C.S. Gold

Levels of host plant resistance to banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), in Ugandan Musa germplasm

Forty-five Musa clones, including endemic and introduced cultivars plus hybrids, were evaluated for resistance against the banana weevil, Cosmopolites sordidus, in a field trial in Uganda. The predominant groups of staple crops, East African highland bananas (Musa spp. AAA) and plantains (Musaspp. AAB), as well as plantain-derived hybrids (AAB × AA), showed the highest levels of susceptibility to this pest. These were followed by dessert bananas (Musa spp. AAA), exotic bananas (Musa spp. ABB) and finally diploids of M. acuminata (AA). Hybrids of banana origin were highly resistant. Some East African highland cultivars, especially brewing types (e.g., Kabula, Bagandeseza, Ediirira), showed intermediate levels of resistance. Among the non-highland bananas, high levels of resistance were observed in Yangambi-Km5 (AAA), Cavendish (AAA), Gros Michel (AAA), Kayinja (ABB, Pisang Awak subgroup), Ndiizi (AB, Ney Poovan subgroup)and Kisubi (Ney Poovan subgroup). The highest resistance was observed in banana hybrids TMB2×7197-2, TMB2×8075-7 and the wild banana Calcutta-4 (AA). These were considered the best sources of resistance for a weevil resistance-breeding programme with the two hybrids commonly used as improved male parents.

In vitro antagonism of endophytic Fusarium oxysporum isolates against the burrowing nematode Radopholus similis

Radopholus similis is one of the key pests of banana worldwide. In this study, nine endophytic Fusarium oxysporum isolates were screened for the production of secondary metabolites antagonistic to R. similis in culture. Undiluted and diluted culture filtrates were tested against motile stages and eggs of R. similis. All isolates tested demonstrated in vitro antagonistic activity, causing paralysis of R. similis motile stages. The percentage of paralysed nematodes increased with increase in the length of exposure time to culture filtrates. After 24 h exposure in culture filtrates up to 100% of the treated nematodes were paralysed compared to 26.5% in the control treatments. Nematode mortality rates after 24 h exposure in culture filtrates ranged from 76.4% to 100%. Paralysis was reversible at lower filtrate concentrations. Radopholus similis males were more sensitive to culture filtrates than females. Culture filtrates of all isolates demonstrated inhibitory effects on hatching of R. similis eggs. The results demonstrate the potential for using endophytic F. oxysporum as biological control agents against R. similis and for toxic derivatives from their secondary metabolism to be used as potential nematicides.

Use of infochemicals in pest management with special reference to the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae)

Infochemicals play an important role in the biology of many insect species. An understanding of their role in plant-herbivore-carnivore interactions can be used in the development of tools for the enhancement of environmentally benign alternatives to synthetic pesticides. This review discusses how chemical information mediates ecological interactions between organisms and the role of infochemicals in integrated pest management. Infochemicals can be used in pest monitoring and in pest control, through mating disruption, mass trapping and to aggregate herbivores at delivery sites for biological control agents. Particular emphasis is placed on the potential of using pheromones and kairomones in the management of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), a pest in plantations of East African highland banana and plantain in most banana-growing regions of the world. Cosmopolites sordidus produces an aggregation pheromone that attracts both males and females. This pheromone has been identified and synthesised and is being recommended as an effective agent in the trapping and control of the weevil. The synergism between banana plant extracts (kairomones) and the synthetic pheromone in attracting C. sordidus should be better exploited. Future research areas that can provide information for the development of an infochemical-based trapping system for the management of C. sordidus are discussed.RésuméLes sémiochimiques jouent un rôle important dans la biologie de beaucoup d’espèces d’insectes. La compréhension de leurs rôles dans les interactions plante-herbivore-carnivore peut-être utilisée pour le développement d’outils destinés à améliorer les techniques de luttes alternatives aux pesticides de synthèse. Cet article montre comment l’information chimique agit sur les interactions écologiques entre organismes et, discute du rôle des infochimiques dans la gestion intégrée des ravageurs. Les sémiochimiques peuvent être utilisés pour surveiller et contrôler les ravageurs, à l’aide de la technique de la confusion sexuelle et du piégeage de masse et pour rassembler les ravageurs en un lieu donné pour les agents de lutte biologique. Une attention particulière a été portée au rôle potentiel de l’utilisation des phéromones et des kairomones dans la gestion du charançon du bananier Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), un ravageur des plantations de bananiers des hautes terres d’Afrique de l’Est et de la plupart des zones productrices de bananes dans le monde. Cosmopolites sordidus émet une phéromone d’agrégation qui attire aussi bien les mâles que les femelles. Cette phéromone a été identifiée et synthétisée et son utilisation recommandée pour piéger et contrôler efficacement le charançon. Le synergisme entre les extraits de bananier (kairomone) et la phéromone de synthèse dans l’attraction de C. sordidus devrait être mieux exploité. Les futurs domaines de recherches pouvant fournir des informations pour le développement d’un système de piégeage à base d’infochimiques pour la gestion de C. sordidus sont discutés.

The use of aggregation pheromone to enhance dissemination of Beauveria bassiana for the control of the banana weevil in Uganda

Abstract Candidate strains of Beauveria bassiana were identified for use in integrated pest management of the banana weevil Cosmopolites sordidus. Horizontal field transmission of B. bassiana between banana weevils using different delivery systems, including aggregation pheromones, was investigated. We observed that infected weevils could transmit the fungal pathogen to healthy individuals. Most dead weevils (52%) due to B. bassiana infection were found at the base of banana plants in the leaf sheath or in the soil near banana plants. Significantly more weevils died from the pathogen in plots where B. bassiana was applied in combination with the pheromone than where it was applied alone. Our data demonstrate that C. sordidus aggregation pheromone can be a valuable tool to enhance the dissemination of B. bassiana for the control of C. sordidus.

Different bioassays for investigating orientation responses of the banana weevil, Cosmopolites sordidus, show additive effects of host plant volatiles and a synthetic male-produced aggregation pheromone

Abstract Three different bioassay methods to investigate the orientation behaviour of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), to host plant volatiles and a synthetic pheromone (cosmolure+) were compared. A locomotion compensator was used to separately record walking tracks in response to three odour sources. The data show that C. sordidus uses odour‐conditioned anemotaxis in its orientation to the odour sources tested. Of the two olfactometers tested, a dual port olfactometer using a continuous airflow showed stronger discrimination by C. sordidus to the different odours compared with a double pitfall olfactometer. The results of all three bioassays indicate that C. sordidus responds in an additive way to the combination of fermentation plant volatiles and the synthetic pheromone.

Enhancing banana weevil (Cosmopolites sordidus)resistance by plant genetic modification: a perspective

Banana weevil is a serious pest of bananas and plantains in Africa. The development of resistant cultivars is seen as the long term and more sustainable control strategy. The difficulty in conventional breeding of bananas and plantains has prompted efforts towards the use of genetic transformation for banana and plantain improvement. In this review, the current status of banana weevil resistance, sources of resistance and resistance mechanisms is assessed. Further, current efforts and future prospects for identifying resistance genes outside the genus Musa with potential to control banana weevil in a transgenic approach are outlined and discussed. Key words : Banana weevil, host plant resistance, pest resistance genes, transgenic plants African Journal of Biotechnology Vol. 2 (12), pp. 563-569, December 2003

Host plant odours enhance the responses of adult banana weevil to the synthetic aggregation pheromone Cosmolure

Abstract Attraction of adult banana weevil, Cosmopolites sordidus to volatiles from banana pseudostem tissue and the synthetic pheromone Cosmolure+ presented singly or in combination, was studied in the laboratory and in the field. Olfactometric studies in the laboratory showed that 50 g of fermented banana pseudostem tissue was as attractive as pheromone but more attractive than 50 g of fresh pseudostem tissue. In the laboratory, volatiles from pseudostem tissue had an additive effect on attraction of weevils to the pheromone but the effect was not significant in the field. Field trials, however, showed that attractiveness to weevils was positively correlated with the amount of fermented tissue added to the pheromone. The results indicate that fresh or fermented pseudostem tissue may enhance pheromone trap catches but the effect was not large enough to warrant their deployment for the optimisation of the infochemical-based trapping system for the management of C. sordidus.

The influence of socio-economic and marketing factors on banana production in Rwanda: Results from a Participatory Rural Appraisal

A participatory rural appraisal was conducted in four banana-producing regions of Rwanda to: (1) determine the importance of bananas as food and cash crops, and (2) to clarify the influence of socio-economic and market factors on banana production. Bananas were generally grown on smallholdings (0.2–1.0 ha). Brewing bananas were the most important cash crop in Kivu Lake Border, Cyangugu and Kigali Rural regions. These were processed into beer at the farm level and sold to local consumers or to intermediaries for sale in the urban areas. Cooking bananas were a key cash crop in Kibungo and an important staple in most study sites. Although the Rwandan government has wished to discourage farmers from growing beer bananas, most farmers expressed unwillingness to switch from brewing to cooking bananas or to annual crops. Brewing bananas required fewer inputs, could be processed into products that had a longer shelf life and were easier to market than cooking bananas. They were preferred over annual crops because they afforded higher returns and a year-round source of income. Brewing bananas were favoured over coffee as the latter required higher levels of inputs, had a less organized market structure, and little potential to absorb increased production.

The influence of crop management on banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) populations and yield of highland cooking banana (cv. Atwalira) in Uganda

A field study was undertaken in Uganda using highland cooking banana (cv. Atwalira) to test the hypothesis that bananas grown under stressed conditions are more susceptible to attack by Cosmopolites sordidus (Germar). Four banana treatments were employed to create different levels of host-plant vitality: (1) high stress: intercrop with finger millet; (2) moderate stress: monoculture without soil amendments; (3) low stress: monoculture with manure; (4) high vigour: monoculture with continuous mulch and manure. Adult C. sordidus were released at the base of banana mats 11 months after planting and populations were monitored for three years using mark and recapture methods. Cosmopolites sordidus density was greatest in the mulched plots which may have reflected increased longevity and/or longer tenure time in moist soils. Lowest C. sordidus numbers were found in intercropped banana. Damage, estimated as percentage corm tissue consumed by larvae, was similar among treatments. However, the total amount of tissue consumed was greater in mulched banana than in other systems. Plants supporting the heaviest levels of C. sordidus damage displayed bunch size reductions of 40-55%. Banana yield losses ranged from 14-20% per plot with similar levels in the intercropped and mulched systems. Yield reductions, reported as t ha-1, were twice as high in the mulched system as in the intercrop. The results from this study indicate that C. sordidus problems are not confined to stressed banana systems or those with low levels of management, but that the weevil can also attain pest status in well-managed and productive banana stands.

Olfactory Responses of Banana Weevil Predators to Volatiles from Banana Pseudostem Tissue and Synthetic Pheromone

As a response to attack by herbivores, plants can emit a variety of volatile substances that attract natural enemies of these insect pests. Predators of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) such as Dactylosternum abdominale (Coleoptera: Hydrophilidae) and Pheidole megacephala (Hymenoptera: Formicidae), are normally found in association with weevil-infested rotten pseudostems and harvested stumps. We investigated whether these predators are attracted to such environments in response to volatiles produced by the host plant, by the weevil, or by the weevil–plant complex. We evaluated predator responses towards volatiles from banana pseudostem tissue (synomones) and the synthetic banana weevil aggregation pheromone Cosmolure+ in a two-choice olfactometer. The beetle D. abdominale was attracted to fermenting banana pseudostem tissue and Cosmolure+, whereas the ant P. megacephala was attracted only to fermented pseudostem tissue. Both predators were attracted to banana pseudostem tissue that had been damaged by weevil larvae irrespective of weevil presence. Adding pheromone did not enhance predator response to volatiles from pseudostem tissue fed on by weevils. The numbers of both predators recovered with pseudostem traps in the field from banana mats with a pheromone trap were similar to those in pseudostem traps at different distance ranges from the pheromone. Our study shows that the generalist predators D. abdominale and P. megacephala use volatiles from fermented banana pseudostem tissue as the major chemical cue when searching for prey.