Rhodnius nasutus

Using mitochondrial DNA sequence analysis, R. nasutus has been dated 66 thousand years, giving rise to stable populations during the Pleistocene-Holocene epochs.[8] This time frame is consistent with the climate change event that took place in South America which marked the end of a major drought and dry season.

R. nasutus is predominantly found in the caatinga biome of Northeast Brazil, although due to increased deforestation and environmental damage the insect has expanded its geographic range and habitat.[9] The species is primarily associated with the Copernicia prunifera palm tree (Carnaúba) in this area, however more recently they have been found colonizing suburban areas such as Jaguaruana, Ceará, and infesting various other palms including Licania rigida (Oiticica).[1] The allocation of chemical measures in rural areas have pushed these insects to colonize closer to localities and urban districts.[4] Migration into central areas of Brazil pose a threat to humans as it increases the risk of contracting Chagas disease.[9][10]

When compared to other species of the genera, R. nasutus is found to thrive better in dryer and warmer conditions.[11] Palms located in semi-arid, higher-altitude environments inhabit greater populations compared to palms located in lower elevations where flooding occurs during rainy seasons.[12]

The insect is found predominantly in the crowns of palm trees, they burrow their bodies into the auxiliary nodes and foliar sheaths of palms, which act as a barrier to protect them from environmental and predatory threats.[12]

More recently, R. nasutus has been found infesting homes and farm buildings, including corrals and coops.[13]

In efforts to inhibit human contraction of diseases harbored by R. nasutus, preventative measures such as chemical controls (insecticides) are distributed to high density Triatomine areas, including human dwellings.[14] Although, the continuous re-infestation of homes that had been treated with insecticides presents the need for further research in controlling populations.[15]

The first insecticide used in Brazil to reduce infestations was a synthetic DDT formulation which was later found to have negative impacts on the environment.[14] In 1970, a lindane and dieldrin compound insecticide was used until a safer organophosphorus and carbamate insecticide was formulated in the 1980's. This insecticide however, emitted a strong odor and stained walls of houses undergoing extermination. The favored and most recent insecticide used on R. nasutus is a pyrethroid formula, although the evolution of insecticide resistance has been documented in some Triatomine species.[14]

Biological controls such as the "Mark-Release-Recapture" (MRR) method, involving the placement and evaluation of trace elements in R. nasutus, allows for long-lasting molecular marking under natural conditions.[16] This method aims to identify host-seeking behaviors of the insect by tracking migration and population dispersion. Understanding the movement of these insect vectors provides important information regarding medical insights and preventative measures towards the transmission of Chagas disease. Other biological controls such as dusting and physically marking the insect are not as effective as growing nymphs will eventually shed the marked cuticle.[16]

R. nasutus is a hematophagous insect and will feed on bloodmeal through all life stages.[17] Their main hosts are birds and mammals, however there is evidence that these insects will find invertebrates hosts and feed on hemolymph.[12]

Compared to other Rhondius species, R. nasutus displays a slower feeding time around 15-20 minutes before full engorgement.[17][18] They are solenophagous insects so in order to feed they must find a suitable blood vessel in their host.[18] During the probing period, the maxillae that is pierced into the hosts skin contract in rapid whip-like movements until a blood vessel is detected from which they can feed on. During feeding the cibarial pump, which is connected to strong muscles in the head, regulate the suction and volume intake of bloodmeal through the proboscis. Saliva plays an important role in the probing period to find blood, as well as the feeding period to regulate the flow of blood via the proboscis. R. nasutus has adapted highly efficient salivary glands which reduces the time is takes for them to find blood vessels.[18]