Orientation of Belminus triatomines to cockroaches and cockroaches’ fecal volatiles: an ethological approach

Most triatomine bugs (Hemiptera: Reduviidae: Triatominae) are hematophagous, though Belminus species can live off of cockroach hemolymph to complete their life cycle. In this work, we described the fixed action pattern (FAP) employed by B. ferroae to identify, approach, and suck on a living cockroach. The FAP described here is composed of the following stereotyped behaviors: (1) visual and/or olfactory detection of the cockroach, (2) reaching, (3) cautious approach, (4) antennal exploration, (5) extension of the proboscis, (6) piercing to sedate, (7) walking away and waiting (postsedation behavior), (8) second cautious approach, (9) extension of the proboscis, (10) piercing to suck hemolymph. The FAP sequence observed suggests that Belminus bugs are not predators like the rest of reduviids (assassin bugs)—but are kleptophagous ectoparasites, since they do not attack and kill a prey but rather steal hemolymph from its invertebrate host. Based on these ethological observations, we propose kleptophagy as a trait that naturally groups the Belminus species into the Triatominae subfamily. In order to identify chemicals cues that could elicit such FAP, we examined the behavior of B. corredori, B. ferroae, and B. herreri in response to the cockroaches’ odor, fresh cockroach feces and fresh rodent wastes. The last two sources were tested based on the assumption that abundant chemicals near host refuges could serve as cues for host orientation. We found that the cockroach odor emanating from a box significantly attracted B. corredori and B. herreri in a still air olfactometer. The three Belminus species approached the captive cockroach after 1 h, but avoided to climb the box. Odors emanating from the cockroach feces attracted B. corredori and B. ferroae in a Y-olfactometer. Triatomines and their hosts have intimately shared the same refuge for millions of years; certain molecules occur across invertebrate and vertebrate refuges and are recurrent in human abodes, thus plausibly explaining how these bugs can readily switch to the domestic habitat, while keeping with their kleptophagous nature.