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A Dissertation

Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of


with a

Major in Entomology

in the

College of Graduate Studies

University of Idaho

and with a Concentration in Ecological Agriculture in the Graduate School Centro Agronómico Tropical de Investigación y Enseñanza by Ruth Dahlquist May 2008 Major Professor: Nilsa A. Bosque-Pérez, Ph.D.

ii iii Abstract The banana weevil is a pest on bananas and plantains throughout the tropics. No published studies exist on the banana weevil in smallholder banana and plantain systems within the Bribri-Cabécar Indigenous Territories in Talamanca, Costa Rica. These include monoculture plantain and organic banana in agroforestry systems. Concerns exist over pesticide use in plantain and conversion of agroforestry systems to monoculture plantain. Alternatives to pesticides in plantain and improved pest management in organic banana to increase profitability of agroforestry systems are needed. Such efforts must be undertaken with an understanding of the socioeconomic and agroecological context of the indigenous territories.

We conducted a livelihoods analysis of cacao agroforestry systems comparing cacao to plantain and organic banana. Existing production data was integrated with data from household interviews to identify factors in the decline of cacao agroforestry systems. We also conducted a rapid rural appraisal with plantain and organic banana producers. Semistructured interviews with 75 farmers examined current pest management practices and perceptions of pest status and biology. In plantain, 63% of farmers used combination nematicide-insecticides for banana weevil control. Most organic banana farmers (61%) did not use banana weevil management practices. We assessed banana weevil damage levels and yield in 21 organic banana agroforestry farms. Yield was correlated with damage in the banana corm cortex, and 94.7% of damage was in the cortex. To determine efficacy of pheromone traps for banana weevil management in smallholder plantain farms, we evaluated weevil damage and yield before and after 58 weeks of trapping. Traps were placed in six farms at recommended rates, and six farms without traps were controls. Weevil damage decreased by 33% in farms with traps, and did not decrease in control farms. There was no reduction in trap catches, indicating that damage reduction can occur without reduction of weevil populations. We evaluated movement patterns of banana weevils in response to host plant volatiles at 1 and 2 m distances in the field. Weevils were tagged, released, and relocated using harmonic radar. Weevils oriented to host plant volatiles at 1 m but not 2 m, and displayed positive orthokinesis at both distances.



Many people have invested a tremendous amount of time and energy in my development as a scientist, as well as in the implementation of an international, interdisciplinary research project. I am deeply grateful to my advisor, Nilsa Bosque-Pérez, for her constant support and encouragement throughout my time here, and for mentoring me in working in the tropics as well as in my professional development. Thanks also to Sanford Eigenbrode for providing guidance in research and teaching, and for passing on his fascination with insect ecology and behavior to his students. I would especially like to thank both Nilsa and Sanford for visiting my field sites in Costa Rica, for being available when I needed input or advice, flexible when things didn’t turn out exactly as planned, and for their contribution to my intellectual growth.

Thanks to my CATIE co-advisor Luko Hilje, whose logistical support in Costa Rica was essential for the completion of my research. I am also grateful for his positive attitude and moral support. Thanks to Eduardo Somarriba, whose experience working in Talamanca over many years was invaluable for my work and also for that of my teammates, and whose longterm commitment to the people of the indigenous territories makes it possible to do research that is relevant there. Thanks to William McLaughlin for guidance in social science methods and in working with communities, and for understanding and supporting what I was trying to

do. My heartfelt thanks to all of the people who assisted in my field work in Costa Rica:

Maximiliano Sánchez Sánchez, Jenaro Trejos Morales, Jorge Valverde, Eliodoro López López, Carlos Soto Navarro, Jeison Chale Rojas, Aquilino Salinas, Jose “Chepe” Vásquez, Longino, Walter Estrada, Rodrigo Guerra, and Marcela Porras. I would especially like to thank Danny Umaña Gutiérrez for coordinating pheromone trap collections and for fixing my blown radiator hose on a national holiday, Harold Carvajal for saving me from endless hours of soldering tiny pieces of metal together, and Enrique Valenciano Ulate for coordinating sampling in remote banana farms. I’d also like to thank my IGERT teammates for being such a great group of people to work with, and the faculty not on my committee who provided technical support over email to Costa Rica. Thanks also to Matt O’Neal, Cliff Gold, and William Tinzaara for their help and advice. I am grateful to the indigenous people of Talamanca for allowing access to their farms and for their participation in my research v

–  –  –



List of Tables

List of Figures


Chapter 1 : Incorporating livelihoods in biodiversity conservation: a case study of cacao agroforestry systems in Talamanca, Costa Rica



Talamanca case study

Site Description

Indigenous territories

Landscape attributes

Description of farms


Integration of local and national information

Household and key informant interviews

Data analysis



Abandonment and shifting of cacao agroforestry systems

Vulnerability context

Structures and Processes: Socioeconomic and institutional factors influencing livelihoods


Addressing the vulnerability context

Improving structures and processes



Chapter 2 : A rapid rural appraisal of pest management practices in plantain and organic banana production and cost-benefits of plantain production in the Bribri-Cabécar Indigenous Territories of Talamanca, Costa Rica




vii 2004 Rapid Rural Appraisal

2006 Plantain Cost-Benefit Analysis

Data Analysis and Triangulation


Rapid Rural Appraisal (RRA)

Plantain Cost-Benefit Study




Chapter 3 : An assessment of banana weevil (Cosmopolites sordidus Germar) populations and damage in smallholder organic banana farms in Talamanca, Costa Rica


Materials and methods

Data analysis


Damage and yield

Effect of management

Farm variables



Chapter 4 : An evaluation of pheromone trapping for banana weevil (Cosmopolites sordidus Germar) management in Costa Rican smallholder plantain farms


Materials and methods

Farm selection

Trapping with pheromone lures

Mating status

Yield and damage measurements

Farmer interviews

Data analysis


Banana weevil damage levels in smallholder plantain farms

Damage levels and yield before and after trapping

Trap catch numbers

Sex ratio and mating status



Chapter 5 : Movement patterns of the banana weevil Cosmopolites sordidus (Germar) in relation to its host plant in Costa Rica


Materials and methods

Data analysis

viii Results

Orientation towards banana pseudostem tissue

Movement distance and depth in soil

Environmental variables

Movement patterns

Effects of release position, direction, and tagging



–  –  –

Table 1.1.

Characteristics of communities sampled

Table 1.2.

Conservation and development efforts promoting cacao in Talamanca................41 Table 1.3. Available estimates of yearly income and benefit/cost ratios for primary cash crops in Talamanca.

Table 2.1.

Ranking of agricultural pests by rapid rural appraisal participants (N=75)...........74 Table 2.2. Summary of the range of pesticide-use regimes in banana and plantain production in Talamanca, Costa Rica

Table 2.3.

Characteristics of agrochemical use by rapid rural appraisal participants in monoculture plantain farms

Table 2.4.

Summary of benefits, costs and agrochemical use in plantain production............78 Table 4.1. Characteristics of farms with pheromone traps.

Table 4.2.

Results of interview data in 2006, prior to placement of pheromone traps in trapping farms

Table 4.3.

Means of damage and yield measurements

Table 4.4.

Damage measurements in 2006 and 2007

Table 4.5.

Yield measurements in 2006 and 2007.

Table 4.6.

Correlation of weekly trap catches and weekly rainfall

Table 4.7.

Mean trap catches and total damage before and after trapping.


List of Figures

Figure 1.1.

Dominant land uses in Talamanca, Costa Rica.

Figure 1.2.

a) Area in Costa Rica harvested for plantain and cacao. b) Costa Rican production volume of plantain and cacao.

Figure 1.3.

Shifts out of cacao agroforestry systems for household parcels whose management began with cacao agroforestry systems in 8 communities in Talamanca..45 Figure 1.4. Factors influencing abandonment and conversion of cacao agroforestry systems in Talamanca.

Figure 1.5.

a) Volume of annual Costa Rican exports of plantain and cocoa beans.

b) Value of annual Costa Rican exports of plantain and cocoa beans

Figure 1.6.

International cocoa bean prices.

Figure 1.7.

Household responses to the question: What are important income sources for your household?

Figure 3.1.

Relationship of yield and banana weevil damage in the banana cortex...............90 Figure 3.2.

Banana weevil damage in Amubri 1, Amubri 2, and Cachabri.

Figure 4.1.

Map of the Valle de Talamanca with location of plantain farms.

Figure 4.2.

Movement of pheromone traps in a grid of 20 m spacing within a 1 ha section of farm

Figure 4.3.

Total corm damage in 2006 and 2007 in trapping and control farms................125 Figure 4.4. Plantain bunch weight in 2006 and 2007 in trapping and control farms............126 Figure 4.5. Means of trap catches for trap rotation periods (each period is 4-5 weeks).......127 Figure 4.6.

Total corm damage vs. mean of trap catches in the first three months of trapping.

Figure 5.1.

Release of weevils in a hexagonal array and measurement of movement parameters.

Figure 5.2.

Average bearing and distance for weevils at each release position for each combination of treatment factors

Figure 5.3.

Effect of banana pseudostem tissue on angle of movement with respect to center of hexagon.

Figure 5.4.

Effect of banana pseudostem tissue on distance moved per night.

Figure 5.5.

Effect of banana pseudostem tissue on depth in soil.


The banana weevil (Cosmopolites sordidus Germar) is an important pest on bananas and plantains (Musa spp.) in Talamanca (E. Somarriba pers. comm.) and throughout the tropics (Gold et al. 2001). While the banana weevil is not considered a major problem in commercial banana plantations, it has eluded control in smallholder production systems. Damage is caused by the larvae, which tunnel into the banana corm. Banana weevil damage can reduce yield and plantation life, and heavy infestation can lead to crop failure in newly planted fields (Gold et al. 2001). Farmers use various control measures, but not all have been evaluated widely for their efficacy or potential integration with other practices (Karamura and Gold 2000). These measures include cultural controls such as clean planting material, intercropping, destruction of residue after harvest, and pseudostem traps. Other possibilities for control include biological control with myrmicine ants (Castineiras and Ponce 1991) or entomopathogens (Pena et al. 1995), botanical or synthetic pesticides (Gold et al. 2001), and mass trapping with pheromone lures (Tinzaara et al. 2002).

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