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March 1998, Volume 19 No. 1

General News

LGB - All's Well That Ends Well?

Results from recent research in both East and West Africa* have indicated that classical biological control may once again be playing a significant part in containing a threat to food security posed by an introduced pest, this time the larger grain borer, Prostephanus truncatus (LGB). An introduced histerid predator, Teretriosoma nigrescens, is having a resounding effect on LGB populations in the natural environment, and in West Africa it has been demonstrated to reduce drastically both LGB populations and maize damage in stores.

The bostrichid LGB from Mesoamerica was accidentally introduced into Africa in the 1980s: it was first recorded in Africa at Tabora in Tanzania in 1981 and was recorded from West Africa for the first time in Togo in 1984. It spread from its sites of introduction, but its appearance in Guinea (Conakry) in 1987 may represent a third and separate introduction. It was immediately identified as a serious threat to food security in Africa where it attacks stored maize and cassava, the staple crops relied on by some 500 million people across the continent, and it seems inevitable that it will eventually spread throughout sub-Saharan Africa. It has caused very high losses of stored maize to individual subsistence farmers, and made storage of maize and cassava more difficult and more expensive. In East Africa, it was farmers in Tabora who, faced with a dramatic increase in losses of maize in stores, first alerted officials; losses for maize stored for three months without pesticide application typically averaged 10%, but some farmers were losing more than 30%, losses far in excess of those experienced before the arrival of LGB. Thus began the process that led to an increase in research on pest management in traditional stores over the last 15 years, and to LGB becoming one of the most thoroughly researched storage pests of recent years.

The initial response to the LGB outbreak, co-ordinated by FAO (the Food and Agriculture Organization of the UN), concentrated on conventional containment and control efforts. Researchers from Britain's Tropical Products Institute (now part of the Natural Resources Institute - NRI), working with the Tanzanian Ministry of Agriculture, found that a mixture of pirimiphos-methyl and permethrin provided adequate control of both LGB and other, more widespread, storage pests. However, for control to be fully effective, farmers had to be persuaded to shell their maize and modify their storage structures to contain the loose grain - considerable changes to their traditional system that not all farmers were prepared to make. In West Africa, researchers from the German agency GTZ (Gesellschaft für Technische Zusammenarbeit) working with the Togolese plant protection service found that a similar 'binary' product could be applied directly to maize stored on-the-cob. Again, some control was provided, although lack of adoption suggests that the method was not entirely satisfactory: on-farm surveys carried out some years later, at the height of the LGB attack in Benin indicated that less than 10% of farmers actually used the binary product recommended by the extension service.

FAO worked with affected countries and their neighbours to establish inspection and quarantine measures which achieved some success in allowing regional trade in maize to continue. But the pest continued to spread... by 1996 it had been officially recorded from Tanzania, Kenya, Uganda, Malawi, Zambia, Rwanda and Burundi (and unofficially from Zaire) in the eastern outbreak area and from Togo, Benin, Ghana, Nigeria, Niger and Guinea (Conakry) in West Africa.

Ironically, perhaps, it was a spin-off from the initial containment effort that subsequently provided a vital key to understanding the ecology of the insect and the true nature of `the LGB problem'. A synthetic aggregation pheromone was developed by NRI with the intention of improving the detection of LGB in infested stores and shipments of maize, so that they could be fumigated. It was only some years later that it was discovered that the pheromone did not attract insects already settled in a satisfactory substrate - and indeed had probably served only to attract flying insects into the shipments where lures had been placed! In the meantime, however, the lures were put to good use in Mexico by entomologists from NRI and INIFAP (Instituto Nacional de Investigaciones Forestales y Agropecuarias - the national agricultural research organization)... who found that the pheromone-baited traps caught large numbers of LGB in various types of forest, from sea level to well over 3000 m altitude, and sometimes far away from any maize cultivation.

Another Mexican researcher then found the LGB attacking dying tree branches that had been girdled by lamiine cerambycids - a situation in which the bostrichid apparently benefits from the higher-than-usual nutrient content of the wood. Researchers from IIBC and KARI (the Kenya Agricultural Research Institute) confirmed that a similar association is formed by LGB with locally occurring ceram bycids in East Africa and went on to show that LGB can breed in the wood of many species of trees provided that moisture content and nutrients are within an adequate range. Studies by German university researchers and IITA (the International Institute of Tropical Agriculture) in West Africa** have helped to show how the pheromone production and aggregation behaviour of this wood feeding insect are well adapted to bring the insect into the limited niche suitable for its reproduction... including, by accident and most unfortunately, human food stores.

The pheromone was also found to attract an histerid predator of the LGB. Fortunately, perhaps, while most international resources were, as usual, ploughed into conventional control efforts, GTZ decided at an early stage of the outbreak in Africa to look into the possibility of classical biological control as perhaps offering a more sustainable long-term solution. Comparative studies showed that grain losses were lower in Costa Rica (part of the pest's area of origin) than in the Togo and Tanzania outbreak areas... and the researchers concluded that the most likely agent responsible was the histerid beetle Teretriosoma nigrescens.

There are no previous records of the successful use of histerids in classical biological control. Indeed, when research by IITA and its collaborators in Mexico and Honduras indicated that severe damage can occur, even in the presence of the predator (which did not seem to show an adequate numerical response to its prey), the prospects of success did not look bright. However, the strong response of the predator to LGB's own aggregation pheromone suggested close, co-evolutionary adaptation to the target pest. Laboratory studies indicated that the predator showed a strong preference for feeding on the larvae of LGB and that, at least in the laboratory, it was able to suppress the pest population. When field-cage trials in Togo showed that the predator could also reduce pest population increase under realistic conditions, T. nigrescens was finally approved for introduction to Africa.

It was released in Togo in 1991 and in Kenya in 1992. However, although it established successfully and began to disperse from the release sites, trap catches were low and the expectations for control were not high. Moreover, initial attempts to follow up the impact of releases in Togo produced equivocal results - with pest populations seemingly lower in some release sites but higher in others - and the research effort there was then interrupted by political turmoil.

The first evidence of a possible classical biological control success came from the dry bushland of East Africa. KARI and IIBC staff found that populations of LGB adults caught in pheromone traps in Kenya's Tsavo National Park and Kibwezi Forest collapsed dramatically in 1995: seasonal peaks of trap catches were 80-90% lower than in previous years and have remained low ever since.

In West Africa, the reduction in trap catches was less precipitate, but the release of the predator has been followed by a progressive reduction in LGB population levels, at least in coastal regions, over the last several years. The situation could not be monitored closely until the predator spread across the border from Togo into Benin. There, a nation-wide trap network was established by researchers from IITA, GTZ and the national plant protection service. Regular sampling of stores allowed the impact of the predator on both dispersing pest populations and those infesting stores to be assessed. In 1996 in southern Benin, peak captures in flight traps were less than half those obtained in 1993 and have been even lower in 1997. Weight losses in experimental stores in the same region fell from some 60% before the predator's arrival to less than 10% in 1995. Surveys in farmers' stores show that LGB has not disappeared completely: 1997 sampling in Benin still detected the pest in about one-third of the stores. However, the current situation certainly represents a vast improvement over that in 1993, whether judged by research data or the farmers' own comments.

The vital question which remains to be answered is whether T. nigrescens will be able to control LGB adequately in all outbreak areas in Africa. Despite its spectacular success in lowland areas of East and West Africa, the slow rate of establishment of the predator at upland sites in Kenya, on the one hand, and the severity of LGB damage sometimes encountered at highland and mid-altitude sites in Mexico, on the other, provide some grounds for concern as to whether the predator may be slightly less versatile, ecologically, than the pest.

If so - and the situation is being monitored across Africa - researchers and plant protection services have some complementary strategies ready to deploy. NRI researchers in Ghana and Kenya and their GTZ and IITA counterparts in Benin have been working for some years, in close collaboration with national agricultural research and extension services, to develop and test IPM strategies to complement classical biological control of LGB - both as an insurance against any local failures of biological control and to moderate the continuing damage caused by other formidable storage pests such as Sitophilus and Sitotroga. A new alliance of entomologists and modellers from IITA, IIBC, and the Danish Institute of Agricultural Sciences are forming a network, beginning in Benin, Ghana and hopefully Kenya, to develop decision support tools (based on modelling and GIS approaches) which will encourage the further refinement of integrated control strategies and guide their deployment to those situations in Africa where they are most needed.

It is too early to declare total victory over the LGB - but thanks to an effective international effort, the initially devastating problems cause by this pest are subsiding to more manageable levels.

*Nang'ayo, F. L. O. (1996) Ecological studies on larger grain borer in savanna woodlands of Kenya. Imperial College of Science, Technology and Medicine, London, Ph. D. thesis, 179 pp.

*Borgemeister, C.; Djossou, F.; Schneider, H.; Djomamou, B.; Degbey, P.; Azoma, B.; Markham, R. H. (1997) Establishment, spread and impact of Teretriosoma nigrescens (Coleoptera: Histeridae), an exotic predator of the larger grain borer in southwestern Benin. Environmental Entomology 26(6) , December 1997.

**Scholz, D. (1997) Dispersal and host-finding behaviour of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). University of Hannover, Germany, Ph. D. thesis, 146 pp.

Contacts: William Meikle, IITA, 08 BP 0932, Cotonou, Republic of Benin [Email: ] and Garry Hill, CABI Bioscience UK Centre (Ascot), Silwood Park, Buckhurst Road, Ascot, SL5 7TA, UK
[E-mail ]

 

USDA Council

A US Department of Agriculture (USDA) Biological Control Workshop was held in late 1996 to provide guidance to the Department on co-ordination, regulation and accountability for the programme area of biological control. Participants included representatives from the major USDA agenies dealing with or with responsibilities in biological control as well as representatives and partners from State Departments of Agriculture and universities. A key recommendation resulting from that workshop was that an action plan be developed to assist the Deputy Secretary in dealing with the issues that were raised. To prepare that plan, a USDA Biological Control Coordinating Council has been established.

Membership on the Council consists of senior representatives from the Animal and Plant Health Inspection Service (APHIS), the Agricultural Research Service (ARS), the Co-operative State Research, Extension and Education Service (CSREES), the Forest Service (FS) and the Natural Resources Conservation Service (NRCS). In addition to the preparation of the action plan, it is envisioned that the Council will remain active, involved in oversight of the development of USDA biological control policy and strategic planning.

 

World Food Prize

The 1997 World Food Prize was awarded in October jointly to two American scientists, Perry Adkisson and Ray Smith, for their leadership in developing and implementing integrated pest management (IPM) approaches to agriculture over three decades which has resulted in dramatic reductions in chemical pesticide use. They are credited with being broadly instrumental in popularizing insect pest control programmes that did not rely exclusively on chemical pesticide application.

Perry Adkisson spent most of his academic career at Texas A&M University, while Ray Smith was at the University of California at Berkeley. In the late 1960s the two men began a series of collaborative efforts aimed at expanding research in the field of insect control as well as practical implementation of integrated pest management programmes. Ray Smith is a highly regarded scientific theorist whose pioneering work laid out the major principles and concepts of IPM. His primary work involved the development of IPM programmes for lucerne and vegetable and fruit crops. He is author and co-author of the seminal publications outlining the conceptual framework on which IPM is based. Perry Adkisson gave practical applications to his colleague's theories. His research first resulted in an IPM programme for cotton which remains in widespread use in the USA and throughout the World. In the 1970s, they were co-leaders, along with Carl Huffaker, of a ground-breaking multi-disciplinary project which used applied ecology and computer technology to develop IPM programmes for a wide variety of crops. And this was followed by another led by them together with R. E. Frisbie which tackled yet more crops. It is largely because of this work that IPM programmes for fruit (notably citrus), vegetables, lucerne, soyabeans, sorghum, cotton, groundnuts and rice have halved insecticide use in the USA, while in cotton the reductions have been over 77% with savings to cotton growers of US$1 billion per year.

Internationally, Adkisson and Smith have promoted IPM through a number of forums, including the USAID-funded Consortium for International Crop Protection and the Food and Agriculture Organization of the UN (FAO) advisory body, the Panel of Experts on Integrated Pest Control. As a consequence of their efforts, IPM is practised on millions of farms throughout the World on a diversity of crops. Under Perry Adkisson's leadership, a permanent IPM facility has been established in Rome to identify, develop and promote pest control programmes for major food crops throughout the World.

 

Prize for Worm Work

In Australia, Dr Robin Bedding of CSIRO (Commonwealth Scientific and Industrial Research Organisation) Entomology has been awarded the 1997 Sir Ian McLennan Achievement for Industry Award for his work on the use of nematodes in biological control. CSIRO Chief Executive Malcom McIntosh said that Bedding's pioneering work on nematodes for control of Sirex woodwasps had already made savings to the Australian pine forest industry of more than Au$50 million per year, and the technology is now being applied on an international scale as Sirex has spread to Brazil, Chile and South Africa [see below]. The species used for control of Sirex, Deladenus siricidicola, has been renamed Beddingia siricidicola in Dr Bedding's honour. And in China, a joint project with ACIAR (Australian Centre for International Agricultural Research) is using another nematode species to control a fruit boring moth (Carposina), which is the most important pest of China's millions of hectares of apple orchards, and other borers responsible for the death of 5% of shade trees in northern China. Dr Bedding's work involved two separate but equally crucial areas of research: firstly the identification of suitable host-specific nematode species and strains, and monitoring and testing to ensure original characteristics and efficacy were maintained; secondly, the development of large-scale methods for mass production of the biocontrol agents, for storing and transporting them in a viable form, and technologies for their application.

Sirex Management in Brazil

An integrated pest management programme for the European woodwasp Sirex noctilio, which is the main pest of Pinus taeda and P. elliottii plantations in Brazil, is incorporating the nematode technique described above with the use of insect parasitoids - an approach which has already been successfully used in Australasia.

The nematode Deladenus siricidicola (= Beddingia siricidicola) was first introduced in 1990, and following initially disappointing results, the introduction of new strains has resulted in increasing parasitism which now stands at 50-80% in all areas. The activity of the nematode has been complemented by that of an accidentally introduced European ibalid parasitoid, Ibalia leucospoides. However, further parasitoid introductions are now underway. The European ichneumonid Megarhyssa nortoni was first imported from Tasmania in 1996 under the auspices of a project involving EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria) and Funcema, the national fund for control of the woodwasp. The first task, successfully completed in the laboratory, was to synchronize the life cycle of the imported parasitoid with that of Brazilian Sirex, which emerge some 30-45 days before their Australian counterparts. First releases were made in 1997 in Santa Catarina State and further releases are planned this year. Another exotic parasitoid, Rhyssa persuasoria, has been imported and is currently undergoing laboratory evaluation.

The IPM of Sirex is mainly developed and funded by EMBRAPA and forest companies, with external technical and/or financial support from the USDA Forest Service, IIBC, the Food and Agriculture Organization of the UN (FAO), the University of Tasmania, Tasmania Forestry and New South Wales Forestry.

Contacts: Edson Tadeu Lede
[E-mail: ], Susete Penteado
[E-mail: ] and Erich Schaitza
[E-mail: ] at Embrapa - Forestry, CP 319, 83411-000 Colombo, Brazil
Fax: +55 41 766 1276

 

Sirex Spreads in South Africa

Sirex noctilio was first recorded in South Africa near Cape Town in 1994 and has since dispersed in a 90-km arc from this site. Management strategies of removing infested trees and introducing the nematode Deladenus siricidicola (= Beddingia siricidicola) were credited with having been instrumental in containing the spread of the pest. However, characteristic exit holes have now been identified in logs originating from a site near Clan William, 205 km to the north, and surveys confirmed its presence else where in the area, near Leipoldtville where local farmers and timber operators say that trees began dying two to three years ago. No infested pines have been found between these sites and the nearest edge of the known range of the original infestation, some 155 km away. None of the Sirex recovered from the Leipoldtville logs were parasitized by D. siricidicola, and this unparasitized source of Sirex will be used to facilitate the establishment of the parasitoid Ibalia leucospoides.

Source: Plant Protection News (the quarterly bulletin of the Plant Protection Research Institute) No. 49. Contact: Dr Geoff Tribe, Insect Ecology Division, Ryan Road, Rosebank 7700,
South Africa
E-mail:
Fax: +27 21 685 2017

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