Insect biodiversity for sustainable management of natural resources

Georg Goergen,

Insect diversity: Tenebrionidae family checklist. Photo by G. Goergen, IITA.
Insect diversity: Tenebrionidae family checklist. Photo by G. Goergen, IITA.

The conservation of biodiversity and the sustainable use of natural resources are guiding principles of the CGIAR and a recognized thematic priority area. The CGIAR is a major player in the collection, characterization, and unrestricted distribution of agrobiodiversity resources and related information on a global scale. Currently, out of 15 centers, 11 house important genebanks amounting to some 650,000 accessions. These provide scientists with the genetic material needed to significantly increase agricultural productivity.

The conservation of genetic resources at IITA is particularly broad in coverage. Thus, collections encompass a wide range of organisms including plants but also associated nonplant biodiversity. Emphasis is placed on the ex situ preservation of plant genetic material. This is reflected in the maintenance of roughly 28,000 germplasm accessions from 19 agricultural crops and their wild relatives. More than half of the genebank’s holdings represent in-trust collections of cowpea for which IITA has received the world conservation mandate. Free and unrestricted public access to this genetic material is ensured through institutional compliance with the international seed treaty developed through the Food and Agriculture Organization with the strong involvement of the CGIAR centers.

Apart from the use of genetically improved crops, agricultural productivity is also strongly influenced by a rich in-field biodiversity comprising organisms such as fungi, bacteria, viruses, nematodes, mites, and insects. Their beneficial or deleterious impact on crops is relatively well understood when interactions are based on simple associations of organisms. However, when many players are acting sometimes across several trophic (nutrition or feeding) levels, the study of ecosystems becomes complicated and knowledge-intensive.

Immature of the whitefly Paraleyrodes minei. Photo by G. Goergen.
Immature of the whitefly Paraleyrodes minei. Photo by G. Goergen.

Generally, a thorough inventory and characterization process is the requisite condition for the sustainable management of this nonplant biodiversity. Related information is primarily stored in research collections to which IITA has been giving growing attention over the last decade. Today, important nonplant collections allow safe diagnostics of plant pathogenic microorganisms used for resistance screening in breeding programs and arthropods/fungi used for biological control (see Korkaric and Beed, this issue).

A collection that has particularly expanded over the last 15 years is the arthropod reference collection at IITA-Bénin, the largest within the whole CGIAR. It encompasses currently more than 350,000 specimens collected in a wide range of agricultural and natural environments throughout West Africa. More than 5,000 species from 330 arthropod families have been identified from the sampled material, but it is estimated that about 40−50% of all known insect biodiversity of the subregion is preserved in this collection, awaiting further study. Serving as the coordination center for the West African node of the global taxonomic network BioNET-INTERNATIONAL, this biodiversity collection is well placed to provide essential services for sustainable natural resource management at the regional level.

The most important service has been the assistance in arthropod identification. Similar to the safe characterization of germplasm when plant material is transferred under the International Treaty on Plant Genetic Resources for FAO, users need reliable and valid entity names for biodiversity monitoring, pest management, biological control, conservation, and compliance with trade-related controls under the prevailing Sanitary and Phytosanitary regulations of the World Trade Organization.

For scientists, farmers, extension and biosecurity agents, quarantine authorities, and any other user throughout the globe, accurate and timely identification is vital. It represents the unique entry point for access to existing information about any organism. Opportunities in West Africa similar to diagnostics services for plant diseases for identifying arthropods are scarce or nonexistent and fees requested by overseas centers of expertise are not affordable for most local users. Thus, by providing the names of, on average, 1,500 submitted arthropod specimens per year, IITA has been instrumental in responding to the regional need for over a decade.

Adult female of Sri Lanka fruitfly Bactrocera invadens. Photo by G. Goergen, IITA.
Adult female of Sri Lanka fruitfly Bactrocera invadens. Photo by G. Goergen, IITA.

Arthropods form the bulk of the roughly 1.8 million species that have been described until today. It is estimated that this number actually represents only a small fraction of all living organisms, the number of yet unnamed species being particularly large in tropical countries. Thanks to regular faunistic activities, IITA has contributed to the discovery and description of more than 120 arthropod species previously unknown to science. Among them are important pests and their natural enemies.

Following climate change, invasive alien species (IAS) are widely regarded as the second-greatest threat to biodiversity worldwide. They represent a growing concern for biosecurity and quarantine services, especially since increased trade and travel are expected to accelerate the rate of pest introductions. For tropical Africa, data sampled over 100 years show a rate of three introductions every two years. The failure to recognize IAS may have dire economic or ecological consequences. Prevention or early detection of such IAS requires considerable knowledge of native and exotic fauna.

For West Africa, IITA-Bénin is at the forefront of IAS surveillance with the detection of the whitefly Paraleyrodes minei Iaccarino, the Sri Lanka fruitfly Bactrocera invadens Drew et al., and lately the papaya mealybug Paracoccus marginatus Williams & Granara de Willink. Such monitoring also led to the recent detection of a new cashew pest, now awaiting description.

Infestation of the papaya mealybug Paracoccus marginatus. Photo by Manuele Tamo, IITA.
Infestation of the papaya mealybug Paracoccus marginatus. Photo by Manuele Tamo, IITA.

Despite the need to maintain the present services and the opportunities arising to work in new fields, the future of the collection remains unsure because of the lack of external funding. This is all the more surprising since new opportunities for the delivery of public goods are now appearing in various areas with significant impact for the sustainable use of natural resources. Thus, the comparatively young age of the collection makes it particularly well suited for the application of novel identification methods such as DNA barcoding.

IITA’s participation could thereby provide important additions to this publicly accessible DNA database thus advancing the goals set by the Consortium for the Barcode of Life (CBOL). Besides agricultural pests and their natural enemies, this technology will also target crop pollinators because of their vital services to ecosystems and the particular concern raised by their global decline. Thus, a full return from past collection efforts will be achieved by applying molecular techniques.

Opportunities to extend biosystematics services at IITA are manifold and crucial for the region that is known to suffer from scanty local capabilities. These include the development of web-based products, the integration of Geographical Information Systems, the provision of online identification tools using high resolution images of important West African arthropod species, and capacity building in the identification of agriculturally relevant groups at various academic levels.

IITA has already an undeniable comparative advantage in biosystematics. This advantage should be preserved in view of its vital support to the successful deployment of plant genetic material for improving food security and reducing poverty in developing countries.

Why manage noncrop biodiversity

Muris Korkaric, and Fen Beed,

When it comes to the diversity of nonplant taxa, the numbers alone are highly impressive. There are an estimated 5–30 million species of microorganisms globally but only two million have been formally described. In 1 g of soil, over a billion bacteria cells can be found, but fewer than 5% of the species have been named or can be grown on artificial media. For fungi, about 1.5 million species are estimated to exist and yet only 5% have been characterized taxonomically.

Disease symptom caused by Colletotrichum fuscum on lettuce leaf. Photo by F. Beed, IITA.
Disease symptom caused by Colletotrichum fuscum on lettuce leaf. Photo by F. Beed, IITA.

Nematodes remain particularly poorly described with only a fraction of the suspected half million found in nature known to man. For insects, arachnids, and myriapods only 1.1 million have been named from a potential 9 million. These numbers compare with an estimated 420,000 seed plants of which most have been described.

Knowledge of biodiversity is uneven, with strong biases towards the species level, large animals, temperate systems, and the components of biodiversity used by people. Although biodiversity underlies all ecosystem processes, modern agriculture is based on a very limited genetic pool of crops and an even more limited exploitation of the genetic resources of nonplant taxa.

This is surprising, considering that as a consequence of their diversity microorganisms and insects play pivotal roles across ecosystems that far exceed those of plants. They provide critical functions and services for food and agriculture. They are indivisibly connected with ecosystem resilience, crop health, soil fertility, and the productivity and quality of food. Modern agriculture in the developed and especially the developing world uses only a small fraction from this rich pool of genetic resources.

Conserving and using nonplant taxa
One of the vital pillars in the work of the Consultative Group on International Agricultural Research (CGIAR) is the conservation and use of agrobiodiversity and related knowledge. Over 650,000 accessions of crop, forage, and agroforestry genetic resources are stored and maintained through the centers’ genebank system and distributed to researchers and breeders throughout the world.

However, scientists from different CGIAR centers are also involved in collection, conservation, and sustainable use of insects and mites, fungi, bacteria, viruses, and nematodes that are either beneficial or antagonistic to crops. These research collections are used in two main areas: (1) crop health and productivity, where the collection supports screening for resistance in breeding programs, pathogen diagnostics, and the development of biological control technologies, and (2) soil health, fertility and ecosystem resilience where for example, collections support the development of biofertilizers.

IITA’s main collections of nonplant taxa are housed at the stations in Ibadan (Nigeria) and Cotonou (Bénin). At the headquarters in Ibadan, the collection and study of plant pathogenic fungi, bacteria, and viruses of important crops are coordinated and collections are maintained. Examples are those for yam and cassava anthracnose, cassava bacterial blight, and soybean rust pathogens.

Aflatoxin-producing fungus Aspergillus flavus growing out of maize grains in a culture medium. Photo by J. Atehnkeng.
Aflatoxin-producing fungus Aspergillus flavus growing out of maize grains in a culture medium. Photo by J. Atehnkeng.

Some of the collections contain large numbers of isolates of the same species which are often unique, not being found elsewhere in the world. International repositories might hold many different species, but tend to store fewer isolates per species and rarely prospect across the developing world. A diverse range of isolates gives a more complete representation of the genetic diversity which can be crucial for understanding evolutionary patterns, pathogen variation, and population dynamics. It helps breeding programs to identify targets for resistance selection.

Collections of isolates of the same species can be used to develop appropriate biocontrol technologies. One such example is IITA’s collection of Aspergillus flavus, a fungus that normally produces aflatoxin, a compound that is toxic to humans and animals. Over 4,500 strains have been collected from Nigeria alone and screened for toxin production and their ability to outcompete other strains when found simultaneously on foodstuffs. The atoxigenic and most competitive strains have been used to formulate aflasafe®, a biocontrol product (see R4D Review September 2009 issue).

Also in Ibadan, collections of beneficial soil microorganisms are studied and maintained. These organisms (such as Rhizobia spp. and mycorrhizae) enhance the nutrient uptake of leguminous crops and can be used as biofertilizers.

At IITA-Bénin, microorganisms and arthropods have been characterized and preserved for use in biological control programs to manage invasive crop pests and weeds. Plant pathogens have been identified and stored since the deployment of appropriate control measures first requires definitive identification of the causal agent of the disease. The biodiversity center maintains over 360,000 insect and mite specimens and is one of the largest reference collections in West Africa (see R4D Review September 2009).

Other IITA stations keep smaller working collections of nonplant taxa. At IITA-Uganda, collections of nematodes, bacteria, and fungi are maintained—mainly those associated with banana production. Certain Fusarium strains, for example, are used for endophyte-improved banana tissue culture for enhanced pest and disease resistance.

Looking like strung beads, these are part of a sample of insects received by the IITA biodiversity center in 12 months. Photo by G. Goergen, IITA.
Looking like strung beads, these are part of a sample of insects received by the IITA biodiversity center in 12 months. Photo by G. Goergen, IITA.

IITA is a lead organization for the conservation and use of nonplant taxa across sub-Saharan Africa. It is now characterizing nonplant taxa collections across the CGIAR as part of the World Bank-funded GPG2 project (Phase II of the Collective Action for the Rehabilitation of Global Public Goods in the CGIAR Genetic Resources System). This is the first system-wide inventory and collation of the existing global, nonplant taxa collections. The aim is to provide a coordinated and harmonized service for research and use of noncrop taxa to support durable farming systems in the developing world.

Future challenges and opportunities
There is a growing appreciation of the fact that farming occurs in an ecological context with complex interactions between crop and nonplant taxa that can be beneficial or antagonistic. There is also increasing demand for sustainable and environment-friendly solutions to manage pests and diseases, with the expectation that the biopesticide market share will increase to over 4.2% by 2010 and, for the first time, reach a market of over US$1 billion. Due to the rate of population increase the World Bank estimates that the global demand for food will double within the next 50 years. At the same time, the amount of arable land is decreasing from pressure from nonfarming activities and the unsustainable farming practices that are causing losses in soil fertility. This scenario is exacerbated by the fact that 40% of what is grown in the world is lost to weeds, pests, and diseases. In developing countries it is common for up to 70% of the yield to be lost due to attacks from insects and microbial diseases.

Therefore, agricultural production needs to be intensified and more marginal land used to produce sufficient food. This requires the deployment of improved land management techniques combined with the selection and distribution of appropriate crop and noncrop germplasm to exploit interactions with beneficial nonplant taxa and resist increased pressure from antagonistic nonplant taxa. Other factors such as climate change are likely to add new layers of complexity to these challenges. To predict risk and develop appropriate adaptation strategies, CGIAR and governments will become increasingly reliant on knowledge of and access to nonplant taxa genetic resources for food and agriculture. This will be used for research, training, or direct use in agriculture and originate, or be found, in a range of countries or centers.

Collections form the mechanism through which information and access to nonplant taxa can be obtained, but the survival of these collections is under threat from funding constraints. Appropriate policies, investments, and collaborations among CGIAR centers and with international collections are urgently needed to recognize noncrop taxa as global public goods. This would facilitate the conservation of collections, increase their visibility, and maximize their use for the benefit of sustainable farming systems. Especially in Africa, where the biodiversity is high, but the taxonomic and technological capacity is limited, work is needed to manage the full potential of nonplant taxa for food and agriculture.