Efficacy of dicyclanil in the prevention of screwworm infestation ( Cochliomyia hominivorax) in cattle castration wounds

A field trial was carried out during summer 1996 in a commercial beef cattle farm located in the central area of Argentina (30°16′S, 60°30′W) to evaluate the efficacy of a new insect growth regulator material (dicyclanil) in the prevention of myiosis caused by screwworm ( Cochliomyia hominivorax) larvae. Forty bull calves ( Bos indicus× Bos taurus), 5 to 6 months old were allocated by ranked pairs to a control (G.1) and a treated group (G.2) of the same number of animals. On day 0, all experimental animals were surgically castrated and calves of group 2 were treated topically with 20 ml as a single dose of a ready-to-use formulation containing 5% w/v dicyclanil. Inspections for screwworm larva infestation were carried out on days 4, 8, 12, 16, 19, 23 and 25 after castration. The incidence of egg masses on the scrotal wounds evidenced a similar challenge for all groups ( P>0.05 χ 2). However, 16 animals of G.1 (80%) and only one of G.2 (5%) developed active myiosis, respectively. This difference was significant ( P=0.003 χ 2).