Larviposition site selection mediated by volatile semiochemicals in Glossina palpalis gambiensis

Abstract

1. Tsetse flies (Diptera: Glossinidae) are K-strategist species and deposit a single larva at 10-day intervals in specific sites. As larviposition site selection strongly impacts reproductive success, the selection of larviposition sites is unlikely to be random and will be subject to strong selective processes, probably mediated by specific cues. 2. This study was designed to assess the existence of an aggregation effect in the palpalis group and to test its potential chemical nature (contact or volatile compounds). The larviposition site selection of Glossina palpalis gambiensis was studied according to the presence of conspecific and heterospecific larvae (morsitans group) buried in substrates. Three sets of experiments were performed with either individual or grouped gravid females and with or without physical access to the substrate. 3. In individual larviposition experiments, females were more likely to select trays with buried larvae than unconditioned sand (63.2% and 36.8%, respectively; P < 0.05). In the grouped experiment with substrate contact, females were more likely to larviposit in trays with conspecific (40%) or heterospecific (33%) buried larvae than in unconditioned sand (22%) or empty trays (5%; P < 0.05). The results were similar without substrate contact, but more pupae were deposited in empty trays (19%). 4. These results provide the first evidence for larval aggregation in G. p. gambiensis and suggest that larviposition site selection is mediated by volatile semiochemicals of larval or pupal origin. However, this larval aggregation does not seem to be species specific and therefore offers new options for the behavioural manipulation of these vectors.

Population genetics of Glossina fuscipes fuscipes from southern Chad

“…Another non-exclusive hypothesis would relate to the density of suitable spots for larviposition. Pregnant females are known to be highly selective before choosing a site where to larviposit (Gimonneau et al, 2021). In zones with higher densities of suitable larviposition spots, females do not need to search far away for larvipositing their larva, while in zones with less suitable larviposition spots, females would spend more time searching for suitable sites and hence, have a higher probability of being captured in biconical traps.…”

Apparent negative density-dependent dispersal in tsetse (Glossinaspp) is an artefact of inappropriate analysis

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted December 17, 2020. ; https://doi.org/10.1101/2020.12.17.423205 doi: bioRxiv preprint pupae occur at a particular site -pupae are best hidden, not advertised. Finally, and most confusingly, it is claimed that the pheromone would have its greatest benefit at low population densities, because sparse populations become extinct if they disperse rapidly (38). This contradicts completely the DM idea that sparse populations evolve to disperse widely: in short, the DM coauthors are themselves arguing against their own notion of NDDD.…”

“…Inspection of the work cited shows, however, that it makes no mention of pheromones of any sort. Laboratory evidence for such a pheromone has indeed been published (36)(37)(38) but no such chemical has ever been shown to produce aggregation of pupae in the field.…”

“…Nonetheless, the suggestion by DM that tsetse dispersal is in some way linked to the existence of a larval deposition pheromone has been reiterated by some of the DM co-authors (38). The arguments adduced in support of this idea are, however, confused or unconvincing in several ways.…”

“…However, the dispersal mechanism just described is clearly PDDD, not NDDD. It is thus most confusing that, as indicated above, at least some of the DM co-authors appear eager to promote this idea (38).…”