Abstract:
Studies were carried out to establish the role and significance of rice stem borers as
pests in rice crop in Kahama District from November, 2013 to May, 2014. Twenty
rice fields in four wards of Kahama District were surveyed to assess the presence of
larvae and adult moths. Each field was divided into four strata within which four
quadrats were established in each. In each quadrat, the damaged rice tillers (dead
heart), damaged panicles (white head) and total number of tillers and panicles were
counted. Stem borer incidences were computed from observations for each of the
studied rice varieties and with reference to the sowing dates. Stem borer larvae were
extracted from each of the damaged tiller and counted to establish stem borer
dispersion. Moths were trapped by a black light trap cascaded with normal light
attached to a white cloth and collected in vials for further identification in the
laboratory. Dispersion was determined by three indices i.e. Morisista’s index, Taylor
power law and Iwao’s mean crowding regression. Statistical packages (GenStat 15
edition VSN international) and (SPSS 16 version IBM Corporation) were used for
data analysis of abundance and incidences respectively. Results indicated that the
most abundant species was Chilo partellus (48.6%) followed by Maliarpha
separatalla (35.4%) and lastly Sesamia calamists (16.1%). Dispersion indices
suggested that borers were highly aggregated along the edges of rice fields compared
to the middle of fields. Behenge and Supa varieties were more susceptible to stem
borer damage than Kalamata and Mayobhe. The best sowing date with minimum
stem borer damage was from 1 to 20, December. The current study has for the first
time confirmed the presence and significance of rice stem borers in the lake zone ofiii
Tanzania that calls for intensive intervention program to ensure farmers of continued
food security and livelihood.
