Is there any relationship between the effectiveness of some Heterorhabditis bacteriophora isolates on the host and their average penetration rate?

Abstract

Entomopathogenic nematodes, such as Heterorhabditis bacteriophora, have been widely recognized for their potential in biological control strategies to manage agricultural pests effectively. This study aimed to evaluate the penetration rate and efficacy of different H. bacteriophora isolates, including two isolates (HB4 and HBNL) and a hybrid strain (HBH), against Tenebrio molitor L. (Col: Tenebrionidae) adults. The research also aimed to determine whether there was a correlation between the mortality caused by these isolates and their penetration. These isolates were applied to T. molitor adults at different concentrations 0.78 IJs (infective juveniles)/cm² (50 IJs/Petri dishes), 1.57 IJs/cm² (100 IJs/Petri dishes), 2.36 IJs/cm² (150 IJs/Petri dishes), 3.14 IJs/cm² (200 IJs/Petri dishes), 3.93 IJs/cm² (250 IJs/Petri dishes), 7.86 IJs/cm² (500 IJs/Petri dishes), 11.8 IJs/cm² (750 IJs/Petri dishes), 15.72 IJs/cm² (1000 IJs/Petri dishes), 19.66 IJs/cm² (1250 IJs/Petri dishes). Another objective of the study was to observe the penetration rate means of these nematodes at consistent concentrations and record the resulting mortality rates. The findings revealed that the highest mortality rate of 100% was achieved at concentrations of 250, 500, 750, 1000, and 1250 IJs/Petri dishes. The HBH hybrid strain also exhibited the highest penetration rate mean of 20.33 IJs at a concentration of 1250 IJs/Petri dishes. These results highlight the efficacy of H. bacteriophora isolates and the hybrid strain in controlling T. molitor adults, with significant mortality rates observed at higher nematode concentrations. The study's emphasis on penetration rate means and the relationship between nematode concentration and pest mortality underscores the importance of optimizing entomopathogenic nematode applications for effective pest management.