Isolating entomopathogenic nematodes from overwintering sites of Sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae) and their pathogenicity power against the pest

Document Type : Complete paper

Authors

• Laleh Ebrahimi ¹
• Maryam Forouzan ²
• Shahla Bagheri Matin ³
• Mohammad Nateq Golestan ⁴
• Mir Reza Jamshid ⁵
• Alireza Haghshenas ⁶
• Shahram Shahrokhi Khaneghah ⁷

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

² 2. Plant Protection Research Department, West Azarbaijan Agricultural and Natural Resources Research and Education Center, AREEO, Urmia, Iran

³ 3. Plant Protection Research Department, Kermanshah Agricultural and Natural Resources Research and Education Center, AREEO, Kermanshah, Iran

⁴ 4. Plant Protection Research Department, Khorasan Razavi Agricultural and Natural Resources Research and Education Center, AREEO, Mashhad, Iran

⁵ 5. Plant Protection Research Department, Lorestan Agricultural and Natural Resources Research and Education Center, AREEO, Khorram Abad, Iran

⁶ 6. Plant Protection Research Department, Isfahan Agricultural and Natural Resources Research and Education Center, AREEO, Isfahan, Iran

⁷ 7. Sunn Pest Research Department, Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

Abstract

Keywords

• native isolate
• Steinernema feltiae
• recycling
• biological control
• LC50

Main Subjects

• Biocontrol of pests

Extended Abstract

Introduction

     Entomopathogenic nematodes (EPNs) are valuable agents of pest biological control. These nematodes are obligate parasites of insects and some other arthropods that, with the help of their symbiotic bacteria, cause the death of their hosts within 48 hours. The Sunn pest, Eurygaster integriceps is one of the most economically important insect pest of wheat and barley. Relying on chemical pesticides in controlling plant pests, in addition to issues related to the occurrence of resistance in pests and increasing the dosage of chemicals and their economic effects, has irreparable effects on the environment and non-target organisms. Therefore, it is necessary to find alternatives to control this pest. Based on the general biology and overwintering behavior of the pest, natural enemies may have an important role in decreasing the population’s level in overwintering sites. The aim of this research was to isolate entomopathogenic nematodes from the soil of the overwintering sites of E. integriceps and evaluate their efficacy against the adult pest.

Method

      In a survey of EPNs in the overwintering sites of sunn pests in Tehran, Lorestan, Kermanshah, Isfahan, West Azarbaijan and Razavi Khorasan provinces for two years (2021-2022), EPNs were isolated using the Galleria-baiting method. Male and female nematodes were collected from five days-infected Galleria cadavers dissected in distilled water. Infective juveniles (IJs) of the nematodes were collected after emergence from Galleria cadavers in White traps. Based on the results of preliminary tests, Lorestan1 isolate was used for the main assay experiments against overwintering adult E. integriceps. Briefly, the experiments were conducted in Petri dishes (nine diameters) which were filled with a fine layer of autoclaved moist sandy soil. Based on the preliminary bioassay results a range of 100-600 IJs per insect was used. IJs were added in certain concentrations in one ml of water to the surface of the soil, separately. Finally, 15 adult insects and 20 wheat grain were placed on the soil. Control received one ml of distilled water without nematodes. The dead and alive insects were counted after four days. The experiment was replicated three times. All dead insects were collected and dissected to ensure presence of nematodes inside the cadavers.

Results

    Sampling from the regions and trapping the sampled soils with G. mellonella larvae led to the isolation of eight EPN isolates. The percentage of positive samples was calculated as 2.2 %. According to the morphological and morphometric measurements, all the isolates identified as Steinernema feltiae with some variations especially in body length. Based on the bioassay results, the values of LC_10, LC₅₀ and LC₉₀ of Lorestan1 S. feltiae isolate were calculated as 98.13, 461.14 and 2167 IJ insect^-1, respectively. Reproduction of the EPNs within the dissected cadavers was observed. In general, temperature, soil texture, soil pH, altitude above sea level, and annual rainfall are among the characteristics that affect the occurrence of the EPNs, although there are other factors as well which could be involved. The percentage of positive samples in soil sampling around the world is reported between 4 and 30% (Abd-Elgawad, 2021; Yuksel & Canhilal, 2019). According to the fact that in this study, soil sampling was carried out from the overwintering sites (altitudes above 1500 meters above sea level) and on the other hand, these samplings were done during the winter or early spring, the range of suitable conditions for capturing the nematodes was much limited. Few studies have been investigated the effect of these nematodes against E. integriceps in the world. Canhilal et al. (2007) reported LC₅₀ values ​​for H. bacteriophora, S. carpocapsae and S. riobravae as 107.1, 66.6 and 65.3 IJ insect^-1, respectively. While this amount for the Iranian S. feltiae isolate was equal to 461.4 nematode infecting larvae per insect.

Conclusions

In overall, eight entomopathogenic nematode isolates were isolated and identified from 360 soil samples of Sunn pest overwintering sites in six provinces of the country from an altitude of 1790 to 2250 m above sea level. All isolates belonged to the species S. feltiae. The efficacy of S. feltiae Lorestan1 against Sunn pest adults was evaluated and the LC₁₀, LC₅₀ and LC₉₀ were calculated. Successful recycling the nematode through the cadavers is a worth attribute for biocontrol agents, however, more researches are needed for understanding the probable role of EPNs in control of E. integriceps. Moreover, the isolates could be assessed to control the other pests.