Laboratory studies of bacteriophagous nematodes as potential vectors of insect pathogens Public Deposited

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  • Three species of bacteriophagous nematodes, Pristionchus lheritieri (Maupas) Paramanov, Pelodera chitwoodi (Bassen) Dougherty and Rhabditis sp. were studied to determine their potential roles as vectors of selected insect pathogens, Bacillus thuringiensis Berliner, Beauveria bassiana (Balsamo) Vuillemin, Metarrhizium anisopliae (Metchnikoff) Sorokin and a nuclear polyhedrosis virus of Trichoplusia ni Hubner. Chlorine tolerances were established for P. lheritieri, P. chitwoodi and Rhabditis sp. Investigations established that B. thuringiensis was more susceptible to the action of chlorine than the nematodes. Feeding studies provided evidence that B. thuringiensis is an unsatisfactory monoxenic associate of P. lheritieri. Chlorination treatments following feeding of B. thuringiensis allowed the development of evidence that all three nematode species do ingest and defecate B. thuringiensis in a viable condition. It was demonstrated that P. lheritieri and Rhabditis sp. retained viable B. thuringiensis up to 36 and 42 hr respectively. P. lheritieri and Rhabditis sp. continued to defecate viable B. thuringiensis up to 33 and 36 hr respectively. Attempts to infect T. ni directly with B. thuringiensis fed nematodes failed. Subcultures of B. thuringiensis defecated by P. lheritieri retained their pathogenicity to T. ni, The insect pathogenic fungi B. bassiana and M. anisopliae proved to be more susceptible to the action of chlorine than the bacteriophagous nematodes. The studies indicate that B. bassiana and M. anisopliae are not a preferred food source for P. lheritieri. Evidence for ingestion of M. anisopliae by P. lheritieri was not obtained. Results failed to demonstrate defecation of viable spores of either fungus. Viable spores of B. bassiana were recovered from the gut of P. lheritieri and subcultured. The subcultured B. bassiana retained pathogenicity to larvae of T. ni. P. lheritieri were positively attracted to and actively fed on the cadavers of nuclear polyhedrosis killed T. ni larvae. Single nematodes, after feeding on T. ni larvae killed by virus, transmitted the virus to cabbage loopers. The nuclear polyhedrosis virus of T. ni proved to be less susceptible to chlorination treatments than the bacteriophagous nematodes. Evidence for active ingestion of virus particles by the nematode was developed by obtaining inoculum suspensions from nematodes which had been exposed to a virus source for various periods of time. A bioassay of these suspensions revealed an apparently greater virulence in those suspensions produced from nematodes having a longer access to virus. These studies provided evidence that bacteriophagous nematodes can have an important role in insect disease development in nature. The nematodes acquired viable fungus, bacterial, and virus pathogens by active ingestion. They retained and actively disseminated bacterial pathogens over an adequate period of time. A fungus pathogen retained virulence after ingestion by the nematode and a bacterial pathogen retained viability and pathogenicity after passage through the nematode gut. A single nematode transmitted enough virus inoculum to cause disease in the insect host. Of the nematode-pathogen associations studied, the intensely virulent nematode-virus complex demonstrated potential for biological control utilization. These factors, added to the mobility, habits, and known insect associations of bacteriophagous nematodes, enhance our understanding of the potential roles of these nematodes in insect disease development.
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