Efficacy of native isolates and commercial products of two entomopathogenic nematode species on model host, Tenebrio molitor (Coleoptera: Tenebrionidae) larvae

Document Type : Complete paper

Authors

1 Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

2 Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran, Iran

3 Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran.

Abstract

Entomopathogenic nematodes are valuable biocontrol agents of pests. The use of indigenous isolates compared to imported isolates has advantages including compatibility with the environment and native pests and not causing adverse effects on indigenous species. In the present study, the effect of native isolates of Steinernema carpocapsae and Steinernema feltiae on model host, Tenebrio molitor was compared with exotic commercial products by two bioassay methods (in Petri dishes and soil). Probit analysis showed a significant correlation between the nematode concentrations and the insect mortality (R2 ≥ 0.90). The Iranian S. carpocapsae isolate showed the lowest LC50 value (5 IJ Larva-1) and the commercial S. feltiae isolate showed the highest LC50 value (7 IJ Larva-1). However, based on the LC50 ratio values there was no significant difference between the four nematode isolates. The comparison of the mortality percentage of the pest in soil bioassay showed a similar effect of native isolates with commercial isolates (P ≤ 0.01). The impact of native nematode isolates on par with commercial isolates which had been selected among numerous isolates, showed their high potential Therefor, basic research with the aim of developing the practical application of these valuable agents is suggested.

Keywords

Main Subjects

Extended Abstract

Entomopathogenic nematodes (EPNs) form Steinernematidae and Heterorhabditidae are valuable biological control agents of the insect pests. EPNs are effective against a wide range of insect pests, including those that live in the soil, on plant surfaces, and in plant tissues. Those nematodes are a promising tool for biological control of insect pests in various settings, including sustainable food production and turf management. Exotic/imported and native/ indigenous isolates of entomopathogenic nematodes (EPNs) have been studied for their potential as biocontrol agents against insect pests in various regions. The use of native isolates compared to imported isolates has advantages including compatibility with the environment and native pests and not causing adverse effects on indigenous species. In the present study, the effect of native isolates of Steinernema carpocapsae and Steinernema feltiae on model host, Tenebrio molitor was compared with exotic commercial products by two bioassay methods (in Petri dishes and soil). In Petri dish assay, based on preliminary experiments a range of 25 - 200 IJs per ml (i.e., 25. 50, 100, 150 and 200 IJs) was used. Infective juveniles were added in 1 ml distilled water to the glass Petri dishes (9 cm diameter) lined with filter paper and 15 T. molitor larvae (average weight 100±2 mg) were placed in each petri dish. The control received 1 ml distilled water without nematodes. A piece of fresh potato was used as feeding source which was renewed daily. Soil bioassay experiments were conducted in Plastic cylindrical dishes (5 cm height and 3 cm diameter) which were filled with 20 g autoclaved sandy soil. Infective juveniles (400 IJs i.e., 80 IJs cm-1) were added in 500µl of water to the surface of the soil. Finally, four larvae (average weight 100±2 mg) were placed on the soil and the dishes were covered with ventilated lids to avoid desiccation. Control dishes received 500µl distilled water without nematodes. A total of 20 insect larvae (i.e. five dishes) were used for each treatment and control in each replication. Both of the Petri dish and soil bioassays were conducted for all four nematode isolates and repeated three times. The dishes were kept at 25±2 °C, 75 ± 5% RH and 16:8 (L:D) photoperiod for four days, then the mortality of the insects was recorded. All dead insects were collected and dissected to ensure presence of nematodes inside the cadavers. LC10, LC50 and LC90 values were obtained by Probit analysis using SAS software. Analysis of variance was done and the means were evaluated by Duncan’s multiple-range test (SAS Institute 2012). For comparison of LC values lethal dose ratios were used (Russell et al. 2007). Probit analysis showed a significant correlation between the nematode concentrations and the insect mortality (R2 ≥ 0.90). The Iranian S. carpocapsae isolate showed the lowest LC50 value (5 IJ Larva-1) and the commercial S. feltiae isolate showed the highest LC50 value (7 IJ Larva-1). However, based on the LC50 ratio values there was no significant difference between the four nematode isolates. Analysis of variance of the results of the soil bioassay showed a significant effect of all four isolates compared to the control (df=4, 8; F value=107.29, P ≤ 0.01). However, comparison of the mortality percentage showed a similar effect of native isolates with commercial isolates (P ≤ 0.01). Although the comparison of the average between isolates indicated that there was no significant difference between the lethality of different isolates. Similarity of the effect of native and exotic isolates against pests has been confirmed in other studies. For example, Lacey et al. (2001) reported that native isolates of EPNs in the Azores archipelago in the Atlantic Ocean were as effective as exotic isolates against the Japanese beetle. Although the yellow mealworm is one of the important pests of stored products in Iran and other parts of the world, it is widely used as a model and laboratory host for microbial agents and EPNs (de Souza et al. 2015) that simulates the sensitivity of the wireworms to the pathogens. The efficiency of Iranian isolates as much as commercial isolates in this study shows the high potential of native isolates in controlling native pests of the country. The impact of native nematode isolates on par with commercial isolates which had been selected among numerous isolates, showed their high potential and the results of this study emphasize the necessity of basic research with the aim of developing the practical application of these valuable agents.

References

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BIOLOGICAL CONTROL OF PESTS AND PLANT DISEASES
Volume 11, Issue 2
January 2024
Pages 57-67

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