Chrysochus auratus, more commonly known as the dogbane beetle, is a leaf beetle primarily found in the eastern United States. The beetle is approximately 8 to 11 mm in length, possessing an oblong and convex shape. The beetle has two pairs of wings, one of which is a pair of copper colored elytra. The beetle is typically found to have a blue-green hue, and its color is often used to ward away potential predators. The beetle is typically found to have a blue-green hue, and its color is often used to ward away potential predators.

Dogbane beetle
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Infraorder: Cucujiformia
Family: Chrysomelidae
Subfamily: Eumolpinae
Tribe: Eumolpini
Genus: Chrysochus
Species:
C. auratus
Binomial name
Chrysochus auratus
(Fabricius, 1775)
Synonyms

Chrysomela aurata Fabricius, 1775

dog bane beetle (Chrysochus auratus)
dog bane beetle (Chrysochus auratus)

A major aspect of these beetles day to day life is sexual reproduction, as the beetles typically live a highly polygamous lifestyle.[1] This beetle has also been found to participate in interbreeding with Chrysocus coblatinus in certain geographic regions, resulting in hybrid offspring. Its diet consists primarily of dogbane (Apocynum), specifically Apocynum cannabinum and Apocynum androsaemifolium.[2] C. Auratus has developed several different adaptations that allow it to eat dogbane, such as its ability to process the dogbane leaf’s toxins. Due to its diet of exclusively dogbane, C. auratus has been considered as a potential mechanism of biological control for agricultural purposes.

Distribution and habitat edit

Chrysochus auratus is generally found in eastern North America, spanning the entire eastern United States and into adjacent southern Canada west of the Rocky Mountains. At the western edge of its range, it extends west of the Rocky Mountains into Arizona and Utah. The related species Chrysochus cobaltinus, in contrast, is found exclusively in western North America, and the two species were historically considered to have allopatric distributions. Recently, at least two narrow regions in western North America have been documented where both C. auratus and C. cobaltinus occur and apparently interbreed.[2]

Diet edit

Beetles of the Chrysochous genus typically feed on dogbane plants (Apocynaceae) and milkweeds (Asclepiadaceae). It has been found that C. auratus exclusively feeds on dogbane plants. More specifically, C. auratus feeds on Apocynum cannabinum and Apocynum androsaemifolium. Larvae of the dogbane beetle will typically feed on the roots of the plants while adults will feed on the leaves of the plants.[3] Plants in the Apocynum genus release toxins, called cardenolides, as a defense mechanism to predators. When ingested, it can be fatal for numerous organisms, as well as humans, resulting in cardiac arrest. Because C. auratus feed exclusively on Apocynum cannabinum and Apocynum androsaemifolium which release toxins, they have developed behavioral and physiological adaptations to overcome these plant’s defenses.

Cardenolides have the ability to bind to and block the function of Na+/K+ - ATPase, which is a transmembrane carrier present in almost all animals and tissues. It controls the balance of cell potentials and is vital to the nervous system, so when poisoned, these systems are affected. Therefore, this type of beetle has adapted to reduce the effects cardenolides has on Na+/K+ - ATPase, preventing it from being poisoned when consuming dogbane leaves. Chrysochus auratus has a single amino acid substitution in its Na+/K+ - ATPase that allows it to achieve this. The dogbane beetle is not only adapted to processing toxic cardenolide, it is also able to accumulate this compound in its own body to deter future predators. Cardenolide is shuttled through the beetle's body into cuticular glands, some of which are located in the elytra or wings. When the beetle senses some form of disturbance that requires a defensive mechanism, the beetle will secrete the cardenolides, poisoning its enemies.[4] This mutation may explain the dogbane beetle's insensitivity to the poisonous compounds, especially because this same mutation has been shown in the cardenolide-insensitive monarch butterfly.[5]

Dogbane beetles have also evolved to develop a behavioral mechanism to allow for feeding on the Apocynum genus. As a defense mechanism to predators, Apocynum cannabinum and Apocynum androsaemifolium (dogbane) produce a toxic sticky white latex when its stems and leaves are broken. When feeding, C. auratus beetles feed on the margins of A. cannabinum and A. androsaemifolium leaves. The beetle will chew a five to seven millimeter channel that sits diagonal from the leaf margin and points in the direction of the leaf’s apex. Because this channel transects the major veins of the leaf, these initial cuts will exude a large amount of latex, as the leaf activates its defensive mechanism. Distal to this initial cut location is the presence of low-latex tissue, which the beetle exclusively feeds on, biting on it in a downward motion. The feeding process typically lasts around one minute, and the beetle will straddle the leaf margins while feeding. As the beetles feed, latex accumulates on the ventral segments of their mouth due to the repetitive downward motion made by their head. Therefore, after feeding has ceased, the beetles will move from the margins of the leaf to the interior portion of the leaf. The beetle will then press its mouth to the surface of the leaf and drag its mouth on the leaf while walking backwards. This method removes the latex buildup from the beetle’s mouth region. Evidence of this behavior can be seen on leaves that have been fed on by C. Auratus, demonstrated by the rings of dried latex that can be found near the site of feeding.[6]

Reproduction edit

Adult male and female dogbane beetles usually copulate every day, about once each day. In this species, males are the picky of the two, and they will search for the fittest females to mate with. The way in which a male chooses which female is the most fit is via chemical signaling systems.[1] Dogbane beetles have notoriously low overall fitness, so the males have evolutionarily become more careful when choosing mates. Dogbane beetles use sex pheromones known as cuticular hydrocarbon signals to find which females are the fittest and which are not going to increase their direct fitness through procreation.[7] They are also known to be polygamous, and procreating often increases fecundity, and in turn fitness.[8] When the male has found a suitable mate, copulation begins. Copulation tends to occur earlier in the day and usually takes from an hour to an hour and a half, because the male perches himself on the female's back after insemination to make sure that she uses his sperm to fertilize her eggs and to keep other males away from the female. No parental care has been reported, except the fecal sac that she surrounds her eggs with when attaching them to the underside of the dogbane leaf.

 
Coupled dogbane beetles

Copulation typically occurs on the Apocynum plant, and after mating, females lay eggs on the underside of the leaves of the host plant and surrounding vegetation. After hatching from the egg in midsummer, the first instar larvae will drop to the ground and burrow into the soil. There, it will feed on tuberous rhizomes of the Apcoynum plants. Since Apocynum contains cardenolides that are very toxic to most animals, the ability of larvae to eat the plant prevents it from being preyed on by parasitic wasps. Soon after, the larvae will then pupate in a chamber in the same soil, and virgin adults remain in these chambers until they are ready to emerge. Adults will choose to come out of the chamber when their bodies have sufficiently hardened. This usually takes place in the early summer, and the adult beetle will stay in the host plant patch for the next six to eight weeks. Dogbane beetles typically produce one generation per year.[9]

Genetics edit

Both Chrysochus auratus and Chrysocus coblatinus are considered to have allopatric distributions. C. auratus has an eastern North American distribution, occupying eastern North America to the west of the Rocky Mountains. C. cobaltinus is exclusively found in western North America. In western North America, there are two regions where the distribution of these two species is sympatric, and there are four additional regions in which the two species are less than 100 km apart. In some of these areas of sympatry, there are areas, coined as “hybrid zones” where the two species participate in interbreeding. One such hybrid zone is located in the low-lying area of the Yakima River valley in Washington state where there is a 75 km wide region where C. auratus and C. cobaltinus interact. Evidence has indicated that this hybrid zone is of post-Pleistocene origin. During the late Pleitocene, central Washington and the Yakima River Valley faced flooding from glacial Lake Missoula. The current geographical distribution of the C. auratus suggests that after the Pleistocene glaciers receded, the population began to expand into south central Washington, resulting in this hybrid zone. In these areas, hybridization is frequent, but hybrid offspring of the two species have low fitness. Therefore, while hybridization is relatively common, positive assortative mating also has been found to occur.[1]

In many cases, the hybrid will be more similar to one parent compared to the other. It has been found that when this is the case, the hybrid is more similar to C. auratus. Hybrid males are also more likely to cluster with C. auratus beetles over C. cobaltinus beetles, and the same applies for hybrid females. If a hybrid female clusters with C. cobaltnius, the cluster likely also contains C. Cobaltinus males, C. auratus males, and hybrid males. Because the hybrids have lowered fitness and are usually sterile, C. auratus and C. cobaltinus ideally want to mate with beetles within their own respective species. However, in hybrid zones where there is a mix of the pure-bred and hybrid beetles, it can be difficult to make distinctions when a male is trying to choose a female mate. Studies have shown that C. cobaltinus males are able to make distinctions between C. cobaltinus and C. auratus females, even in hybrid zones.[10]

Physiology edit

Adult dogbane beetles are typically an iridescent blue-green color, an appearance that plays to their advantage as it wards off predators. The beetle is typically eight to eleven millimeters in length with an oblong and convex shape. It has a bluish black undersurface. The beetle possesses a pair of antennae that are long and twelve joined. They are located between the eye and frontal ridge of the head and are widely separated at their base.

 

The Chrysochus auratus is divided into three large divisions: head, thorax, and abdomen. It shares this external anatomy with most other insects. Its hind two pairs of legs are attached to the thorax, and it has a highly chitinized body. The head and thorax have deep punctures intermingled with smaller punctures all throughout. This beetle also has a blunt mandible, characteristics of its herbivorous diet. It has a longer left mandible than the right side which fits into an indentation in the left mandible. Attached to its thorax, C. auratus beetles possess two pairs of wings. The first pair of wings or elytra are heavily chitinized and are not used for flight. Their main purpose is to protect the more fragile hind wings. The elytra also form the hard case of the beetle, covering the entire dorsal surface of the beetle, and giving off a coppery tinge. The elytra, similar to the head and thorax, contains punctures, but they are smaller and more irregular compared to other parts of the body. The second pair of wings is primarily used for flight and is membranous in texture. While C. auratus do not migrate, they do use their wings to fly between plants in their host patch. The wings have complex venation that vary between beetles. When the wings are folded, certain portions of the wing will reverse. This species of beetle has also adapted to have a large hypopharynx, which allows it to lap up juices from the plants on which it preys.[11]

Agricultural Use edit

Due to C. auratus' use of Apocynum as a food source, the beetle has been considered as a potential mechanism of biological control for Apocynum. Apocynum (dogbane) is a native perennial weed that affects lowbush blueberries. The above-the-ground portion of the dogbane plant interferes with blueberry harvest and can prevent growth of blueberries, by shading the blueberry plant. The latex sap in the dogbane leaves can also potentially poison blueberries. Controlling the spread of this dogbane is difficult, as there are only few effective herbicides, many of which harm the blueberry plant as well. Because C. Auratus naturally feeds on dogbane, the beetle has been considered as a biological mechanism of control. Research on this topic has consistently shown that while an inundation of C. Auratus could cause a significant effect of spreading dogbane, natural populations of the beetle would not cause enough of an effect to single handedly control the population. Therefore, many integrated management programs for dogbane proliferation are working on strategies to conserve and augment the C. Auratus population for agricultural use.[12]

C. auratus has also been considered as a potential mechanism of biological control for a nonnative European vine called Vincetoxicum rossicum. Because C. auratus feed on plants in the Apocynaceae family, which this vine also falls under, it has been considered as a potential solution to prevent the spread of the vine. However, experiments showed that while C. Auratus is very reproductively successful on Apocynum cannabinum and Apocynum androsaemifolium leaves, this success does not apply to Vincetoxicum rossicum. This beetle lays its eggs on the underside of leaves, and experiments showed that Vincetoxicum rossicum leaves were an oviposition sink for C. auratus eggs, meaning that depositing eggs on the underside of these leaves resulted in a low probability of successful development and survival for their larvae. Therefore, C. auratus was concluded to not necessarily be a successful avenue for Vincetoxicum rossicum control.[13]

References edit

  1. ^ a b c Peterson, Merrill; Honchak, Barbara; Locke, Steranie; Beeman, Timothy; Mendoza, Jessica; Green, Jabin; Buckingham, Kati (May 2007). "Relative Abundance and the Species-Specific Reinforcement of Male Mating in the Chrysochus (Coleoptera: Chrysomelidae) Hybrid Zone". Evolution. 59 (12). doi:10.1111/j.0014-3820.2005.tb00976.x. S2CID 25481151.
  2. ^ a b Peterson, M. A.; Dobler, S.; Holland, J.; T., L.; Locke, S. (2001). "Behavioral, Molecular, and Morphological Evidence for a Hybrid Zone Between Chrysochus auratus and C. cobaltinus (Coleoptera: Chrysomelidae)" (PDF). Annals of the Entomological Society of America. 94 (1): 1–10. doi:10.1603/0013-8746(2001)094[0001:BMAMEF]2.0.CO;2.
  3. ^ MacEachern-Balodis, M.C., Boyd, N.S., White, S.N. et al. Examination of dogbane beetle (Chrysochus auratus) feeding and phenology on spreading dogbane, and considerations for biological control. Arthropod-Plant Interactions 11, 807–814 (2017). https://doi.org/10.1007/s11829-017-9535-3
  4. ^ Estelle Labeyrie, Susanne Dobler, Molecular Adaptation of Chrysochus Leaf Beetles to Toxic Compounds in Their Food Plants, Molecular Biology and Evolution, Volume 21, Issue 2, February 2004, Pages 218–221, https://doi.org/10.1093/molbev/msg240
  5. ^ Karageorgi, Marianthi; Groen, Simon C.; Sumbul, Fidan; Pelaez, Julianne N.; Verster, Kirsten I.; Aguilar, Jessica M.; Hastings, Amy P.; Bernstein, Susan L.; Matsunaga, Teruyuki; Astourian, Michael; Guerra, Geno (2019-10-17). "Genome editing retraces the evolution of toxin resistance in the monarch butterfly". Nature. 574 (7778): 409–412. doi:10.1038/s41586-019-1610-8. ISSN 0028-0836. PMC 7039281. PMID 31578524.
  6. ^ Williams, Charles. (1991). Host plant latex and the feeding behavior of Chrysochus auratus (Coleoptera: Chrysomelidae). The Coleopterists Bulletin. 45. 195-196.
  7. ^ Kerins, Hallie (2000). "Reproductive Character Displacement and X-linkage of Cuticular Hydrocarbons in Chrysochus beetles". WWU Honors Program Senior Projects. 227 – via CEDAR.
  8. ^ Larson, Erica; Brassil, Margaret; Maslan, Jonathan; Juárez, Danielle; Lilagan, Flordeliza (September 2019). "The Effects of Heterospecific Mating Frequency Strength of Cryptic Reproductive Barriers". Journal of Evolutionary Biology. 32 (9): 900–912. doi:10.1111/jeb.13495. PMID 31162735. ProQuest 2235068440.
  9. ^ Peterson, M., K. Monsen, H. Pedersen, T. McFarland, J. Bearden. 2005. Direct and indirect analysis of the fitness of Chrysochus (Coleoptera: Chrysomelidae) hybrids.. Biological Journal of the Linnean Society, 84: 273-286.
  10. ^ Estelle Labeyrie, Susanne Dobler, Molecular Adaptation of Chrysochus Leaf Beetles to Toxic Compounds in Their Food Plants, Molecular Biology and Evolution, Volume 21, Issue 2, February 2004, Pages 218–221, https://doi.org/10.1093/molbev/msg240 Kerins, Hallie (2000). "Reproductive Character Displacement and X-linkage of Cuticular Hydrocarbons in Chrysochus beetles". WWU Honors Program Senior Projects. 227 – via CEDAR.
  11. ^ Wilson, Sloan Jacob (1934). "The Anatomy of Chrysochus auratus, Fab., Coleoptera: (Chrysomelidae) with an Extended Discussion of the Wing Venation". Journal of the New York Entomological Society. 42 (1): 65–85. ISSN 0028-7199. JSTOR 25004541.
  12. ^ MacEachern-Balodis, M.C., Boyd, N.S., White, S.N. et al. Examination of dogbane beetle (Chrysochus auratus) feeding and phenology on spreading dogbane, and considerations for biological control. Arthropod-Plant Interactions 11, 807–814 (2017). https://doi.org/10.1007/s11829-017-9535-3
  13. ^ R. B. deJonge, R. S. Bourchier, S. M. Smith, Initial Response by a Native Beetle, Chrysochus auratus (Coleoptera: Chrysomelidae), to a Novel Introduced Host-Plant, Vincetoxicum rossicum (Gentianales: Apocynaceae), Environmental Entomology, Volume 46, Issue 3, June 2017, Pages 617–625, https://doi.org/10.1093/ee/nvx072

External links edit