Pathogenicity of indigenous entomopathogenic nematodes from Benin against mango fruit fly (Bactrocera dorsalis) under laboratory conditions

Bactrocera dorsalis fruit fly is the economically most significant tephritid pest species on Mango, Mangifera indica L., in Benin, and entomopathogenic nematodes (EPNs) represent good candidates for its control in the soil. In this study, the susceptibility of larvae and pupae of B. dorsalis to 12 EPN isolates originating from Benin was investigated. The effect of nematode concentrations (20, 50, 100, 200 and 300 Infective Juveniles (IJs)/B. dorsalis larva) and of different substrate moisture content (10, 15, 20, 25 and 30% v/w) on B. dorsalis mortality at the larval stage was studied. Also, the reproduction potential inside B. dorsalis larvae was assessed. Our results revealed that the susceptibility of B. dorsalis larvae was significantly different among the 12 tested nematode isolates with H. taysearae isolate Azohoue2 causing the greatest insect mortality (96.09 +/- 1.44%). The lowest insect mortality (7.03 +/- 4.43%) was recorded with Steinernema sp. strain Bembereke. Significant differences in insect mortality were recorded when EPNs were applied at varying IJs concentrations. A concentration of 100 nematodes of either H. taysearae Azohoue2 or H. taysearae Hessa1 per B. dorsalis larva was enough to kill at least 90% of B. dorsalis larvae. Larvae were less susceptible to nematodes at higher moisture content (25% and 30%). In addition, pupae were less susceptible to nematodes than larvae. Furthermore, the tested nematode isolates were able to reproduce inside B. dorsalis third instar larva with the Heterorhabditis isolates giving the greatest multiplication rate (59577.2 IJs +/- 14307.41)

Searching for Better Methodologies for Successful Control of Termites Using Entomopathogenic Nematodes

Termites are social insects reported from many countries of the world. Some species of them are known to be beneficial to man, whereas some others cause substantial losses (billions of US dollars annually) of properties and amenities. Various preventive and remedial methods are used to control undesirable termite species. The current review paper gives an overview of beneficial and detrimental activities of termites. Methods of control of undesirable species of termites are given and their advantages and disadvantages are discussed. We emphasized on the use of entomopathogenic nematodes (EPNs) as effective, environmentally safe and sustainable biological control method against termites. Species of EPNs recovered in Africa are documented. Some techniques used to collect termites and to maintain them for experiments and also to propagate, to formulate, to store, and to check for the quality of EPNs for application in the laboratory and in the field are also discussed. The environmental factors affecting the potential of EPNs to control termites are discussed. The information provided in this chapter will help researchers to enhance their skills of the use of EPNs against termites by selecting from the methodologies described here the best ones to adapt to particular experimental conditions, especially in African soil conditions

Characterization of biocontrol traits of heterorhabditid entomopathogenic nematode isolates from South Benin targeting the termite pest Macrotermes bellicosus

Twenty-nine Beninese isolates of Heterorhabditis sonorensis and one local isolate of H. indica were screened in bioassays for their pathogenicity against Macrotermes bellicosus and for their tolerance to heat (40 A degrees C), desiccation (25 % glycerine) and hypoxic conditions. The bioassays showed significant differences among isolates for all tested traits. Most of the isolates (73 %) killed more than 80 % of the insects. The greatest survival of infective juveniles to heat (8 h), desiccation (8 h), and hypoxia (72 h) was observed with the H. sonorensis isolates Kassehlo (72.8 %), Setto1 (72.5 %), and Kissamey (81.5 %, respectively). Hierarchical cluster analysis identified six clusters. One of the clusters grouped three isolates of H. sonorensis (Zoundomey, Akohoun and Kassehlo) that scored well for all traits. These latter isolates were similarly effective by suppressing within five days a population of M. bellicosus naturally imprisoned in 1,000 cm(3) containers and inoculated with a single two-weeks-old EPN-infected Galleria larva

Influence of pesticides, soil temperature and moisture on entomopathogenic nematodes from southern Benin and control of underground termite nest populations

The influence of three pesticides on the viability and infectivity of four Beninese isolates of entomopathogenic nematodes (EPN), Heterorhabditis indica Ayogbe1, H. sonorensis Azohoue2, H. sonorensis Ze3, and Steinernema sp. Bembereke, was determined. The impact of both soil temperature and soil moisture on the virulence of these EPN to Trinervitermes occidentalis was investigated in laboratory assays. The effect of EPN-infected Galleria mellonella larvae on underground populations of Macrotermes bellicosus was also examined. All tested Heterorhabditis species were more tolerant to glyphosate and fipronil than the Steinernema species. Heterorhabditis sonorensis Azohoue2, showed the best results with 63.2% termite mortality at a soil temperature of 35 degrees C. The increase of soil moisture to 20% (w/w) did not negatively influence the virulence of tested EPN. The underground populations of 71% or 60% treated nests were controlled by H. sonorensis Azohoue2-or H. indica Ayogbe1-infected G. mellonella larvae, respectively

Effectiveness of different Heterorhabditis isolates from Southern Benin for biocontrol of the subterranean termite, Macrotermes bellicosus (Isoptera: Macrotermitinae), in laboratory trials

The host-finding ability of 28 Heterorhabditis sonorensis isolates and one H. indica isolate from southern Benin and one H. indica isolate from India was examined in vertical migration sand bioassays against workers of a target citrus termite pest, Macrotermes bellicosus. Thereafter, nine selected isolates were subjected to further investigations on virulence. Our results revealed that both H. sonorensis and H. indica isolates exhibit a cruiser type of search strategy and were capable, to various degrees, of migrating, infecting and killing workers of M. bellicosus in sand columns up to 20 cm long over a period of 3 days. However, only three isolates of H. sonorensis caused 100% mortality to M. bellicosus at the greatest depth tested. The exotic H. indica isolate (LN2) did not show strong finding ability compared to the indigenous one. Concerning virulence, differences were observed among isolates for their ability to invade workers of M. bellicosus. After 12 h post exposure, H. sonorensis from Ze (Ze2) and H. sonorensis from Azohoue (Azohoue2) exhibited the lowest invasion time with IT50 = 3.35 and 3.67 h, respectively, and a higher penetration rate (11.4% and 10%, respectively) compared with the other isolates. In the concentration-mortality test, we found that, based on 95% confidence limits, all H. sonorensis and H. indica isolates appeared to be equal, with LC50 values ranging from nine to 16 infected juveniles (IJ) termite I. Interestingly, 40 II termite(-1) were enough to cause 80% mortality to M. bellicosus. Contrary to the LC50, the results of our studies clearly demonstrate that M. bellicosus exhibits a time-dependent susceptibility to the tested nematode isolates. So, the lowest LT50 was observed for H. sonorensis Ze2 (LT50 = 23.30 h), the highest for H. sonorensis Yokon (34.76 h). The LT50 of the indigenous H. indica isolate was estimated to 24.07 h. In addition, all selected isolates were able to reproduce in M. bellicosus workers. The highest reproduction potential in M. bellicosus was observed with H. sonorensis Yokon with 20 213 IJ/termite followed by H. sonorensis Ze2 with 19 368 IJ/termites. All tested Beninese EPN isolates were pathogenic to the citrus termite pest M. bellicosus, with H. sonorensis Ze2 being the most virulent

Comparative susceptibility of Macrotermes bellicosus and Trinervitermes occidentalis (Isoptera: Termitidae) to entomopathogenic nematodes from Benin

The differential susceptibility of two termite species, Macrotermes bellicosus and Trinervitermes occidentalis, to four entomopathogenic nematodes (EPN) isolates from Benin, Heterorhabditis indica Ayogbel, H. sonorensis Azohoue2, H. sonorensis Ze3 and Steinernema sp. Bembereke, was bio-assayed in laboratory tests. Soldiers of both M. bellicosus and T occidentalis were similarly susceptible, but more susceptible than workers. Forty-eight h post-exposure of workers of M. bellicosus to 50 infective juveniles (IJ) of H. indica Ayogbel, H. sonorensis Azohoue2, H. sonorensis Ze3 and Steinernema sp. Bembereke for each termite resulted in 96.3, 87.9, 94.5 and 75.0% mortality, respectively, whereas under the same conditions, these EPN isolates caused 91.7, 98.5, 75.0 and 95.0% mortality of workers of T occidentalis. Soldiers of M. bellicosus were the most invaded with 13.2-18.6% of applied IJ. Based on concentration-mortality data, the isolates H. indica Ayogbel and H. sonorensis Ze3 were more virulent to M. bellicosus with LC50 values of 11 IJ, whereas Steinernema sp. Bembereke was the most virulent to T occidentalis with LC50 values of 12IJ. However, none of these isolates showed the highest penetration rate. All tested EPN isolates can recycle in both M. bellicosus and T occidentalis. Our EPN repellent-dispersing assay did not show evidence that M. bellicosus and T occidentalis would be able to detect the presence of D. of any EPN isolates/species. However, it was observed that nematode dispersal occurred by infected termites or phoresis

Tolérance de quelques accessions de patate douce (Ipomoea batatas L.) cultivées au sud-Bénin aux charançons de la patate douce (Cylas spp.) sous infestation naturelle

Objectif: Identifier les accessions indigènes de patate douce les plus tolérantes aux charançons de la patate douce, Cylas spp., en milieu réel.Méthodologie et résultats: L’essai a été réalisé avec 42 accessions de patate douce dans un champ paysan à forte infestation de Cylas spp., au sud-Bénin. Un dispositif en blocs incomplets avec six répétitions a été utilisé. Neuf groupes d’accessions ont été identifiés. Le plus faible taux d’infestation (0,00±0,00%) des racines tubéreuses a été enregistré dans le groupe 4 ayant un péricarpe et une pulpe de couleur orange et le plus faible rendement (2,40±1,71t/ha). Le plus fort taux d’infestation (36,74±6,24%) a été enregistré dans le groupe 8 ayant un péricarpe et une pulpe de couleur crème et un rendement moyen (6,79±0,73t/ha). Le plus haut rendement (10,31±0,97t/ha) et le poids moyen des racines tubéreuses le plus élevé (443,20±53,30g) ont été obtenus dans le groupe 6 ayant le plus faible nombre de racines tubéreuses par plant (1,00±0,00). Les accessions du groupe 2 ont donné le plus grand nombre de racines tubéreuses par plant (2,77±0,43). Le plus faible poids moyen des racines tubéreuses (133,33±42,49g) a été enregistré dans le groupe 9.Conclusion et application des résultats: Les accessions du groupe 4 semblent intéressantes pour un programme de lutte contre Cylas spp. Celles des groupes 2 et 6 présentant de très bons paramètres agronomiques pourraient être utilisées comme «parents» dans un programme de sélection et d’améliorations variétales pour soutenir les performances des accessions du groupe 4. La lutte variétale contre Cylas spp. peut être menée au champ en utilisant l’accession V37, seule accession de patate douce appartenant au groupe 4 mais tout en l’améliorant génétiquement pour de plus grandes productions.Mots clés: Accessions indigènes de patate douce, infestation naturelle, Cylas spp., paramètres agromorphologiques, tolérance, sud-BéninEnglish Title: Tolerance of some sweet potato (Ipomoea batatas L.) accessions cultivated in southern Benin to sweet potato weevils (Cylas spp.) under natural infestationEnglish AbstractObjectives: To Identify the most tolerant indigenous sweet potato accessions to the sweet potato weevils, Cylas spp. in the natural environment.Methodology and Results: The experiment was conducted with 42 sweet potato accessions in a farmer field with a heavy infestation of Cylas spp. in southern Benin. An incomplete block design with six repetitions was used. Nine groups of accessions were identified. The lowest infestation rate (0.00±0.00%) of tuberous roots was recorded in group 4 with an orange pericarp and pulp and the lowest yield (2.40±1.71 t/ha). The highest infestation rate (36.74±6.24%) was recorded in group 8 with a creamy pericarp and pulp and a mean yield (6.79±0.73 t/ha). The highest yield (10.31 ± 0.97 t/ha) and the highest tuberous root weight (443.20 ± 53.30 g) were obtained in group 6 with the lowest tuberous root number (1.00 ± 0.00) per plant. Group 2 accessions, however, yielded the highest tuberous root number (2.77 ± 0.43) per plant. The lowest tuberous root weight (133.33 ± 42.49 g) was recorded in group 9.Conclusions and application of findings: Sweet potato accessions of group 4 seem interesting for a control program against Cylas spp. Sweet potato accessions of groups 2 and 6 with very good agronomic parameters could be used as "parents" in a selection and varietal improvement program to support the performance of group 4 accessions. The varietal control against Cylas spp. can be done in the field using accession V37, the unique accession of sweet potato belonging to group 4, but by improving it genetically for highest yields.Keywords: Indigenous accessions of sweet potato, natural infestation, Cylas spp., agro-morphological parameters, tolerance, southern Beni

First record on the distribution of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) in Southern Benin

For the first time, surveys of entomopathogenic nematodes (EPN) were conducted in five departments in the Guinean zone of Southern Benin. Out of 84 prospected sites and 280 collected soil samples from agricultural and natural vegetation, 26 (31.0%) and 32 (11.4%) were positive for EPN, respectively. Identification of the EPN was based on analyses of sequences of the ITS rDNA region and morphological/morphometric investigations. Two species were found, Heterorhabditis sonorensis and H. indica. This is the first record of H. sonorensis since its description from the Sonora desert in Mexico. Heterorhabditis sonorensis was the most common species, showing a preference for semi-closed habitats such as citrus orchards, other fruit production fields and woodland with soils having sand and organic matter content ranging between 53.6-89.5% and 0.1-4.7%, respectively, and a pH from acidic (4) to neutral (7.1). Entomopathogenic nematodes were not recovered from crop fields (maize, cassava, groundnut and bean) and soil samples with less than 50% sand content. Heterorhabditis indica was associated with citrus orchards and fruit fields on sand to sandy clay soils, with pH slightly acidic (pH = 5.4-6.4), but not with woodland. Discriminant analysis identified five major environmental variables, longitude, organic matter content and texture (silt, sand and clay content) to be the most important abiotic factors detemining the occurrence of EPN in soil from Southern Benin. Using these parameters, redundancy analysis revealed that H. sonorensis and H. indica prefer soils with high sand or organic matter content located in the more eastern longitude. No significant difference was observed in EPN species preferences taken individually, in terms of studied ecological parameters