Celastrina humulus

Scott & D. Wright, 1998

Hops Azure

Celastrina humulus, the hops azure, is a rare North American in the Lycaenidae. It is locally abundant in Colorado and Montana, with concentrated along the Front Range of Colorado. The exhibits a facultative mutualistic relationship with ants, mediated by -plant . Its survival is tightly linked to the availability of wild hops (Humulus lupulus var. neomexicanus), with patch occupancy and extinction probabilities strongly influenced by host plant patch area.

Pronunciation

How to pronounce Celastrina humulus: //sɛˈlæstrɪnə ˈhjuːmjʊləs//

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Habitat

Riparian systems where wild hops (Humulus lupulus var. neomexicanus) occurs. Occupancy probability is directly influenced by total area of plant patches; smaller patches have higher extinction rates and lower occupancy. At the U.S. Air Force Academy study site, the showed high in riparian areas with abundant wild hops.

Distribution

North American . Documented from Colorado and Montana, with study concentrated along the Front Range of Colorado. The has been intensively studied at the U.S. Air Force Academy riparian system in Colorado, where it is locally abundant.

Diet

Larvae feed on pollen-bearing inflorescences of wild hops (Humulus lupulus var. neomexicanus). Larval performance varies with -plant phenological stage; early-stage inflorescences enable greater weight gain.

Host Associations

Humulus lupulus var. neomexicanus - larval food plantWild hops; larvae feed specifically on pollen-bearing inflorescences. -plant flowering mediates mutualism.

Behavior

Exhibits facultative mutualism that is mediated by -plant . The likelihood of ant tending is lowest for larvae on host plants with early-stage inflorescences. can thermoregulate through such as basking or sitting in shade. Patch extinction and probabilities are extremely low; the shows high site fidelity once established.

Ecological Role

Participates in a facultative mutualism with ants, serving as a myrmecophile. The relationship is context-dependent: early-stage plant inflorescences enhance larval growth but reduce recruitment due to higher concentrations of soluble proteins and α-acids (humulone and cohumulone).

Human Relevance

Subject of conservation concern due to rarity and . Monitoring protocols have been developed using occupancy modeling, with detection probability influenced by cloud cover, wind speed, and solar exposure. Detection probability was 69% on first visit and 64% on second visit at study sites.

Similar Taxa

Celastrina ladon (Spring Azure)Similar blue coloration and spring period; distinguished by plant specificity (C. humulus restricted to wild hops) and geographic range (C. humulus to Colorado/Montana region versus broader eastern North American distribution of C. ladon). C. humulus has been treated as with C. ladon in some taxonomic treatments but is now recognized as a distinct .

More Details

Ant Mutualism Mechanism

Early-stage plant inflorescences contain the greatest concentrations of soluble proteins and α-acids (humulone and cohumulone), which enhance larval weight gain but reduce recruitment to sugar-protein baits in experimental trials. This creates a trade-off between growth and protection.

Population Dynamics

Multi-year occupancy studies show higher than expected detectability (69% first visit) and occupancy probability (77%) compared to assumed 30% baseline. Patch extinction and probabilities are extremely low, suggesting stable once established in suitable with sufficient plant area.