Borer Prostephanus Truncatus Research Articles

Distribution of and association between the larger grain borer Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in maize stores

Interspecific interactions between the larger grain borer Prostephanus truncatus and the maize weevil Sitophilus zeamais were studied during two storage seasons in maize stores, in Bénin. Maize ears, randomly sampled from farmers’ grain stores, were ‘reared out’, i.e., kept for 4 weeks under controlled conditions for F 1 to emerge, and periodically sampled, in order to examine colonisation patterns of P. truncatus and S. zeamais. For both storage seasons, P. truncatus and S. zeamais populations were sparsely aggregated and not associated with each other. The degree and strength of association increased with each monthly sampling occasion with the Ochiai, Jaccard and Dice indices of association. By the fourth sampling occasion, P. truncatus was found on most ears and on some ears in very high numbers (>300 insects). Almost all ears with P. truncatus contained at least a few S. zeamais individuals, but many ears with S. zeamais contained no P. truncatus.

A novel 8.7 kDa protease inhibitor from chan seeds ( Hyptis suaveolens L.) inhibits proteases from the larger grain borer Prostephanus truncatus (Coleoptera: Bostrichidae)

A novel trypsin inhibitor purified from chan seeds ( Hyptis suaveolens, Lamiaceae) was purified and characterized. Its apparent molecular mass was 8700 Da with an isoelectric point of 3.4. Its N-terminal sequence showed a high content of acidic amino acids (seven out of 18 residues). Its inhibitory activity was potent toward all trypsin-like proteases extracted from the gut of the insect Prostephanus truncatus (Coleoptera: Bostrichidae), a very important pest of maize. This activity was highly specific, because among proteases from seven different insects, only those from P. truncatus and Manduca sexta (Lepidoptera: Sphingidae) were inhibited. This inhibitor has potential to enhance the defense mechanism of maize against the attack of P. truncatus.

Damage and Loss Caused by the Larger Grain Borer Prostephanus truncatus

An overview of information on damage caused by the larger grain borer is provided, including details of early studies examining commodities that might be attacked and the importance of LGB field infestations in relation to storage losses. In addition, examples are given from published information on the weight losses that can result from LGB infestation in maize and cassava, with case studies. Problems in applying conventional methods of loss assessment to commodities attacked by LGB are highlighted, to suggest the need to develop alternative techniques. Experiences in developing and applying novel approaches to loss assessment for LGB are reported. Examples are also given to show how loss and damage estimates have been used to describe the impact of the pest on farmers, and on local, regional and international grain trading.

Function of Aggregation Pheromone in the Larger Grain Borer Prostephanus truncatus: Variation in Response to Individuals as Evidence for a Role in Sexual Selection

The ability of both male and female Prostephanus truncatus beetles to distinguish between the aggregation pheromone signals of two closely located conspecific male beetles was investigated by using an olfactometer. Beetles detected variation between male signalers and visited some signalers more than others. Beetles of both sexes were found to make the same choices. These patterns of preference were found to be mirrored in trap catches of dispersing beetles when single males were used to bait flight traps that were placed in pairs in a woodland habitat in Ghana. The results are discussed with reference to the hypothesis that males signal primarily to attract mates and, therefore, features of the aggregation-pheromone signal may be sexually selected. The implications of the results for current and possible future pest-management tools are also explored.

A review of investigations to improve pest managemet of stored maize in smallholder farms in Kenya

A 4-year project in Kenya to develop management strategies for the larger grain borer (Prostephanus truncatus) in smallholder maize stores is described. The entomological investigations included behavioural and ecological studies of pest activity in experimental and farmers' maize stores and the natural environment, the use of insecticides to protect maize stored as grain and cobs and the release of a biological control agent. The latter was a predatory beetle; this marks the first release of a biological control agent against a storage pest in East Africa. The operation of a national trapping network to assess the extent and future spread of the pest and predator and target control campaigns is outlined. Recommendations for the control of the stored product pests, resulting from these investigations, were tested for likely adoption and modification in the light of socioeconomic surveys and a cost-benefit analysis. A decision tree approach to managing stored product pests is suggested which allows extension workers and farmers to decide the necessity of pesticide application when assessing how best to protect stored maize.

The response ofTeretriosoma nigrescens lewis (Col.: Histeridae) to the pheromone ofProstephanus truncatus (Horn) (Col.: Bostrichidae)

Adults of the histeridTeretriosoma nigrescens Lewis, a predator of the Larger Grain BorerProstephanus truncatus (Horn), were captured under field conditions in Costa Rica within the same pheromone traps as the stored product pest. Neither insect could be found in unbaited traps. The possible kairomonal importance of the prey's pheromone is discussed.

Current Status of the Larger Grain Borer Prostephanus truncatus (Horn) in Africa

Since it was first reported in Tanzania in 1981 the Larger Grain Borer (LGB) has spread from a small area in the northwest of the country to 17 of the 20 regions. Only in the extreme south, along the Mozambique border, has the pest not been found. It has also become established in Kenya, Burundi, Togo and Benin. LGB can cause very high weight loss in farm stored maize and dried cassava, commodities on which it if able to breed. After 5 months storage during the dry season in western Tanzania, mean losses of 9% were found, a much higher level than losses of less than 1 % which would be expected in LGB-free areas in East/Central Africa. Application of 0.5% permethrin dust at 2.8 ppm provides excellent protection against LGB when applied to loose maize grain for 1 year. However, the storage of shelled maize predisposes towards the development of Sitophilus species which can result in high losses being sustained. A ”cocktail“ of permethrin and pirimiphos-methyl, applied at 3.3 and 17.7 ppm respectively, successfully controls all storage pests and is currently being used in an extensive control campaign in Tanzania. A multi-donor funded control and containment campaign, co-ordinated by FAO, has been in operation in Tanzania since 1984. The programme is comprised of a training element for agricultural staff and several field extension campaigns which assist with insecticide distribution and with dissemination of information to farmers. The primary objectives of the programme are to reduce farm storage losses and to contain LGB within the areas it is now found. In some regions, where LGB is relatively isolated, attempts are being made to eradicate it.