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Stiretrus anchorago

By Brian Scholtens

Geographic Range

Stiretrus anchorago occurs in the Nearctic Region from New England and Ontario south to Florida and Mexico. Its range extends as far west as Iowa, Kansas, and Texas. It has also been reported from California. (Blatchley, 1926; McPherson, 1982)

Habitat

Stiretrus anchorago can be found primarily in open areas, including waste areas, old fields and agricultural fields, where it often feeds on pest herbivores. It also occurs along the margins of hammocks and swales in Florida. (Blatchley, 1926; Howard and Landis, 1936; McPherson and Mohlenbrock, 1976; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008; Richman and Whitcomb, 1978; Waddill and Shepard, 1975)

Physical Description

Adult: Stiretrus anchorago is a striking species of stink bug with quite variable coloration. The color ranges from solid steel blue (form violaceus) to blue-black with red, orange and cream markings on the pronotum, scutellum, and sides of abdomen (form anchorago - mainly northern), to reddish brown with mainly yellow markings (form fimbriatus - mainly southern). Other color variants are known, including form personatus, with a red pronotum, a wide, blue-black median stripe extending from the front of the pronotum to the tip of the scutellum, and two spots on each side of the pronotum. The species is easily distinguished by the scutellum, which is unusually large and U-shaped, nearly reaching the end of the abdomen, and resembling a shield bug (Scutelleridae). (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

Eggs: The eggs are darkly pigmented, nearly black, from 1.24 to 1.35 mm in length (mean = 1.30 mm) and 0.86 to 1.13 mm in diameter (mean = 1.03 mm). Their upright shape is oval, being widest at the middle. They have serrated ridges in a reticulated pattern. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

First Instar: The earliest instar is 1.24 to 1.35 mm (mean 1.31 mm) long and 1.27 to 1.30 mm (mean 1.28 mm) wide. It is round or oval and widest at the third or fourth abdominal segment. The dorsal surface is mainly fuscous, with a reddish-orange median marking and reddish-orange eyes. The ventral surface is reddish-orange. The legs are fuscous. The antennae are four-segmented, about 1.10 mm long and lighter colored than the head. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

Second instar: The second instar is 2.27 to 2.43 mm (mean 2.37 mm) long and 2.19 to 2.30 mm (mean 2.23 mm) wide. The shape is similar to the first instar. The entire dorsal surface is black, and the eyes are bright red. The ventral surface is mainly reddish-orange. The legs are pale yellow, except for the coxae, the proximal half of the femora, and distal half of the second tarsus, which are all fuscous. The antennae are 1.84 mm long. The first and last segments are fuscous, and the middle two are pale. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

Third instar: This stage is 3.46 to 3.89 mm long (mean 3.73 mm) and 3.24 to 3.29 mm wide (mean 3.26 mm). The coloration is very similar to the second instar, but the legs are entirely pale except the distal third of the second tarsus, and the basal segment of the antenna is pale. The antennal length is 2.49 mm. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

Fourth instar: The fourth instar is 4.75 o t5.35 mm long (mean 5.00 mm) and 4.21 to 4.64 mm wide (mean 4.44 mm). The coloration is basically identical to the third instar, but the forewing pads extend to the caudal edge of the metatergum. The antennal length is 3.37 mm. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

Fifth instar: The final nymphal instar is 6.48 to 8.32 mm long (mean 7.16 mm) and 5.29 to 5.89 mm wide (mean 5.58 mm). The head coloration is similar to the third and fourth instars, with the antennal length 4.39 mm. The thorax is mainly black dorsally, with a yellow, triangular, median mark on the mesothorax, and sometimes with yellowish lateral spots on the pro- and mesothorax. The forewing pads extend to the middle of the third abdominal segment, with the hindwing pads visible between them. The legs are similar to the fourth instar. The dorsal abdomen is still black, but the ventral surface is yellow-orange, with five median spots. (Blatchley, 1926; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008)

  • Sexual Dimorphism
  • female larger
  • Range length
    7 to 11.5 mm
    0.28 to 0.45 in

Development

Stiretrus anchorago has incomplete metamorphosis typical of true bugs (Hemiptera). The egg stage lasts 8 to 11 days, first instar 4 to 8 days, second instar 3 to 8 days, third instar 3 to 7 days, fourth instar 4 to 6 days, and the fifth instar 7 to 15 days. There is no information on the length of the adult stage. The species is presumed to be bivoltine over most of its range because of the appearance of adults twice during the season. Adults diapause over winter and start laying eggs early in the spring. The second generation starts egg-laying in late May or early June. Females lay several egg masses, with about 4 days in between each mass. The eggs are laid in a double row, with a mean of 11.4 eggs per mass. The first instar hatches and remains near the eggs without feeding. After molting to the second instar, the nymphs become predators on smaller insects and this continues through the adult stage. Nymphs stop feeding for about 2 days before each molt. (Oetting and Yonke, 1971; Rebagliati, et al., 2005; Richman and Mead, 2008; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

This species has 14 chromosome pairs, which is the most common number for species in their order (Pentatomidae). Males have XY chromosomes, while females have XX chromosomes. (Oetting and Yonke, 1971; Rebagliati, et al., 2005; Richman and Mead, 2008; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

Reproduction

Stiretrus anchorago has two generations per year over most of its range. Both males and females will have multiple matings with different individuals. Individuals are otherwise solitary. (Aldrich, et al., 1986; Kochansky, et al., 1989; Oetting and Yonke, 1971; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

Recently, it has been determined that males have a pheromone-producing structure on the underside of the abdomen. This consists of a set of velvety patches of darker color. These patches emit 6,10,13-trimethyl-1-tetradecanol, with a small amount of other components. This compound has been shown to attract both males and females in the field, but they rarely approach closely to the source. Evidently there are other important cues need for the final attraction, possibly visible cues. (Aldrich, et al., 1986; Kochansky, et al., 1989; Oetting and Yonke, 1971; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

Adults breed and lay eggs continuously while alive. Females lay a mean of 11.4 eggs per mass, with at least one female recorded laying 6 masses, for a total of about 68 to 70 eggs per female. Although generations may overlap, there are two generations per year, with the first generation reproducing from early spring through May and the second generation reproducing from late May or early June through fall. Immatures are independent, the only adult contribution being nutrients in the egg. Reproduction is only known to be sexual, with internal fertilization of ova. (Oetting and Yonke, 1971; Richman and Mead, 2008; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

  • Breeding interval
    Individuals breed continuously as adults, with adults occurring early in the season through about June and starting again in early August. Females lay eggs about every 4 days during the mating season.
  • Breeding season
    Adults mate continuously while alive, from early in season to about June, and then from early August into the fall.
  • Average eggs per season
    about 68-70
  • Range gestation period
    8 to 11 days

There is essentially no parental investment in this species, except nutrients deposited in eggs. (Oetting and Yonke, 1971; Richman and Whitcomb, 1978; Waddill and Shepard, 1974)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

Individuals of Stiretrus anchorago live no more than a few weeks to months. Under captive rearing the egg stage lasts 8 to 11 days, first instar 4 to 8 days, second instar 3 to 8 days, third instar 3 to 7 days, fourth instar 4 to 6 days, and fifth instar 7 to 15 days. No data are available on the length of adult life in this species, but adults have been reported from throughout the summer, indicating an overlap of the generations, and an indication that individuals live at least a few weeks as adults. The last generation of the year overwinters as adults, and thus has a longer adult lifespan, although mostly inactive. (McPherson, 1982; Oetting and Yonke, 1971)

Behavior

Stiretrus anchorago is a solitary species. It actively moves through its environment seeking prey. Although it has fully developed wings as an adult it doesn't generally fly, as is true of most stink bugs. (Blatchley, 1926; McPherson, 1982)

Home Range

This species does not exhibit territorial behavior and has no defined home range. It moves freely throughout its habitat. (Blatchley, 1926; McPherson, 1982; Richman and Mead, 2008)

Communication and Perception

As with many insects, this species apparently communicates mainly by using olfaction and vision. Males are known to release a pheromone that attracts females (and other males), but attracted individuals do not approach closely to artificial sources of the pheromone, and it is presumed that they use visual attraction at close range. Although this has not been studied, the species presumably uses its antennae for olfaction (typical of insects), and probably detects potential prey item using largely scent and, at close range, vision. Typical of all stink bugs, this species has thoracic glands that produce a musty odor when handled, presumably as an anti-predator mechanism. (Aldrich, et al., 1986; Blatchley, 1926; Kochansky, et al., 1989; McPherson, 1982; Rebagliati, et al., 2005; Staddon, 1979)

Food Habits

First instars of this species do not feed, but evidently need a source of water for survival. Stiretrus anchorago is a predator from the second instar through adulthood. It is known to be an insectivore, feeding on the larvae of Lepidoptera and Coleoptera. It consumes larvae by stabbing them with its beak (rostrum), secreting digestive enzymes, and then sucking back the digested contents. In the Lepidoptera, it has been found feeding on black swallowtails (Papilio polyxenes), sleepy oranges (Eurema nicippe), Baltimore checkerspots (Euphydryas phaeton), soybean loopers (Pseudoplusia includens), cabbage loopers (Trichoplusia ni), gypsy moths (Lymantria dispar), and tent caterpillars (Malacosoma americanum). Among beetles (Coleoptera), it has been recorded feeding on the larvae of alfafa weevils (Hypera postica), Mexican bean beetles (Epilachna varivestis), squash beetles (Epilachna borealis), Colorado potato beetles (Leptinotarsa decemlineata), sumac flea beetles (Blepharida rhois), green tortise beetles (Nuzonia pallidula), ragweed leaf beetles (Zygogramma suturalis), leaf beetles (Zygogramma heterothecae), spotted asparagus beetles (Crioceris asparagi), cottonwood leaf beetles (Chrysomela scripta), and elm leaf beetles (Xanthogaleruca luteola). At least one species of tortoise beetle (Hemisphaerota cyanea) uses long strands of frass to protect itself from some predators, and Stiretrus anchorago is deterred by this defense, so not all Chrysomelidae are used as prey. (Blatchley, 1926; Dietz, et al., 1976; Eisner and Eisner, 2000; Hayslip, et al., 1953; Howard and Landis, 1936; McPherson and Mohlenbrock, 1976; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008; Richman and Whitcomb, 1978; Richman, 1977; Scholtens, 1990; Waddill and Shepard, 1974; Waddill and Shepard, 1975)

Observations of adults probing the flowers of goldenrod may indicate some nectar feeding, but this has not been confirmed. (Blatchley, 1926; Dietz, et al., 1976; Eisner and Eisner, 2000; Hayslip, et al., 1953; Howard and Landis, 1936; McPherson and Mohlenbrock, 1976; McPherson, 1982; Oetting and Yonke, 1971; Richman and Mead, 2008; Richman and Whitcomb, 1978; Richman, 1977; Scholtens, 1990; Waddill and Shepard, 1974; Waddill and Shepard, 1975)

  • Animal Foods
  • insects

Predation

Typical of all stink bugs, this species has thoracic glands that produce a musty odor when handled, presumably as an anti-predator mechanism. No predators have been recorded. (Eger and Ables, 1981; Oetting and Yonke, 1971)

Ecosystem Roles

This species is one of many fairly generalist insect predators that feed by using sucking mouthparts to take in nutrients from a prey item. It may have an impact in some agricultural settings, where it can be fairly common. It is most likely to have an impact on the specific beetle, moth, or butterfly populations that it utilizes as its main food sources, but it was only a minor source of mortality in one detailed study of survivorship in the Baltimore checkerspot butterfly (Euphydryas phaeton). It also serves as a host for tachinid flies (Cylindromyia fumipennis). The tachinid fly was reared from adults twice, with the larvae emerging from the adult bug, forming its pupa, and emerging about 10 days later. (Blatchley, 1926; Eger and Ables, 1981; Hayslip, et al., 1953; Howard and Landis, 1936; McPherson, 1982; Oetting and Yonke, 1971; Richman, 1977; Scholtens, 1990; Waddill and Shepard, 1974; Waddill and Shepard, 1975)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There may be some benefit that this species provides in agricultural fields, at least in southern parts of the United States. It has been noted as a predator in both soybean and alfalfa fields and is known to consume major herbivores on these crops. No controlled studies have documented a significant positive effect on production. (DeCoursey and Allen, 1968; Hayslip, et al., 1953; Howard and Landis, 1936; McPherson, 1982; Richman and Mead, 2008; Richman, 1977; Waddill and Shepard, 1974; Waddill and Shepard, 1975)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There is no indication that this species has a negative impact on humans. People may occasionally experience the musty odor emitted from the "stink" glands, but this causes no real discomfort. (Blatchley, 1926; McPherson, 1982; Staddon, 1979)

Conservation Status

Stiretrus anchorago is not listed as an endangered or threatened species on any international, national, or state lists.

Contributors

Brian Scholtens (author, editor), University of Michigan Biological Station, Catherine Kent (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

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

chemical

uses smells or other chemicals to communicate

diapause

a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

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

fertilization

union of egg and spermatozoan

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

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.

oviparous

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

pheromones

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

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.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

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.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Aldrich, J., J. Oliver, W. Lusby, J. Kochansky. 1986. Identification of male-specific exocrine secretions from predatory stink bugs (Hemiptera, Pentatomidae). Archives of Insect Biochemistry and Physiology, 3: 1-12.

Blatchley, W. 1926. Heteroptera or true bugs of eastern North America with especial reference to the faunas of Indiana and Florida. Indianapolis, IN: Nature Publication Company.

DeCoursey, R., R. Allen. 1968. A generic key to the nymphs of the Pentatomidae of the eastern United States (Hemiptera: Heteroptera). University of Connecticut Occasional Papers (Biological Science Series), 1: 141-151.

Dietz, L., J. Van Duyn, J. Bradley, R. Rabb, W. Brooks, R. Stinner. 1976. A guide to the identification and biology of soybean arthropods in North Carolina. North Carolina Agricultural Experiment Station Technical Bulletin, 238: 1-264.

Eger, J., J. Ables. 1981. Parasitism of Pentatomidae by Tachinidae in South Carolina and Texas. Southwestern Entomologist, 6: 28-33.

Eisner, T., M. Eisner. 2000. Defensive use of a fecal thatch by a beetle larva (Hemisphaerota cyanea). Proceedings of the National Academy of Sciences, 97: 2632-2636.

Hayslip, N., W. Genung, E. Kelsheimer, J. Wilson. 1953. Insects attacking cabbage and other crucifers in Florida. University of Florida Agricultural Experiment Station Bulletin, 534: 1-57.

Howard, N., B. Landis. 1936. Parasites and predators of the Mexican bean beetle in the United States. U.S. Department of Agriculture Circular, 418: 1-12.

Kochansky, J., J. Aldrich, W. Lusby. 1989. Synthesis and pheromonal activity of 6,10,13-trimethyl-1-tetradeconal for predatory stink bug, Stiretrus anchorago (Heteroptera: Pentatomidae). Journal of Chemical Ecology, 15: 1717-1728.

McPherson, J. 1982. The Pentatomoidea (Hemiptera) of northeastern North America with emphasis on the fauna of Illinois. Carbondale, IL: Southern Illinois University Press.

McPherson, J., R. Mohlenbrock. 1976. A list of the Scutelleroidea of the La Rue-Pine Hills Ecological Area with notes on biology. Great Lakes Entomologist, 9: 125-169.

Millar, J. 2005. Pheromones of true bugs. Topics in Current Chemistry, 240: 37-84.

Oetting, R., T. Yonke. 1971. Immature stages and biology of Podisus placidus and Stiretrus fimbriatus (Hemiptera: Pentatomidae). Canadian Entomologist, 103: 1505-1516.

Rebagliati, P., L. Mola, A. Papeschi, J. Grazia. 2005. Cytogenetic studies in Pentatomidae (Heteroptera): A review. Journal of Zoological Systematics and Evolutionary Research, 43: 199-213.

Richman, D. 1977. Predation on the alfalfa weevil, Hypera postica (Gyllenhal), by Stiretrus anchorago (F.) (Hemiptera: Pentatomidae). Florida Entomologist, 60: 192.

Richman, D., F. Mead. 2008. "Predatory stink bug, Stiretrus anchorago (Fabricius) (Insecta: Hemiptera: Pentatomidae)" (On-line pdf). Accessed June 13, 2012 at edis.ifas.ufl.edu/pdffiles/IN/IN38600.pdf.

Richman, D., W. Whitcomb. 1978. Comparative life cycles of four species of predatory stink bugs. Florida Entomologist, 61: 113-119.

Scholtens, B. 1990. Pre-alighting host plant location in the Baltimore checkerspot butterfly, Euphydryas phaeton, and its implications for host range evolution in butterflies. Ann Arbor, MI: University of Michigan.

Staddon, B. 1979. The scent glands of Heteroptera. Advances in Insect Physiology, 14: 351-418.

Waddill, V., M. Shepard. 1975. A comparison of predation by the pentatomids, Podisus maculiventris (Say) and Stiretrus anchorago (F.), on the Mexican bean beetle, Epilachna varivestis Mulsant. Annals of the Entomological Society of America, 68: 1023-1027.

Waddill, V., M. Shepard. 1974. Biology of a predaceous stink bug, Stiretrus anchorago, (Hemiptera: Pentatomidae). Florida Entomologist, 57: 249-253.

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