Other Flies

Stable flies on grazing cattle

• In most parts of Australia stable flies are rarely a problem on pastured cattle and animal treatments are seldom warranted.
• The economic threshold for treatment is about 20 stable flies per animal.

When to treat

Stable flies (Figure 1) are widespread in Australia, but usually reach pest levels only in cattle feedlots and dairies, where they can cause significant production losses if not controlled effectively. When stable flies are present, they frequently bite cattle on the front legs or belly and affected animals can often be seen stamping their front feet to dislodge the flies. In most parts of Australia stable flies seldom reach economically important levels on pastured cattle and animal treatment to protect cattle against stable flies is seldom warranted.

Studies in the USA suggest that the economic threshold for treatment is about 20 stable flies per animal.

Figure 1. A stable fly showing its biting mouthparts. Image courtesy of the Jess Morgan, Queensland Department of Agriculture and Fisheries.

How to treat

There are pour-on and spray products available for cattle and nearly all of these are synthetic pyrethroids (deltamethrin and zeta-cypermethrin) and provide some repellency as well as insecticidal effect (Table 1.) An alternative approach is to control fly numbers in the environment as they spend a lot of time off the animals. This can be done by seeking out the breeding site of stable flies and to remove or treat the larval breeding medium (see control of stable flies in cattle feedlots).

Treatment methods

Table 1. Different methods of application for stable fly control.

Mosquitoes and midges

Many species of mosquitoes will feed on cattle. When at epidemic levels, such as following recent rains or in very wet environments, attacks by mosquitoes may be enough to cause loss of condition in cattle, reduction in milk yield and in severe instances even death. These effects are most likely due to the irritation caused by mosquito bites, when cattle react with vigorous stamping of the feet, switching of the tail, twitching of the skin and tossing of the head. Cattle under attack by high mosquito numbers can lose up to 166 mL of blood per night, suggesting that there may also be a direct effect due to blood loss. Mosquitoes have been observed to bite most body areas on cattle, but when mosquitoes are in high numbers attacks are usually most intense on the legs and underline. In most instances, mosquitoes bite mainly at night, with peaks from 6:30 pm to 8.00 pm and another similar peak after sunrise. However, different species of mosquito vary in their feeding times and some also bite during the day.

Mosquitoes are known to be vectors of a wide range of diseases, but in Australia the main concern for cattle is the virus bovine ephemeral fever (BEF) (three-day sickness), that can cause widespread sickness and death in some animals. The causal virus has been isolated from both mosquitoes and biting midges (Culicoides sp.) (Figure 2) in Australia but various factors suggest that mosquitoes are the principal vectors. Most outbreaks of BEF are associated with the rapid growth of mosquito and biting midge populations in wet periods.

The majority of products registered for use against midges on cattle are pour-on products containing a synthetic pyrethroid (SP). A topical repellent aerosol spray containing citronella and pyrethrin (SP) is also available.

There are a number of products registered for use against mosquitoes on cattle and most are based on repellent compounds such as pyrethrins, citronella and DEET, designed mainly for application to individual animals as hand sprays. Repellents are often a better option than insecticides with pests such as mosquitoes that transmit disease as non-repellent insecticides may not kill the insect until it has already bitten the host and transmitted the disease. Most repellent compounds are not long lasting and require frequent re-application to give good protection.

Figure 2. Mosquito and midges can transmit disease, cattle are best treated with repellent compounds to deter biting. Image courtesy of Leanne Nelson, Biosecurity Queensland