Field abundance of serangium parcesetosum (col., coccinellidae): a predator of cassava whitefly (hom, aleyrodidae) in two cassava growing agro-ecological zones of Uganda

Abstract

The whitefly, Bemisia tabaci, is a major pest of cassava in Africa where it causes direct feeding damage on the leaves and indirectly through sooty mould production. This pest is also a vector of cassava mosaic begomoviruses and cassava brown streak viruses which are main production constraints to cassava in sub-Saharan Africa. Much as numerous efforts have been made to control CBSD and CMD in Uganda, mainly through breeding of resistant varieties, limited effort has focused on controlling the vector directly. The use of synthetic pesticides to control whiteflies on cassava is also ineffective, not economical and causes adverse effects on the environment. Therefore, there is need to develop an integrated approach in the management of this pest with predator (Serangium parcesetosum) being explored as an option. This research was carried out to provide more information on this predator so as to bridge the knowledge gap towards its positive use in controlling whiteflies in cassava. A study was conducted to ascertain the abundance of Serangium parcesetosum; a predator of cassava whitefly, its field relationship with the prey as well as the influence of climatic factors on its population. This trial was established in two agro-ecological zones of Uganda, namely; North Western Savannah Grassland (Lira) and the Kyoga Plains (Kamuli) in the first rains of 2017. Results revealed that both mean adult and larvae of Serangium parcesetosum per plant were more abundant in Kamuli (4.92 and 11.75) as compared to Lira (0.39 and 0.51) respectively. Improved broad-leafed cassava varieties; Narocass1 and Nase 14 were more preferred by Serangium parcesetosum than the slender long leafed landrace, Njule red. However, there was no significant difference between the varieties in Lira (P < 0.489) and Kamuli (P < 0.598) respectively. Irrespective of location, 27% and 30% increment in the mean adult and larvae Serangium parcesesotum population per plant was registered respectively and this was attributed to the mean whitefly nymph population per plant observed. In both locations, a slight increment in the Serangium parcesesotum population per plant was associated with the mean maximum monthly temperature. A similar trend was recorded with the total monthly rainfall in Kamuli while the reverse was true for Lira where, 14.3 % (p< 0.460) and 16.6 % (p<0.422) decrease in the mean adult and larvae Serangium parcesesotum population per plant respectively was registered. Generally, this study revealed that agro-ecological zone (location) and cassava age were the main drivers of whitefly population which directly influenced the Serangium parcesesotum population observed. Rainfall and temperature were also reported to influence the predator population but at minimal level