BIOLOGICAL CONTROL OF THE LARGER GRAIN BORER, PROSTEPHANUS TRUNCATUS (HORN) (COLEOPTERA: BOSTRICHIDAE)

Authors: Meikle, William; REES, DAVID - CSIRO CANBERRA; MARKHAM, RICHARD - IITA BENIN

Submitted to: Integrated Pest Management Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2002
Publication Date: 1/7/2002
Citation: MEIKLE, W.G., REES, D., MARKHAM, R. BIOLOGICAL CONTROL OF THE LARGER GRAIN BORER, PROSTEPHANUS TRUNCATUS (HORN) (COLEOPTERA: BOSTRICHIDAE). INTEGRATED PEST MANAGEMENT REVIEWS. 2002.

Interpretive Summary: 1. Problem: Prostephanus truncatus, a beetle, is an important introduced pest of stored maize and cassava in Africa. While claims have been made that P. truncatus has been successfully brought under biological control, an understanding of the history of the biocontrol effort, and a survey of the most recent literature on the subject, are needed place such claims in proper perspective and to judge whether further work is required. 2. Approach: Articles, with an emphasis on peer-reviewed journal articles, theses and internally-published documents were consulted in trying to understand the state of our knowledge with respect to the biological control of P. truncatus. One author (D. Rees) was the first to realize the potential of the most commonly-accepted biological control agent against P. truncatus, Teretrius nigrescens. A historical approach was used to illustrate the roles that different researchers and research institutions played in the biocontrol effort, and in the final section the most recent articles were used to evaluate the current status of the effort. 3. Results: It is clear from an examination of the literature that few avenues for biocontrol of P. truncatus have been overlooked. Many species of pathogens and parasitoids have been considered and evaluated, both in the New World tropics and in Africa. Thus far, the predator T. nigrescens has been the most logical focus of a biocontrol project. However, the most recent work in West Africa indicates that 1) P. truncatus is still a serious pest, and 2) T. nigrescens is at best only a partial solution. Close examination of previous work, in addition to new surveys and analyses, fail to support initial reports of P. truncatus control. The rush to claim T. nigrescens as a biological control success story may have contributed to a subsequent lack of funding by donors, and of interest by researchers.

Technical Abstract: The highly destructive outbreak of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), in Tanzania in the early 1980s attracted the attention of the international research community because of considerable human suffering and economic losses and because the possibility of its accidental introduction from the New World Tropics had been foreseen and to some extent investigated. As an exotic outbreak pest in Africa, P. truncatus was at an early stage considered a candidate for classical biological control and studies were initiated early in the outbreak, both to compare the pest¿s population dynamics in Africa and Central America, and to look for co-adapted natural enemies that might be contributing to its population regulation in the insect¿s area of origin. This account describes the attempts to identify, evaluate and measure the impact of natural enemies of P. truncatus, in the form of predators, parasitoids and pathogens. Although a predator, the predator, Teretrius nigrescens (Coleoptera: Histeridae) became the main focus of the biological control effort, and was mass-produced and released in many African countries, its impact is still a matter of debate and P. truncatus is still, at least locally, a very serious pest of stored products.