Multiporous plate sensilla in parasitic hymenoptera: their ultrastructure and phylogenetic relationship

Abstract

Hymenopterous parasites perceive stimuli in their environment primarily via sensory sensilla on their antennae. The ultrastructure of multiporous plate sensilla (MPS) was studied in the Ichneumonoidea and the Chalcidoidea. Phylogenetic relationships of the MPS were determined and their evolutionary pathway was proposed. Internal and external cuticular structure was observed with scanning electron microscopy and the internal cellular structure was observed with transmission electron microscopy. Externally the MPS are elongated, dome-shaped structures with cuticular pores. The distal tip is not attached to the antennal surface in the Chalcidoidea. The distal and proximal ends are similar in the Ichneumonoidea, and the entire sensillum is surrounded by a cuticular collar. Internally two longitudinal cuticular invaginations divide the dome of the sensillum into a median and two lateral channels. Neurons in the center of the antenna send dendrites to the sensilla. The dendrites consist of a proximal part containing cell organelles and a distal part containing neurotubules, a ciliary region is present at the junction of the two parts. The distal part of the dendrites branch, turn a 90° angle and enter the median channel, traversing the longitudinal axis of the sensillum. One or more neurotubules are contained in each dendritic branch, some of which come in contact with the pore tubules that are present in the pore chambers. An inner sheath cell surrounds the dendrites and an outer sheath cell surrounds the inner sheath cell and fills the two lateral channels. The structure of the MPS is similar in the males and females of the Ichneumonoidea. A phylogenetic relationship was observed..