Period of time and movement distances between feeding and postfeeding defecation in Triatoma pallidipennis (Heteroptera: Reduviidae)

Abstract

Defecation time is one of the key parameters used to estimate the efficiency of a Triatomine species as a vector of Trypanosoma cruzi. There is controversy among experts as to whether triatomines that defecate 1–10 min after feeding are efficient vectors, with a different perspective on the distance moved from the host to defecate in the case of triatomines after feeding. The aim of the present study was to determine the period of time and movement distances between feeding and defecation of third-, fourth- and fifth- nymphal instars and adults of Triatoma pallidipennis specimens that defecated between 1 and 10 min and to estimate the distance where the host could still be in contact with deposited feces and potentially become infected with T. cruzi. Twelve drops of non-toxic coloring were deposited to simulate triatomine feces close (< 10 cm) to 20 dogs, and their movements were observed to estimate the chances of becoming “infected”. The mean postfeeding defecation delay was between 2 and 10 min in the five studied instars, with significantly (p = 0.03) longer times in the fourth-instar nymphs and males. The mean distance moved after feeding until defecation was ranged from 5.3 cm in third-instar nymphs to 19.6 cm in males, with significant differences (p < 0.01) only in males. All the studied dogs had accidental contact with at least three drops (mean of five drops) during their movements. Triatoma pallidipennis remains at its host for only a few seconds postfeeding; however, it defecates close enough to a host to expose it to its feces due to host movement. According to the results obtained, the delay should be complemented by the observation of distance moved to defecate to more accurately estimate the efficiency as a vector of T. cruzi of a triatomine species.