Ultrastructural Morphology of two Sensilla Placodea on the Antenna of a Parasitic Wasp

Abstract

Females of the wasp Tetrastichus hagenowii (Hymenoptera: Chalcidoidea) lay their eggs in cockroach egg cases, the young hatch and feed on the cockroach eggs. Prior to egg deposition the parasites follow a complex behavioral sequence, including tapping their antennal tips on the eggcase, thus enabling them to detect various mechanical and chemical properties of the cockroach egg case and determine its suitability for oviposition (unpublished data).Sensory sensilla occur along the entire length of the female antenna (Fig. 1). Two of the more prominent sensilla were studied by scanning and transmission electron microscopy, these are both sensilla placodea (PI and P2 in Figs. 1 and 2) which are chemoreceptors (1). Numerous hair-like sensilla (H) and a few bulb-like sensilla (B) are also present (Figs. 1 and 2). Sensilla placodea occur frequently on hymenopteran antennae (1), but the occurrence of two types on the same insect has not been reported previously.