Chrysochus auratus (Fabricius 1775)

Dogbane plants (Apocynaceae) eaten by dogbane beetles contain cardenolides, which deter pathogens and herbivores. Cardenolides are bitter and toxic to insects. However, many herbivorous insects, such as dogbane beetles, have developed adaptations that allow them to ingest and sequester the toxin. Dogbane beetles can use the compounds as a defense mechanism against predators in the same way that plants do. When the beetle is disturbed, cardenolides released through glands on the pronotum and elytra deter predation. Larvae that have high concentrations of the toxin are parasitized less frequently by parasitic wasps.

Anti-predator Adaptations: aposematic

Adult dogbane beetles are distinctly colored, iridescent blue-green chrysomelids with elytra that have a copper shine. The antennae and legs are a bluish-black. The head and thorax have sporadic punctures that are deep and minute. They have long, 12-jointed, filiform antennae that are located between the eyes and frontal ridge. The mandibles are blunt and built for a herbivorous diet. The left is longer than the right and fits into a groove in the right. Their large hypopharynx is thought to be an adaptation to lapping the juice of milkweed plants. Larvae have a white body and brown head.

Range length: 8 to 11 mm.

Sexual Dimorphism: sexes alike

Other Physical Features: ectothermic ; bilateral symmetry

After adults emerge in early summer, they spend their 6 to 8 week lifespan on host plants, mating an average of once per day.

Typical lifespan
Status: wild: 42 to 56 days.

Dogbane beetles are found in areas where host plants live. They feed and live mainly on dogbane plants (Apocynaceae), especially Indian hemp (Apocynum cannabinum) and spreading dogbane (A. androsaemifolium). Indian hemp, often regarded as a weed, can be found throughout the entire United States in various soil types. It prefers open habitats where it can spread, such as roadsides, fields, railroad tracks, lakeshores, and disturbed areas. Spreading dogbane is found in the northeastern United States. This plant also spreads easily and can survive in a number of habitats. It prefers forests, forest edges, streambanks, and fields with sandy or gravelly soils.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: savanna or grassland ; forest ; scrub forest

Other Habitat Features: suburban ; agricultural ; riparian

Dogbane beetles live in the Nearctic Region throughout the eastern United States and southern Canada. The western boundaries of its range are the Rocky Mountains, Utah, and Arizona.

Biogeographic Regions: nearctic (Native )

Dogbane beetles feed mainly on dogbane plants (Apocynaceae), specifically Indian hemp (Apocynum cannabinum) and spreading dogbane (Apocynaceae androsaemifolium). They are also known to feed on milkweed (Asclepiadaceae). To deter herbivores, dogbane plants expel a milky latex that dries and sticks to mouthparts of other insects. Dogbane beetles do not cut leaf veins prior to feeding like many herbivorous insects. They feed on the low-latex tissue of the distal part of leaves. After feeding and accumulating latex on mouthparts, dogbane beetles place their mouthparts on the leaf and walk backward in order to rub the latex off. Walking backward prevents the insect from walking through the latex smear and accumulating latex on its feet. Latex bands of approximately 2 mm in width and 2 cm in length have been observed on dogbane plants. Dogbane beetle larvae feed on the roots of the host plants.

Plant Foods: leaves; roots and tubers; flowers

Primary Diet: herbivore (Folivore )

Dogbane beetles eat and live on dogbane plants (Apocynaceae), specifically Indian hemp (Apocynum cannabinum) and spreading dogbane (A. androsaemifolium). They also occasionally live and feed on milkweed plants (Asclepiadaceae).

Species Used as Host:

• dogbanes (Apocynum cannabinum)
• Indian hemp (Apocynum cannabinum)
• spreading dogbane (Apocynum androsaemifolium)
• milkweed (Asclepiadaceae)

There are no known positive economic impacts of dogbane beetles on humans.

Leaf beetles in the Chrysomelid family use visual, olfactory and chemical cues when colonizing a host plant. Dogbane leaf beetles in particular use chemical signaling systems in mating. Cuticular hydrocarbon (CHC) signals serve as sex pheromones. CHCs are sex-specific and species-specific and influence male dogbane beetles in mate choice. It is thought that the species-specific aspect of these pheromones suggests that evolutionary forces are selecting against interspecific mating.

Communication Channels: visual ; chemical

Other Communication Modes: pheromones

Perception Channels: visual ; chemical

Dogbane beetles are not known to be endangered. Their conservation status is not evaluated by the IUCN Red List of Threatened Species.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

First instar larvae hatch from eggs in midsummer and burrow into the soil where they feed externally on host plant roots. Larvae pupate in a chamber in the soil, where they remain until their bodies harden enough to burrow up to the surface in early summer. Adults mate and lay eggs throughout the rest of the summer after emergence.

Development - Life Cycle: metamorphosis ; diapause

There are no known negative economic impacts of dogbane beetles on humans.

Dogbane beetle males and females mate an average of once per day during their lifetime, taking multiple mates. Males actively search out and choose females to mate with; female choice is ineffective. The entire mating process usually lasts over an hour and a half due to postcopulatory mate guarding, where males ride on the females backs after insemination in order to ensure that the female uses his sperm to fertilize her eggs. Mating usually takes place early in the day.

Interspecies mating has been observed between dogbane beetles and cobalt milkweed beetles (Chrysochus cobaltinus) toward the western boundary of the dogbane beetle range. Viable hybrid offspring are produced. In areas where both species are present, hybrids make up 10-15% of the total combined populations. Hybrid offspring have an intermediate morphology; they range from blue-green in color to brown-purple with brown abdominal sterna, which contrasts with the shiny green of dogbane beetles and blue of cobalt milkweed beetles. As adults, F1 offspring mate as frequently as non-hybrids, but they cannot reproduce. Dogbane beetle males are generally less choosy than cobalt milkweed beetles. For those that live in the hybrid zone, however, males of both species are usually more choosy.

Mating System: polygynandrous (promiscuous)

Dogbane beetles lay eggs on leaves and stems of host plants and nearby vegetation in masses of egg capsules. The capsules are usually 3 mm wide by 2 mm tall.

Breeding interval: Dogbane beetles produce one generation each year.

Breeding season: Adults mate from mid to late summer.

Key Reproductive Features: seasonal breeding ; sexual ; fertilization (Internal ); oviparous

No information is available on parental care. Females provision eggs, which are left on plants to mature on their own.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female)

Nothing indicating that the species is rare or threatened. Within its range, it is commonly reported.

Adults emerge from underground in early summer, and are present during the remaining summer months. The Strickland Museum specimens indicate that C. auratus is common into late summer, as many specimens were collected between June and August.

Found across the United States, from southern Canada to New Mexico (Dobler & Farrell 1999), east of the Rocky Mountains. In Utah and Arizona, species can be found extending west into the Rocky Mountains (Peterson et al. 2001). In Canada, species can be found in eastern Alberta, and southern Saskatchewan. Specimens from the Strickland Museum have been collected from the Medicine Hat area, New Jersey, and Chicago.

6.8-11.3 mm in length. Vivid metallic golden green in colour, with green abdominal sterna (Peterson et al. 2001). Antennae and legs are dark blue in colour, and antennae are filiform and 12-jointed. The mandibles are adapted for herbivory, and the left is longer than the right. The left mandible rests inside a groove on the right (Wilson 1934).

Species occupies habitat where host plants are found, and range from riparian to agricultural areas. Often found in open, disturbed areas, or along forest edges, lakeshores, and areas with gravelly soil. (Dobler & Farrel 1999 and Peterson et al. 2001).

Along with C. colbaltinus, C. auratus is the only North American representative of the genus (Peterson et al. 2001). Their host plants provide them with chemical compounds called cardenolides, which are used for predator defense (Dobler & Farrell 1999). Species exhibit little sexual dimorphism. They produce a single generation per year. First instar larvae hatch in midsummer, and burrow into the soil, where they pupate. The average lifespan is approximately 6 to 8 weeks. They mate once per day during their lifespan, usually early in the day, and males engage in post-copulatory mate guarding, which can last for 1.5 hours. They have been found to engage in interspecific copulation with C. colbaltinus, producing viable offspring with unique behaviour and phenotype, although hybrids tend to be sterile (Peterson et al. 2001).

Species feeds on dogbane plants, Apocynaceae (Dobler & Farrell 1999). The larvae are obligate root feeders, and adults eat the leaves of larval host plants (Peterson et al. 2001). Species has been reported to feed on milkweed plants, but research with food choice trials has indicated that many individuals will only feed on dogbane species (Dobler & Farrell 1999).

dog bane beetle (Chrysochus auratus)

Chrysochus auratus, the dogbane beetle, of eastern North America, is a member of the leaf beetle subfamily Eumolpinae. It is primarily found east of the Rocky Mountains. Its diet mainly consists of dogbane (Apocynum), specifically Apocynum cannabinum and Apocynum androsaemifolium, and occasionally it eats milkweed. It is 8-11 mm long and has a convex, oval shape.