Persistence of two Salmonella enterica ser. Montevideo strains throughout horn fly (Diptera: Muscidae) larval and pupal development

Authors: Olafson, Pia; Temeyer, Kevin; Lohmeyer, Kimberly - Kim; Edrington, Thomas; LONERAGAN, GUY - Texas Tech University

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2016
Publication Date: 1/1/2017
Citation: Olafson, P.U., Temeyer, K.B., Lohmeyer, K.H., Edrington, T.S., Loneragan, G. 2017. Persistence of two Salmonella enterica ser. Montevideo strains throughout horn fly (Diptera: Muscidae) larval and pupal development. Annals of the Entomological Society of America. 110(4):54-60.

Interpretive Summary: Strains of Salmonella enterica can be subdivided into groups that differ in their genetic composition, including genes that influence microbial ecology and bacterial transmission. Salmonella 1110 and 304 are two representatives from different groups, and these strains were used throughout this study to evaluate interactions between the bacteria and the various stages of horn fly development. Sterilized cattle dung was inoculated with Salmonella monocultures, and horn fly larvae were exposed to a low, medium and high concentration of each strain. Salmonella can support development of horn fly immature stages, and concentration-dependent differences in larval and pupal survival suggested that Salmonella 304 is toxic when larvae are reared in a high concentration. Larvae were then reared on sterilized cattle dung inoculated with a medium or high concentration, and viable bacteria were quantified from larvae, pupae, and newly emerged adults. Both strains survived pupation, and quantities of Salmonella 1110 were stationary through the mid-pupal stage, after which quantities declined in pupae reared in the medium concentration and increased 2-fold in pupae reared in the high concentration. Quantities of Salmonella 304 remained stationary throughout pupal development when reared in the medium concentration, yet increased 23-fold when reared in the high concentration. At high densities, properties of Salmonella 304 may influence its interaction with horn fly larvae, enabling the bacteria to evade degradation when the larval gut is being destroyed and to subsequently proliferate during the late stages of pupal development. These may account for the observed toxic effect on both larval and pupal survival. The Salmonella strains were rarely cultured from newly emerged adults, indicating that Salmonella present in larvae and pupae are not efficiently transferred to the adult stage.

Technical Abstract: Strains of Salmonella enterica can be subdivided into clades that differ in their composition of genes, including those that influence microbial ecology and bacterial transmission. Salmonella serovar Montevideo strains 1110 and 304, representatives of two different clades, were used throughout this study to evaluate interactions with the various stages of horn fly development. Sterilized cattle dung was inoculated with Salmonella monocultures, and horn fly larvae were exposed to 103, 105, and 107 CFU/g per strain. Salmonella can support development of horn fly immature stages, and concentration-dependent differences in survival suggested that Salmonella 304 is toxic when larvae are reared in a high concentration. Larvae were then reared on sterilized cattle dung inoculated with either 105 or 107 CFU/g, and viable bacteria were quantified from larvae, pupae, and newly emerged adults. Each strain was cultured from larvae at a mean ~105 regardless of strain or concentration. Both strains survived pupation, and quantities of Salmonella 1110 were stationary through the mid-pupal stage, after which quantities declined in pupae reared in 105 CFU/g and increased 2-fold in pupae reared in 107 CFU/g. Quantities of Salmonella 304 remained stationary throughout pupal development when reared in 105 CFU/g, yet increased 23-fold when reared in 107 CFU/g. At high densities, properties of Salmonella 304 may influence its interaction with horn fly larvae, enabling the bacteria to evade degradation during larval gut histolysis and to subsequently proliferate during the late stages of pupal development. These may account for the observed toxic effect on both larval and pupal survival. The Salmonella strains were rarely cultured from newly emerged adults, indicating that transstadial carriage to the adult stage is inefficient.