Cosmopolites sordidus (Germar), commonly known as banana corm weevil, is an important economic pest in Asia that can cause severe yield loss depending upon the stage at which infestation occurs. In spite of its economic importance, little is known about the population structure of this pest in India. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) were used to characterize the population genetic structure of C. sordidus collected from five hot spot locations in India. Nineteen RAPD primers and five selective AFLP primer combinations generated 147 and 304 amplification products, respectively. UPGMA dendrograms generated with both marker systems failed to reveal populations clustered based on geographic distance, which was confirmed by the Mantel test, which did not show a strong correlation between genetic distance and geographic distance. Values of indices of genetic identity showed that the populations were closely related. Though the gene flow estimate (Nm) between the populations was 0.469, suggesting restricted gene flow, the populations are not genetically distinct. These observations suggest that the range expansion of this banana pest in India has taken place through transport of infested corms and plant material, resulting in genetically close populations that are geographically distinct. These results provide important information on the population structure of this pest in India, which will aid in designing suitable strategies for its control and management, especially with respect to insecticide resistance.

Introduction. Small-scale bananaproducers in Tanzania are facing constraints caused by the destructiveactivities of the banana weevil (Cosmopolites sordidus Germar).Many currently used methods of addressing the problem are ineffective ortoo expensive for local farmers to implement. Materials and methods.A combination of two integrated pest management (IPM) tools (regulartrapping in combination with field sanitation) was tested at twofarmer-managed sites (Bujela and Kyimo) and one researcher-managedsite (SUA-Morogoro). Treated areas were surrounded by untreatedcontrol areas where no trapping and limited sanitation was done.Changes in population densities were estimated by the mark-recaptureprocedure and the Lincoln index. Results and discussion. Aftereight months, weevil populations in the cleaned and trapped areashad been reduced by 33% (Bujela), 33% (Kyimo) and 74% (SUA). Thechange in population sizes in the control areas differed greatly,possibly due to discrepancies in field management between farmers’ andresearchers’ practice. Trap types, areas and sites affected thenumber of weevils captured. Disc-on-stump (DOS) traps captured moreweevils than corm disc (CD) and pseudostem (PS) traps. Weevils respondedmore strongly to traps in the clean area at SUA compared with theother two sites, probably because the more rigid sanitation practicesat SUA meant that volatiles from the traps were less likely to bemasked by volatiles from surrounding residues. Conclusion.Regular trapping with field sanitation can greatly reduce populationsof banana weevils, but strict adherence to method execution is requiredin order to gain favourable results.

A survey on the occurrence of entomopathogenic nematodes (EPNs) was conducted in selected banana fields from three regions in Tanzania, namely Mbeya (Southern Highlands), Morogoro (Lowland) and Pwani (Coast). The main objective of this study was to isolate EPNs naturally occurring in banana fields in Tanzania and to test their effect on banana weevil (Cosmopolites sordidus Germar 1824). We report for the first time the presence of EPNs in Tanzania where four (4.4%) out of 90 samples contained nematodes in the genera Steinernema and Heterorhabditis. EPNs were only isolated in the coastal region in soils with a high sand content. The virulence of nine EPN isolates was tested against larvae and adults of C. sordidus. All isolates caused mortality of the larval stages, whereas the adults appeared resistant to nematode infection. Larval mortality was found to increase significantly with increasing nematode dose. It was also shown that nematodes were able to penetrate and establish in the banana weevil larvae in increasing numbers with increasing nematode dose. The study indicates the potential for including EPNs in management strategies of banana weevil.

Use of host plant resistance for the management of the banana weevil Cosmopolites sordidus (Germar) requires development of rapid cultivar screening methods. A previous study showed prolonged development of larvae feeding on excised plant material of resistant cultivars and suggested partial breakdown of resistance in such plant material. In the current study, development and survivorship of larvae feeding on potted plants of banana cultivars with differing levels of resistance were evaluated. Weevil performance was evaluated on one susceptible (Atwalira), one intermediate (Kabula) and four resistant cultivars (FHIA 17, Kayinja, Kisubi and Yangambi Km5). Differences in development of larvae feeding on the susceptible Atwalira and intermediate/resistant cultivars became apparent at 15 days after infestation of plants. Differences in survivorship of larvae feeding on different cultivars were not statistically significant. Results of this study show that experiments using potted plants can be used to screen for resistance to banana weevil based on the development of larvae. The influence of previous feeding damage to banana plants on larval development and survivorship in a susceptible (Atwalira), an intermediate (Kabula) and a resistant cultivar (Kisubi) was also examined. While no effects on larval development rate were apparent, survivorship was reduced in previously attacked plants for the intermediate cultivar, indicating that resistance may be induced by previous weevil attack of plants.

Host plant resistance is an important tool in the management of the banana weevil Cosmopolites sordidus (Germar). Although ovipositing females do not discriminate between resistant and susceptible cultivars, plants of resistant cultivars have smaller larval populations and sustain less damage in the field. These observations suggest that lower damage levels observed in resistant cultivars reflect larval success. This study was carried out to evaluate laboratory screening of banana cultivars as a rapid screening method for resistance to the banana weevil by determining the influence of cultivars on weevil survivorship, development duration and adult weight. Larvae were raised on corm pieces of two susceptible, three intermediate and four resistant cultivars, resistance categories having been determined from a previous field screening trial. The developmental period was prolonged in resistant cultivars. However, cultivars had less influence on survivorship and adult weight. Moreover, the ranking of survivorship did not correlate with resistance levels observed in the field. The implications of these findings for laboratory screening of cultivars for resistance to C. sordidus are highlighted.

Laboratory trials were conducted in Uganda at the Kawanda Agricultural Research Institute to determine attraction, eclosion success and larval survivorship of the banana weevil Cosmopolites sordidus (Germar) on crop residues of different ages. In the first experiment, studies focused on different types and ages of residues of one susceptible highland banana clone ‘Nabusa’ (genome group AAA-EA). Corms attracted 65% of the test weevils, pseudostems 30%, while 5% were non-respondents. Oviposition levels and the number of eggs per female were higher on young than old corms. Eclosion rates of < 1-day-old eggs inserted into corm pieces of residues (cultivar ‘Kisansa’, genome group AAA-EA) declined from 66% in residues collected < 2 days after harvest (DAH) to 58% in residues collected >30 DAH. To assess immature survival, < 1-day-old 1st instar larvae were put on banana corms of suckers and crop residues of the cultivar Kisansa in single rearing chambers. The number of surviving individuals was recorded at 3-day intervals until adults emerged. Survivorship was 12% on sword suckers, 10% on maiden suckers and 7% on flowered plants; and 12% on residues collected < 2 DAH and 5% on residues collected >30 DAH. Larval duration and mean days taken for adult emergence increased with plant and crop residue age. Females emerging from the different plant and residues treatments were similar in weight. The data suggest that all aged residues are suitable hosts for C. sordidus, suggesting that sanitation practices should be implemented soon after harvest.

The banana weevil (BW), Cosmopolites sordidus (Coleoptera: Curculionidae), is one of the most important insect pests of bananas and plantains. The mobility and the origin of BW infestations at the Canary Islands (Tenerife, La Gomera and La Palma) have been analysed using Random Amplified Polymorphic DNA (RAPD) as molecular markers. Populations from Costa Rica, Colombia, Uganda and Madeira were also included for comparison. One hundred and fifteen reproducible bands from eight primers were obtained. The level of polymorphism in the populations from the Canary Islands (40–62%) was in the range of those found in other populations. Nei's genetic distances, pair-wise fixation index (FST) values indicate that the closest populations are Tenerife populations among themselves (Nei's genetic distance=0.054–0.100; FST=0.091–0.157) and Costa Rica and Colombia populations (Nei's genetic distance=0.049; FST=0.113). Our results indicate the existence of BW local biotypes with limited gene flow and affected by genetic drift. These results are compatible with a unique event of colonization at Tenerife; whereas, the outbreaks in La Gomera and La Palma may come from independent introductions. The Madeira population is phylogenetically and geographically closer to the Canary Islands populations, suggesting that it is the most likely source of the insects introduced in the Canary Islands.

The effect of covering post-harvest banana stumps with soil on banana weevil Cosmopolites sordidus (Germar) oviposition levels was investigated at three locations, Sendusu, Kawanda Agricultural Research Institute (KARI) and Ntungamo district of southwestern Uganda. In the first experiment oviposition levels were assessed in a banana system comprising growing plants and residues. Oviposition increased on sword suckers, reaching a peak 1–7 days after harvest and decreased thereafter. In the second experiment conducted on farmers' fields, corms received 70% of the eggs and pseudostems 30%. The area 5–10 cm below the collar received 27% of the eggs, the area 0–5 cm above the collar 30% and the area 5–10 cm above the collar 0.3%. The remaining eggs (43%) were laid 0–5 cm below the collar. The effect of stump height and covering the stumps was evaluated in both the wet and the dry seasons at Kawanda and Ntungamo. Cutting stumps to the ground level alone had no effect on oviposition. Covering post-harvest banana stumps reduced C. sordidus oviposition in the wet but not in the dry season.

The banana weevil, Cosmopolites sordidus (Germar), is a nocturnal insect that is not readily observed in banana fields. Knowledge on its distribution is essential for the design of management strategies that target the adult stage. Marked weevils were released into seven-year-old banana plots. Ten days later the plots were systematically sampled for adult weevils by first removing the banana leaf mulch and residues, searching subsections of the soil to depths of 3 and 25 cm and, finally, removal and dissection of the banana mats. Of the marked weevils, 62, 56 and 82% respectively, were recovered in three trials. Most weevils were found in close association with either the banana mat (46–66%) or with cut residues lying on the ground between the mats (24–31%). Lesser numbers were found in the leaf mulch and in the top 3 cm of soil away from the mat. The distribution of weevils is likely to be influenced by crop management practices and the availability of residues and by the presence of mulch. Implications for banana weevil IPM are discussed.

—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.

The influence of banana weevil, Cosmopolites sordidus (Germar)(Coleoptera: Curculionidae), population density on oviposition rates and larval survivorship was studied in the laboratory at the Kawanda Agricultural Research Institute in Uganda. This study was undertaken to elucidate the relationship between density-dependent factors and rates of banana weevil increase in the field. Oviposition substrates (corm pieces) were offered to a range of densities of weevils maintained in buckets. Mean oviposition rates per female at densities of 10, 20 and 40 females per bucket were 29, 37 and 53%, respectively, lower than that at a density of 5 females. Nevertheless, total oviposition for the same groups was 1.4, 2.5 and 3.7 times higher than that of the 5-female group. Providing fresh corms daily instead of every five days did not increase oviposition. Larval survivorship was slightly higher at lower densities of immatures following insertion of different densities of eggs or first instars into banana corms. The results suggest that density-dependent factors can influence oviposition rates of individual weevils and survivorship of immatures, but appear to exert only modest influence in reducing banana weevil population growth. More likely, high mortality of weevil immatures under field conditions and/or higher rates of adult mortality and emigration than previously postulated contribute to the slow population build-up of this pest.

Simple methods for production of all life stages of the banana weevil on its natural diet, banana rhizome and pseudostem are presented. Their effectiveness, labour demands and applicability for different purposes are discussed. The most effective method for the production of eggs, pupae and adults is the utilization of the rhizome part of suckers, whereas larvae are easier to recover from pseudostem. The hatchability of the eggs produced is high.