The secretion, morphology, and chemical composition of the peritrophic
envelope were studied in the phlebotomine sand fly Lutzomyia spinicra
ssa Morales, Osorno-Mesa, Osorno and Hoyos, a suspected vector of Leis
hmania braziliensis in Colombia and Venezuela. Viewed under light micr
oscopy, the envelope matured rapidly and could be dissected from the b
lood bolus as early as 12 h and until 36 h after feeding; subsequently
it began to degrade. The envelope was initially a closed sac around t
he blood meal, but opened posteriorly in most flies by 6 h. The poster
ior opening may facilitate the migration and establishment of La. braz
iliensis in the hindgut. Secretion of envelope precursors was from the
entire midgut epithelium. Electron microscopy revealed that electron-
dense precursor material (possibly chitin) was present, bathing the mi
crovilli during the first 12 h after blood feeding. This secretion app
eared to originate from the bases of the microvilli. From 1 to 36 h, a
n electron-lucid precursor material (possibly protein) was secreted fr
om the entire length of microvilli and from their bases. Both precurso
rs appeared to be formed at the epithelial surface, not associated wit
h secretory vesicles. The envelope developed rapidly from precursor ma
terial, and by 6 h a defined electron-lucid structure was present abov
e the microvilli. Most mature envelopes (12-36 h) were 0.5-2.1 mu m th
ick, multilayered, wholly electron-lucid, and composed of microfibrils
and granules. Electron-dense components were seen in some envelopes a
t 24-36 h. An anterior hyaline plug was present from 12 to 36 h. Envel
opes were composed of chitin, protein, and glycoprotein, based on chem
ical and histochemical tests. The likely presence of several amino aci
ds (lysine, aspartic acid, and glutamic acid) that may cross-link chit
in and protein was demonstrated by a positive ninhydrin-Schiff test. T
his study constitutes the first ultrastructural investigation of perit
rophic envelope development by a New World sand fly.