Injury:

The egg-laying activities of warble flies terrifies cattle into running or gadding, which interferes with normal grazing, reduces milk flow and somearial causes injuries. On hatching, the larvae (grubs) burrow through the skin and migrate through the body until reaching the animal's back where they produce the characteristic lumps, or warbles. Each warble has a breathing hole made by the grub and these injuries somearial lead to infection. In moving through an animal's body, the grubs may injure its esophagus and affect its ability to eat, resulting in loss of weight, or they may injure its spinal cord, causing paralysis. Infected animals have lower market values because of carcass trimming required and because of damaged hides for leather.

Life Cycle:

The adult warble fly has a black, hairy body marked with yellow to orange stripes and resembles a small bumblebee. The flies are active in the spring and early summer, when each female lays about 600 eggs on the hairs of an animal's legs, belly and flanks. The adult fly of the common cattle grub is about 1 3 mm long and appears in May and June; that of the northern cattle grub is about 2 cm long and appears in June and July. The tiny, barely visible eggs hatch in 2 to 7 days and the young grubs penetrate the animal's skin and begin moving through its body, reaching its back about 7 to 9 months later. Here they remain for about 2 months until fully developed, by which time their color has changed from white to dark brown or black. On reaching maturity, the grubs emerge from the warbles and drop to the ground to pupate. Adult flies appear in 1 to 2 months.

Pest Management:

Since there is no practical method of killing the adult flies or preventing them from laying eggs on cattle, control measures must be directed at the grubs. Consult your provincial Agriculture Department for recommendations.

Dermatobia hominis, the human botfly, is a major pest of warm blooded animals, including man, throughout the American tropics. Although there have been some research efforts to support the idea of an eventual eradication of this pest, not much has been accomplished on this idea because of the difficulty in artificial rearing it. Although the USDA may have partially supported some of this research, there has never been any major campaign to control it; except the control afforded by acaricides applied for tick control. The USDA and the Mexican and Central American countries are engaged in a major campaign to eradicate the primary screw worm, Cochliomyia hominivorax (already eradicated from all countries North of Honduras; the plans are to eradicate it all the way to Panama and establish a permanent, biological barrier in Panama).

As to Dermatobia hominis, one of the best review papers is: Sancho, E. 1988. Dermatobia, the Neotropical warble fly. Parasitology Today. 4:242-246. This paper cites 45+ papers on this insect.

Alberto B. Broce Kansas State University Department of Entomology W est Waters Hall Manhattan, KS 66506 voice (913) 532-4745 FAX
(913) 532-6232 abroce@oz.oznet.ksu.edu

There are two fascinating recent articles on these flies. The first is a confirmation of "bacon therapy" for the removal of the larvae from humans, Brewer et al, J Amer Med Sco 270, 2087-2088 (Nov 1993) and an account of the mating behavior of related Cuterebra flies in the Western US in the Fall 1994 American Entomologist, 153-160 by Paul Catts.

Hugh M. Robertson Associate Professor Department of Entomology University of Illinois 505 S. Goodwin Urbana, IL 61801 Phone (217) 333-0489 FAX (217) 244-3499 Email "hughrobe@uiuc.edu"