Distribution of rice stem borers and their parasitoid in irrigated low land rice ecosystem in Kilombero valley, Morogoro, Tanzania

Abstract

Distribution of rice stem borers and their parasitoid, in irrigated low land rice ecosystem in Kilombero district, Morogoro, Tanzania was studied from March – July 2017 in randomly sampled thirty rice fields. Rice stem borer larvae was sampled at two growth stages of rice, the vegetative stage and reproductive stage using 1m2 quadrat. The study revealed the presence of one species of parasitoid from family braconidae (Cotesia flavipes) which was found parasitizing the stem borer larvae. The density of borers (larvae), parasitoids and parasitism rates were respectively 103.82, 16.2 and 47.91% recorded during reproductive stage. Relatively lower values were recorded during the vegetative stage with mean density of 71.13 stem borers, 10.18 parasitoids and 36.39% parasitism rates. Chilo sp was highly parasitized on compared to Sesamia calamistis due to their greater abundance. The Morister’s index suggested an aggregated dispersion of both stem borers and parasitoids. The aggregation of borers and parasitoid (C. flavipes) were recorded more at edges of the field than at the middle of the field suggesting their sources to be from other hosts rather than rice crop