By Marineide M. Aguillera
Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philisophy. August 1992
The bacteria Xenorhabdus spp., X. bovienii, Pseudomonas aureofaciens, Ochrobactrum anthropi, Xanthomonas maltophilia and an unknown genus characterized as a Gram-negative coccus related to Paracoccus denitrificans, were associated symbiotically with third-stage infective juveniles of the entomopathogenic nematode Steinernema scapterisci. First stage juveniles which hatched from sterilized eggs developed to adults and reproduced on cultures of each of the bacteria. The nematode also developed and reproduced on cultures of Xenorhabdus nematophilus, a symbiont of S. carpocapsae, and on cultures of Pseudomonas f luorescens and Escherichia coli. The life cycle (egg to egg) was completed in four days on all bacteria except E. coli, on which it took five days. Reproduction was excellent on P. aureofaciens (> 6,400-fold) , X. nematophilus (> 5,900-fold), and P. fluorescens (> 3,900fold). All the infective juveniles examined retained bacteria (5 to 60 cells per infective juvenile) in the intestinal vesicle regardless of the origin of the bacteria.
All Xenorhabdus species, P. aureofaciens, and E. coli were pathogenic to a mole cricket, Scapteriscus borellii or to the house cricket, Acheta domesticus. No differences occurred in mortality of S. borellii whether infective juveniles of S. scapterisci were reared in vivo or on monoxenic cultures with 0. anthropi, P. aureofaciens, X. nematophilus or an unknown coccus (genus undetermined).
Of three culture media tested, production of S. scapterisci on X. nematophilus was best in a semi-solid dog food medium, producing an average of 3.8 x 101 juveniles/ml medium (96.7% infective juveniles) from an initial inoculum of 200 nematodes/ml.
The LD50 of S. scapterisci to Scapteriscus spp. was 4,000 infective juveniles, whereas the LD 50 to a field cricket, Gryllus rubens, and the lubber grasshopper, Romalea guttata, was 1,000 infective juveniles.
The ability of S. scapterisci to reproduce and retain cells of several bacteria and to be as pathogenic to insects while having various bacterial associations, may contribute to its chances to survive in nature and compensate for the low number of bacterial cells retained by infective juveniles.