Management of ectoparasites with biological control organisms.

Biological control is not a new concept, but for many reasons it is gaining interest for control of livestock ectoparasites. These reasons will be discussed, both from a political view and from environmental and economic views. The US government has vowed to reduce pesticide use by the year 2000, but other forces may drive this change even faster. Pesticide costs are high, and efficacy against some pests is questionable. Also, many producers are concerned about the environment, and are anxious to do their part to reduce chemical pollution. Specialised training is required to reduce on-the-farm difficulties involved with the use of biological-control organisms. Otherwise, how do producers or veterinarians purchase and use biocontrol organisms, and how do they critique what has been purchased? Included is a short summary of the three most common ectoparasites of livestock, and the type of biological-control strategies being developed to combat them. Much of the classical work has been done on filth fly control, most likely because of the nuisance status of flies, and because of the availability of candidate beneficial organisms, particularly parasitic wasps. And finally, two fly-control success stories will be briefly described. Tremendous strides have been made in house-fly and stable-fly control with parasitic wasps on feedlots, but more work is needed to better understand the habits of immature fly populations. A predaceous fly is being tested for pest fly control in dairies. Larvae of this fly can kill 15-20 house-fly larvae daily, and the adults do not become pestiferous on farms or around homes. Biological control will be an important part of livestock pest control in the future, but its implementation will require a corps of educated producers who are confident that biological control can work for them.