Biological control of the cypress aphid in Mafuga, Kabale district

Abstract

The population of the cypress aphid, Cinara cupressi and the level of tree damage by the aphid before and after the release of a Host specific parasitoid, Pauesia juniperorum were monitored in Mafuga, Kabale district from 1995 - 2000. Observations were also made on the presence of parasitized mummies after parasitoid release to determine parasitoid establishment, and on the presence of any local natural enemies. Results showed that aphid population had two peaks, namely from August to September and January to mid February. Peak aphid population coincided with the dry seasons. During the first month after parasitoid release, parasitized mummies were recovered from the release cages. However, subsequent samplings between 1995 and 1998 did not recover any mummies in the cypress plantation until March 1999, thus indicating that the parasitoid had established. Surveys and samplings in surrounding cypress plantations revealed that the parasitoid had dispersed up to more than 20 km from the release site. The percentage parasitism of 8.1% is high enough, and combined with the rate of dispersal, the parasitoid should control the aphid and reduce aphid damage to trees. Results also indicate that tree damage levels dropped from damage Category 3 (26 - 60% crown damage) in 1995 - 1997 to category 2 (11 - 25% crown damage) in 1998 - 1999. Tree damage for the year 2000 was also in category 2 but tending more to category 1 (0 -10% crown damage). A number of indigenous natural enemies were recovered but they are not effective because they are general feeders.