Risks associated with dispersive nocturnal flights of sylvatic Triatominae to artificial lights in a model house in the northeastern plains of Colombia.

BACKGROUND: Control initiatives and continuous surveillance of vector-borne transmission have proved to be effective measures for diminishing the incidence of Chagas disease in endemic countries. However, the active dispersal of infected sylvatic adult triatomines by flight represents one of the main obstacles to eliminating domestic transmission. METHODS: In order to determine the risk that active dispersal of sylvatic adult triatomines represents in Colombian northeastern plains, we quantified the distribution and abundance of triatomines in palm trees (primarily Attalea butyracea) using live bait traps. Directional light traps were used to estimate the frequency of sylvatic triatomine dispersal and their possible origin. Finally, the effect of environmental parameters and artificial light sources on the take-off of sylvatic Rhodnius prolixus was evaluated in field experiments. RESULTS: R. prolixus was found in 90 % of the palm trees that densely aggregated toward the northern portion of the study area. R. prolixus, and three other sylvatic triatomine species were found to actively disperse and were attracted to the directional light traps (Triatoma maculata, Panstrongylus geniculatus and Psammolestes arthuri). Temperature, relative humidity, wind speed and night luminosity did not affect the active dispersal of the triatomines which is higher the first two hours after sunset. Artificial lights from houses at 60 and 110 m played a key role in the directionality of the R. prolixus take-offs. Trypanosoma cruzi was isolated from R. prolixus, T. maculata and P. geniculatus and was genotyped as T. cruzi I, III and IV. CONCLUSIONS: Our results highlight the potential risk in Colombian northeastern plains of actively dispersing sylvatic triatomines and their role in the domestic introduction of Discrete Typing Units of T. cruzi associated to sylvatic foci of Chagas disease transmission.

Searching for triatomines. A new method for field search using UV light.

Detection of triatomine bugs within a house is essential for the estimation of Chagas disease transmission risk and for evaluating the success of insecticidal control attempts. Small residual populations could represent an important risk but are difficult to detect by time manual sampling. Faecal marks from triatomines are clearly detectable with an ultraviolet (UV) light on most of the materials frequently used in rural buildings. A new method for finding triatomines is proposed here, based on the unexplored property of faeces to fluoresce when exposed to UV light.

The inheritance of radiation induced semi-sterility in Rhodnius prolixus.

Eggs from crosses of 40 adult male R. prolixus irradiated with 6K rad gamma-rays with normal females had a mean fertility of 23.9%, only 2 crosses being completely sterile. The 86 F1 progeny of both sexes, when outcrossed with normal mates, had a mean egg fertility of 12.6;, and 43 of these matings were completely sterile. Twenty-eight "F2" bugs reared from F1 X normal crosses were mated with normal partners and had a mean fertility of 44.6%, 6 of them being fully fertile, a reversal towards normal fertility. Cytogenetic examination of F1, "F2" and "F3" males showed that these changes in fertility correlated well with the degree of chromosomal abnormality found. The very high recovery rate of translocations in F1 generation males can be related to the holocentric chromosomes of these bugs which precludes the formation of dicentric chromosomes which are inviable in monocentric species. In F1 and "F2" males the majority of one bug was found with a ring of IV chromosome association and it is suggested that chromosome morphology, combined with a low chiasma frequency, favours chain association. Most chain multivalents showed linear orientation which may lead to duplication deficiencies and zygotic death. However, "parellel", "indifferent" and the more stable "convergent" modes of chain orientation were also all observed indicating that survival of some translocations in this species may be possible. The survival to the "F2" generation of chromosomal fragments confirmed the holocentric nature of triatomine chromosomes. It is suggested that semi-sterile males would prove more effective than releases of completely sterile males for reducing wild populations of R. prolixus, because of the delayed effects of sterilizing radiation consequent upon the holocentric structure of triatomine chromosomes.

PIP: The inheritance of radiation induced semisterility in the insect Rhodnius prolixus is reported. Eggs from crosses of 40 adult male R. prolixus irradiated with 6 K rad gamma-rays with normal females had a mean fertility of 23.9%, with only 2 crosses demonstrating complete sterility. 86 F1 progeny of both sexes were then outcrossed with normal mates. A mean egg fertility of 12.65 was seen with 43 completely sterile matings. 28 ''F2'' bugs were then mated with normal partners and had a mean fertility of 44.6%, 6 of them being fully fertile. Cytogenic studies were performed on F1 males, ''F2,'' and ''F3.'' The degree of chromosomal abnormality correlated with fertility level. All F1 males examined (49) showed chromosomal abnormalities in their spermatocytes so that in every male at least 1 interchange was evident. The majority of eggs from the 1st egg batch had only a single translocation while in later batches 2 and 3 translocations were found frequently. The high recovery rate of translocations in F1 generation males can be related to the holocentric chromosomes which are inviable in monocentric species. The majority of F1 and ''F2'' males had translocations associated as chains of 3 or 1 or as chains of 4. Only 1 bug was found with a ring of 4 chromosome association. Most chain multivalents showed linear orientation which may lead to duplication deficiencies and zygotic death. The survival of some translocations of this species is possible as suggested by the presence of ''parallel,'' ''indifferent,'' and the more stable ''convergent'' modes of chain orientation. The fertility of F1 males could also be related to their birth order. Males were significantly less fertile than their female counterparts. The control of this population of insects could most effectively be accomplished by the release of semisterile males as opposed to completely sterile males because of the delayed effects of sterilizing radiation consequent upon the aholocentric structure of triatomine chromasomes.