A Sustainable Pest Management Strategy for Sweetpotato weevil in Cuba: A success story

Transcription

1 A Sustainable Pest Management Strategy for Sweetpotato weevil in Cuba: A success story A. Lagnaoui 1, F. Cisneros 1, J. Alcazar 1, F. Morales 2 1 International Potato Center (CIP), Apartado 1558, Lima 12, Peru. 2 Instituto Nacional de Investigaciones de Viandas Tropicales (INIVIT), Santa Clara, Cuba. ABSTRACT Sweetpotato is one of the most important staple foods in Cuba, covering around 60,000 ha each year. The potential to increase sweetpotato production is limited by damage from the sweetpotato weevil. The weevil is present in all provinces of Cuba, causing up to 45% damage in the absence of control measures. The Asian sweetpotato weevil, Cylas formicarius (Fabricius), is the single most important sweetpotato pest in the Caribbean. Farmers in Cuba used to spray their fields times a season. With such an intensive spray schedule, weevil damage rarely exceeded 10%. With the elimination of subsidized pesticides, Cuban farmers faced losses of 40 to 50% of total production. CIP initial work on sweetpotato weevil management concentrated on the use of sex pheromone traps. They proved very effective, and farmers showed great interest. CIP, in collaboration with INIVIT, developed an IPM strategy based on several management components. The most effective component is the use of pheromone traps to lure and eliminate male weevils. The naturally occurring insect-killing fungus, Beauveria bassiana, proved very effective against the weevils, including larvae, pupae and adults. A cottage level industry for producing the fungus has been established in Cuba. The technology is low-cost, effective and has been adopted by many farmers. Use of the fungus is particularly attractive because it relieves farmers of the high cost of chemical pesticides. The use of ants against weevils is another component of the IPM strategy adopted for the sweetpotato weevil, in Cuba. Two species of predatory ants, Pheidole megacephala and Tetramorium guineense, are common inhabitants of banana plantations. Our collaborators at INIVIT have devised a simple system using rolled banana leaves as temporary nests" to transport the ants from their natural reservoir to sweetpotato fields, where they prey upon weevils and other insects. Setting up colonies in the field 30 days after planting with nests/ha can keep weevil infestations at low levels (3-5%). INTRODUCTION Sweetpotato is a major staple food in several low-income regions of the world. It not only plays a vital role in human consumption and animal feed, it also prevents soil erosion by producing an efficient ground cover through its rapid growth (Gregory, 1992). Recent analysis by economists at the International Potato Center (CIP) indicates that in the near future, sweetpotato is likely to make a growing contribution to the global food system, as a source of starch and animal feed in Asia and as a source of vitamin A in Africa (CIP, 1999). Sweetpotato is one of the most important staple foods in Cuba, with around 60,000 ha being planted each year. One of the major constraints to Keywords: Beauveria bassiana, Cylas formicarius, Integrated Pest Management (IPM), sex pheromone, sweetpotato weevil, 1

2 sweetpotato production in Cuba is the high loss from insects, especially Cylas formicarius. The potential to increase sweetpotato production is limited by damage from the sweetpotato weevil. The weevil is present in all provinces of Cuba, causing up to 45% damage in the absence of adequate control measures (Alcazar et al., 1997). Widespread weevil damage has led to a decrease in the total acreage planted to sweetpotato in the provinces most affected. Despite this decrease and a noticeable shift to other crops with higher market value in some provinces in Cuba, sweetpotato remains an important commodity in most provinces, and plays a vital role in the human diet (Maza et al. 2000). The Asian sweetpotato weevil as a pest The Asian sweetpotato weevil, Cylas formicarius, has been associated with Ipomoea species since at least the 1500's. As a pest of sweetpotato for several hundred years, the sweetpotato weevil has been particularly devastating, severely reducing yields and greatly affecting the quality of damaged tubers. The weevil is the single most serious threat to sweetpotato production globally. The species Cylas formicarius is the most widely distributed sweetpotato weevil worldwide. It is common in North America, the Caribbean, Africa and Asia (Wolfe, 1991). Most of the IPM research on this pest is concentrated in the south of the United States and in Asia, where sweetpotato is cultivated intensively. In Cuba, the pest has been reported in all provinces of the island, causing an estimated 40 to 50% loss of production. For several years, insecticides were readily available in Cuba and frequently used on all crops, including sweetpotato. Farmers sprayed their fields times a season. With such an intensive spray schedule, weevil damage rarely exceeded 10%. In the past, nearly all pesticides were imported from the former Soviet Union. The list of insecticides used on sweetpotato included such toxic compounds as Dimethoate, Methamidophos and Dieldrin. With the disappearance of Soviet-subsidized pesticides, Cuban farmers faced greater losses of up to 50% of total production. Need for an IPM strategy For several years during The Cuban Crisis", farmers were left to their own devices in dealing with sweetpotato weevils. Pesticides became scarce and expensive, and were used mainly on high-value crops. There were very few options to recommend at the time when the International Potato Center (CIP) initiated a collaborative project with the Instituto Nacional de Investigaciones de Viandas Tropicales (INIVIT) in Efforts were made to compile all the research information available in Cuba about the subject. Also, CIP drew on its recent experience with this pest with the neighboring Dominican Republic. This exercise helped identify knowledge gaps about the pest and its population dynamics, and point to the available control options. Several control components were identified and tested, the most important being crop sanitation, cultural practices, sex pheromones, Beauveria bassiana and predatory ants. A simple integrated pest management strategy was developed (Fig. 1). Planting Material Early on, it was noted that infested planting material contributed greatly to the dissemination of the weevil (Alcazar et al., 1997). Research data showed that 95% of the sweetpotato weevil eggs were laid in the lower 35 cm of the stems. Healthy planting material consisted of the apical parts of the stems, disinfected in a solution of insecticide to kill any remaining insects in the stems (Fig. 2). Large quantities of healthy sweetpotato cuttings were produced by local cooperatives under the leadership and guidance of INIVIT. Crop rotation At the time when pesticides were widely used, growers and cooperatives in Cuba concentrated on maximizing yields, with little consideration of pest management alternatives. Crop rotation was one of these, and was also recommended for white potato pathogens. Rotation of sweetpotato with white potato resulted in a drastic decline in populations of sweetpotato weevils over a two-year period (Fig. 3). Irrigation Sweetpotato is usually planted during the rainy season in Cuba. However, dry periods at the end of the season may cause the soil to crack. Such cracks provide a favorable environment for sweetpotato weevil infestation. Irrigation is recognized as an effective control measure, and is widely used by growers. Soil moisture is also necessary for the development of the entomopathogenic fungi that can play a major role in reducing weevil populations. 2

3 Fig. 1. Population dynamics of the sweetpotato weevil and the range of management options available in Cuba. Fig. 2. Sweet potato cuttings dipped in a solution of Beauveria bassiana 3

4 Fig. 3. Predatory ants, Pheidole megacephala and Tetramorium guineeuse prey upon sweetpotato weevils. Sex Pheromones The International Potato Center's previous experience with this pest was in the Dominican Republic, where sweetpotato weevil management concentrated on the use of sex pheromone traps. They proved very effective, and were readily used by farmers throughout the Caribbean region (Alvarez et al., 1996). This project identified and researched several management components for the weevil. The most important component of the IPM strategy is the use of pheromone traps for luring and eliminating male weevils. Host plant resistance Selection of early and deep rooting varieties (INIVIT B-88 and Yabu-8) seems to help reduce the levels of weevil infestation (Lima and Morales, 1992). However, breeding for resistance to sweetpotato weevil did not result in useful levels of resistance. Several approaches were used over the years and by several institutions to screen and select clones for weevil resistance. A review of the various researches conducted in the USA, AVRDC, IITA and CIP is found in Collins et al. (1991). Research data indicate various levels of resistance to the sweetpotato weevil, but these levels are all too low to withstand high pest pressures. Biological Control One of the problems that plagues the use of pathogenic fungi is the lack of soil moisture in fields infested with sweetpotato weevils. However, sweetpotato is mainly planted in the rainy season in Cuba. In addition, local strains of Beauveria bassiana were isolated and mass-produced. This naturally occurring insect-killing fungus is now used in several countries, including Cuba, to control the sweetpotato weevil. The fungus has been found to be effective against the weevils, including larvae and pupae as well as adult weevils. A cottage level industry for producing the fungus has been established in Cuba. The technology is low-cost, effective and has been adopted by some farmers and their families. Use of the fungus is particularly attractive because it relieves farmers of the need for costly and toxic insecticides. The fungus has been shown to be safe to humans and wildlife. Cuban scientists have investigated the use of predatory ants against weevils for some years (Martinez, 1965 and Morales, 1992). Two species of predatory ants, Pheidole megacephala and Tetramorium guineense, are common inhabitants of 4

5 Fig. 4. Sweet potato weevils infected with the fungus, Beaveria bassiana. banana plantations. Our collaborators at INIVIT have devised a simple system using rolled banana leaves as temporary nests" to transport the ants from their natural reservoir to sweetpotato fields, where they prey upon weevils and other insects. Setting up colonies in the field 30 days after planting with nests/ha can keep weevil infestation at low levels (3-5%). Adoption of IPM technologies and their impact Since 1993, when CIP launched a collaborative project with INIVIT in Cuba, this project has identified several integrated pest management (IPM) components for controlling the weevil. The most important component of the resulting IPM strategy is the use of sex pheromones in mass traps that lure and kill male weevils. Since the onset of the IPM project, more than 120,000 traps have been used each year (16 traps/ha). Ironically, despite their strong effect, pheromones also represent the weakest link in the management strategy, because they must be imported from the Netherlands. Due to the current lack of funds, the cost of importing the pheromone components has become prohibitive, threatening the sustainability of this IPM success story. This project resulted in a significant reduction in sweetpotato weevil damage from an average of 45% to fewer than 6%. Yields have increased from 6 mt/ha to 15 mt/ha nationally. Presently, half of the total area planted in sweetpotato in Cuba is under an integrated pest management program, using combinations of various locally available components. REFERENCES Alcázar, J., F. Cisneros, and A. Morales Large-scale implementation of IPM for sweetpotato weevil in Cuba: A collaborative effort. In: CIP Program Report International Potato Center, Lima, Peru, pp Alvarez, P., V. Escarramán, E. Gómez, A. Villar, R. Jiménez, O. Ortiz, J. Alcázar and M. Palacios Economic impact of managing sweetpotato weevil (Cylas formicarius) with sex pheromones in the Dominican Republic. In: Case Studies of the Economic Impact of CIP Related Technology, T. Walker and C. Crissman (Eds.). International Potato Center, Lima, Peru, pp Castiñeiras, A., T. Cabrera, A. Calderón, and 5

6 Fig. 5. Sweet potato weevil infestation in the initial year of the IPM program implementation (1994)) and four years later (1998) in six provinces of Cuba. Fig. 6. Implementation of the integrated management of the sweet potato weevil Cylas formicarius in Cuba. INIVIT-CIP

7 O. Obregón Virulencia de cuatro cepas de Beauveria bassiana sobre adultos del Cylas formicarius elegantulus (Coleoptera: Curculionidae). Ciencia y Técnica en la Agricultura. Serie: Protección de Plantas (Cuba). 7, 1: CIP Research Preview. Sweetpotato: A Sleeping Giant. International Potato Center Annual Report. Collins, W. W., A. Jones, M. A. Mullen, N.S. Talekar and F. W. Martin, Breeding sweetpotato for insect resistance: a global overview. In: Sweetpotato Pest Management: A global perspective, R.K. Jansson and K.V. Raman (Eds.). Westview Press, Boulder, Colorado, USA, pp Gregory, P Feeding tomorrow's hungry: The role of root and tuber crops. In: Sweetpotato Technology for the 21st Century, W. A. Hill, C. K. Bonsi and P. A. Loretan (Eds.). Tuskegee University, USA. Lima, M. and A. Morales Estudios Comparativos de Clones Precoces de Boniato. Agr. Eng. Thesis, Universidad Central de Las Villas, Villa Clara, Cuba. Martínez, A Plagas Agrícolas de Cuba. Dirección General de Capacitación, INRA, La Havana, Cuba. 48 pp. Maza, N., A. Morales, O. Ortiz, P. Winters, J. Alcázar and G. Scott, Economic Impact of IPM on the Sweetpotato Weevil (Cylas formicarius Fab.) in Cuba. International Potato Center (CIP), Lima, Peru. 52 pp. Morales, A., M. Lima, M. Castellón, L. Morales, D. Rodríguez, H. Fuentes and N. Maza Mejoramiento Genético para Resistencia a Cylas. Paper presented at the Taller de Manejo Integrado de Cylas Formicarius. Santo Domingo, República Dominicana. June 20-23, (Unpublished mimeograph). Wolfe, G.W The origin and dispersal of the pest species of Cylas, with a key to the pest species groups of the world. In: Sweetpotato Pest Management. A Global Perspective, R.K. Jansson and K.V. Raman (Eds.). Westview Press, Boulder, Colorado, USA, pp