Triatoma infestans

Most people, except perhaps entomologists, would describe Triatoma infestans as ugly. It is about one inch long (equal to the combined length of 12,500 T. cruzi trypomastigotes). It has two pairs of long, bent legs covered with fine hairs protruding from an oval‑shaped abdomen. A third pair of legs extends like arms from a trapezoidal, horny thorax adjacent to protruding bulbous eyes (see Figure 3). The legs are angularly bent, with thick femurs, long tibias, and short tarsus and nails, enabling it to rapidly move across floors and walls, cling to ceilings, and carry many times its weight in blood. Transparent parchmentlike wings cover the center of its back like a cloak. Extended, they are inadequate for flying, but are used for gliding from heights and for mounting during sex. A pincher‑shaped head protrudes from the thorax, with a proboscis folded back underneath which swings down, half‑open like a jackknife, to pierce the skin and suck blood.

A principal biological characteristic of Triatoma infestans, as well as other triatomines, is obligate bloodsucking by nymphs and adults of both sexes. Their great success in obtaining blood meals is due primarily to their being nocturnal predators as well as to the biochemical and physiological adaptation of species members to profoundly different ecological niches. They insert their probosces into sleeping mammals, employing a generalized anesthetic so as not to alarm their victims while they leisurely fill up on blood. Different hormones such as ecdysone and juvenile hormones regulate the biochemical and physiological changes in the tegument as they molt and transform through five stages to adulthood.

Blood provides triatomines with a protein‑ and lipid‑rich diet (Brenner 1987). Their metabolism has adapted to this diet, and their energy requirements and ATP (adenosine triphosphate) production are provided largely by fatty acid metabolism and the tricarboxylic acid cycle. Consequently, lipid metabolism is more important than carbohydrate metabolism in triatomines. Their use of fatty acids as a source of ATP production in substitution of carbohydrates has many advantages including large fuel stores and high ATP yield per molecule.

Triatomines vary in color and size, according to species. Colors vary from light yellow to black; some animals have different patterns of grey, green, orange, white, or yellow spots, principally on the connexivum. Size varies within the subfamily from 5 to 45 millimeters (about the size of an average cockroach) and is a key characteristic in distinguishing species as well as sex, with adult males being larger than females.

Triatomines make a squeaky shrill sound by rubbing their suction tube against ridges in its protective sheath under their bellies. Their front wings are leathery and their back wings are membranous, at best serving to glide several hundred meters. Although there is great variation between species in the use of wings for flight, some are capable of flying considerable distances, which is important in the colonization of new habitats and in the spreading of Chagas’ disease.

Nymphs are wingless and remain in the area where the eggs are deposited. Nymphs, as well as adults, are superb crawlers, with three pairs of highly developed legs. Because the nymphs are small, they can more easily hide, enter through bedding, and take a blood meal than the larger adults. Mosquito netting is ineffective against nymphs, which can crawl underneath the netting or arise from under the mattress.

Triatomines search out warm‑blooded animals in rooms and corrals by means of temperature gradients detected by their antennae. Carbon dioxide produces increased activity of the bugs. Another factor attracting them are feces left by a previous bug. Triatoma infestans and Rhodniusprolixus habitually defecate after a blood meal, and pheromones have been found in their feces. (Pheromones are hormones whose presence communicates certain biological activity response between members of the same species; a good example is a bitch in heat attracting male dogs.) Pheromonal attraction can be greatly lessened by house and personal hygiene, thus eliminating fecal matter for the insects’ sensors.

Pheromones not only attract unfed bugs to a blood source, their aggregation toward fecal matter may also be important in the maintenance of the correct gut fauna by coprophagy (Molyneux and Ashford 1983:79). As is the case with many hematophagous insects, Triatoma infestans and Rhodnius prolixus need bacterial and fungal symbionts for digesting blood.