Examination of the interior of sand fly (Diptera: Psychodidae) abdomen reveals novel cuticular structures involved in pheromone release: Discovering the manifold

The males of many species of New World Phlebotomines produce volatile terpenoid chemicals, shown in Lutzomyia longipalpis s.l. to be sex/aggregation pheromones. Pheromone is produced by secretory cells which surround a cuticular reservoir which collects the pheromone and passes it through a cuticular duct to the surface of the insect. The pheromone then passes through specialised cuticular structures on the abdominal surface prior to evaporation. The shape and distribution of the specialised structures are highly diverse and differ according to species. In this study we used SEM to examine the interior cuticular pheromone collection and transport structures of 3 members of the Lu. longipalpis s.l. species complex and Migonemyia migonei. We found a new structure which we have called the manifold which appears to be a substantial extension of the interior tergal cuticle connected in-line with the cuticular duct and reservoir. The manifold of the Campo Grande member of the complex is longer and wider than the Jacobina member whereas the manifold of the Sobral member was shorter than both other members of the complex. Overall, the secretory apparatus of the Sobral member was smaller than the other two. The manifold of M. migonei was very different to those found in Lu. longipalpis s.l. and was positioned in a pit-like structure within the tergal cuticle. The secretory reservoir was connected by a short duct to the manifold. Differences in the size and shape of the manifold may be related to the chemical structure of the pheromone and may have taxonomic value. Examination of the interior cuticle by SEM may help to locate the secretory apparatus of vector species where pheromonal activity has been inferred from behavioural studies but the external secretory structures or pheromones have not yet been found. Author summaryThe males of many species of New World sand flies produce volatile chemicals shown in Lutzomyia longipalpis s.l. to be attractive to females and other males. These sex/aggregation pheromones are produced by secretory cells which surround a cuticular reservoir that collects the pheromone and from which it passes through a cuticular duct and a specialised structure on the surface of the abdomen, from where it evaporates. We examined by SEM the structure of the interior cuticular secretory apparatus of 3 members of the Lutzomyia longipalpis s.l. species complex and Migonemyia migonei and found a new structure associated with pheromone release that we have called the manifold. The manifold appears to be a substantial extension of the interior tergal cuticle that is connected in-line with the duct and reservoir. Significant differences in size and shape of the manifold between members of the Lu. longipalpis complex were observed. The M. migonei secretory apparatus were substantially different in appearance to those of Lu. longipalpis with the manifold positioned in a pit-like structure within the tergal cuticle. These differences which may have taxonomic value and may be related to the chemical structure of the pheromone or phylogenetic differences.

Automated summary

SEM examination revealed substantial differences in the interior cuticular secretory apparatus of different species of New World sand flies, which may be related to the chemical structure of pheromones and potentially have taxonomic value. The discovery of a new structure associated with pheromone release, named the manifold, provides insights into pheromone production in these insects.