International Pesticide Benefits Case Study No. 67, November 2012
Leonard Gianessi and Ashley Williams
The tomato leafminer Tuta absoluta is native to South America where its preferred host crop is the tomato. Tuta absoluta was detected in Europe for the first time in Spain in 2006. Since then, it has rapidly invaded other European countries and spread throughout the Mediterranean basin, including North Africa and the Middle East . The pest found a perfect environment in the Mediterranean region where it can breed between 10-12 generations per year . Each female can lay 250-300 eggs on tomato plants in her lifetime.
Infestation of tomato plants occurs throughout the entire crop cycle. Larvae are easily found throughout the plant, mining the leaves, buds, flowers and fruits . On leaves, the larvae feed inside between the leaf layers forming leaf mines which reduce photosynthetic capacity. Tomato plants can suffer enough leaf damage to completely die. Larvae can form extensive galleries in the stems which damage the development of the plant. Larvae also feed upon fruits, forming chewed out areas filled with excrement that become open areas for invasion by secondary pathogens, leading to fruit rots . If attacked when very small, the fruit suffers severe malformation and can stop growing altogether . Insect scratches on the fruit result in fruit discard; however, infested fruit do not always show visible symptoms (tunnel holes are small and often hidden by the calyx). Larvae were found in canned tomatoes in Italy in 2008 . Potential yield loss (quantity and quality) is significant and can reach 100% if the pest is not adequately managed .
Initial infestations in Mediterranean countries caused losses of up to 100% in fields because many farmers were not aware of the insect and the speed with which it can spread . In the Mediterranean basin, the principal control strategy against Tuta absoluta is the use of chemical insecticides . Research has demonstrated that insecticides can provide 95% control of T. absoluta . Eggs and larvae are significantly reduced for 2-3 weeks after application. Repeat applications provide coverage of new growth (where T.absoluta moths normally lay their eggs). Some indigenous natural enemies are reported to be feeding on this exotic pest, and several species of native predatory bugs are successfully used within integrated pest management programs, resulting in high levels of efficacy against T. absoluta . The fact that many of the available insecticides used to control T. absoluta are not highly toxic to these predators has contributed to this biological control .
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3. Sannino, L. and B. Espinosa (Eds.). 2010. Tuta absoluta: Biology Guide and Integrated Control Approaches. Supplement 1 to issue 46/2010 of L’Informatore Agrario.
4. IRAC. 2010. The Tomato Leafminer, Tuta absoluta, Recommendations for Sustainable and Effective Resistance Management. Available at: http://www.irac-online.org
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