Sensilla of haematophagous insects sensitive to vertebrate host-associated stimuli

Abstract

The morphology of the sensilla sensitive to vertebrate host-associated stimuli is diverse reflecting the numerous independent origins of haematophagy within the insects. Using electron microscopic techniques, the sensilla of mosquitoes and blackflies have been the most thoroughly studied, although numerous works have been conducted on other blood-feeders. Notably lacking are fine structure studies on blood-feeding maggots and ectoparasitic, adult Muscomorpha. In comparing blood-feeders with other insects it becomes apparent that: (1) carbon dioxide plays a significantly greater role in location of food by haematophagous insects than by phytophagous and saprophagous species; (2) only in blood-feeders do the adenosine phosphate nucleotides, a single group of compounds, appear to be the phagostimulants for almost all species; and (3) feeding deterrents are unknown in haematophagous insects. When the sensory complements of the various groups of blood-feeders are compared, three points emerge. First, reduction in numbers of olfactory chemosensilla that mediate odour cues used in long-distance, host-orientation occurs in male nematocerans and in females of completely autogenous species of mosquitoes and black flies. Second, there is a striking correlation between the number of labial chemo- and mechanosensilla and the feeding behaviour of the insect. Third, there is a possible positive correlation between the number of chemosensitive antennal neurones and the distance travelled by the insect to the host.