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 or pupa with the Heterorhabditis isolates giving the greatest multiplication rate (59577.2 IJs ± 14307.41).

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