Effectiveness of a biological control agent Palexorista gilvoides in controlling Gonometa podorcarpi in conifer plantations of Uganda

Abstract

Widespread defoliation of plantation forests by insect pests causes economic losses worldwide. Successful pest outbreak management requires knowledge of effective pest management options. Currently, such knowledge is inadequate for Gonometa podocarpi an indigenous pest that has devastated conifer plantations in Uganda since the 1960s. The pest is a serious defoliator of conifers in East Africa and was first described from Mt. Elgon Kenya, where its larvae were defoliating indigenous conifer; Podocarpus spp. The pest has since adapted to feeding on exotic conifers. There have been several serious resurgences of this pest in Uganda, the latest being 2011 and 2012. Studies carried out during the peak of these outbreaks in Muko, Kiriima and Mafuga Central Forest reserves in South Western Uganda established G.podocarpi infestations in Kiriima and Mafuga but none in Muko. The studies also identified a tachnid fly, Palexorista gilvoides as a potential biological control agent for G. podocarpi. Field and laboratory studies further established that P. gilvoides is a larval parasitoid of G.podocarpi, with parasitism levels of 43.0 and 62.0% in the field and laboratory respectively. These levels of parasitism are considered high enough to control the pest. However, causes of this pest resurgence need further investigations.

Keywords: Defoliator, parasitoid, parasitism, pest outbreak, resurgence