1

Keywords: Beauveria bassiana, Cylas formicarius, Integrated Pest Management (IPM), sex phero-mone, sweetpotato weevil,

A Sustainable Pest Management Strategy for Sweetpotatoweevil in Cuba: A success story

A. Lagnaoui1, F. Cisneros1, J. Alcazar1, F. Morales2

1 International Potato Center (CIP),Apartado 1558, Lima 12, Peru.

2 Instituto Nacional de Investigacionesde Viandas Tropicales (INIVIT),

Santa Clara, Cuba.

��������

Sweetpotato is one of the most important staple foods in Cuba, covering around 60,000ha each year. The potential to increase sweetpotato production is limited by damage from thesweetpotato weevil. The weevil is present in all provinces of Cuba, causing up to 45% damagein the absence of control measures.

The Asian sweetpotato weevil, Cylas formicarius (Fabricius), is the single most importantsweetpotato pest in the Caribbean. Farmers in Cuba used to spray their fields 10 - 12 times aseason. With such an intensive spray schedule, weevil damage rarely exceeded 10%. With theelimination of subsidized pesticides, Cuban farmers faced losses of 40 to 50% of total produc-tion.

CIP initial work on sweetpotato weevil management concentrated on the use of sexpheromone traps. They proved very effective, and farmers showed great interest. CIP, in col-laboration 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 effectiveagainst the weevils, including larvae, pupae and adults. A cottage level industry for producingthe fungus has been established in Cuba. The technology is low-cost, effective and has beenadopted by many farmers. Use of the fungus is particularly attractive because it relieves farmersof the high cost of chemical pesticides.

The use of ants against weevils is another component of the IPM strategy adopted forthe sweetpotato weevil, in Cuba. Two species of predatory ants, Pheidole megacephala andTetramorium guineense, are common inhabitants of banana plantations. Our collaborators atINIVIT have devised a simple system using rolled banana leaves as “temporary nests" to trans-port the ants from their natural reservoir to sweetpotato fields, where they prey upon weevilsand other insects. Setting up colonies in the field 30 days after planting with 60-110 nests/hacan keep weevil infestations at low levels (3-5%).

International Potato Center (CIP) indicates that inthe near future, sweetpotato is likely to make agrowing contribution to the global food system, asa source of starch and animal feed in Asia and as asource of vitamin A in Africa (CIP, 1999).Sweetpotato is one of the most important staplefoods in Cuba, with around 60,000 ha being plantedeach year. One of the major constraints to

���������

Sweetpotato is a major staple food in severallow-income regions of the world. It not only playsa vital role in human consumption and animal feed,it also prevents soil erosion by producing an efficientground cover through its rapid growth (Gregory,1992). Recent analysis by economists at the

2

sweetpotato production in Cuba is the high lossfrom insects, especially Cylas formicarius. Thepotential to increase sweetpotato production islimited by damage from the sweetpotato weevil.The weevil is present in all provinces of Cuba,causing up to 45% damage in the absence of adequatecontrol measures (Alcazar et al., 1997). Widespreadweevil damage has led to a decrease in the totalacreage planted to sweetpotato in the provincesmost affected. Despite this decrease and a noticeableshift to other crops with higher market value in someprovinces in Cuba, sweetpotato remains an importantcommodity in most provinces, and plays a vital rolein the human diet (Maza et al. 2000).

The Asian sweetpotato weevil as a pest

The Asian sweetpotato weevil, Cylasformicarius, has been associated with Ipomoeaspecies since at least the 1500's. As a pest ofsweetpotato for several hundred years, thesweetpotato weevil has been particularly devastating,severely reducing yields and greatly affecting thequality of damaged tubers. The weevil is the singlemost serious threat to sweetpotato productionglobally. The species Cylas formicarius is the mostwidely distributed sweetpotato weevil worldwide.It is common in North America, the Caribbean,Africa and Asia (Wolfe, 1991). Most of the IPMresearch on this pest is concentrated in the south ofthe United States and in Asia, where sweetpotato iscultivated intensively. In Cuba, the pest has beenreported in all provinces of the island, causing anestimated 40 to 50% loss of production.

For several years, insecticides were readilyavailable in Cuba and frequently used on all crops,including sweetpotato. Farmers sprayed their fields10 - 12 times a season. With such an intensive sprayschedule, weevil damage rarely exceeded 10%. Inthe past, nearly all pesticides were imported fromthe former Soviet Union. The list of insecticidesused on sweetpotato included such toxic compoundsas Dimethoate, Methamidophos and Dieldrin. Withthe disappearance of Soviet-subsidized pesticides,Cuban farmers faced greater losses of up to 50% oftotal production.

Need for an IPM strategy

For several years during “The Cuban Crisis",farmers were left to their own devices in dealingwith sweetpotato weevils. Pesticides became scarceand expensive, and were used mainly on high-valuecrops. There were very few options to recommend

at the time when the International Potato Center(CIP) initiated a collaborative project with theInstituto Nacional de Investigaciones de ViandasTropicales (INIVIT) in 1993. Efforts were made tocompile all the research information available inCuba about the subject. Also, CIP drew on its recentexperience with this pest with the neighboringDominican Republic. This exercise helped identifyknowledge gaps about the pest and its populationdynamics, and point to the available control options.Several control components were identified andtested, the most important being crop sanitation,cultural practices, sex pheromones, Beauveriabassiana and predatory ants. A simple integratedpest management strategy was developed (Fig. 1).

Planting Material

Early on, it was noted that infested plantingmaterial contributed greatly to the dissemination ofthe weevil (Alcazar et al., 1997). Research datashowed that 95% of the sweetpotato weevil eggswere laid in the lower 35 cm of the stems. Healthyplanting material consisted of the apical parts of thestems, disinfected in a solution of insecticide to killany remaining insects in the stems (Fig. 2). Largequantities of healthy sweetpotato cuttings wereproduced by local cooperatives under the leadershipand guidance of INIVIT.

Crop rotation

At the time when pesticides were widely used,growers and cooperatives in Cuba concentrated onmaximizing yields, with little consideration of pestmanagement alternatives. Crop rotation was one ofthese, and was also recommended for white potatopathogens. Rotation of sweetpotato with whitepotato resulted in a drastic decline in populations ofsweetpotato weevils over a two-year period (Fig. 3).

Irrigation

Sweetpotato is usually planted during therainy season in Cuba. However, dry periods at theend of the season may cause the soil to crack. Suchcracks provide a favorable environment forsweetpotato weevil infestation. Irrigation isrecognized as an effective control measure, and iswidely used by growers. Soil moisture is alsonecessary for the development of theentomopathogenic fungi that can play a major rolein reducing weevil populations.

3

����� �� ��� �� �� ������� ������ ��� � �������� ��� ���������� �����

����� �� ����� ���� ��� ����� ��� �� ���� �� ���� ��� �� � ��� ��� � � ���� ������� � �� ��� ��� ��� �

4

Sex Pheromones

The International Potato Center's previousexperience with this pest was in the DominicanRepublic, where sweetpotato weevil managementconcentrated on the use of sex pheromone traps.They proved very effective, and were readily usedby farmers throughout the Caribbean region (Alvarezet al., 1996). This project identified and researchedseveral management components for the weevil.The most important component of the IPM strategyis the use of pheromone traps for luring andeliminating male weevils.

Host plant resistance

Selection of early and deep rooting varieties(INIVIT B-88 and Yabu-8) seems to help reduce thelevels of weevil infestation (Lima and Morales,1992). However, breeding for resistance tosweetpotato weevil did not result in useful levels ofresistance. Several approaches were used over theyears and by several institutions to screen and selectclones for weevil resistance. A review of thevarious researches conducted in the USA, AVRDC,IITA and CIP is found in Collins et al. (1991).Research data indicate various levels of resistanceto 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 ofpathogenic fungi is the lack of soil moisture in fieldsinfested with sweetpotato weevils. However,sweetpotato is mainly planted in the rainy season inCuba. In addition, local strains of Beauveria bassianawere isolated and mass-produced. This naturallyoccurring insect-killing fungus is now used in severalcountries, including Cuba, to control the sweetpotatoweevil. The fungus has been found to be effectiveagainst the weevils, including larvae and pupae aswell as adult weevils.

A cottage level industry for producing thefungus has been established in Cuba. The technologyis low-cost, effective and has been adopted by somefarmers and their families. Use of the fungus isparticularly attractive because it relieves farmers ofthe need for costly and toxic insecticides. Thefungus has been shown to be safe to humans andwildlife.

Cuban scientists have investigated the use ofpredatory ants against weevils for some years(Martinez, 1965 and Morales, 1992). Two speciesof predatory ants, Pheidole megacephala andTetramorium guineense, are common inhabitants of

����� �� ��� ���� ���� � ������� ������� ���� ��� ������������ ��������� �������� ���� �� ������

5

banana plantations. Our collaborators at INIVIThave devised a simple system using rolled bananaleaves as “temporary nests" to transport the antsfrom their natural reservoir to sweetpotato fields,where they prey upon weevils and other insects.Setting up colonies in the field 30 days after plantingwith 60-110 nests/ha can keep weevil infestation atlow levels (3-5%).

Adoption of IPM technologies and theirimpact

Since 1993, when CIP launched a collaborativeproject with INIVIT in Cuba, this project hasidentified several integrated pest management (IPM)components for controlling the weevil. The mostimportant component of the resulting IPM strategyis the use of sex pheromones in mass traps that lureand kill male weevils. Since the onset of the IPMproject, more than 120,000 traps have been usedeach year (16 traps/ha). Ironically, despite theirstrong effect, pheromones also represent the weakestlink in the management strategy, because they mustbe imported from the Netherlands. Due to the currentlack of funds, the cost of importing the pheromonecomponents has become prohibitive, threateningthe sustainability of this IPM success story.

This project resulted in a significant reduction

in sweetpotato weevil damage from an average of45% to fewer than 6%. Yields have increased from6 mt/ha to 15 mt/ha nationally. Presently, half ofthe total area planted in sweetpotato in Cuba isunder an integrated pest management program, usingcombinations of various locally availablecomponents.

�� �������

Alcázar, J., F. Cisneros, and A. Morales.1997. Large-scale implementation of IPMfor sweetpotato weevil in Cuba: Acollaborative effort. In: CIP ProgramReport 1995-96. International PotatoCenter, Lima, Peru, pp 185-190.

Alvarez, P., V. Escarramán, E. Gómez, A.Villar, R. Jiménez, O. Ortiz, J. Alcázarand M. Palacios. 1996. Economic impactof managing sweetpotato weevil (Cylasformicarius) with sex pheromones in theDominican Republic. In: Case Studies ofthe Economic Impact of CIP RelatedTechnology, T. Walker and C. Crissman(Eds.). International Potato Center, Lima,Peru, pp 83-94.

Castiñeiras, A., T. Cabrera, A. Calderón, and

����� � ��� �� �� ������ ������ ���� �� ���������������� ������

6

����� !� ��� �� �� ����� ���� ���� ��� �� ���� �� � �� ��� �"�#� ����� �� ������ ���� $�%% &&� ��� ����� � ��� � �$�%%'&� ��� ��(� ��������� ��� ��� �

����� )� "����� ���� ��� �� ���� �� � � ���� ��� �� ���� �� ����� ����� ����������� ��� ��� �� � "*"+",-�"�� �%%'

7

Central de Las Villas, Villa Clara, Cuba.Martínez, A. 1965. Plagas Agrícolas de

Cuba. Dirección General deCapacitación, INRA, La Havana, Cuba.48 pp.

Maza, N., A . Morales, O. Ortiz, P. Winters,J. Alcázar and G. Scott, 2000. EconomicImpact 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. 1994. Mejoramiento Genéticopara Resistencia a Cylas. Paper presentedat the Taller de Manejo Integrado deCylas Formicarius. Santo Domingo,República Dominicana. June 20-23, 1994.(Unpublished mimeograph).

Wolfe, G.W.. 1991. The origin and dispersalof the pest species of Cylas, with a keyto the pest species groups of the world.In: Sweetpotato Pest Management. AGlobal Perspective, R.K. Jansson andK.V. Raman (Eds.). Westview Press,Boulder, Colorado, USA, pp. 13-43.

O. Obregón. 1984. Virulencia de cuatrocepas de Beauveria bassiana sobreadultos del Cylas formicarius elegantulus(Coleoptera: Curculionidae). Ciencia yTécnica en la Agricultura. Serie:Protección de Plantas (Cuba). 7, 1: 65-74.

CIP. 1999. Research Preview. Sweetpotato:A Sleeping Giant. International PotatoCenter Annual Report.

Collins, W. W., A. Jones, M. A. Mullen, N.S.Talekar and F. W. Martin, 1991.Breeding sweetpotato for insect resistance:a global overview. In: Sweetpotato PestManagement: A global perspective, R.K.Jansson and K.V. Raman (Eds.).Westview Press, Boulder, Colorado, USA,pp. 379-398.

Gregory, P. 1992. Feeding tomorrow'shungry: The role of root and tuber crops.In: Sweetpotato Technology for the 21stCentury, W. A. Hill, C. K. Bonsi and P.A. Loretan (Eds.). Tuskegee University,USA.

Lima, M. and A. Morales. 1992. EstudiosComparativos de Clones Precoces deBoniato. Agr. Eng. Thesis, Universidad