The effects of banana weevil, Cosmopolites sordidus, damage on highland banana growth, yield and stand duration in Uganda

A trial to determine yield losses in East African highland banana (cv. Atwalira) to banana weevil was run between 1994 and 2001 at the International Institute of Tropical Agriculture's Sendusu Farm in Namulonge, Uganda. Banana weevil adults were released into weevil‐infestation plots, while weevils were excluded from controls by trapping and later application of chlorpyrifos. Weevil migration and reproduction in control plots reduced treatment differences in damage during the first 3 yr. Thereafter, weevil damage was heavy in infested plots and negligible in controls. High levels of weevil attack resulted in reduced bunch weights, plant losses, mat disappearance and fewer harvested bunches, with estimated yield losses averaging 42% over the final 4 yr of the trial. The data confirm the importance of banana weevil as an important production constraint of highland banana and support farmer reports that banana weevil attack contributes to shortened plantation life.     

Migration potential of the banana weevil Cosmopolites sordidus

• 1 The banana weevil Cosmopolites sordidus Germar (Coleoptera: Curculionidae) is a major pest in banana (Musa spp.) growing areas. The weevil is known to be relatively sedentary and closely associated with its host plant but little is known about the species' ability to migrate between banana fields and in nonhost habitats.
• 2 Mark–recapture experiments were conducted to assess the weevils' migration potential, possible differences between the sexes, and the relative attractiveness of pseudostem and pheromone baits.
• 3 One thousand two hundred marked weevils were released in the nonhost habitat at five distances (5, 10, 20, 40 and 70 m) from fresh pseudostem, and from pitfall traps baited with 45 mg of sordidin.
• 4 Two hundred males and 200 females were marked and released at five distances (5, 10, 20, 40 and 70 m) from the pheromone traps.
• 5 Distance and distance/bait interactions had a significant effect on recaptured weevils (binary logistic regression). The two baits were almost equally attractive to weevils in the range 0–10 m, whereas the pheromone was more attractive in the range 10–100 m.
• 6 Distance, bait and distance/bait interactions had a significant effect on the time elapsed from release to recapture (regression with life data) but the pattern observed was not consistent.
• 7 There was no significant difference between males and females with respect to distance or time elapsed from release to recapture.
• 8 The results obtained in the present study show that the migration potential of the banana weevil is greater than previously reported. This should be taken into account when new banana fields are established with clean planting material.

     

Pathogenicity of Beauveria bassiana,Metarhizium anisopliae and Serratia marcescens to the banana weevil Cosmopolites sordidus

Two exotic fungal isolates, one of Beauveria bassiana (268–86) and another of Metarhizium anisopliae (100–82), three local isolates of B. bassiana (isolates I, II, III) and one of the entomogenous bacteria Serratia marcescens, were tested for pathogenicity against the banana weevil Cosmopolites sordidus. All four isolates of B. bassiana and the one of M. anisopliae were found to be pathogenic to third—instar larvae of C. sordidus, causing mortalities of 98–100% by 9 days post—exposure to dry fungal spores. M. anisopliae was the least pathogenic to larvae with LT₅₀ of 4.2 days, compared to 3.5, 3.3, 3.6 and 4.0 respectively for isolates I, II, III and 268–86. B. bassiana was also pathogenic to adult C. sordidus, causing mortalities varying from 63–97% by 35 days post—exposure depending on isolate. As for larvae M. anisopliae exhibited low pathogenicity for the adult C. sordidus. In general, all the fungi tested were less pathogenic to adult weevils (LT₅₀ = 17.5; 12.5; 8.0 and 22.0 days) for isolates I, II, III and 268–86 respectively, while isolate 100–82 failed to kill 50% of adults even by 35 days post—exposure. Incubation of dead weevils in a moist environment led to development of surface mycelia starting from intersegmental junctions. Histopathology revealed extensive destruction of internal organs by hyphae which invaded most of the organs. The LT₅₀ for S. marcescens against C. sordidus larvae was 2.8 days. However, the bacterium did not kill adult C. sordidus even at 10 times the concentration applied on larvae.     

Feeding behaviour and efficiency of banana weevil (Cosmopolites sordidus) larvae on banana cultivars of varying resistance levels

Nutrient composition, secondary plant substances and other host quality characteristics govern resistance and influence herbivore feeding. The current study was carried out to compare aspects of feeding behaviour and food utilization of banana weevil (Germar) (Coleptera: Curculionidae) larvae feeding on banana cultivars with different levels of resistance. In the first study, penetration times of larvae into tissue of seven banana cultivars (two susceptible, three intermediate and four resistant) were compared. Day‐old larvae were placed on corm or pseudostem tissue of these cultivars and time taken to penetrate the tissue was recorded. Larvae generally took longer to tunnel into resistant cultivars, although Yangambi Km5 (resistant) did not fit this pattern. In the second set of studies, food consumption and growth of larvae were compared on cultivars: (i) Kisubi (resistant) vs. Atwalira (susceptible); and (ii) Mbwazirume (intermediate) vs. Kayinja (resistant). Day‐old larvae were offered weighed pieces of corm that were changed every 4–7 days. At each corm change, weights of the larvae, corms and frass were measured. Changes in corm and larval weight were calculated to determine larval growth and amount of tissue consumed. Larvae feeding on resistant cultivars had lower consumption and growth rates and longer developmental duration. It was concluded that low food consumption rates contribute to delayed development of larvae feeding on resistant cultivars. Differences between resistant and susceptible cultivars in food utilization may be of limited consequence for the cultivars tested. This is one step in identifying the factors influencing weevil development rates in cultivars of different resistance levels. If these factors are identified, they can be targeted in breeding for resistance.     

Effects of two pheromone trap densities against banana weevil, Cosmopolites sordidus, populations and their impact on plant damage in Uganda

Abstract:  An on-farm study to evaluate the effect of pheromone trap density on the population of the banana weevil, Cosmopolites sordidus (Germar) (Col., Curculionidae) was conducted in Masaka district, Uganda. The pheromone used was Cosmolure+, a commercially available weevil aggregation pheromone. Forty-two farms were assigned to one of three treatments: 0, 4 and 8 pheromone traps/ha. Pheromone lures were changed monthly at which time the traps were moved to a different location within the stand. Adult weevil population densities were estimated by using mark and recapture methodology at 0, 6, 12, 18 and 21 months, while damage to the banana corm was assessed at 0, 3, 6, 12, 18 and 21 months since the start of the experiment. Pheromone trap captures were generally low: about 10 weevils per trap per month. There were no significant differences in mean catches of C. sordidus per trap per month except for February 2002 when doubling the pheromone trap density decreased weevil catches. Although not significant, decreased efficiency was also the trend in higher trap densities over all the data sets. Doubling the number of traps increased the number of weevils caught per hectare per month from 0.4 to 0.6%. There was no significant difference in plant damage between the pheromone treatments in low- compared with high-trap densities. There were generally no significant differences in weevil populations and plant damage between pheromone-treated and control farms. Possible reasons for the low-trap efficacy in this study are discussed.     

Volatile components of banana pseudostem of a cultivar susceptible to the banana weevil

Volatiles from banana (‘githumo’'cultivar) pseudostem were trapped using porapak S. The trapped volatiles were desorbed from porapak columns by elution with dichloromethane and analysed using GC and GC-MS. The volatile compounds identified included -pinene, β-pinene, β-myrcene, limonene, -cubebene, -copaene, -cedrene, β-caryophyllene and -humulene.     

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.     

Partial characterization of the proteolytic enzymes in the gut of the banana weevil, Cosmopolites sordidus, and effects of soybean Kunitz trypsin inhibitor on larval performance

The proteolytic enzymes in the gut of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), have been characterized. Both larvae and adults rely on a complex proteolytic system based on at least cathepsin D‐, cathepsin B‐, trypsin‐, chymotrypsin‐, leucine aminopeptidase‐, carboxypeptidase A‐, and carboxypeptidase B‐like activities. All endoproteolytic activities were higher in the anterior section of the gut, whereas the exopeptidases were evenly distributed in the anterior and middle sections, and almost no activity was detected in the posterior section. Gelatin‐containing gels confirmed the spatial organization of the proteolytic digestive process. According to this proteolytic profile, the STI (soybean Kunitz trypsin inhibitor) was tested in vivo to establish its potential as a resistance factor against C. sordidus. Newly hatched larvae fed on diets containing 0.2% (w/w) STI experience lower survival rates and display significant reductions in larval growth. Biochemical analysis carried out on guts of larvae reared on STI‐treated diet showed a reduction of trypsin‐like activity compared to that from larvae fed on control diet. This decrease was compensated with an induction of cathepsin B, whereas cathepsin D, chymotrypsin, and leucine aminopeptidase were not affected. These results are discussed as a basis for selecting appropriate inhibitors to obtain transgenic banana and plantain plants with enhanced resistance to this pest.     

Dactylosternum abdominale (F.) (Coleoptera: Hydrophilidae): A predator of the banana weevil

The efficacy of predators of the banana weevil was investigated under laboratory and field cage conditions for the different breeding sites of the pest viz. the growing banana sucker and the spent pseudostem and residual rhizome of the sucker after the harvest of the bunch. The indigenous Dactylosternum abdominale (Hydrophilidae) reduced weevil multiplication in suckers by up to 50% and in residual stumps of harvested suckers by 39%. In spent pseudostems D. abdominale reduced the multiplication by 40–90% at different predator population densities while Thyreocephalus interocularis (Staphylinidae) reduced it by 42%. Other predators were unimportant.     

Efficacy of cultural control measures against the banana weevil, Cosmopolites sordidus (Germar), in South Africa

The banana weevil, Cosmopolites sordidus, is the most important insect pest of banana and plantain in the world. Cultural control methods were investigated over 2 years in southern KwaZulu‐Natal, South Africa. Harvesting at ground level and dissection of remnants (treatment 1), and covering the base of the mat (entire plant consisting of several meristems) with soil and moving debris to the inter‐row (treatment 2), were compared to a positive control that involved treatment of plants with a registered pesticide (treatment 3), and a negative control that involved harvesting at 150 cm from the collar with no soil or sanitation amendments (treatment 4). Yield, weevil damage and pseudostem girth of plants were measured from August to November annually, while adult beetle densities were assessed over 4 weeks in October/November and April. Nematode samples were taken and analysed in October/November every year. Damage parameters included the coefficient of infestation, the percentage coefficient of infestation (PCI) at two intervals, the summed PCI value, the percentage cross‐sectional damage of the central cylinder and cortex, and the mean cross‐sectional damage percentage. A randomized block design with three replicates was used in the trial. The parameters were similar before the onset of the trial. Fruit yield and plant girth, corrected by nematode densities, were not significantly different in any treatment, nor were the nematodes controlled. Soil cover and recession of remnants was the only effective treatment, significantly reducing the CI, but not the adult density or the other damage parameters. Soil cover showed promise as a cultural control method because it only needs to be applied seasonally and reduced the percentage cross‐sectional damage of the central cylinder, the damage parameter most closely related to yield, by 14%.     

Dual inoculation of Fusarium oxysporum endophytes in banana: effect on plant colonization,growth and control of the root burrowing nematode and the banana weevil

The burrowing nematode (Radopholus similis (Cobb) Thorne) and the banana weevil (Cosmopolites sordidus Germar, Coleoptera: Curculionidae) are major pests of banana (Musa spp.) in the Lake Victoria basin region of Uganda. Among biological options to control the two pests is the use of non-pathogenic Fusarium oxysporum Schltdl.: Fries endophytes of banana. We investigated the ability of endophytic F. oxysporum isolates Emb2.4o and V5w2 to control the banana weevil and the burrowing nematode, alone and in combination. Plant colonization by the endophytes was determined by inoculating their chemical-resistant mutants separately and in combination, onto banana roots. Plant growth promotion was determined by measuring plant height, girth, number of live roots and fresh root weight at harvest, and control of the nematode and weevil was determined by challenging endophyte-inoculated plants with the pests 8 weeks after endophyte inoculation. Endophytic root colonization was highest in plants inoculated with both endophytes, compared with those inoculated with only one of the endophytes. Root colonization was better for isolate V5w2 than Emb2.4o. Dually inoculated plants showed a significant increase in height, girth, fresh root weight and number of functional roots following nematode challenge. Nematode numbers in roots were reduced 12 weeks after challenge of 8-week-old endophyte-inoculated plants. Significant reductions in weevil damage were observed in the rhizome periphery, inner and outer rhizomes, compared with endophyte non-inoculated controls. We conclude that dual inoculation of bananas with endophytic isolates Emb2.4o and V5w2 increases root colonization by the endophytes, reduces nematode numbers and weevil damage, and enhances plant growth in the presence of nematode infestation.     

Oviposition and feeding behaviour by the vine weevil Otiorhynchus sulcatus on red raspberry: effects of cultivars and plant nutritional status

• 1 The vine weevil Otiorhynchus sulcatus is a major pest of horticultural crops worldwide, with root‐feeding larvae causing most damage. Adult oviposition aboveground may therefore influence levels of damage as the larvae are relatively immobile after oviposition.
• 2 The present study investigated feeding and oviposition behaviour on red raspberry Rubus idaeus using intact plants, ensuring that choices reflected the realistic differences in cultivar appearance and chemical composition. Previous studies investigating vine weevil feeding and oviposition on other crops have used excised plant material, which may inadvertently influence behaviour.
• 3 Adult weevils significantly preferred to feed on particular cultivars in the choice experiment (e.g. Tulameen), although they consumed significantly more foliage (0.22–1.03 cm²/day) on different raspberry cultivars (e.g. Glen Moy, Glen Rosa and a wild accession) in no‐choice situations.
• 4 In choice experiments, weevils tended to avoid laying eggs on some cultivars (e.g. Glen Moy and the wild accession). The number of eggs laid (1.91–4.32 eggs per day) did not, however, differ significantly between the cultivars in a no‐choice situation. Foliar nitrogen and magnesium concentrations were positively, although weakly, correlated with the total number of eggs laid.
• 5 The present study highlights the importance of considering both choice and no‐choice tests when assessing crop susceptibility to attack because weevils may avoid feeding on certain cultivars (e.g. Glen Moy) when given a choice, although this would cause significant damage to such cultivars if they were grown in monoculture (i.e. when there is no alternative).

     

Species associations and nurse plant effects in patches of high-Andean vegetation

Abstract. In high-elevation communities of the southern Andes, plant cover is low due to severe environmental conditions and vegetation occurs mostly as isolated small (< 1 m²⁾ patches. Most patches are dominated by flat cushion plants. We evaluated patterns of plant species co-occurrence and species affinity for patches with and without cushion plants and different species richness. We mapped and recorded species composition of patches occurring within two 20 m × 20 m plots at the NE slope of Cerro Chall-Huaco, Nahuel Huapi National Park, Argentina. In these plots, we identified 32 and 24 plant species, and a maximum of 15 and 12 species per patch, respectively. The community was characterized by positive associations between species. Patches in which either of the common cushion plants Mulinum leptacanthum and Oreopolus glacialis occurred sustained richer communities than patches in which they were absent. Patches dominated by different cushion plants did not differ in species composition, but species differed in their affinities for patches with different numbers of species. Because richness increased with patch size and patch size with time, differential affinities of plant species suggest that successional changes take place in the patches. Some small herbaceous species appear to act as late colonizers, mostly restricted to species-rich patches. Flat cushion plants are considered ‘nurse plants’; they strongly modify micro-environmental conditions and allow establishment and survival of associated species.     

Mycorrhizal fungi reduce the negative effects of nitrogen enrichment on plant community structure in dune grassland

Nitrogen (N) inputs to ecosystems have increased worldwide, often leading to large changes in plant community structure and reducing plant diversity. Yet, the interaction of increased N availability with other factors that determine plant community composition, are still poorly understood. Here, we test whether the impact of N addition on plant communities depends on the presence of arbuscular mycorrhizal fungi (AMF). AMF are widespread plant symbionts that facilitate growth of many plant species. We hypothesize that AM fungi reduce the negative impact of N addition on plant communities by supporting growth of species that are sensitive to N enrichment.We established experimental grassland microcosms consisting of 18 plant species. These microcosms were subjected to high and low N supply and were inoculated with AMF or remained nonmycorrhizal. Both N addition and AMF had a big impact on plant community composition, but with opposite effects. N addition induced a 2.8‐fold increase in grass biomass and reduced legume biomass. Grasses dominated the microcosms at high N supply, especially when AMF were absent. In contrast, AMF enhanced biomass of all legumes species (on average 6.8‐fold) and reduced the relative abundance of grasses. The proportion of legume biomass out of total shoot biomass at high N supply was 19% with AMF and only 3% without AMF. Our results show that responses of plant communities to N enrichment depend on AMF and that AMF can reduce the negative impact of increased N availability on plant community structure by reducing grass dominance.