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)

Molecular diversity of Photorhabdus and Xenorhabdus bacteria, symbionts of Heterorhabditis and Steinernema nematodes retrieved from soil in Benin

The diversity of 43 bacterial strains isolated from Beninese entomopathogenic nematodes was investigated molecularly by analyzing the 16S rRNA, recA, and gyrB genes. Based on 16S rRNA sequence analysis, 15 bacterial strains were identified as Xenorhabdus sp., 27 strains as Photorhabdus sp., and one as Serratia sp. The Xenorhabdus strains were isolated from Steinernema nematodes and identified as Xenorhabdus indica based on 16S rRNA gene and concatenated recA and gyrB sequence analysis. However, analysis of 16S rRNA and concatenated recA and gyrB gene sequences of the Photorhabdus strains, all isolated from Heterorhabditis nematodes, resulted in two separate sub-clusters (A) and (B) within the Photorhabdus luminescens group, distinct from the existing subspecies. They share low sequence similarities with nearest phylogenetic neighbors Photorhabdus luminescens subsp. luminescens Hb(T), Photorhabdus luminescens subsp. caribbeanensis HG29(T), and Photorhabdus luminescens subsp. noenieputensis AM7(T)

Steinernema kandii n. sp. (Rhabditida: Steinernematidae), a new entomopathogenic nematode from northern Benin

Two nematode isolates from the genus Steinernema were collected in northern Benin. Morphological, morphometric, molecular and cross-hybridisation studies placed these nematodes into a new species, Steinernema kandii n. sp., within the bicornutum-group. Phylogenetic analyses based on both ITS and D2-D3 regions of 28S rDNA revealed that S. kandii n. sp. is different from all known Steinernema species and sister to S. abbasi (97.3-97.6% ITS nucleotide similarity) and S. bifurcatum (98.3-98.4% D2-D3 similarity). Steinernema kandii n. sp. can be separated from other members of the bicornutum-group by the greater infective juvenile (IJ) max. body diam. of 35 (27-48) mu m (type isolate). It differs from S. abbasi by the greater IJ body length 707 (632-833) mu m (type isolate), EP distance 55 (52-60) mu m (type isolate), spicule length 67 (57-75) mu m (type isolate) and the occurrence of one pair of genital papillae at the cloacal aperture

Evaluation of the ability of indigenous nematode isolates of Heterorhabditis taysearae and Steinernema kandii to control mango fruit fly Bactrocera dorsalis under laboratory, semi-field and field conditions in Northern Benin

We investigated the use of entomopathogenic nematodes to biologically control Bactrocera dorsalis in mango orchards. One isolate of Steinernema kandii (Thui) and two of Heterorhabditis taysearae (Hessa1 and Korobororou F4) were studied for their invasion time and virulence to third instar larvae of B. dorsalis in laboratory and semi field tests, respectively. In addition, the persistence of the same nematode isolates in soil under field conditions was tested. Results showed that all three nematode isolates could penetrate insect larvae after 2 h of exposure time. Furthermore, under semi field conditions, insect mortality was significantly different among EPN application times. The three nematode isolates were highly pathogenic to B. dorsalis with H. taysearae Hessa1 being the most virulent (70.84% +/- 10.46 [SEM] mortality) when EPNs were applied three days before insect introduction in the experimental pots. Moreover, Steinernema kandii persisted in soil up to 32 weeks after nematode application whereas both H. taysearae isolates persisted 30 weeks post application in the mango orchard. In general, four weeks upon nematode application, the density of infective juveniles decreased considerably and remained variable the following sampling dates