The role of the different fermentation media and infection processes on the infectivity of the bacterial symbionts to Spodoptera littoralis (biosduval) (Lipedoptera: Noctuidae)

Abstract

Bacterial symbionts are one of the most toxic bacteria to insect pests. They have been isolated from the intestine of the entomopathogenic nematodes. Ten strains of the entomopathogenic nematodes, that may be different, have been isolated out of different soil fauna having different crops from different Governorates in Egypt. The bacterial symbionts in these strains have been isolated and tested for production parameters using four different media. Experiments showed that both Loria Broth (LB), and Nutrient Broth (NB) gave good results in laboratory production of bacterial symbionts, concerning stability, cell size, and pigment production during culturing. Experiments using different techniques of introducing the bacterial symbionts to larvae of the cotton leafworm showed that the injection technique was the most effective among all the tested techniques. This is followed by oral and forced feeding which seemed to give equal results. On the other hand, toxicity experiments showed that the four bacterial isolates named, G-NRC-A₃, SH-NRC-A₅, SH-NRC-A₆, and N.Sinai-NRC-A₈, besides the bacterial symbiont of Steinernema abbasi, Flavimonas oryzihabitans, all give 100% mortalities to Spodoptera littoralis larvae after 24 h post-treatment at the higher dose (5×10⁴ cells/10 μl) but at the lower doses 5×10³ and 5×10² cells/10 μl of injection solution, a 100% mortality was reached after 72 h post-treatment.