Anatomical and Histological Changes in Internal Organs of Adult Trypodendron lineatum, Gnalhotrichus retusus, and G. sulcatus (Coleoptera: Scolytidae)1

Abstract

Changes during adult life in 3 ambrosia beetles, the striped ambrosia beetle, T. lineatum (Olivier); G. sulcatus (LeConte); and G. retusus (LeConte), were found in midgut epithelium, malpighian tubules, salivary glands, mycetangium, fat body, and the indirect wing musculature. In all 3 species the midgut epithelium secretes holocrinously and independently of the food content of the intestine. After each secretion cycle the new epithelium is formed from nidi in T. lincatum, and from caeca in G. retusus and G. sulcatus. The developmental and secreting cycle of the cells of the malpighian tubules occurs after the changes in the midgut epithelium. The fat body and wing muscles serve to provide energy, the fat body being activated and depleted during the dispersal flight and in the mature female, during egg maturation; the wing muscles degenerate in burrowing beetles of both sexes. Both tissues are regenerated before the adults re-emerge. In the fungus-storing gland (mycetangium) occurring in female T. lineatum and male Gnathotrichus the cells surrounding the lumen are activated when the ambrosia fungus is introduced as the beetle leaves the pupal cradle, usually after transformation into adult stage in T. lineatum and at the end of hibernation in Gnathotrichus. Secretion by the mycetangial cells and fungus growth occur during the dispersal flight. After the gallery is started, most of the fungus is released; the rest, along with the mycetangial epithelium, deteriorates. The salivary glands are larger in the female T. lineatum and in the male Gnathotrichus. They grow during dispersal flight in both sexes and continue to increase in the female of all 3 species during the early stage inside the gallery.