Abstract
The study aimed to evaluate the efficacy of the EPNs against the larvae of Egyptian cotton leaf worm Spodoptera littoralis (Boisduval) and the black cutworm Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) in vitro before in vivo study. The susceptibility of both larval species to the entomopathogenic nematode species, Steinernema monticolum and Heterorhabditis bacteriophora, was evaluated under laboratory conditions. The concentration of 400 IJs/dish for S. monticolum achieved up to 97.77 and 95.55% mortality rates of the 5 larval instars from 2nd to 6th instars of S. littoralis and A. ipsilon, respectively after 72 h. The concentration of 800 IJs/dish recorded larval mortality rates of 41.86 to 100% against 2nd to 6th instars of A. ipsilon larvae, after 72 h. At the lowest concentration (50 IJs/dish), the larvae of S. littoralis were more susceptible to H. bacteriophora than the larvae of A. ipsilon. The data indicated that 200 IJs/dish was the most effective concentration for all larval stages of both insect pests because the mortality percentage was 100%.
Highlights
The Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.), and the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), are the most important insect pests on many crops as they cause economic losses (El-Sheikh et al 2013)
Extensive studies have been conducted in the field of biological control of insect pests, using many bio-control agents such as entomopathogenic nematodes (EPNs)
Susceptibility of immature stages of S. littoralis and A. ipsilon to EPNs The bioassay of Steinernema monticolum The data obtained from Table 1 show that the susceptibility of S. littoralis 2nd larval instar to infection with the nematode S. monticolum, after 72 h with the concentrations 50, 100, 200, 400, 800, and 1600 infective juveniles (IJs)/dish, was 77.78, 83.33, 88.66, 91.11, 100, and 100% of percentage mortalities, respectively
Summary
The Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.), and the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), are the most important insect pests on many crops as they cause economic losses (El-Sheikh et al 2013). The Heterorhabditidae and Steinernematidae families live in soils and are deadly parasites to a wide range of insects (Stuart et al 1997; Orozco R.A. et al 2014). They are environmentally safe agent as they do not cause any harmful effects either to humans or farm animals and are beneficial insects (van Zy C. and Malan A.P. 2014). Heterorhabditidae and Steinernematidae have a symbiotic association with the entomopathogenic bacteria genera Photorhabdus and Xenorhabdus, respectively, and both effectively parasitize and kill their insect hosts (Ehlers 2001). The bacteria grow rapidly in the hemolymph of insect host and produce toxins that kill the host by means of inducing septicemia within 24 to 72 h of infection (Ehlers 2001 and Griffin et al 2005). The application of EPNs is widespread in many parts of the world and could be grown experimentally in large quantities at relatively low costs (Shapiro-Ilan et al 2006 and Mutegi et al 2018)
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