Comparative Vertical Migration of Three Different Strains of Heterorhabditis bacteriophora and a Single Strain of Heterorhabditis megidis in Sand at 25°C

Attila Sándor Csontos,Parwinder S Grewal,Michael G Klein

doi:10.34101/actaagrar/11/3444

Attila Sándor Csontos, Parwinder S Grewal + Show 1 more

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https://doi.org/10.34101/actaagrar/11/3444

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Abstract

Heterorhabditis bacteriophora and Heterorhabditis megidis) were tested for downward migration in 9.5 cm vertical sand columns at 25°C with and without a larva of the wax moth, Galleria mellonella, at the bottom. The number of infective juveniles (IJs) in the upper section decreased since the IJs gradually migrated down toward the Galleria larvae into the lower section of the shell vials. Only the isolate OH 25 behaved differently, because the number of IJs decreased this isolate in the lower section. This isolate was the quickest, since after 12 hrs, most IJs could be found in the lower section of the vials from this isolate. The number of IJs was so small in the lower section that 12 hrs after injection, only the isolates MHG 3 and OH 25 could kill the Galleria larvae.Besides the fact that mortality occurred among the Galleria larvae with the above isolates, neither IJs nor adults could be detected in either living or dead Galleria larvae 12 hrs after IJ injection. It is noteworthy that the behavior of the isolate Megidis was different from the other isolates: the number of IJs was so negligible in the lower section of the vials that even after 36 hrs none of the Galleria died and, consequently, neither adults nor IJs could be detected after dissecting the Galleria larvae. Each isolate could reach the lower section of the vials, yet only the isolate Megidis could not infect and kill the host. After dissecting the larvae, most IJs and adults could be found in the isolate MHG 3 (95 IJs and adults altogether) 36 hrs after injection.

Highlights

Laboratory studies show that nematodes respond positively to many chemical stimuli produced by insects (Gaugler et al, 1980)
It is noteworthy that the behavior of the isolate Megidis was different from the other isolates: the number of infective juveniles (IJs) was so negligible in the lower section of the vials that even after 36 hrs none of the Galleria died and, neither adults nor IJs could be detected after dissecting the Galleria larvae
The number of IJs recovered in the lower section in most of the isolates increased as time went by

Summary

Introduction

Laboratory studies show that nematodes respond positively to many chemical stimuli produced by insects (Gaugler et al, 1980). Many factors influence nematode movement in soil. The most important factors are soil texture (Georgis and Poinar, 1983), temperature (Steiner, 1996), behavior of the nematode species (Grewal et al, 1994), genetic differences of species and strains (Glazer et al., 1991), presence or absence of a host (Molyneux, 1983) and moisture (Molyneux and Bedding, 1984). There are many stimuli that play an important role in the host-finding tactic of the nematodes, it seems that neither of the stimuli is predominant, but rather more stimuli influence and integrate together this process (Gaugler et al, 1980). The host-finding tactic of entomopathogenic nematodes can be “cruiser” (actively searching foragers), “ambusher” (sit-and-wait foragers) or “intermediate” (Kaya and Gaugler, 1993). Direct response to host chemical cues (Lewis et al, 1992), active dispersal and an inability to nictate are the characteristics of cruisers, such as Heterorhabditis bacteriophora (Poinar) and Heterorhabditis megidis (Poinar), whereas less dispersing activity and active nictating are characteristic features among ambushers (Campbell and Gaugler, 1993)

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