Genetic variability among three Egyptian isolates of Heterorhabditis indica using a new marker technique (SCoT)

Background Entomopathogenic nematodes (EPNs) are a group of nematode families, have the ability to search for their hosts, and are considered as promising biological control candidates for insect pests, providing protection to non-target organisms and the environment. Results This study was conducted to isolate indigenous EPN isolates from Egyptian agricultural soils for further use in biological control programs and study their genetic polymorphism among the previously isolated isolates under accession no. MH553167 and MK300683 and the new isolate (MH496627), using the start codon targeted (SCoT) marker. One out of 15 soil samples obtained from a banana cultivated field was positive for the presence of EPNs, using the Galleria baiting method. Morphological analysis and sequencing of the internal transcribed spacer (ITS) region suggested that the isolate obtained belongs to Heterorhabditis indica. The sequence of the ITS was submitted to the National Center for Biotechnology Information (NCBI) and registered under accession no. MH496627. Ten SCoT primers were used in the study; the polymorphic bands were 68 out of 76 with 89% as polymorphism percentage. The highest numbers of bands were 10 bands generated by SCoT 1 and SCoT 18 while SCoT 48 and SCoT 60 recorded the lowest band number (5 bands). Conclusions The present study is considered as a preliminary study to demonstrate the effectiveness of the SCoT marker for the first time in assessing genetic relationships in EPNs.

PERFORMANCE OF ENTOMOPATHOGENIC NEMATODES ON NEOLEUCINODES ELEGANTALIS (GUENÉE) (LEPIDOPTERA: CRAMBIDAE)

The use of entomopathogenic nematodes in pest management is an alternative to reduce the yield and/or damage losses caused by pests in several crops. The present study aimed to evaluate the performance of Heterorhabditis indica (Nemata: Rhabditida) and Steinernema carpocapsae (Nemata: Rhabditida), in pre-pupae of Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae) and determine the temporal viability of the pathogenicity of S. carpocapsae applied to soil. The nematode species were diluted in distilled water to 50, 65, 83, 107, 138, 178, 229, 295, 380 and 500 infective juveniles per pre-pupae (IJs insect-1) of N. elegantalis. The mortality of pre-pupa of N. elegantalis was higher as the concentrations of both studied species increased. The nematode S. carpocapsae was the most effective, causing mortality of 82.93% in the concentration of 65 IJs insect-1 and an LC50 of 24.32 IJs insect-1. In the pathogenicity test, S. carpocapsae was applied in the concentration of 100 JI/cm² in pots previously planted with tomato seedlings. As positive control was used tomato seedlings treated with distilled water. S. carpocapse presented soil viability of 24 days. Thus, S. carpocapsae can be an important tool in the integrated pest management (IPM) of N. elegantalis.

Native Philippine Heterorhabditis indica isolates from banana and rice fields and preliminary results of their virulence against the larvae of super worm (Zophobas morio Fabricius Coleoptera: Tenebrionidae)

Background Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae are used as biological control agents of several insect pests in lieu of synthetic pesticides. Results Using an insect-baiting technique, naturally occurring EPN isolates were collected from banana and rice fields in the municipality of Hagonoy, the Philippines. A total of 4 isolates were recovered from all the sites namely, HBP1, HBP2, HR3 and HR4. By combining morphometrical and ITS rDNA data, all the isolates were identified as Heterorhabditis indica. To initially assess their infectivity, virulence tests were conducted on the last instar larvae of the super worm, Zophobas morio Fabricius (Coleoptera: Tenebrionidae), the model insect. HR3 isolate had the highest percentage mortality (56%), followed by HBP1 and HBP2 (33%), which were comparable to the available nematode in the market, Heterorhabditis bacteriophora (44%), whereas the lowest was obtained in HR4 isolate (11%). Conclusions This study accounted 4 more H. indica isolates in addition to pre-existing isolates in the country, expanding its habitat range and geographic distribution. This also provides baseline information on the potential biocontrol utilization of native EPNs against soil-dwelling insect pests of agricultural crops. Further investigations are required to assess their efficacy against several other insect pests of economic importance for the integrated pest management (IPM) programmes in the country.