Panstrongylus megistus

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Geographic Range

Panstrongylus megistus mainly inhabits southeastern Brazil, though there are populations in some areas of Argentina, Paraguay, and Uruguay, bordering Brazil. (Lent and Wygodzinsky, 1979)

Habitat

Panstrongylus megistus is present in many rural habitats throughout Brazil. Specifically, many populations of Panstrongylus megistus occupy sylvatic, or wooded habitats. They live in parasitic association with nesting vertebrates such as rodents and opossums and also in decaying tree cavities. One of the main aspects separating Panstrongylus from other genera of the Triatominae is habitat. The other genera are associated with terrestrial rocky habitats.

However, Panstrongylus megistus also colonizes domestic and peridomestic habitats such as chicken houses, or guinea pig enclosures. Populations have adapted to human dwellings, hiding in cracks during the day and coming out to feed at night. The species is present in more humid habitats as compared to its relatives. Laboratory populations require 100% humidity to survive. (Gaunt M, 2000; Lent and Wygodzinsky, 1979)

Physical Description

Panstrongylus megistus is similar to other members of the Triatominae in physical appearance. The species have hemielytra (modified forewings) and mouthparts adapted for piercing blood vessels. Their heads are forwardly directed, freely moveable, and are set on an identifiable neck. The head is flattened, though elevated on the posterior half, and has 3 sclerite sections, the clypeus and two genae. For the mouthparts, the rostrum is the modified labium that protects the stylets. The stylets consist of transformed mandibles and maxillae which assist in feeding. The compound eyes on the head are associated laterally and are usually black. There are also two smaller ocelli, or simple eyes, behind the compound eyes. The thorax consists of a pronotum, a dorsal shield-like sclerite which covers the first two-thirds of the thorax, and a scutellum, which covers the final third. The ventral sclerite is called the prosternum which is smaller than the pronotum. There are two pairs of wings: the hindwings and the hemelytra, associated with the mesothorax. Further, there are six legs associated with the thorax.

The species can be identified from other Triatomines by several features. The species' color is overall dark brown or black though it has red and yellowish brown markings going down its neck and thorax. There is sexual dimorphism in body length: the females are usually larger than the males. The length of the male ranges from 26 to 34 mm and the length of the female ranges from 29 to 38 mm. In addition, the male has larger compound eyes than the female. Panstrongylus megistus is such among the larger of the Triatomines, which range from 5 mm to 44 mm. The ratio of the head length to eye width is around 1.5, which makes the head appear elongate, although less so than other Triatomines. (Lent and Wygodzinsky, 1979)

  • Sexual Dimorphism
  • female larger
  • Range length
    26 to 38 mm
    1.02 to 1.50 in

Development

Eggs hatch between 10 and 50 days after oviposition, depending on temperature. The first instar nymph hatches from the egg. The nymphal instars live in the same areas and feed on the same hosts as the adults. In Panstrongylus megistus, a distinguishing feature from other Triatomines is that the first instar nymph has specialized tarsal hairs. The nymph is usually 0.254 cm long. The species goes through incomplete metamorphosis also termed hemimetbolism. There are 5 nymphal instars, all of which feed on blood, followed by the final adult form, which is distinguished from the 5th nymphal instar by its two pairs of wings. The first nymphal instar has a pink abdomen. The second instar is similar to the first morphologically but has an increased size. In the third instar, the future locations of the wings are outlined, become more pronounced in the fourth, and are almost complete yet non-functional in the fifth. The adults also have a completely sclerotized abdomen. The full length of the development from first nymphal instar to adult takes up to 2 years in Panstrongylus megistus, which is much longer than most other Triatomines. (Lent and Wygodzinsky, 1979)

Reproduction

Panstrongylus megistus is a polygynandrous species. Mating involves complex courtship behavior during which a female can reject a male. Female individuals usually mate only once with a single specific male, but multiple times with many males over a lifespan. This is due to the high rejection probability of a second copulation attempt within a short time span. Females mate an average of 2.6 times over their lifetime, which is a much lower mating frequency than other triatomines. The probability of mating increases with the increasing time since the last meal. Copulation, which can go from 5 to 15 minutes, begins when the male stands parallel to the female and immobilizes her with three of his legs. How this species locates, selects, and defends mates is currently unknown. (Lent and Wygodzinsky, 1979; Pires, et al., 2002a)

Panstrongylus megistus is oviparous, and each female can produce up to 1,000 eggs in a single lifespan. Eggs are laid within 10 to 30 days of copulation, and may be laid continuously for several months. They are deposited on substrate and the degree to which the eggs cluster depends on the habitat in which they are produced. Sylvatic populations and domestic populations tend to differ on the closeness of the eggs to one another, with sylvatic being closer together. Panstrongylus megistus prefers to lay its eggs in lower temperatures than at which the adults survive. (Lent and Wygodzinsky, 1979; Pires, et al., 2002a)

  • Breeding interval
    Breeding interval for Panstrongylus megistus is currently unknown.
  • Breeding season
    Breeding season for Panstrongylus megistus is currently unknown.
  • Range number of offspring
    500 to 1000
  • Range gestation period
    10 to 40 days
  • Average age at sexual or reproductive maturity (female)
    720 days
  • Average age at sexual or reproductive maturity (male)
    720 days

Panstrongylus megistus exhibits no parental investment after females oviposit. The nymphs are on their own from hatching. (Gaunt M, 2000; Pires, et al., 2004)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Panstrongylus megistus is known to live a maximum of 2 years. Factors that affect lifespan are currently unknown.

  • Typical lifespan
    Status: wild
    2 (high) years

Behavior

Members of the species are nidicolous in that they live in the nests of their host species and aggregate together. Panstongylus megistus come out at night to feed on blood from mammalian hosts, but are sessile during the day. They are attracted by host odor as well as heat radiated from the host's body. The species can feed on the hosts associated with it in sylvatic habitats, such as opossums and rodents, or humans in domestic/peri-domestic habitats. Individuals are attracted by light during their night-flights, especially those in domestic and peri-domestic habitats. (Gaunt M, 2000; Lent and Wygodzinsky, 1979)

Home Range

Exact home range size of Panstongylus megistus is currently unknown.

Communication and Perception

Panstrongylus megistus produces a song which entomologists have analyzed but have been unable to produce a reason for sound production in the bugs. In addition, the antennae contain chemo-receptors which help the bugs aggregate to their own excrement or cuticular substances through detection of pheromones. Further, pheromones are involved in aggregation during the day when the insects are inactive and remain hidden. The chemo-receptors also function to locate the mammalian hosts through odors the host produces. They can perceive light through their compound and simple eyes (ocelli) as evidenced by their attraction to light at night. (Lent and Wygodzinsky, 1979; Pires, et al., 2002b)

Food Habits

Panstrongylus megistus are strictly haemophagous meaning they feed on the blood of mammals, including rodents, opossums, and humans. They feed by mouthparts modified for solenophagy, or vessel-feeding. These insects use chemo-receptors to sense a suitable blood vessel from which to feed. The specialized mouthpart stylets have apically serrate mandibles, which serve to perforate the epidermis of the host. Then the maxillae are introduced and they intercept the blood vessels from which the blood is withdrawn. A salivary anticoagulant is introduced so that more blood can be withdrawn from the blood vessel. During feeding, the posterior part of the rostrum is flexed upward. The bites are generally painless. These bugs prefer the soft tissue of the eye or lips, hence giving the name "kissing bugs." For non-human hosts, however, the bugs prefer to feed from below the host, or from the host's ventral side. All nymphal instars and the adults feed on blood. The species is unique in that in can go long periods without a blood meal. Also, Panstrongylus megistus defecates very quickly after feeding, leading to its importance as a vector of Chagas disease since the protozoan is transmitted through the feces. (Gaunt M, 2000; Lent and Wygodzinsky, 1979; Pires, et al., 2002a)

  • Animal Foods
  • blood

Predation

Host species including opossums and rodents are known to eat Panstrongylus megistus. In addition, birds such as chickens in peri-domestic habitats eat this species. (Lent and Wygodzinsky, 1979)

Ecosystem Roles

Panstrongylus megistus is strictly a parasite. They may also be prey for the species with which they are associated, such as opossums and rodents. As a vector of Chagas disease, they infect human and non-human hosts with the protozoan Trypanosoma cruzi. Host populations are not affected by the actual blood-feeding since bites are painless and relatively little blood is lost. (CFSPH, 2006)

Species Used as Host

Economic Importance for Humans: Positive

There is no known positive economic importance of Panstrongylus megistus. (Gaunt M, 2000)

Economic Importance for Humans: Negative

Panstrongylus megistus is an important vector of Trypanosoma cruzi, the agent that causes Chagas' disease, a degenerative, often fatal ailment. Panstrongylus megistus acquires the protozoan from a mammalian reservoir host, such as the rodent or opossum it's associated with. It transmits this protozoan to humans through its feces. After depositing its feces on the human, an individual insect often feeds close to where it deposited the fecal matter. The protozoan may then enter the small perforation produced by the insect's mouthparts and thereby infects the human. Panstrongylus megistus defecates immediately following feeding and has short intervals between defecations, which makes it an excellent vector for the disease. The disease initially causes flu-like symptoms such as fever or headache but can progress to heart failure and malformation of the intestines over a long time. The disease affects over 15 million people and can kill up to 30,000 people annually. There are not many effective medications for the disease. (Gaunt M, 2000; Lent and Wygodzinsky, 1979; Pires, et al., 2002a)

Conservation Status

Currently, Panstrongylus megistus has no conservation status. (Lent and Wygodzinsky, 1979)

Contributors

Haidar Skeirek (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polarized light

light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sanguivore

an animal that mainly eats blood

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

CFSPH, 2006. "Center for Food Security and Public Health - Iowa State University" (On-line pdf). Accessed March 21, 2010 at http://www.cfsph.iastate.edu/FastFacts/pdfs/chagas_F.pdf.

Gaunt M, M. 2000. The ecotopes and evolution of triatomine bugs (triatominae) and their associated trypanosomes. Mem Inst Oswaldo Cruz, 95: 557-565.

Lent, H., P. Wygodzinsky. 1979. Revision of the Triatominae (Hemiptera, Reduviidae), and their significance as vectors of Chagas' disease. Bulletin of the American Museum of Natural History, 163: Article 3.

Pires, H., M. Lorenzo, C. Lazzarri, L. Diotaiuti, G. Manrique. 2004. The sexual behaviour of Panstrongylus megistus (Hemiptera: Reduviidae): an experimental study. Memórias do Instituto Oswaldo Cruz, 99 (3): 295-300.

Pires, H., C. Lazzarri, P. Schillman, L. Diotaiuti, M. Lorenzo. 2002. Dynamics of Thermopreference in the Chagas Disease Vector Panstrongylus megistus (Hemiptera: Reduviidae). Journal of Medical Entomology, 39: 716-719.

Pires, H., M. Lorenzo, L. Diotauiti, C. Lazzari, A. Figueiras. 2002. Aggregation behaviour in Panstrongylus megistus and Triatoma infestans: inter and intraspecific responses. Acta Tropica, 81: 47-52.