Influence of Different Species of Steinernema and Heterorhabditis on Galleria mellonella and Spodoptera littoralis

Abstract

Entomopathogenic nematodes (EPNs) can be used efficiently as biological control agents against specific insects. Galleria mellonella (Gm) and Spodoptera littoralis (Sl) are considered important agricultural pests. The aim of this study was to evaluate the susceptibility of their larvae to ascending levels of four species of EPNs, Steinernema carpocapsae (Sc), S. arenarium (Sa), Heterorhabditis bacteriophora (Hb) and H. indica (Hi) as well as the ability of nematodes to penetrate and reproduce within their hosts. Fifth larval instar of Gm and Sl were used to evaluate the effect of four inoculum doses [200,400,800, and 1600 infective juveniles (IJs)] of each nematode species. Percentage of insect mortality (% M) and the nematode-rate of reproduction (Rr) were calculated after 24 and 48 hrs. The data confirmed that H. bacteriophora was the highest effective species on both insects. The % M was 75.7, 79.7, 82.3, and 83% after 24 hrs and 98.0, 99.3,100 and 100% after 48 hrs in Gm for these doses, respectively. On the other hand, the corresponding mortalities were 75.0, 78.3, 81.7, and 83.8% after 24 hrs and 97.3, 98.3, 100 and 100% after 48 hrs in Sl. The highest initial EPN population that could penetrate the insect (pi) was achieved by Hb in Gm (295 IJs) at 1600 IJs, while it was 221.7 IJs in Sl larvae at the same inoculum. The highest final population and Rr were obtained at the inoculum level of 200 and 400 IJs. in Gm and Sl, respectively. The study documented that Heterorhabditis and Steinernema can be used effectively in Gm and Sl management. Moreover, Hb is the most suppressive species tested against the two lepidopteran hosts.