphos provided 91%, 88% and 53% control of horn flies, respectively.

CONTROL OF HOUSE FLY AND STABLE FLY BREEDING IN RHINOCEROS DUNG WITH AN INSECT GROWTH REGULATOR USED AS A FEED ADDITIVE

An insect growth regulator (IGR), Thompson-Hayward TH 6040 (N-(4-chlorophenyl)-N′-(2,6-difluorobenzoyl)urea), incorporated in the feed of rhinoceroses at rates of 1 and 0.1 mg/kg inhibited development of Musca domestica L. and Stomoxys calcitrans (L.) in the feces.

Sustained-Release Systems for Livestock Pest Control

Insects, ticks, and mites cost the livestock industry an estimated

Larvicidal Activity of Merck MK-933, an Avermectin, Against the Horn Fly, Stable Fly, Face Fly, and House Fly

3 billion annually.1 Two-thirds of this loss is suffered by the beef cattle industry. Despite continued interest in alternate methods of control, insecticide treatments are currently the most widely used and most effective means of control of these pests. It appears that pesticides will continue to be a vital part of the producers’ defense despite the inherent problems of chemical control. Although pesticides may not be the sole control method, they are likely to be a major tool in pest-management systems.