Insecticidal wound treatment of livestock on Isla de la Juventud, Cuba: An efficient suppression method of new world screwworm Cochliomyia hominivorax prior to the release of sterile insects

Abstract

A two-year pilot trial was conducted on the Isla de la Juventud, Cuba to assess the effect of insecticidal treatment of wounds of livestock on the wild New World screwworm Cochliomyia hominivorax (Coquerel) population. On average, 338 921 and 369 622 animals were inspected every month in 2001 and 2002, respectively out of a total livestock population of 86 000. The average monthly infestation rate (number of positive screwworm myiasis cases as a proportion of total animals inspected) declined from 0.058 during the first quarter of the programme to 0.005 in the last quarter, i.e. a statistically significant reduction of 92%. The trial demonstrated that a systematic animal inspection programme coupled with insecticidal wound treatment can effectively suppress New World screwworm. The impact of the suppression programme on the adult fly population, sampled using vertical sticky traps, was less clear. Fly sampling data from the southern part of the island - an area with very few livestock - indicated little impact and the dynamics of the fly population showed a seasonal pattern. In the north, the fly population remained stable and fairly low in 2001 due to the insecticidal treatment of wounds, but increased in 2002, possibly as a result of migration from the south in the aftermath of a hurricane that created unfavourable conditions in the south. The paper argues that a systematic wound treatment programme, possibly combined with a dense adult fly trapping network should be implemented in screwworm area-wide integrated pest management (AW-IPM) programmes well before the release of sterile insects. This will enable the sterile males to compete effectively with the wild males and exploit the inverse-density dependence of the sterile insect technique (SIT). In countries with low labour costs, this strategy will make AW-IPM programmes with an SIT component more cost-effective.