PROGRESSIVE PRODUCER

CATTLE ECTOPARASITES AND THEIR CONTROL

by Alec Gerry, Ph.D., Professor and Cooperative Extension Specialist in Veterinary Entomology, University of California, Riverside

Insects, ticks and mites that harm cattle by feeding on to cattle. More importantly, cattle grub eggs deposited blood, skin, tissue, hair or exudates (tears or mucus) at the on cattle legs hatch into fly larvae that burrow into the external body surface of cattle, are commonly described as cattle skin and then migrate through the cattle body until external parasites or “ectoparasites.” Cattle ectoparasites reaching the back of their host. Once at the back, cattle are often further classified as either permanent, grubs chew an opening in the skin (a “warble”) allowing intermittent or temporary ectoparasites according to the the maggot to get air. Cattle grubs remain in the warble to degree of association with their animal host. Permanent complete their immature life and then they will drop to the ectoparasites spend their entire life on a single animal, ground to transform to the adult stage. while intermittent ectoparasites spend much of their life Temporary ectoparasites include the biting flies such on a single host animal but also spend part of their life as the horn fly, stable fly, face fly, biting midges, black flies, in the surrounding habitat off the host, and temporary horse and deer flies and mosquitoes. Of these pests, the ectoparasites make only brief contact with an animal to most economically damaging in the U.S. are the horn fly, feed on blood or body exudates. stable fly and face fly. Horn flies bite cattle on the back

Information on the biology and management of during cool weather but move to the belly to feed on ectoparasites is available through a national extension sunny days with high temperatures. Horn flies bite many website (Figure 1) managed by veterinary entomologists times each day and remain on the cattle body even when throughout North America as part of a USDA multistate not biting. project. In contrast, stable flies bite cattle on the legs and

Permanent ectoparasites include the many different lower belly and leave their host after biting to rest in the species of cattle lice and cattle mites. Feeding by lice and surrounding environment and digest the bloodmeal. Both mites can be very irritating to their cattle host, potentially horn flies and stable flies acquire blood by tearing through resulting in dermatitis and hair loss. Hide damage can also the skin resulting in painful bites and considerable cow occur as cattle rub and scratch against objects in their discomfort. environment to relieve the itching caused by lice and mite Face flies feed on eye and nasal excretions, rather feeding. Lice and mites are typically very host specific than blood, and while they do not deliver painful bites, (only live on cattle) and because they lack wings, they they will use their mouthparts to scrape at softer tissues can only disperse to new cattle during direct contact with around cattle eyes causing irritation to cattle eyes. Face infested cattle. Therefore, limiting movement of animals flies can transmit pathogens to cattle eyes including among herds can help prevent spread of lice and mites. infectious bovine keratoconjunctivitis ( “bovine pinkeye”)

Intermittent ectoparasites in the U.S. include ticks and eyeworms. When fly activity is high, cattle express and cattle grubs. While some ticks will spend their life on a single animal (i.e., the ear tick), most ticks will feed on three different host animals taking one blood meal for each tick life stage (larva, nymph, adult tick). These three-host ticks drop off the host after feeding for several days, and then they remain in the environment until they digest the host blood and transform to the next life stage or lay eggs and die for adult female ticks. Some ticks such as the Foothill Abortion tick (Pajaroello tick) are unusual in that they will feed on many hosts, taking small bloodmeals during each short feeding period.

Adult cattle grubs are also called “heel flies” because the adult flies hover near and land on the lower legs of cattle where they lay their eggs. The presence of heel flies can cause cattle to engage © UC RIVERSIDE in a panicked running behavior called “gadding” that can result in injury Cattle on pasture in the Sierra Nevada foothills of California. Image by Alec Gerry.

fly-repelling behaviors such as leg stamps, head tosses fresh cattle feces. Stable fly management is challenging, and tail swishing. Cattle held in groups (on pasture or in but some relief to cattle can be achieved using insecticides pens) will aggregate into a group (“bunching”) providing applied to cattle as liquid sprays. The online pesticide some protection from biting to cattle in the middle of the group. database will lead you through a series of selections to

High biting fly activity will result in lower cattle find the right product for you. weight gains (and reduced milk yields for dairy cows) as cattle spend time and energy repelling or avoiding the biting flies. The remaining biting flies (biting midges, black flies, horse and deer flies, and mosquitoes) can be problematic in some settings and may be responsible for transmission of pathogens (e.g., bluetongue virus is transmitted to cattle by biting midges) but are not usually economically important pests of beef cattle in North America.

Control of ectoparasites starts with herd and pasture management. Limiting movement of cattle among herds can help reduce the transfer of some ectoparasites such as lice, mites and ticks from infested herds. Where cattle will be introduced to a herd, a careful ectoparasite evaluation of cattle to be introduced or prophylactic treatment of these cattle within insecticides can reduce ectoparasite introduction into the herd. Some ticks can be managed by leaving pasture without cattle for a season (“pasture spelling”) so that ticks are unable to find a host. This strategy is generally most effective for pastures where deer and Figure 1. USDA multistate project website providing information on other large animals are also excluded. Two of the biting ectoparasite biology and management (veterinaryentomology.org). flies, horn flies and face flies, develop as immature flies only in fresh cattle feces, so disturbance of cow pats can reduce abundance of these flies. Cow pats can be disturbed by high density of cattle (such as in feed lots) or by the action of other animals including dung beetles and birds (chickens held on cattle pasture will scratch through cow pats to eat immature flies).

Ectoparasites can also be managed using insecticides and parasiticides, and this may be necessary when ectoparasite activity reaches levels that can cause economic damage to cattle producers. Veterinary entomologists in North America have developed an online searchable pesticide database called VetPestX (Figure 2) that producers can utilize to find suitable insecticides for control of ectoparasites. Control of lice, mites and ticks can be achieved using injectable parasiticides, topically applied insecticides or cattle ear tags. Cattle grubs are controlled with parasiticides and Figure 2. VetPestX is an online, searchable database for insecticides dewormers. Horn flies and face flies can be managed registered in each state for application against ectoparasites by animal commodity. This is a resource developed by USDA multistate project with ear tags, topically applied insectides and feed- members to support extension agents and animal producers and is through insecticides that will kill the immature flies in available at https://www.veterinaryentomology.org/vetpestx.