Tenth Quarterly Report November 1992 - January 1993

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Kenya Agricultural Research Institute
LGB aerial populations at Kiboko have continued to be monitored using delta, suction and sticky traps. Eleven LGB -positive sites were reported in the national monitoring survey during the quarter [Sections A.2 - A.3]. 2. Intensive TN monitoring in the release cribs at Makueni and Wundanyi has continued and the results of the analysis of destructive and non-destructive samples during the first 24 weeks of storage have been provisionally evaluated. At Makueni there is evidence that the TN has caused a reduction in LGB infestation but heavy damage has nevertheless happened mainly due to the activities of other species. Sitophilus sp. (mainly S.zeamais) numbers appeared to increase whereas, curiously, Gnatocerus maxillosus populations dropped in cribs where TN was released compared to the Icontrols'. There has been a general increase in TN levels at Makueni. A detailed study on LGB/TN population dynamics is underway. At Wundanyi TN has had no measurable effect on LGB populations so far. At Makueni, TN has spread from the original release cribs to 75X of the neighbouring control cribs after 30 weeks compared to only 11X in Wundanyi. Up to the end of December six of the eight pheromone traps set in a lkm-radius circle were TN-positive at Makueni whereas all have been negative at Wundanyi. One specimen of TN was found in the Kiboko Range Research Station transect 5-6 km from Makueni. [Section A.4] 3. Plans for a second release of TN by the Ministry of Agriculture in March-May in Kitui and Loitokitok have been formulated [Section B.1] 4. The results of a study on the spatial distribution of LGB in a granary are summarised and work on a search for LGB parasitoids described [Sections A.5-A.6]. 5. In the maize cob crib-storage trials at 24 weeks heavy damage occurred in untreated cobs at both the Coast and at Kiboko. Husk removal before storage had a significant positive effect. The insecticides provided a statistically significant reduction in damage in cobs without husks with the 17.8 ppm pirimiphos-methylj 1.7 ppm deltamethrin mixture having a slight edge over the 17.8 ppm pirimiphos-methylj 3.3 ppm permethrin dust. No statistically significant differences could be detected between spray and dusts at Kiboko. The order of effectiveness at both sites was:treated cobs without husks> treated cobs with husks>untreated cobs without husks> untreated cobs with husks. [Section A.7]. 6. In the loft trial in which maize cobs were stored over a cooking hearth the results suggest that after 24 weeks' storage there are indications that heavier losses occurred