Assessment of biocontrol potential of different Steinernema species and their bacterial symbionts, Xenorhabdus species against larvae of almond moth, Ephestia cautella (Walker)

Abstract

The almond moth, Ephestia cautella is a serious pest of stored food commodities including dried figs, dates, raisins, cocoa beans. The control of E. cautella infestations in storage that mostly relies on toxic insecticides or fumigants has caused emergence of resistant pest populations as well as residues on the commodities. Entomopathogenic nematodes (EPNs) and their endosymbionts are one of the emerging approaches in eco-friendly pest management and pose no health risk to humans and the environment. Therefore, here we evaluated the toxicity of different EPN species (Steinernema feltiae, S. carpocapsae, and S. bicornotum) and their endosymbiotic bacteria (Xenorhabdus nematophila, X. bovienii, and X. budapestensis) on the 3rd and 4th instars larvae of E. cautella under controlled conditions. The IJs of EPNs were applied to concrete arenas in Petri dishes at three concentrations (50, 100, and 200 IJs/cm2). Oral and contact toxicity of the cell-free supernatants and cell suspension of symbiotic bacteria (4x107 cells/mL) were tested against both larval instars of E. cautella. Steinernema carpocapsae and S. feltiae induced mortalities over 80% at their lowest concentrations against both larval instars after 24 h of application. Oral and contact treatments of cell-free supernatants and cell suspensions were lethal for both larval instars; however, higher mortalities were generally obtained from direct exposure of larvae to cell-free supernatants and cell suspensions. The contact treatment of X. nematophila exhibited the highest virulence, causing 70 and 82.5% mortalities in 3rd and 4th instar larvae after 72 h of application, respectively. The anti-feedant activity of cell-free supernatants and cell suspensions was also observed in both instars in oral treatments. The findings of this study suggest that EPNs and their symbiotic bacteria have enormous potential for the eco-friendly control of E. cautella.