Chrysochus cobaltinus

Chrysochus cobaltinus, the cobalt milkweed beetle or blue milkweed beetle, is a member of the diverse family leaf beetles (Chrysomelidae). It occurs in the Western United States and British Columbia.

Chrysochus cobaltinus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Chrysomelidae
Genus: Chrysochus
Species:
C. cobaltinus
Binomial name
Chrysochus cobaltinus
LeConte, 1857
Synonyms[1]

Appearance

C. cobaltinus has an iridescent cobalt-blue exoskeleton. Both sexes range from 6–9 millimetres (0.24–0.35 in) in length, with clubbed antenna. The elytra usually have more or less evident epipleura, changing within the varying species within the Chrysomelidae. It rarely has an exposing pygidium. The body is oval, although the ventral is not prominently convex.

Behavior

C. cobaltinus is similar to click beetles in being able to launch themselves a couple times the length of their body.

Both adults and larvae feed on milkweed plants. Adults typically feed on the foliage and flowers of the newly developed milkweed plant. When a large community appears, they consume a large portion of the leaf tissue from the plant, which causes significant damage to the plant. The adults eat holes in the leaves of milkweed, appearing in spring as the days become warmer and the milkweed leaves begin to develop. During the spring they disperse in large numbers on various plants within the same area of distribution.

Life cycle
Chrysochus cobaltinus mating

Adults emerge in early summer and persist on milkweed plants in patches for approximately six weeks. Females are highly polyandrous; males engage in extended periods of post-copulatory mate guarding.[3]

The adult females lay their eggs on the leaves of the milkweed plants; the larva consumes the leaf tissue between the veins, leaving nothing but a skeleton. On occasion the larva also eats the root system of the plant. C. cobaltinus larvae in large numbers can consume all the plant's leaves. This apparently does not kill the plant; it goes dormant until the following year, although if the larvae consume the root system of the plant, it will eventually wither away.

Range

C. cobaltinus ranges in High Plains from British Columbia south through Washington, Idaho, Montana, Oregon, California, Nevada, Utah, and Colorado to Arizona and New Mexico.

At least two regions of sympatry between C. cobaltinus and Chrysochus auratus have been documented in western North America.[4]

gollark: My theory of what's up, copied from the forum thread:If many new eggs are being introduced to the system, then that will most affect the stuff which is rarest, by making it rarer by comparison, but commons will stay the same. As for why it happened now? Weekly updates, possibly.Example:Imagine there are 200 dragons, 5 of which are golds.The ratio of golds to total dragons is now 5:200 = 1:40. If the target ratio is 1:50 then prices will be higher to compensate.Now imagine there are an extra 200 dragons added, none of which are golds.The ratio would then be 5:400 = 1:80. Then, assuming the same target, prices will drop.This is of course simplified, and the ratios may not work like this, but this matches observed behavior pretty well.
gollark: That why was rhetorical.
gollark: As I said on the forums:```That makes sense. If many new eggs are being introduced to the system, then that will most affect the stuff which is rarest, by making it rarer by comparison, but commons will stay the same. As for why it happened now? Weekly updates, possibly.```
gollark: Why?
gollark: I think it's just halloween.

References
  1. Horn, G. H. (1885). "Contributions to the Coleopterology of the United States (No 4)". Transactions of the American Entomological Society. 12: 128–162. doi:10.2307/25076454. JSTOR 25076454.
  2. Marshall, T. A. (1864). "Corynodinorum Recensio". Zoological Journal of the Linnean Society. 8 (29): 24–50. doi:10.1111/j.1096-3642.1864.tb02004.x.
  3. Dickinson, J. L. (1995). "Trade-offs between postcopulatory riding and mate location in the blue milkweed beetle". Behavioral Ecology. 6 (3): 280–286. doi:10.1093/beheco/6.3.280.
  4. 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.
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