عزل وتشخيص النيماتودا الممرضة للحشرات في بعض محافظات العراق وتقييم قابليتها الامراضية ضد حشرة حفار اوراق الطماطة Tuta absoluta تحت الظروف المختبرية

Isolation and identification of Entomopathogenic nematodes in some Iraqi governorates and evaluation of their pathogenicity against the tomato leaf miner Tuta absoluta under laboratory conditions

Abstract

A survey study was conducted in some areas of Karbala Governorate and some neighboring governorates during the year 2023-2024 to investigate and detect the presence of entomopathogenic nematodes (EPNs) and isolate them from the soils of those areas. Sixteen sites were selected to isolate those entomopathogens, including citrus and palm orchards and others, including regions of Karbala Governorate (Al-Hussainiya, Al-Wand, Al-Hur Al-Saghir, Tawrij), Baghdad (Al-Yusufiyah, Al-Rashidiya, Al-Jadriya, Al-Taji, Abu Ghraib), Najaf Governorate (Kufa, Al-Abbasiya, Al-Hurriyah), Babylon Governorate (Sadd Al-Hindiya, Hamza Al-Gharbi), Diyala Governorate (Baqubah), and Al-Qadisiyah Governorate (Ghammas), with six samples for each area. Several chemical properties of soil samples were measured, including salinity EC, pH, and organic matter O.M. The study results for different soil samples showed that the salt concentration ranged between 0.1 – 8.22 mS/cm, the pH values ranged between 6.7 – 7.3, and the organic matter values ranged between 0.97 – 2.72%. The isolated and phenotypic diagnosis results supported by a molecular diagnosis of EPNs proved the presence of two species Oscheius myriophilus isolated from Baghdad Governorate (Al-Yusufiyah) and Al-Qadisiyah Governorate (Ghammas). The complete mitochondrial genome was obtained for the first time in Iraq using Next Generation Sequencing (NGS) technology. Also, the species Heterorhabditis indica isolated from Baghdad Governorate (Al-Rashidiyah) was obtained. One mitochondrial gene was obtained and registered in the World Gene Bank under the serial numbers PQ346375.1 and PQ324366.1, respectively.
The biological study included rearing the larvae of the greater wax worm Gelleria mellonella in the laboratory as a sensitive host to detect the presence of EPNs using the trap insect method. The results showed the presence of EPNs in the study areas (Al-Yusufiyah, Al-Rashidiyah, Al-Tajji, Hamza Al-Gharbi, and Ghammas) only.
It was found that the local isolates Oscheius myriophilus isolated from Al-Yusufiyah and Ghammas had high pathogenicity on the fourth instar larvae of the greater wax moth G. mellonella, as they achieved the highest larval mortality rate of 50-70% at a concentration of 10 Ijs/larva, while the isolates from Al-Rashidiyah, Hamza Al-Gharbi and Al-Tajji showed low pathogenicity as the mortality rates ranged between 10-30%. The results also showed that using local and commercial entomopathogenic nematodes to study their efficiency in controlling the third-stage larvae of the tomato leaf miner Tuta absoluta, through the pathogenicity of the local species in the regions of Ghammas and Youssefiya Oscheius myriophilus and the commercial Heterorhabditis bacteriophora and c Steinernema arpocapsae, where the local and commercial isolate of the species H. bacteriophora is very effective in mortality the third-stage larvae of the tomato leaf miner under laboratory conditions. Three concentrations were used, namely 100, 300, and 500 Ijs/ml larvae for each of the local and commercial isolates, where the highest percentage of larval killing was achieved, reaching 100% at a concentration of 500 Ijs after 5 days of treatment with the local isolate O. myriophilus and the commercial H. bacteriophora for the stage larvae. The third is for the tomato leaf miner, while the commercial isolate of the species S. carpocapsae showed low pathogenicity against the larvae of the tomato leaf miner, with a mortality rate of 30, 43, and 40%, respectively, after 5 days of treatment compared to the control treatment. The results also showed that the effectiveness of the plant insecticide Oxymatrine on the third-stage larvae of the tomato leaf miner T. absoluta was relatively weak, as it achieved the lowest mortality rate of 30%, 36%, and 40%, respectively, at concentrations of 1.8, 1.5, and 1 ml/L after 5 days of treatment compared to local and commercial isolates of EPNs.
The results showed the compatibility of local and commercial insect pathogenic nematode isolates at 100, 300, 500 Ijs/ml concentrations with the chemical insecticide Oxymatrine at concentrations of 1.8, 1.5, and 1 ml/l. The lowest rate of killing infectious stages (Ijs) was recorded, as the general rate of the local isolates of Ghammas and Al-Yusufiyah of the species O. myriophilus reached 19.86% and 23.19% respectively after 5 days of treatment with the pesticide, followed by the commercial isolate H. bacteriophora, as the general rate of killing infectious stages (Ijs) reached 21.25% after 5 days of treatment, followed by the commercial isolate S. carpocapsae, which was more sensitive to the chemical pesticide, as the killing rate of infectious stages reached 29.25% after 5 days of treatment. The local and commercial EPNs species recorded a decrease in the mortality rates of infectious stages when mixed with the pesticide with a reduction of the pesticide concentration at a concentration of half the field of 1.5 ml and less than half the field of 1 ml, i.e., a direct relationship. It is possible to match these pathogenic nematodes to insects and mix them with the plant-based pesticide Oxymatrine for the strongest synergistic effect in controlling insect pests.