Oviposition-Site Selection of Phlebotomus papatasi (Diptera: Psychodidae) Sand Flies: Attraction to Bacterial Isolates From an Attractive Rearing Medium

Abstract

Phlebotomine sand flies are worldwide vectors of Leishmania parasites as well as other bacterial and viral pathogens. Due to the variable impact of traditional vector control practices, a more ecologically based approach is needed. The goal of this study was to isolate bacteria from the most attractive substrate to gravid Phlebotomus papatasi Scopoli sand flies and determine the role of bacterial volatiles in the oviposition attractancy of P. papatasi using behavioral assays. We hypothesized that gravid sand flies are attracted to bacterially derived semiochemical cues associated with breeding sites. Bacteria were isolated from a larvae-conditioned rearing medium, previously shown to be highly attractive to sand flies. The isolated bacteria were identified by amplifying and sequencing 16S rDNA gene fragments, and 12 distinct bacterial species were selected for two-choice olfactometer bioassays. The mix of 12 bacterial isolates elicited strong attraction at the lower concentration of 107 cells per ml and significant repellence at a high concentration of 109 cells per ml. Three individual isolates (SSI-2, SSI-9, and SSI-11) were particularly attractive at low doses. In general, we observed dose-related effects, with some bacterial isolates stimulating negative and some positive dose–response curves in sand fly attraction. Our study confirms the important role of saprophytic bacteria, gut bacteria, or both, in guiding the oviposition-site selection behavior of sand flies. Identifying the specific attractive semiochemical cues that they produce could lead to development of an attractive lure for surveillance and control of sand flies.

Microbial ecology of sand fly breeding sites: aging and larval conditioning alter the bacterial community composition of rearing substrates

“…Eggs are typically laid in soil rich in organic material on which the larvae feed and develop through four instars before pupation and adult emergence [ 15 ]. The coprophagic diet of larvae is consistent with the strong preference of New and Old World sand flies for different sources of decomposing organic matter, often from fecal sources [ 16 – 19 ], and there is strong evidence that microbes play an important role in mediating this attraction [ 20 , 21 ]. There is also some evidence that bacteria are beneficial for the development of larvae [ 20 ], but this concept is still poorly understood.…”

“…It is possible that larval conditioning leads to a decrease in the relative abundance of bacteria that are unattractive or even repellent and/or to an increase in the relative abundance of bacteria that are attractive to sand flies. In a previous study, Kakumanu et al [ 21 ] identified three bacterial isolates ( Microbacterium sorbitolivorans , Bacillus zhangzhouensis , Sphingobacterium phlebotomi ) that were highly attractive to sand flies at low concentrations but were repellant at high concentrations. In contrast, Sphingobacterium daejeonense was repellent at low concentration but tended to be attractive (but not significantly so) at high concentrations.…”

“…Consistent with this hypothesis was the finding that some bacteria isolated from larval conditioned substrates [ 19 ] were highly attractive to gravid Ph. papatasi females [ 21 ]. Specifically, three individual isolates ( Microbacterium sorbitolivorans , Bacillus zhangzhouensis , Sphingobacterium phlebotomi ) were particularly attractive at low doses.…”

“…Specifically, three individual isolates ( Microbacterium sorbitolivorans , Bacillus zhangzhouensis , Sphingobacterium phlebotomi ) were particularly attractive at low doses. Similarly, a mixture of 12 bacterial isolates was also attractive at low doses but at high doses was highly repellant [ 21 ]. Although informative, this study [ 21 ] was based on only a few culturable isolates and therefore, did not represent the entire bacterial community of the substrates.…”

“…Similarly, a mixture of 12 bacterial isolates was also attractive at low doses but at high doses was highly repellant [ 21 ]. Although informative, this study [ 21 ] was based on only a few culturable isolates and therefore, did not represent the entire bacterial community of the substrates. Furthermore, the bacterial community structure among conditioned and aged substrates or the changes within each over time has not been compared.…”