FIGURE 1.

Scanning electron micrographs of antennal sensilla of spotted alfalfa aphid Therioaphis trifolii (Monell). (A) The antenna consists of six segments, including a scape (Sc), a pedicel (Pe), and four flagella (F1–F4). The primary rhinaria are located on the fifth (F3, white arrow) and sixth segments (F4, black arrow), the secondary rhinaria on the third segment (F1, brace). (B,C) The primary rhinaria on the 6th segment composed of one large placoid sensillum (P.S), two stellate sensilla (S.S), and two–three coeloconic pegs (S. CoI and S. CoII). (D) The stellate sensilla and (E) placoid sensilla at higher magnification, showing many pores on the surface of these sensilla. (F) The placoid sensillum (P.S) on the 5th segment of the primary rhinarium surrounded by a fringed cuticular ridge. (G) The distribution of the secondary rhinarium on the 3rd segment of the antennae. (H) The secondary rhinarium shown at high magnification, which was in the boxed areas in (G).