G.N. KIBATA & F.L.O. NANG’AYO

The outbreak of LGB in Tanzania and its subsequent spread to adjoining countries of Eastern Africa occasioned unusually higher losses in maize from the typical losses of about 2-5% (de Lima, 1979) to losses ranging from 9 to 34% Hodges et al. (1983). In Kenya alone, this represents an estimated loss of up to 200,000 mt per year (Farrell et al., 1996).

Since the first outbreak in 1983 (Kega & Warui, 1983), LGB has been confined to the southeastern districts of Kenya (largely a maize deficit zone). However, the threat for LGB to spread to the principal maize growing areas has always loomed large especially with the advent of liberalised maize trade policy that came in force in 1994. It is against this background that an Integrated Pest Management Initiative for LGB, funded by UK ODA (Overseas Development Administration), was launched in Kenya during 1990 to 1993. The broad aims of this initiative were to reduce the impact of LGB on farm-stored maize through the development of an integrated pest management strategy for important post harvest pests of maize. Various approaches were adopted including national monitoring for LGB distribution, implementation of phytosanitary regulations, studies on ecology of LGB, chemical, biological and cultural control measures.

Monitoring the distribution of the LGB in Kenya was commissioned by KARI in 1991 in response to a threat posed by the insect to the country’s maize reserves. A network of pheromone baited delta traps was set up to generate spatial and temporal data on the LGB distribution within Kenya, to warn of new outbreaks and thus help in focussing control operations to outbreak areas. A total of 44 permanent trapping sites (currently reduced to 31) were chosen from the key maize growing areas across the country. Traps are set up regularly for 2 weeks in every 4 with the help of field extension staff from the

Ministry of Agriculture who also count and record the number of adult LGB caught during the two-week trapping period. The traps are then sent back to the National Agricultural Laboratories where precise identification of LGB catches is made.

Over the years, LGB has been confined to the southeastern parts of the country. The spread of LGB has been slow but steady with trap catches being recorded for the first time in Mwea (Central Kenya) and Kisii (Western Kenya) in 1995. The following year witnessed the occurrence of LGB at Nakuru, Thika, Migori and Kisumu. Latest records of LGB in 1997 were made in Mwingi, Makueni, Isebania and Busia. Unusually high catches were made at Nakuru in the second quarter of 1997 but this could have been linked with infested maize brought in from outside the area. The current distribution of LGB (Fig. 1) shows that the pest is a real threat to maize storage in the country. The spread of LGB to Rift Valley and farther still to Western Kenya is very significant in terms of Kenya’s food security as the pest is now present in the maize surplus areas where losses are likely to be high arising from extended periods of storage. The occurrence of LGB in the principal maize growing areas of Kenya has already been communicated to the Ministry of Agriculture who will soon mount LGB awareness campaigns in the affected areas.

The quarantine restrictions imposed on Taita-Taveta region, through legal notices under the provisions of the Plant Protection act (Cap 324) were rigorously implemented through the civil service machinery. These restricted all maize movement from the infested area into the hinterland. Initially the quarantine was effective but the shortage of inspectors as well as lacks of good will from traders gradually frustrated the intervention. Contract supply of clean maize to outbreak area was also frustrated by logistics, disbursement of funds and bureaucracy. Provision of free insecticides was also not sustainable once donor funding (ODA, GTZ) ceased. However, national LGB surveys and regular monitoring was maintained and was eventually replaced by the LGB pheromone traps network.

A thorough understanding of insect ecology is considered pivotal to the successful implementation of IPM strategies against insect pests and LGB is no exception. The KARI/IIBC/NRI LGB project undertook an ecological study that sought to elucidate the host range of LGB, to investigate the phenology of LGB in the field and to study field-store migration patterns of LGB amongst other things.

As a typical bostrichid, LGB was demonstrated to have the capacity to breed in a wide range of woody hosts (Table 1) some of which are important agroforestry species. During field surveys carried out in eastern Kenya, two native tree species, Commiphora africana (Arn.) Engl. and Commiphora riparia Engl. were found to support breeding populations of LGB emphasising the need to appreciate the natural environment as a reservoir for LGB (Nang’ayo et al., 1993). The abundance of LGB in the natural environment appeared positively correlated with ambient relative humidity and temperature (Nang’ayo, 1996) but was not synchronised with maize harvest and storage patterns in Eastern Kenya, perhaps not surprising for an insect believed to evolved as a wood borer. With many woody species appearing to support breeding populations of LGB, farmers could be advised to avoid potential hosts of LGB when constructing maize stores.

Other findings indicate that maize cobs and stovers also harbour sufficient numbers of LGB and should be buried or destroyed to reduce potential sources of infestation (Wekesa, 1994). Heavily infested stores were also found to influence pre-harvest infestation suggesting that where circumstances allow, stores should be sited as far as practically possible from the maize fields.

Initial research indicated that pyrethroids were superior to organophosphates in the control of LGB. Permethrin 0.5% dust admixed with shelled maize at 50 gm per 90 kg bag conferred the desired control. Permethrin 25% Emulsifiable concentrate sprayed on storage structures at 80 mg per square metre gave satisfactory protection from LGB (Muhihu, Kibata 1995). It was however realised that pyrethroids were ineffective on other stored product pests, which co-existed with LGB in the storage environment. More investigations revealed that insecticide cocktails (Pyrethroid/OPs) were better alternatives for grain conservation in the LGB infested region (Mutambuki et al., 1989).

60 gm of Actellic super of sumicombi can be applied to the surfaces of layers of cobs from one full standard 90 kg capacity gunny bag.

Each cob layer of 15 cm deep or less should be sprinkled with insecticide evenly. Insecticide sprays with the recommended products can be applied to cob maize and as residual treatment of empty stores.

An important consideration in the decision making is the benefit likely to be accrued from the use of insecticides.

In 1992, following many years of study by several research organisation in Africa and meso-America, a predatory beetle, Teretrisoma nigrescens Lewis (Coleoptera: Histeridae) was introduced into the hot and dry parts of eastern Kenya through a joint KARI/IIBC/NRI initiative. Subsequent monitoring of the spread and impact of the predator has shown that T. nigrescens has established and spread tens of kilometres downwind from its original release site and, is associated with a strong reduction in catches of LGB adults in pheromones traps (Nang’ayo et al., in press). While it not possible to equate the reduction in larger grain borer adult incidence in the natural environment with reductions in rural maize stores, it is to be expected that reductions in levels of background populations of the pest in the environment are likely to result in low pest incidence in stores. Indeed, data from on-farm storage trials in West Africa show a considerable reduction of LGB infestation and decreasing maize losses with the establishment of T. nigrescens. Future predator releases and impact evaluation are planned for the wetter cooler principal maize growing areas which have only recently fallen to the LGB advance.

Public awareness of LGB

Public awareness is facilitated through the production of posters, radio programs (with assistance from the Agricultural Information Centre) and technical information leaflet (produced by KARI for extension staff). A significant outcome in this regard was the production of a comprehensive training manual for the control of the LGB in Kenya through a joint venture between the Ministry of Agriculture, GTZ, and KARI. The manual is made for use by the extension staff while disseminating information on improved storage to farmers and maize traders.