Friday 10 Oct 2014
   
Protecting African tomatoes from spider mites  
   

Problem Statement: During the last two decades small-scale farmers in southern Africa (mainly Zimbabwe, Zambia, Malawi and Mozambique) faced increasing problems with spider mites (Acari) on tomatoes. The mites caused devastating losses of up to 90% of the yield. They were generally identified as Tetranychus urticae Koch, 1836, by the national authorities, a known and common pest of many vegetables and other important crops worldwide.

Methods: Based on the assumption that T. urticae was the pest species to combat, a USD 800,000 project was initiated in the 1990’s to develop integrated pest management (IPM) strategies. One objective was to reduce the use of broad spectrum insecticides as these were thought to severely harm the natural enemies of spider mites (e.g. Phytoseiulus persimilis Athias-Henriot, 1957). The identity of the pest species was checked at the beginning of the IPM project by the Agricultural Research Council - Plant Protection Research Institute in Pretoria (ARC-PPRI), South Africa, with an astonishing result: the damage on the tomatoes was caused by the species Tetranychus evansi Baker & Pritchard, 1960, not T. urticae. This finding triggered crucial changes to the project and management strategy. Molecular tools were developed to distinguish T. evansi from T. urticae. The plan to implement an IPM strategy was dropped. Instead surveys were initiated to search for potential biological control agents in South America.

Outcomes and Impact: Spider mites are particularly difficult to identify because they are minute (about 0.5 mm) and only a few taxonomist in Africa have the necessary expertise. With the development of a molecular method, complementing the classical taxonomy based on morphological characters, T. evansi now can easily, cost-efficiently and reliably be identified.

T. evansi is an invasive alien species in Africa probably introduced from South America. No indigenous predatory mites and only a few other southern African predator species attack this pest. Therefore, the original approach to preserve natural enemies through reduction of pesticide use would have been ineffective. Instead, hopes rested on finding biological control agents in South America. Biological control benefits growers, consumers and the environment alike. No money needs to be spent on pesticides and growers and customers, as well as the environment, are not subjected to insecticides. The predatory mite Phytoseiulus longipes Evans, 1958, was identified as the most promising candidate and introduced into Kenya, where it is currently tested in the field. Thus, the correct species identification triggered a complete change in the pest control strategy, avoiding a waste of almost USD 1 million.

Lessons: Proper identification of the target pest is indispensable for the development of IPM and biological control strategies. In the case of spider mites in Africa, lack of taxonomic expertise is a severe obstacle. Currently only ARC – PPRI in South Africa can offer reliable and affordable identification services, based also on molecular methods. Building and maintaining taxonomic capacity in Africa is critical for the advancement of pest control.


References:

1. Fiaboe, K.K.M.; Fonseca, R.L.; Moraes, G.J. de; Ogol, C.K.P.O. and Knapp, M. (2006) Identification of priority areas in South America for exploration of natural enemies for classical biological control of Tetranychus evansi (Acari: Tetranychidae) in Africa. Biological Control 38, 373-379. 2. Furtado, I.P.; Kreiter, S.; Garcin, M.-S.; Knapp, M. (2007) Potential of a Brazilian population of the predatory mite Phytoseiulus longipes as a biological control agent of Tetranychus evansi (Acari: Phytoseiidae, Tetranychidae). Biological Control 42, 139-147. 3. Furtado, I.P.; Moraes, G.J. de; Kreiter, S.; Knapp, M. (2006) Search for effective natural enemies of Tetranychus evansi in south and southeast Brazil. Experimental and Applied Acarology 40, 157-174.

Contributor:

M. Knapp and F. Haas; ICIPE – African Insect Science for Food and Health, P.O. Box 30772-00100 Kasarani, Nairobi, Kenya, mknapp@icipe.org, fhaas@icipe.org, http://www.icipe.org.

Regions:

Africa

Themes:

invasive alien species

agriculture

biological control

 
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