March 1997 Vol.18 No.1

General News

Cassava Mite Control...At Last

The cassava green mite, Mononychellus tanajoa, is at last being brought under biological control in Africa, some 25 years after its accidental introduction into Uganda.

Following its introduction in the early 1970s, the green mite quickly spread to 27 countries in the cassava belt of Africa, causing an estimated 30 to 50% reduction in yield on a continent where the crop had been relatively free of major arthropod pests. It threatened production in many marginal areas where cassava is often the last crop available for harvest when all other crops have failed. This mite is now widely acknowledged as the most serious arthropod pest of cassava in Africa since the control of the cassava mealybug, Phenacoccus manihoti. Early efforts to control the mite included the use of chemicals, but the futility of this approach quickly became clear, given the low income of most cassava farmers. Control efforts eventually shifted to host plant resistance breeding and biological control.

Following unsuccessful attempts by IIBC to introduce natural enemies in the 1970s, the Biological Control Programme of the International Institute of Tropical Agriculture (IITA) initiated a project to control M. tanajoa using classical biological control in 1984. The strategy was to begin experimental releases immediately with the best known and most common natural enemies available from the neotropics, while learning more about the conditions in Africa which cause pest outbreaks, in collaboration with universities in Africa, Europe and the United States.

Natural enemies of the mite family Phytoseiidae were identified as the most promising predators of green mite, and consequently an extensive foreign exploration effort was launched by IITA in collaboration with the Empresa Brasileira de Pesquisa Agropecaria (EMBRAPA) and the Centro Internacional de Agricultura Tropical (CIAT). Among the more than 50 phytoseiid species found associated with the mite in the neotropics, ten species were identified as promising and shipped to IITA for evaluation. Parallel to the foreign exploration, trained national colla-borators initiated experimental releases and follow-up monitoring across the continent. Between 1984 and 1988, nearly 5.2 million phytoseiids belonging to 7 species of Colombian origin were released at 341 sites in 10 countries. None of these species ever became established in the wide range of agronomic and ecolog-ical conditions tested, apparently because of inadequate alternative food sources when green mite den-sities were low and during extended periods of low relative humidity.

Foreign exploration was adjusted in 1988 to focus on neotropical regions that were agrometeorologically homologous to areas in Africa subje-cted to severe green mite damage. This was based on biotic potential studies completed in Africa. Natural enemies associated temporally and spatially with green mite and capable of surviving periods of low prey densities on alternative food sources in the new target areas were given selection priority. Several natural enemy candidates were immediately identified in northeast Brazil and shipped to Africa. Subsequently, more than 6.1 million phytoseiids of five species of Brazilian origin were released in 365 sites in 11 countries between 1989 and 1995. Three of these species are now established in Africa.

Neoseiulus idaeus was first released in 1989, and is now established in Benin and Kenya. This predator has had relatively little success in dispersing, and presently covers less than 10 km2 in both countries combined. It persists on cassava and associated weeds as long as sufficient tetranychid prey, a dietary requirement, are present. Unfortunately, there is little evidence of any impact by this predator on green mite.

Typhlodromalus manihoti was also first released in 1989. It is established in Benin, Burundi, Ghana and Nigeria, where it covers an area of ca 1350 km2. T. manihoti continues to persist more than six years after release in some locations, but spreads slowly at around 2 km per year. It feeds and reproduces on green mite and a common alternate host mite on cassava, Oligonychus gossypii. Well established T. manihoti populations reduce green mite populations by two thirds.

The big surprise was the esta-blishment of Typhlodromalus aripo. It was first released in late 1993, and is now established in more than 1000 locations in 11 countries, including Guinea-Conakry, Sierra Leone, Ghana, Togo, Benin, Nigeria, Cameroon, Uganda, Kenya, Burundi and Zambia. T. aripo spreads at a rate of ca 12 km in the first season, and up to 200 km in the second season. It now covers an estimated 200,000 km2, mostly in West Africa. This predator develops on spider mite prey, pollen, honeydew and plant exudates, but requires green mite, red spider mite or maize pollen to reproduce.

T. aripo reduces green mite popula-tions by more than 50% once esta-blished. Results from an impact trial in a dozen farmers' fields in southeast Benin show a 32% increase in crop yield when T. aripo is present.
T. manihoti also shows promise as a control agent in humid areas. This species will be selectively promoted in those countries with a national capacity to maintain and mass produce the species for experimental releases. The impact of T. manihoti and T. aripo will continue to be measured in field trials in different ecological zones as efforts are made to distribute the predator to new ecozones, countries and regions.

Theoretical questions concerning natural enemy selection, dispersal, mechanisms of pest regulation, and single vs multiple introductions among others are being addressed in this project. Research on other candidate natural enemies, including fungal pathogens, that show potential in specific ecological zones will continue, particularly on phytoseiids adapted to the mid-altitude ecozones of east and southern Africa. The campaign to control M. tanajoa in Africa is becoming an outstanding biological control success.

For further information contact: J.S. Yaninek, IITA PHMD, BP 08-0932, Cotonou, Benin;

Email: s.yaninek@cgnet.com;

fax: +229 35 05 56.

Microbial Cultures

The UK government has decided that the Biotechnology and Biological Sciences Research Council is to coordinate operation of the UK's microbial culture collections. This will enable their development as a world class national collection and enable them to realise their potential as a prime national asset for the UK research community and industry. Individual collections will retain their own identity. The objectives of the decision are to protect the repository of microbial diversity represented in the collections while optimising opportunities for this to be exploited.

To facilitate collaboration, the collec-tions will be grouped around three nodes: industrial; medical; and agricultural and mycological. The agricultural and mycological node will centre on the International Mycological Institute, a sister institute of IIBC within CAB International.

For further information on the BBSRC scheme contact: Dr Chris Miller, Biotechnology and Biological Sciences Research Council, Polaris House, North Star Avenue, Swindon SN2 1UH, UK; and on the agricultural and mycological node: The Director, International Mycological Institute, Bakeham Lane, Egham, Surrey TW20 9TY, UK;

fax: +44 1784 470909.

Starfish Dilemma

The Japanese starfish Asterias amurensis was introduced into the harbour at Hobart, Tasmania, in the early 1980s in ballast water from a ship arriving to take on freight. Since then it has become the dominant species in the area, preying on bivalve molluscs and damaging the local shellfishing industry. Massive egg production and a long planktonic larval stage has led to fears that it will infest other parts of Australia and possibly New Zealand.

Meanwhile, back in Japan, A. amurensis populations are under threat from a parasitic ciliate, Orchitophyra stellarum, which attacks the sperm of starfish, effectively castrating them. The ciliate is a north Atlantic species, accidentally in-troduced into Japanese waters around 1990. Since A. amurensis is an impor-tant research organism in Japan, scientists there are having to import starfish from Tasmania for their work!

The temptation to import the ciliate into Tasmania as a biological control agent needs to be approached with caution. O. stellarum is not host specific and parasitises several other species of starfish, so native Australian species are also at risk. Also, the biology of the ciliate is not well understood. The accidental introduction into Japan is an ideal opportunity to study the potential of the parasite without endangering nontarget species in Tasmania.

Pesticide Reductions in Southeast Asia

The Indonesian government is banning 28 hazardous pesticide active in-gredients for use in all crop production, according to a statement by the Indonesian Minister of Agriculture. The decree was issued because of concerns about the impact of these pesticides on human health and the environ-ment. Since the 1986 Presidential decree which banned these same 28 active ingredients for use on rice and implemented IPM for rice nationwide (see BNI 8(1) 5), the Minister of Agriculture stated that Indonesian farmers have adopted other pesticides that are "relatively safe and less harmful to human health and the environment". The Minister's state-ment did not mention use of non-pesticide alternatives.

The decree is structured to phase out pesticide formulations containing banned active ingredients as their registrations run out. With very few exceptions, no new agricultural use registrations will be issued for products made with these active ingredients. Some formulations must be removed from Indonesia or destroyed within one year of the decree whether or not the registra-tions have expired.

The South Korean Ministry of Agriculture and Forestry has annou-nced national targets for reducing pesticide use by 50% by the year 2004. The reduction targets are based on 1993 usage levels, when South Korea used 25,999 metric tonnes of active ingredients. Between 1980 and 1995, pesticide use in the country increased approximately 63%. Much of this growth was due to insecticide use on fruits, vegetables, ornamentals and greenhouse crops; insecticides used on paddy rice account for appro-ximately 26% of pesticide use in South Korea.

The Ministry of Agriculture and Forestry proposes using integrated pest management and "safe pesticide use" strategies for reaching reduction targets, but it does not provide details of how those programmes would work. Government institutions that will be affected by the new policies are in the process of developing strategies for achieving these targets. There is currently an active IPM training programme being supported by the UN Development Programme in the country, and for further information on this, contact: Kevin Gallagher, Asian Sustainable Agriculture Research and Consulting, Seokchon Bld. #401, 1551-5 Seocho-dong, Seocho-gu, Seoul 137-070, Republic of Korea;

Email: kevin@soback.kornet.nm.kr;

fax: +82 2 585-0504.

Meanwhile, the World Bank has been criticised by more than 100 envir-onmental, consumer and deve-lopment groups worldwide for wa-tering down its policy of minimizing pesticide use and promoting integrated pest management mea-sures that involved farmers taking a lead in developing locally appropriate methods. The bank is accused of diluting its recommendations because of a failure to implement them, rather than pursuing them more vigorously. The bank denies the charge, claiming that it has merely rewritten the guidelines in a clearer format - obviously not clearly enough for its critics!