Attraction and oviposition preferences of Phlebotomus papatasi (Diptera: Psychodidae), vector of Old-World cutaneous leishmaniasis, to larval rearing media

Abstract

BackgroundAs part of a project aimed at developing oviposition attractants for the control and surveillance of Phlebotomus papatasi (a vector of Old-World cutaneous leishmaniasis), we tested the hypothesis that gravid sand flies are attracted to chemical cues emanating from the growth medium of conspecific larvae - predominantly larvae-conditioned host feces that represents a suitable oviposition site. We report the results of a systematic assessment of media from various developmental stages of the sand fly using oviposition and olfactometer behavioral assays.MethodsWe conducted multiple-choice oviposition assays in 500 mL Nalgene jars. Six treatments were placed on separate filter paper discs at the bottom of the jar: 2nd/3rd larval instar medium, 4th larval instar/pupae medium, frass from expired colonies, larval food (aged rabbit chow and rabbit feces mix), rabbit feces, and a solvent (water) control. Fifty gravid females were introduced into each jar. Cumulative number of eggs laid on each filter paper per jar was counted at different time intervals from digital images. Attraction of gravid sand flies to these six treatments was assayed with a 3-chamber linear olfactometer. Twenty gravid females were transferred to the middle chamber of the olfactometer and their distribution in treatment and control chambers was recorded after 3 h.ResultsAlmost no eggs were oviposited during the first 72 h following a blood-meal. Cumulative egg deposition increased drastically in the next 24 h (hours 73–96), with a slight non-significant increasing trend thereafter. Comparing mean cumulative egg deposition among the six treatments, we found that significantly more eggs were oviposited on 2nd/3rd larval rearing medium followed by 4th instar/pupae rearing medium. Oviposition preference did not vary over time. The olfactometer results were consistent with the oviposition assays, with 2nd/3rd larval rearing medium being the most attractive, followed by 4th instar/pupae rearing medium.ConclusionThe key finding of this study is that gravid, laboratory reared, Ph. papatasi sand flies are significantly more attracted to rearing medium of the most biologically active larval stages (2nd/3rd instar and 4th instar/pupae). This finding indicates that sand fly-digested host food and feces is attractive to gravid females and suggests that the larvae and larval gut microbiome may be involved in conditioning the oviposition substrate and possibly the production of oviposition attractants and stimulants.

The egg and larval pheromone dodecanoic acid mediates density-dependent oviposition of Phlebotomus papatasi

“…The strong oviposition deterrent effect of second-/ third-instar larvae observed here is particularly interesting because in a previous study [24], we showed that rearing medium of second-/third-instar larvae was the most attractive and oviposition stimulating medium compared with virgin rearing media or rearing media of older stages (note that in those experiments rearing media tested did not contain any larvae). That attraction was shown to be driven by bacterial odorants (unpublished data).…”

“…Interestingly, in three other African sand fly species, all conspecific stages, including older larval stages, stimulated oviposition [33]. However, these results might be related to the use of crushed samples possibly releasing their excreta and gut microbes that might be attractive and/or stimulate oviposition [24].…”

“…Furthermore, our study is the first to demonstrate that, in addition to eggs, first-instar larvae also emit DA. Another compound isolated, for the first time, from both eggs and first-instar larvae is isovaleric acid, which is also produced by an attractive saprophytic bacterium that we recently isolated (unpublished data) from an attractive larval rearing medium [24]. We have shown that conspecific eggs produce these two compounds but it is not yet clear if firstinstar larvae are producing these compounds or acquire them by feeding on egg chorions [39] or possibly by being "anointed" with egg-specific pheromone.…”

“…For example, for Lutzomyia longipalpis, a New World species, volatiles from rabbit and chicken feces were attractive to gravid females [20][21][22][23] and hexanal and 2-methyl-2-butanol were identified as active compounds [21]. Similarly, Phlebotomus papatasi (vector of cutaneous leishmaniasis in the Middle East) [22,[24][25][26] and Phlebotomus argentipes (vector of visceral leishmaniasis in India) [27] were shown to be strongly attracted and/or stimulated to oviposit by cow and rabbit feces and larval frass.…”

Effects of larval rearing substrates on some life-table parameters of Lutzomyia longipalpis sand flies

“…longipalpis females were stimulated by hexanal and 2-methyl-2-butanol present in chicken and rabbit feces [ 34 ]. The microbial communities on the larval substrates can also play an essential role in the inducement of oviposition by sand fly females [ 35 ]. However, there was no correlation between the gut microbiota of sand flies with chicken shelter or colony substrates.…”