Problem Statement: It is believed that the Larger Grain Borer (LGB), Prostephanus truncates, was introduced into Tanzania in the late 1970’s, most likely in maize provided as food aid or in the sacks used to transport this maize. When the pest was reported, stored maize was treated as other stored product pests, but without any success. Due to these ineffective control measures and lack of understanding of the pest involved, the LGB spread at an alarming rate, with a major impact upon food supplies. LGB was accidentally introduced in shipments of maize into Togo in West Africa. In addition to attacking grain, LGB also attacks stored cassava.

Methods: LGB specimens were taken to the Natural History Museum in London where a definitive identification was made and natural enemies indicated from its native areas in Mexico and Costa Rica. One of these, a small black beetle which preys on the grubs (larva) of the Larger Grain Borer, was then introduced into Tanzania to destroy the Larger Grain Borer.

Outcomes and Impacts: By 1998, 13 African countries confirmed the presence of the pest. The area of spread in East Africa is now estimated at one million square kilometres, with one third of this area being affected in West Africa. LGB cost Tanzania roughly US$91 million annually in lost maize intended for consumption or export. Losses of cassava have been assessed to be as high as 35 per cent in 5-6 months storage and up to 60 per cent for storage over 9 months, losses which cost West Africa up to US$800 million. In addition to the physical losses, significant effort has been needed to contain the invasive pest. Between 1984 and 1992, the average annual cost to the Tanzanian government was more than US$ 3 million.

Lessons: If the LGB had been recognised from the outset, its spread would have been greatly reduced, crop losses would have been significantly lower and the need for cost control programmes much reduced. Early recognition depends on appropriate identification support tools (user friendly keys), supported by taxonomists.