Spread of larger grain borer still a concern

By Henry Neondo

Kenya’s leading entomologists have expressed concern over the spread of the Larger Grain Borer (LGB), Prostephanus truncatus, the most devastating storage pest of maize and cassava in Kenya.

According to the scientists based at the International Centre of Insect Physiology and Ecology (ICIPE) and the Kenya Agricultural Research Institute (KARI), the LGB has continued to causes losses in maize estimated at 30-90 per cent, leading to grain loss of 162 million tonnes per year, valued at Sh 8.1 billion (US$100 million) annually in Kenya alone since its accidental introduction into Kenya in the early 1980s, through the Kenya-Tanzania border town of Taveta, the LGB.

Between July and September 2004, researchers from ICIPE and KARI conducted a monitoring programme using pheromone traps in farmers' fields in five major maize growing areas, including Kitale, Kakamega, Kilifi, Kitui and Thika. Kitale recorded the highest number of LGBs per trap, followed by Kakamega, Thika and Kitui, while Mombasa had the lowest figure.

The spread of the LGB was initially monitored by KARI between 1991-97, and was by then limited to areas of low maize production such as Machakos, Kitui and Makueni Districts, parts of the rift valley and the Kenyan coast.

"Considering that Kitale is Kenya's most important producer of maize, the high number of LGBs recovered in traps from that area is an issue of major concern.

There is need for concerted efforts to deal with this pest, which is now threatening maize production in the country," said Dr Josephine Songa, a KARI research scientist.

In the early 1980s to the late 1990s, chemical control strategies of the LGB were used with considerable success.

However, due to insecticide resistance by the LGB as well as cost implications and the associated environmental and safety concerns, these methods are no longer effective nor sustainable.

"The appropriate and farmer-friendly control option is therefore classical biological control, which involves importing natural enemies for management of the LGB," Dr Charles Omwega, regional coordinator of ICIPE's biocontrol of stemborer programme said.

He added that KARI in collaboration with the ICIPE are in the process of importing different strains of a natural enemy (histerid beetle), also known as Terretrius nigrescens, from Mexico for the control of the LGB in the different maize growing areas of Kenya.

However, in addition to these efforts, farmers are advised to use recommended storage practices in order to reduce infestation in their store.

Some of the recommended storage practices include, emptying and cleaning the store before putting in new grain, harvesting early in order to prevent LGB infestation of the grain in the field, and shelling of maize before storage, as maize on the cob is more easily damaged by this pest.