CABI - Biocontrol News and Information 25(1) March News

Biocontrol News and Information

March 2004, Volume 25 No. 1

IPM Systems

This section covers integrated pest management (IPM) including biological control, and techniques that are compatible with the use of biological control or minimize negative impact on natural enemies.

Saving the Cedars of Lebanon

The biggest stand of cedars (Cedrus libani) in Lebanon has been the site of a major pest outbreak for the past decade. The insect responsible, unknown from anywhere else in the world, is a web-spinning sawfly that was first identified in 1998 as a new species of Cephalcia, and named C. tannourinensis after the village of Tannourine in north Lebanon where it was first detected. The 600-ha cedar forest it had infested is the largest of the 12 stands on Mount Lebanon and represents about one-third of the total cedar forest in the country.

Historically, cedars have always been the symbol of Lebanon and their health is a public issue. Back in the 950s B.C., it was said that King Hiram of Tyre (Lebanon) provided King Solomon with cedar logs to build his temple. Lebanon's flag features a green well-spread Cedrus libani, a symbol of power and immortality. The threat to cedars from the previously unknown pest therefore prompted great concern.

For more than a decade, the villagers of Tannourine had seen the forest turning brown each July, looking as if it was swept by a fire. Year after year, the alarming symptoms of needle browning worried the local community to the extent of calling for the relevant ministries and municipalities of the region to declare an emergency. This led to a management programme for the problem being initiated in 1998 under the guidance of Mr Guy Demolin, a forest entomologist from INRA (Institut National de la Recherche Agronomique, France), who was urgently called upon to identify the insect and advise on methods that would best solve the problem with least adverse effects on the other organisms present in the forest. Mr Demolin worked closely with Mr Nabil Nemer, a researcher in the Entomology Laboratory at the American University of Beirut, on the life cycle of Cephalcia tannourinensis and the choice of treatment method. Field visits were made to assess the damage and learn about the habits of this previously unknown species. The work was financially supported by a number of French and Lebanese NGOs and the Lebanese Ministry of Agriculture, while technical and scientific collaboration was provided by entomologists from the American University of Beirut (Nasri Kawar and Nabil Nemer) and the Lebanese University (Linda Kfoury).

The wasp-like C. tannourinensis, described by Henri Chevin in 2002, is a hymenopteran in the family Pamphiliidae. Adults swarm from mid-April to mid-June and females have a high egg laying potential of up to 50 eggs per female. Eggs are placed on the needles of a new bud and as the buds open, the eggs hatch and the larvae start chewing on the needles. Each larva passes through three instars and eats about seven needles before it matures. The voracious appetite of the larvae causes the trees to turn rusty-brown and eventually die. After their last moult, the larvae drop to the ground in July and make a hole for hibernation. The duration of the pupal stage has not been determined yet and could extend for several years depending on climatic conditions.

Soil sampling has been conducted monthly since 1999. The number of prepupae in a 40 ∞ 40 ∞ 40 cm sample is counted in order to assess their density in the soil, and thus gain an accurate estimate of the population. Prepupae have the capacity to enter prolonged diapause and may emerge as adults the following spring or in later years. Thus regular monitoring is necessary to assess changes in the underground population of prepupae and predict outbreaks.

Aerial treatment using the insect growth regulator (IGR) diflubenzuron was carried out by a helicopter equipped with ultra low volume (ULV) sprayers. Diflubenzuron is particularly effective against insect larvae and also acts as an ovicide, killing insect eggs. It is used against lepidopteran caterpillars and sawfly larvae and is not harmful to bees. It has been the sole product used during the spraying activities in Tannourine for the past 4 years and has been successful in suppressing the insect population. However, other measures such as monitoring and integrated pest management (IPM) have also been explored during the implementation of the FAO (Food and Agriculture Organization of the UN) project, described below.

Two other insect pests were also identified in Tannourine, which multiplied as a result of the weakness of the attacked trees and contributed to their decline. Ernobius sp., a coleopteran belonging to the family Anobiidae, was found feeding on 'emergency' buds produced by defoliated cedar branches whose needles have been eaten by C. tannourinensis. The second pest was a cecidomyiid fly, Dasineura cedri, which completed the cocktail of fatal pests attacking the trees.

FAO had received a proposal for follow-up integrated management in Tannourine forest. After some coordination meetings in the presence of the FAO regional coordinator and FAO forest officers, FAO approved funding for a 2-year project. Achievements of this project include the development of a methodology for monitoring insect populations, the utilization of pheromones for monitoring, and the introduction of an IPM programme against C. tannourinensis. Workshops for training young scientists also took place and publications were prepared for use in public awareness campaigns on forest health issues.

The first phase of the project, which extended from July 2001 until January 2002, featured several activities which focused on the development of survey and sampling techniques for collecting data on the population of C. tannourinensis. A first inception workshop was held and specialized training in France was also organized for three engineers from the Ministry of Agriculture.

The second phase of the project, extending from 15 April until 15 October 2002, covered the pest control evaluations to appraise the efficacy and/or safety of the spraying operation, the training course in Lebanon and surveys to evaluate C. tannourinensis populations before and after treatment. Surveys to monitor the other forest entomofauna were also carried out during this phase. A second training course was held, attended by 26 participants.

The last phase of the project dealt with laboratory identification of the entomofauna collected from the cedars and the preparation of printed material on cedar forest insects to be distributed to relevant parties or people interested in forest problems.

In 2003, no spraying was undertaken against the previously harmful pest. The underground prepupal monitoring of C. tannourinensis carried out by the engineers from the Ministry of Agriculture in collaboration with the American University of Beirut and the Lebanese University showed an average of 70 prepupae/m2. In comparison with the average in 1999 (626 prepupae/m2), the population has been reduced by approximately 90%.

This FAO project has allowed the Ministry of Agriculture and particularly the Directorate of Rural Development and Natural Resources to deal with a new pest problem and has also provided the technical and scientific methodologies to manage the insect. This is a unique experience since the insect pest in question is new to science and the lessons learnt from its management could be used for the other cedar forests in the region.

By: Nabil Nemer and Jenny Nasr

Contact: Nabil Nemer,
Faculty of Agricultural and Food Sciences,
American University of Beirut, P.O. Box 11-0236,
Riad El Solh 11072020, Beirut, Lebanon.
Email: nn04@aub.edu.lb
Fax: +961 1 744460

Malaria High on ICIPE's Agenda

Malaria causes over one million deaths worldwide each year, and 90% of these deaths occur in Africa. The announcement by ICIPE (International Centre for Insect Physiology and Ecology) in Nairobi that it is establishing Africa's first factory to produce Bacillus thuringiensis (Bt) for malaria control signals its commitment to the continent-wide drive to tackle malaria. Although both B. thuringiensis var. israelensis (Bti) and B. sphaericus (Bs) are successfully used against malaria in other parts of the world, they have not been widely used in Africa, partly because of the high cost of obtaining them from the industrialized nations where large-scale production is centred, and also because larval control has been a neglected area of mosquito control since the failure of malaria eradication in the 1970s.

In fact, there are very few facilities with the capacity for producing large volumes of biopesticide in Africa. Bt is potentially useful against a range of important agricultural pests, such as stem-borers, as well as public health pests, so ICIPE's venture is pioneering in potentially more ways than one.

The first phase of the project will see the setting up of a demonstration facility at ICIPE's Duduville headquarters at Kasarani near Nairobi, together with research into market access for the product. Equipment was supplied by Kernel (Wuhan Province) and financed by the Ministry of Science and Technology, China. Production know-how and the Bt strains to be produced will come from both ICIPE and Kernel gene banks. Additional funding for the plant's commissioning is being provided by UNDP (UN Development Programme), UNICEF (UN Children's Fund), Biovision - Switzerland and Kernel. For the test phase, ICIPE is hoping to obtain further funding from UN agencies, governments and other sources.

The search for the silver bullet for malaria is over. Experts now agree that an integrated management strategy, using old and new mosquito control methods combined with drugs (and perhaps in the future a vaccine), is more likely to succeed. This recognition is mirrored in the multidisciplinary research of ICIPE's Human Health Division, which includes eco-epidemiology, vector ecology and behaviour, and community-based intervention studies. The aim is to provide biologically based tools and strategies to control the vectors and break the cycle of transmission, which can be integrated with disease management.

Growing Populations

Who is most at risk? ICIPE's studies show that children are both most at risk and the largest reservoir of infection. A study of the dynamics of gametocytes of the malarial parasite, Plasmodium falciparum, in asymptomatic children in western Kenya revealed that children under 5 years of age constitute the most important infectious reservoir, with 68% harbouring gametocytes for more than a week.

Where do the mosquitoes come from? Knowing where they breed is a first step in developing effective interventions. Studies in various parts of Kenya have revealed natural and man-made breeding sites.

Mapping of larval habitats during an outbreak in western Kenya revealed that over 90% of the larval sites were man made.
In coastal Kenya, empty coconut husks, abandoned swimming pools and water collection points were major breeding sites.
Tree ponds were found to be important in sustaining mosquito populations over the dry season in both urban and rural sites.

With more people migrating to the cities, it is important to know whether the ecology of the malaria vector changes in the urban environment. In addition, new migrants tend to move into unplanned housing areas, where drainage is often poor. Are these populations more at risk from malaria? The short answer is, 'yes'. A survey to map habitat types and vector distribution in Kisumu, on the shores of Lake Victoria, showed that although mosquito larvae were found in all habitats, they were predominant in poorly drained peri-urban areas. In truly urban habitats, 64% of larval breeding sites were man-made and therefore not sensitive to rainfall. It is therefore becoming increasingly difficult to control malaria in urban areas because of encroaching unplanned, poorly drained areas where malaria vectors have been noted to breed in polluted habitats.

What of the countryside? Agricultural production remains the backbone of the Kenya economy, and the health of the rural population is of prime importance to this. Do agricultural developments such as irrigation alter the prevalence of malaria? Surveys of villages in the Mwea Rice Irrigation Scheme (in the central highlands) and villages nearby showed that although the irrigation scheme villages had up to 130-fold higher densities of mosquitoes ( Anopheles arabiensis ) than villages outside the scheme, malaria cases were lower by 40% inside the Scheme. The difference was attributable partly to differences in agricultural practices (see below). Children were again found to be at greatest risk, with those under 10 years old having the highest gametocyte levels.

Understanding Mosquito Development

Equally useful is to know why mosquitoes choose particular breeding sites, what affects the development of the larvae, and what factors contribute to the ability of the adult mosquitoes to transmit disease (vector competence and transmission intensity). Behavioural and chemical studies are used in this context to assess how factors, both abiotic (e.g. soil composition) and biotic (e.g. soil microflora, presence of competing species), affect choice of oviposition site. Other research has shown that sugar composition is an important factor in plant-feeding behaviour by adult mosquitoes. Chemical signals have been identified that may be implicated in host preference or location: human foot odour analysis showed large difference in attractiveness and chromatographic profiles.

Genetic studies are being conducted on both mosquitoes and parasites to unravel the mechanisms regulating the successful development and transmission of the malarial parasite. Molecular analysis is also helping to elucidate the genetic structure of mosquito and parasite populations.

With the results from such studies, a picture begins to emerge of what constitutes the ideal (and less-than-ideal) breeding conditions for both mosquito and parasite, while potential intervention points can also be identified: useful information to feed into a developing integrated management strategy.

Prospects for Indigenous Solutions

Exploring the potential of native biodiversity has identified a number of promising control possibilities.

DEET (N,N-Diethyl-3-methylbenzamide) is the most commonly used commercial insect repellent, but there may be concerns about its toxicity when applied to the skin over a long period. Five new repellents with higher activity than DEET were identified during the screening of 250 indigenous plants, and a number of compounds are undergoing market testing. Six plants with potent repellent and fumigant toxicity discovered through bioprospecting show promise for extraction of essential oils by thermal methods, such as from small stoves.

Ten plants with promise as larvicides were also found, including neem (Azadirachta indica) and Melia spp., and are currently being tested in the western highlands of Kenya.

Bti and Bs are now being field tested in the Mwea Rice Irrigation Scheme (see below). Studies in Eritrea have shown these biopesticides to be as effective as temephos in causing larval mortality, with a duration of activity of 2-3 weeks, and they could provide effective mosquito control if applied to all larval habitats. The new Bt demonstration factory (see above) will provide volumes adequate for large-scale field testing and public health applications.

Another project soon to start will research the potential for natural herbal medicine in combating malaria. The project will involve dose-ranging clinical trials of Artemisia annua tablets for their efficacy, safety and tolerability in uncomplicated Plasmodium falciparum malaria. The Artemesia will come from pilot field production sites in Kenya and Ethiopia. A comprehensive bibliography (including Chinese sources and references) on the distribution, agronomy and utilization of Artemisia is also being compiled.

New Tools

Molecular tools developed at ICIPE allow rapid identification of field-collected material, including mosquitoes of the Anopheles gambiae complex and bloodmeal sources, which provides support to behavioural and epidemiological studies. However, biotechnology and the unravelling of the Anopheles mosquito genome may have more to offer in the future.

The potential for genetic modification as a tool in malaria control has been hotly debated. One mechanism could involve release of mosquitoes genetically modified to have a lower than normal ability to transmit the disease. Other avenues ICIPE will soon work on include the genes expressing odour reception, with a view to both potential manipulation and rational design of new attractants and repellents. Safety and social issues aside, could such an approach contribute to malaria management? A key question is whether introduced (parasite-inhibiting) genes would spread and fix in the population. Research at ICIPE is investigating whether the dynamics of introduced genes can be predicted on the basis of fitness traits and whether introgression of introduced genes happens at the same rate across the mosquito genome.

Helping Communities

While the research outlined above is expected to lead to new control measures that can be implemented as part of an integrated management strategy, ICIPE's community-based intervention and training are helping to alleviate malarial problems now. For example:

In western Kenya, in conjunction with other research and development partners, ICIPE provided training on malaria management for local communities in Kisii and Gucha districts. This gives them the knowledge to be able to assess their health and environment and control malaria.
Community groups in Malindi, on the Kenya Coast, have developed an awareness of malaria and mosquito control under the umbrella of the Greentown Movement, with various initiatives including a 'Malaria Mosquito Day'. ICIPE helped build on this with a Trainer of Trainers (TOTs) workshop on mosquito recognition (especially of larvae in water bodies) and effective facilitation and communication skills, giving trainees the skills to make decisions about control options. Community groups were also given training on how to impregnate bednets, and the use of neem and repellents.
Farmers in the Mwea Rice Irrigation Scheme participated in a project, described in more detail below, in which various options were selected for integration in a mosquito control programme.

The potential for integrating the research outlined in this article is well illustrated by the ecosystems approach taken at the Mwea Rice Irrigation Scheme. Links between health, agriculture and the environment are particularly apparent in irrigation schemes. Baseline data collected by ICIPE indicated that almost a quarter of children had malarial parasites in their blood. The community and ICIPE came up with a strategy to tackle malaria through better management of the ecosystem. The first phase involved:

Training farmers in better environmental management, including draining and maintaining previously clogged irrigation ditches to reduce mosquito breeding sites.
Educating and training community-based organizations, farmers and National Irrigation Board staff to improve participation and information sharing.
Encouraging farmers to keep cattle or other livestock, as the animals attracted mosquitoes away from humans. To this practice was attributed the lower incidence of malaria (despite higher mosquito densities) than in villages outside the scheme.

The second phase involves pilot studies on the use of Bti and Bs as larval control agents to limit mosquito populations. Training is being provided for farmers on their use, and their efficacy is being assessed.

In addition to those cited in the text, ICIPE gratefully acknowledges funding from the following sources: ABC Fogarty. Government of Finland. International Development Research Centre (IDRC), Canada. Swiss Development Corporation (SDC). Singenberg Foundation (through ARPPIS, African Regional Postgraduate Program in Insect Science). US National Institutes of Health (NIH), International Collaborations in Infectious Disease Research (ICIDR); US National Science Foundation (NSF). UNDP/World Bank/World Health Organization Special Programme for Research and Training in Tropical Diseases (TDR). WOTRO, Netherlands. They are also delighted to acknowledge the many partners who have contributed to the above work: CGIAR System-wide Initiative on Malaria and Agriculture (SIMA). International Water Management Institute. Merlin. WHO Africa Regional Office. Kenya: Kenya Medical Research Institute (KEMRI), Centre for Biotechnology Research and Development; Kenyatta University, Department of Zoology; Ministry of Health, Department of Vector-borne Diseases, National Malaria Control Programme; Ministry of Agriculture and Livestock, National Irrigation Board; Moi University; Municipal Council of Malindi; Office of the President, District Commissioner, Kisii District. Netherlands: University Medical Centre, Nijmegen, Department of Medical Microbiology. Tanzania: Ifakara Health Research and Development Centre. UK: University of Edinburgh, Institute of Cell, Animal and Population Biology. USA: State University of New York, Department of Biological Sciences; University of Illinois; University of Miami School of Medicine, Department of Epidemiology and Public Health; Valent BioSciences Corporation.

Contact:

John Githure,
Head, Human Health Division.
Email: jgithure@icipe.org

Hans Herren, Director-General.
Email: hherren@icipe.org

ICIPE, PO Box 30772-00100, Nairobi, Kenya.
Fax: +254 20 860110/803360