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.
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.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- savanna or grassland
- Wetlands
- marsh
- Other Habitat Features
- suburban
- agricultural
- riparian
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
).
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.
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.
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.
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.
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.
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.
- Other Physical Features
- ectothermic
- bilateral symmetry
- polymorphic
- Sexual Dimorphism
- female larger
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.
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.
- Development - Life Cycle
- metamorphosis
- diapause
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.
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.
- Mating System
- polygynandrous (promiscuous)
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
There is essentially no parental investment in this species, except nutrients deposited
in eggs.
- Parental Investment
-
pre-hatching/birth
-
provisioning
- female
-
provisioning
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.
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.
- Key Behaviors
- flies
- diurnal
- motile
- hibernation
- solitary
Home Range
This species does not exhibit territorial behavior and has no defined home range.
It moves freely throughout its habitat.
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.
- Other Communication Modes
- pheromones
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.
Observations of adults probing the flowers of goldenrod may indicate some nectar feeding,
but this has not been confirmed.
- Primary Diet
- carnivore
- 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.
- Anti-predator Adaptations
- aposematic
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.
- tachinid flies ( Cylindromyia fumipennis )
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.
- 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.
Conservation Status
Stiretrus anchorago is not listed as an endangered or threatened species on any international, national, or state lists.
Additional Links
Contributors
Brian Scholtens (author, editor), University of Michigan Biological Station, Catherine Kent (editor), Special Projects.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- 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.
- 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.
- 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.
- 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.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- 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).
- 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
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- 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.
- solitary
-
lives alone
- visual
-
uses sight to communicate
- chemical
-
uses smells or other chemicals to communicate
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- visual
-
uses sight to communicate
- chemical
-
uses smells or other chemicals to communicate
- 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.
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
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