Integrated Pest Management in Pasture Cattle

Amber Robinson | | June 2013 | Edited by Jennifer Enzie and Cody Creelman

 

Flies are pests.  Their blood sucking ways decrease the amount of time cattle spend eating and average daily gains decrease.  Imagine.  Each fly takes between 24 to 38 blood meals per day.  Energy that should be going to growth is instead used to swat, head turn and kick at flies.  In Alberta, Horn Fly (Haematobia irritans) is a vector for pinkeye (infectious bovine keratoconjunctivitis caused by bacterial infection with Moraxella bovis) and several Staphylococcus spp. bacteria, which cause mastitis.

Do your cattle need treatment?

Here in Alberta those west of Highway 22 do not tend to treat.  Those in the eastern or northern areas do tend to treat for Horn Flies. Typically we think cattle need treatment when 50 flies per head are present, though the economic threshold of cost: benefit ratio is reached once 200 flies are present.

Control of Horn Fly

Insecticides are our most powerful tool to decrease fly populations.  Earlier in May of this year we posted information on DISVAP products (Summer fly control products) that include foggers, wall spray, and an aerosol mist.  Other products include ear tags, pour-ons, dips, back rubs and dust bags (Fly control: the basics).  Producers should administer pyrethroid insecticides by only one method, don’t double up. It is important to follow label directions carefully, accurately mixing dilutions so that dosages are according to label. Mixing a pyrethroid spray at stronger than label recommendations may have greater side effects.

Side effects

Side effects of insecticides are not fully understood.  We do know that fly resistance to some insecticides has developed. Development of new insecticides is a costly and challenging process.  Chemical use also increases the risk of residues in meat for both the domestic and export markets. Some consumers are demanding a product that is as ‘natural’ as possible.  Furthermore, there continues to be controversy over potential adverse consequences of insecticides.  In some studies, pyrethroid compounds have been linked to decreasing semen volume, sperm morphology and motility, and reducing a bull’s ability to pass a breeding soundness evaluation.  Pyrethroid compounds have also been linked to decreased human male fertility.  Dichlorvos, which is used in DISVAP products, has been shown to be highly toxic to honey bee and beetle populations.  Considering these potential adverse effects have led some producers to look for non-chemical alternatives for fly control.

Non-chemical control options

In this article we take a closer look at four fly control alternatives that do not rely on chemical products: genetics, pasture management, physical removal and biological controls.  These alternative tactics are from the field of study called Integrated Pest Management, which uses both chemical and non-chemical methods to reduce pest populations.  Non-chemical methods are worth considering to address the goal of decreasing the overall fly populations, thereby reducing the number of fly bites and decreasing our dependence on insecticides.

Genetics

There are three ways producers can use genetics to select for cattle less affected by horn flies.  First, breed smaller cattle.  Angus cows, averaging <112.5 cm in height at the hip, had significantly lower numbers of horn flies than Angus cows that measured 112.5 to  >126cm in height at the hip.  Secondly, cattle with denser hair and greater sebum production (i.e. Brahman) tend to have fewer horn flies present.  Similarly, as the percentage of Brahman in an individual increased, the lower the numbers of insect-resistant horn flies biting. Finally, genotyping and selecting fly resistant individuals can also be used to reduce fly impacts.  Specific single nucleotide polymorphisms (SNPs) have been associated with fewer horn flies (T-318C SNP and C1286T SNP).  Although the exact physiological mechanism of their association with less horn flies is not well understood, it is speculated that the SNP’s are related to the cytochrome P450 and prolactin promoter gene regions.  Outside of breeding selection, pasture management is a key component to reducing fly bites.

Pasture management

Pasture rotation and vegetation are used to reduce cattle exposure to fly populations. The life cycle of a horn fly from egg to adult varies between 10 and 20 days depending on the temperature and time of year.  Thus, pasture rotation just before the fly can complete its life cycle can be an effective method to reduce cattle exposure biting flies.  Additionally, providing shade can also reduce cattle exposure to flies.  Flies tend to leave cattle when the animals enter darkened spaces.  By providing shady treed areas cattle can seek relief from sunny, high fly density areas.  Products used to physically remove flies also take advantage of the tendency for flies to avoid darkened areas.

Physical removal: walk through tents and screens 

Two structures can be built or purchased to physically remove flies from cattle: a walk through tent or stand alone screens.  The walk-through horn fly trap is an old idea in use since 1949, though has undergone some modern alterations. Essentially these traps utilize the horn fly’s reluctance to enter a darkened building to remove the flies from the animals and then trap or kill the flies with sticky traps, electrocution, or simple desiccation as they leave the animals. Modern designs of this technique are reported to provide 60 to 80% (up to 96%!) reduction of fly numbers.

For example, one trap used black lights and an electrocution grid inside the tent.  This model was successful in during the first year cattle learned to use it.  Horn fly densities decreased from >1,400 flies to less than 200 flies per animal when cattle walked through twice a day.  During the second year horn flies were at even lower levels.  Amazingly, no insecticides were used during this study.

Stand-alone screens do not require the cattle to interact with them, so are an appropriate option for high-density cattle areas such as home pens.  These large black screens heat up with sunshine and are of contrasting color to the surrounding environment.  Between the warmth and high visual contrast, these screens look like a potential meal to flies.  As biting flies tend to circle a host before landing, screens take advantage of this behavior.   There is a transparent clear plastic area that looks to the fly like an open space and instead causes the fly to hit the plastic and bounce into a tray of soapy water.  Common dish soap diluted in water prevents flies from escaping and leads to flies drowning.

The Epp’s Biting Fly Trap™ company suggests the screens capture nearly half a kilogram of biting flies per day.  They recommend that a producer use at least one trap for every 20 acres of pasture.  With seasonal storage, and bi-weekly insect scooping + ¼ cup dish soap, this unit should last years.

Biological Control: using natures fly predators

A gram-positive soil dwelling bacterium, Bacillus thuringiensis, has been shown to have isolates that are highly toxic to horn fly larvae.  This bacterium has been successfully used to reduce invasive Gypsy Moth populations and does not affect bees, beetles, spiders, mammals, plants or fish.  It has been used since 1961 to reduce caterpillar populations without resistance developing.  Unfortunately, current commercial products using this bacterium are not specific to horn fly larvae.

Other insects can also be used to reduce horn fly populations.  Histerid and Staphylinid beetles are predators on horn fly larvae and eggs. Two beetle species, Phelister panamensis and P. haemorrhous, cause significant reductions in horn fly progeny at predator:prey ratios of 1:100 or less for horn fly eggs, larvae and pupa.  Dung burying and predatory coleopteran beetles also reduce horn fly populations, as do parasitic wasps.

Lastly and certainly the most entertaining player for biological control is fungi.  Under laboratory conditions all life stages of horn flies are killed by entomopathogenic fungi isolates from the Hyphomycetes class.  Research is currently being undertaken to feed cattle capsules of this fungi to reduce nematode loads and may be extended to horn fly parasites.