STRUCTURE AND SPATIAL PATTERN OF THE SENSILLA OF THE BODY SEGMENTS OFINSECT LARVAE

We describe the types and patterns of sensilla present on the thorax a nd abdomen of newly hatched larvae of representative species of severa l insect orders, among them Saltatoria, Mantodea, Blattaria, Heteropte ra, Lepidoptera, and Diptera. Sensilla of non-Dipteran species almost exclusively comprise mechanoreceptive hairs or bristles (trichoid sens illa) of various sizes and numbers. In higher Dipterans, peg sensilla (sensilla basiconica, sensilla coeloconica) and so-called papilla sens illa predominate. The pattern of early larval sensilla falls into thre e main classes, which can be described as 1) fixed pattern, 2) variabl e pattern, and 3) variable pattern with fixed elements. In larvae exhi biting a fixed sensillum pattern (found in all Dipteran species invest igated), sensilla are invariant in number; they are precisely placed i n relationship to each other and typically form a single row behind th e middle of each segment. A variable pattern (common in most insect gr oups) typically consists of several rows of relatively evenly spaced s ensilla encircling the middle of each segment. In animals with a varia ble pattern including fixed elements, some sensilla, recognizable by t heir size or shape, are precisely placed, whereas other sensilla surro unding them are variable. (C) 1997 Wiley-Liss, Inc.