The structure and defensive efficacy of glandular secretion of the larval osmeterium in Graphium agamemnon agamemnon Linnaeus, 1758 (Lepidoptera: Papilionidae)

Histomorphological study of the larval (final instar) osmeterium gland in Graphium agamemnon agamemnon Linnaeus shows that each fully protruded Y-shaped osmeterium is composed of 2 elongated hollow tubular arms, which arise from a basal peduncle. The surface of the osmeterium has irregular folds, and papillae arise from some cells. There is an oval opening (gland pore, structurally less complicated than in other evolved species) in the proximal second seventh of the segment on each tubular arm on its posterior face. Histologically, 2 main types of secretory cells can be observed (excluding the muscle fiber cells and supporting cells): i) ellipsoid gland cells within the gland pore region and ii) tubular arm cells extending from the upper part of the ovoid gland pore region to the distal part of the tubular arms. The defensive efficacy of the osmeterial secretion in larvae was also examined, both in the laboratory and field, and was observed to be very complicated.