Sheep parasites
Choosing a chemical group to treat blowflies and
lice
Bob Armstrong, Geoffrey Knights and Wendy McLeish, Agency for Food and Fibre Sciences
Introduction
Once you have decided to treat sheep to control blowflies and/or lice ensure that you do it effectively and avoid negative after-effects. You should:
- positively identify the target parasite (blowfly or louse) and select a pesticide known to be effective against it
- determine the best method of application of that pesticide, given the length of wool on the sheep
- ensure that you have the appropriate equipment and that it operates in line with the manufacturer's specifications
- consider occupational health and safety (OH&S) and environmental effects of using the pesticide
- check the withholding period (WHP), export slaughter interval (ESI) and the rehandling period
- consider economic aspects of using the pesticide, including the cost per head, persistency, labour costs and time required
- assess the condition of the sheep to be treated and ensure that the application method will not unduly stress them
- apply the pesticide according to the instructions on the label
- dispose of excess pesticide according to the instructions on the label.
Most of the pesticides currently available for use on sheep are synthetic compounds belonging to the IGR, ML, OP and SP chemical groups as shown in the following table.
Chemical groups and their active ingredients
| Chemical group | Abbreviation | Active ingredients |
| Insect growth regulator | IGR |
Diflubenzuron, triflumuron Cyromazine, dicyclanil |
| Macrocyclic lactone | ML | Ivermectin |
| Organophosphate | OP | Diazinon, propetamphos |
| Spinosyn | Spinosad | |
| Synthetic pyrethroid | SP | Alphacypermethrin, cyhalothrin, cypermethrin, deltamethrin |
| Other | Amitraz, magnesium fluorosilicate, piperonyl butoxide, rotenone, sulphur |
Insect growth regulator
The IGR chemical group controls parasites by interfering with the larval stages of the life cycle. IGR products are used to control blowflies and body lice and can be applied as a dipping, jetting, spray-on or backline treatment.
The IGR group has two sub-groups with different modes of action: diflubenzuron and triflumuron on the one hand and cyromazine and dicyclanil on the other. Diflubenzuron and triflumuron affect deposition of chitin, which forms the exoskeleton of the insect. Humans do not have any tissues made of chitin and no chronic effects on human health are known. However many aquatic invertebrates have exoskeletons containing chitin. The active ingredients cyromazine and dicyclanil affect the cuticle of the insect but their mode of action has not been definitively established.
Macrocyclic lactone
The ML chemical group controls parasites by reducing the insect's motor activity, causing paralysis, with the result that the insect falls from the host. Although ML products have selected toxic effects on insects they have little effect on mammals. ML products are used to control blowflies and body lice and can be applied as a long wool jetting treatment.
Organophosphate
The OP chemical group kills parasites through its effect on the insect's nervous system. OP products are used to control blowflies and body lice and can be applied as a dipping, jetting or backline treatment or blowfly strike dressing.
Spinosyn
The spinosyn chemical group controls parasites by interfering with their nervous system. It provides four to six weeks protection against blowfly strike and can be used to control lice in long wool. Spinosyn can be applied as a jetting treatment or blowfly strike dressing. As spinosyn breaks down rapidly, has no adverse OH&S or environmental effects, and has a nil WHP it can be used within the last two months prior to shearing.
Synthetic pyrethroid
The SP chemical group is related in chemical structure to the plant extract pyrethrin. Like the OP group, SP products kill parasites by interfering with their nervous system. They are used to control body lice and can be applied as a dipping or backline treatment.
Other chemicals
Magnesium fluorosilicate is used to control body lice and can be used in organic production systems. Amitraz, piperonyl butoxide, rotenone and sulphur are additives used to enhance the activity of active ingredients in other chemical groups.
Further information
For further information contact the DPI Business Information Centre on 13 25 23 (Queensland residents) or 07 3404 6999 (non-Queensland residents) between 8 am and 6 pm weekdays, or e-mail callweb@dpi.qld.gov.au
The book Blowflies and lice information manual: A practical approach to producing low residue wool (DPI Shop Online) takes you step-by-step through best practice management of blowflies and lice following an integrated pest management approach to reducing pesticide use and residues on wool.
The Quick guide to commonly used treatments for blowflies and lice lists commonly used pesticides.
This DPI Note is also published on the DPI's PrimeNotes CD-ROM.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No: SW0095 . Date created: April 2002 . Revised: September 2003
