Introductory Remarks: Symposium on Differentiation of Trypanosomatids

Leishmania differentiation in the gut of phlebotomine sand flies was evaluated based on five light and electron microscopic studies of natural (Leishmania panamensis/Lutzomyia gomezi, Leishmania chagasi/Lutzomyia longipalpis) and unnatural (Leishmania mexicanalLutzornyia abonnenci, Leishmania panamensis/Phlebotomus papatasi, Leishmania major/Lutzomyia longipalpis) life cycles. In the bloodmeal, transformation of amastigotes into stumpy promastigotes occurred before or during division. Further division in pairs or rosettes resulted in the development of spatulate and/or elongate nectomonad (free-swimming) promastigotes. Elongate, short, and metacyclic nectomonad promastigotes, and nectomonad paramastigotes were present in the midgut lumen. Dividing short promastigotes predominated in the cardia, and appeared to generate metacyclic forms which were observed in three life cycles. Haptomonad (attached) forms of Leishmania panamensis in the hindgut were primarily spatulate promastigotes (natural host) or pear-shaped promastigotes (unnatural host); paramastigotes and dividing forms were rare. At the stomodeal valve, short haptomonad promastigotes predominated in unnatural hosts, while both short and pear-shaped haptomonads were abundant, along with paramastigotes in natural hosts. Haptomonad paramastigotes and pear-shaped promastigotes colonized the esophagus, while paramastigotes predominated in the pharynx. Metacyclics were free-swimming in the lumen of the foregut. Supplementary key words. Haptomonad, life cycle, nectomonad, paramastigote, promastigote, Psychodidae, Trypanosomatidae. IONEERING studies of Leishmania differentiation in phleP botomine sand flies were reported by Killick-Kendrick, Molyneux and colleagues during the mid-1970s [17, 18, 321. For the first time, the development of parasites in the sand fly gut was examined by electron microscopy. This resulted in the description of two distinct forms of promastigotes in the midgut, termed nectomonads and haptomonads, and the discovery of a paramastigote form of Leishmania occurring in the hindgut and foregut. Previous to these investigations, the Leishmania life cycle in sand flies was thought to consist only of the amastigote form taken in with the bloodmeal, and the promastigote [ 121. Perhaps due to the difficulty of colonizing and maintaining sand flies in the laboratory at that time, these studies were done using i This paper was originally presented as part of the symposium on ‘‘Differentiation of Trypanosomatids,” ~~l~ 1 1, 1992, University of British Columbia, Vancouver, B.C., Canada.