Behavior and Ecology

attracting bugs to a host is unclear, but a pheromone in the feces of nymphal and adult T. infestans and in nymphal R. prolixus attracts unfed nymphs. Soon after feeding, these species defecate on or by the host, so that such a pheromone might attract other bugs to a source of blood.

The probing response begins when the rostrum is swung forward. The third segment is flexed upward so that optimal contact with a host occurs when the bug is at the side and just below a host. The serrated mandibular stylets are used to cut through the epidermis of the host, then anchor the mouthparts while the maxillary stylets probe for a blood vessel. When a vessel is penetrated, the left maxillary stylet slides posteriorly on the right stylet, disengaging the two stylets so that the left folds outward from the food canal. The purpose of this action is not known. It may allow a larger opening for ingestion of blood cells, or it may be a mechanism for holding the capillary lumen open (Lehane 1991).

The amount of blood ingested depends on the duration of feeding. This, in turn, is governed by the presence of chemicals in the blood of the host that stimulate the onset of feeding and by stretch receptors in the abdomen of the bug that stimulate cessation. Known phagostimulants of triatomines include various nucleotides and phosphate derivatives of nucleic acids. The salivary glands contain an anticoaguJin that presumably helps maintain the flow of blood during feeding.

The time required to engorge fully varies from 3 to 30min. During feeding, the abdomen becomes visibly distended. Adult bugs may imbibe, blood equivalent to about 3 times their body weight, while nymphs may imbibe 6 to 12 times their unfed weight. Blood meals are stored in the anterior, widened portion of the midgut before the blood is passed to the narrower, posterior portion where digestion occurs. After engorging, the bug removes the rostrum from the host and, in most species, defecates on or near the host before crawling away to seek shelter. The interval between feeding and defecation is a major factor in determining the effectiveness of a species as a vector of Trypanosoma, cruzi. Schofield (1979) reviewed the behavior of triatomines, with particular attention to their role in trypanosome transmission.

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