Pheromone Gland Development and Pheromone Production in Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae)

Abstract

The sand fly Lutzomyia longipalpis (Lutz & Neiva) (Diptera: Psychodidae: Phlebotominae) is the main vector of American visceral leishmaniasis. Adult males produce a terpenoid sex pheromone that in some cases also acts as male aggregation pheromone. We have analyzed the correlation between male pheromone production levels and pheromone gland cell morphogenesis after adult emergence from pupae. The abdominal tergites of L. longipalpis males were dissected and fixed in glutaraldehyde for transmission electron microscopy, or the pheromone was extracted in analytical grade hexane. Pheromone chemical analysis was carried out at 3- to 6-h intervals during the first 24 h after emergence and continued daily until the seventh day. All extracts were analyzed by gas chromatography. For the morphological analysis, we used insects collected at 0-6, 9-12, 12-14, and 96 h after emergence. Ultrastructural data from 0- to 6-h-old adult males revealed smaller pheromone gland cells with small microvilli at the end apparatus. Lipid droplets and peroxisomes were absent or very rare, but a large number of mitochondria could be seen. Lipid droplets started to appear in the gland cells cytoplasm approximately 9 h after adult emergence, and their number and size increased with age, together with the presence of several peroxisomes, suggesting a role for these organelles in pheromone biosynthesis. At 12-15 h after emergence, the lipid droplets were mainly distributed near the microvilli but were smaller than those in mature older males (4 d old). Pheromone biosynthesis started around 12 h after emergence and increased continuously during the first 3 d, stabilizing thereafter, coinciding with the period when males are more able to attract females.

The peroxisome: an update on mysteries

“…Plant (and animal) peroxisomes have been associated with the synthesis of hormonal signal molecules: in addition to the core b-oxidation pathway, peroxisomes in plants contain an increasing amount of auxiliary enzymes, and their role in the synthesis of jasmonate and auxins is becoming more and more evident (Baker et al 2006;Kienow et al 2008;Wiszniewski et al 2009). Similarly, peroxisomes in animals may play a role in the synthesis of pheromones as suggested for Caenorhabditis elegans (Joo et al 2009(Joo et al , 2010 or diptera (Spiegel et al 2011). Noteworthy, peroxisomes in plants and fungi house a series of specialized enzymes involved in the synthesis of various secondary metabolites (Bartoszewska et al 2011b).…”

“…Furthermore, peroxisomes have been found to contribute to biotin synthesis in fungi and plants (Tanabe et al 2011); in the latter, their contributions to the synthesis of vitamin K1 (Babujee et al 2010) and glycine betaine synthesis/acetaldehyde oxidation have been described (Fujiwara et al 2008;Mitsuya et al 2009Mitsuya et al , 2011. The peroxisomal localization of the pre-squalene segment of the pathway of isoprenoid/cholesterol biosynthesis remains still under debate for mammals (Kovacs et al 2002;Hogenboom et al 2004a, b, c;Wanders and Waterham 2006;Kovacs et al 2007); in plants, by contrast, new studies provide evidence that the final four steps of the pathway are localized to peroxisomes (Sapir-Mir et al 2008;Clastre et al 2011;Simkin et al 2011;Thabet et al (2000), Wiszniewski et al (2009) Pheromone production 9 Joo et al (2009Joo et al ( , 2010, Spiegel et al (2011) Isoprenoid biosynthesis 9 ? /- Hogenboom et al (2004a, b, c), Kovacs et al (2007), Sapir-Mir et al (2008), Clastre et al (2011), Simkin et al (2011), Thabet et al (2011) Biotin synthesis 9 9…”

The Lutzomyia longipalpis complex: a brief natural history of aggregation-sex pheromone communication

“…Recent chemical analyses of age-related pheromone content in males confirm a gradual increase in pheromone production in synchrony with the pheromone gland cells maturation [83]. This study did not examine the pattern in even older males, thus whether a decline in pheromone content commensurate with senescence is unknown [81].…”

“…Nonetheless, age-related signal degradation is one mechanism that honesty can be maintained within the system and this may be adaptive in L. longipalpis because on average, older males sire fewer viable offspring [81]. It is interesting to note that in L. longipalpis males, the genitalia undergo a 180° rotation after emergence, taking 24 h for the insects to become sexually mature [28] and pheromone biosynthesis commences around 12 h after emergence, increasing until three days of age and then stabilizing thereafter [83]. Noteworthy also then, is the fact that L. longipalpis, males commence the adult stage of their lives with no ability to attract females, at least from a distance and, if the pheromone signal deteriorates with old age, they are similarly less capable of attracting females as they senesce.…”

“…Some chemical signals might be expressed in relation to body condition or vary with age; others may more reliably reflect an individual’s genetic quality. The costs of production are rarely demonstrated in insects (but see Johansson et al [94]), however these can be inferred indirectly in species where signal production commences after adult eclosion (as is the case for L. longipalpis [83]). Recent transcriptomics and proteomics studies have revealed much about the biosynthetic pathway for glandular secretions in Lutzomyia including the specific enzyme pathways involved in sesquiterpenoid biosynthesis [95, 96].…”