COMPARATIVE EXTERNAL ULTRASTRUCTURE AND DIFFUSION PATHWAYS IN STYLOCONIC SENSILLA ON THE MAXILLARY GALEA OF LARVAL MAMESTRA-CONFIGURATA (WALKER) (LEPIDOPTERA, NOCTUIDAE) AND 5 OTHER SPECIES

The external ultrastructure of sensilla on the maxillary galea are inv estigated in Mamestra configurata and five other lepidopterous larvae using scanning electron microscopy. The galea and lacinia, comprising the mesal lobe of the maxilla, are either completely separate, fused, or incompletely fused in these species. The distal surface of the mesa l lobe of all species examined bears two styloconic sensilla, three ba siconic sensilla, and three trichoid sensilla, whereas the midventral wall of this lobe bears a campaniform sensillum. The latter sensillum is visible in only three of the six species examined. The styloconic a nd basiconic sensilla occupy a ventro anterior location, whereas the t richoid sensilla are positioned dorsoposteriorly. Interspecific compar isons of galeal size, as well as sensillar size, shape, and position a re made for all species. The styloconic sensilla are the only sensilla r type permeable to an aqueous solution of cobalt chloride when viewed by brightfield light microscopy in all species examined. Cobalt ions permeate through the terminal pore of each styloconic peg and percolat e through the fenestrated fibrillar pore matrix, located directly belo w the pore. These ions permeate along the dendritic channel and accumu late in the adjacent sensillar sinus surrounding the peg and/or style by way of a presumably permeable dendritic sheath in all species, but to varying extents. The cuticular sidewall pores surrounding the termi nal pore also appear to be permeable to cobalt ions in all the species examined. In most species examined, the styloconic sensilla are only minimally permeable to mercury ions. In these species, mercury ions pe rmeate through the terminal pore, but become trapped within the plug o f fenestrated fibrils within it. The sidewall pores are not permeable to mercury ions in any of the species examined. The styloconic sensill a are not permeable to lead ions in M. configurata or Malacosoma lutes cens, the only species tested. (C) 1996 Wiley-Liss, Inc.