Karner blue
The Karner blue is an endangered species of small blue butterfly found in some Great Lakes states, small areas of New Jersey, the Capital District region of New York, and southern New Hampshire in the United States. The butterfly, whose life cycle depends on the wild blue lupine flower, was classified as an endangered species in the United States in 1992.
First considered a subspecies of Plebejus melissa, it was first identified and described by novelist Vladimir Nabokov. The name originates from Karner, New York in the Albany Pine Bush, where it was first discovered.
In the novel Pnin, Nabokov describes a score of Karner blues without naming them.
Lupine blooms in late May. There are two generations of Karner blues per year, the first in late May to mid June, the second from mid-July to mid-August.
Local conservation efforts, concentrating on replanting large areas of blue lupine which have been lost to development, are having modest success at encouraging the butterfly's repopulation. The Necedah National Wildlife Refuge in central Wisconsin is home to the world's largest population of Karner blues, which benefit from its vast area of savanna and extensive lupine.
In 2003, the Canadian Species at Risk Act listed the Karner blue as being extirpated from Canada. In 2012, after an unusually hot and dry year, the Karner blue was also extirpated in the Indiana Dunes National Park.
Description
The male and female of this small butterfly are different in appearance. The topside of the male is silvery or dark blue with narrow black margins. The female is grayish brown, especially on the outer portions of the wings, to blue on the topside, with irregular bands of orange crescents inside the narrow black border. The underside of both sexes is gray with a continuous band of orange crescents along the edges of both wings and with scattered black spots circled with white.Distribution and habitat
The Karner blue butterfly occurs in portions of eastern Minnesota, Wisconsin, Michigan, and New York. Reintroductions have been initiated in Ohio, Indiana, Illinois and New Hampshire. The Karner blue butterfly appears extirpated from Iowa, Pennsylvania, Massachusetts, Maine, and Ontario in Canada.Although Karner blue butterflies are characteristic of oak savannas and pine barrens habitats, they also occur in frequently disturbed areas such as rights-of-way, old fields, and road margins. In east-central New York, Karner blue butterflies occurred in 3 rights-of-way habitat types: wild lily-of-the-valley-starflower, sweetfern-whorled yellow loosestrife, and blackberry-sheep sorrel. An index of Karner blue population size was highest in the wild lily-of-the-valley-starflower type. In this habitat, mosses, wild lily-of-the-valley, grasses, and starflower had the highest cover. Coverage in the sweetfern-whorled yellow loosestrife type was dominated by grasses, sweetfern, mosses, and whorled yellow loosestrife. In the blackberry-sheep sorrel type, the dominants included grasses, northern dewberry, other blackberries, and sheep sorrel.
Wild lupine
Several studies have found a positive relationship between measures of wild lupine and Karner blue butterfly abundance. However, available evidence suggests that senescent wild lupine is a poor larval food source. The effects of other phenological stages are more ambiguous. In west-central Wisconsin, Karner blue butterfly abundance was negatively associated with the abundance of reproductive lupine and positively related with the frequency of immature wild lupine. However, a feeding trial found that Karner blue butterfly fed 1st year wild lupine had one of the lowest survival rates observed and significantly longer larval durations than larvae fed older wild lupine that did not flower, was flowering, had recently flowered, or was grown in shade and was in seed. In addition, on sites in Wisconsin and Minnesota, the number of 1st flight oviposition sites on nonreproductive and reproductive wild lupine was similar.Many other factors may influence the quality of wild lupine as a Karner blue butterfly food resource. At Indiana Dunes National Park, wild lupine with Karner blue butterfly feeding damage had significantly larger leaves and longer and thicker stems than plants without feeding damage. In addition, larval length was positively associated with wild lupine height in central Wisconsin. Higher nitrogen concentrations in wild lupine leaves resulted in significantly shorter larval durations in a feeding trial. In 1995, in west-central Wisconsin, significantly more Karner blue butterfly larvae were observed in oak-pine barren plots where mildew infection was delayed compared to areas where wild lupine were infected earlier. However, in a feeding trial larval duration of Karner blue butterflies fed mildew-infected wild lupine was not significantly different from treatments that resulted in the shortest larval durations. Karner blue butterfly fed water-stressed wild lupine had significantly longer larval durations than many treatments including larvae fed flowering wild lupine, shade-grown wild lupine in seed, or mildew-infected wild lupine. Although Karner blue butterflies have been shown to benefit from their association with ants, wild lupine with Karner blue butterfly larvae in the Allegan State Game Area in Michigan were not detectably closer to ant hills than wild lupine without caterpillars.
Canopy cover
Due to effects of environmental variation and differing requirements among life stages, broods, and sexes, Karner blue butterflies require a mosaic of sun and shade.Adult Karner blue butterflies' preference for open, sunny areas has been well documented. Increased lupine and nectar abundance, higher temperatures allowing for longer activity periods, and ease of finding mates have been suggested as possible reasons for adult preference of open areas.
Adult Karner blue butterfly females are more likely to use shaded habitats than males. Avoiding harassment by males and compromising between greater amounts of wild lupine in open areas and better quality of wild lupine in shaded areas have been suggested as possible reasons for increased occurrence of females in shade.
Differences between broods have also been observed. In west-central Wisconsin, abundance of spring adults positively correlated with decreasing canopy cover, while correlation with summer adults was very weak. At Indiana Dunes National Park, cover at late summer oviposition sites was significantly higher than at late spring oviposition sites. In Wisconsin and Minnesota, late spring oviposition sites occurred in partial and closed habitats significantly more than expected based on the number of nectar flowers and the cover and number of wild lupine stems, while summer oviposition sites did not differ significantly from expected. The different brood responses to shade may be due to the direct impact of varying environmental conditions over the course of the season on Karner blue butterflies and the associated effects on wild lupine.
Larvae in shaded habitat apparently have an advantage over those in open areas. The increase in larvae in shaded habitats is likely due to effects of shade on wild lupine.
Shade-grown wild lupine has been shown to provide higher quality larval resource than sun-grown lupine. Several reasons for this have been suggested. An often cited reason for the dependence of larvae, especially 2nd-brood larvae, on shaded habitat is the possibility of early senescence of wild lupine in open areas resulting in a lack of larval food. Shade-grown wild lupine being more nutritious, possibly due to nitrogen content limiting photosynthesis to a greater extent in open areas, was one of several explanations. The size of wild lupine has been positively associated with Karner blue butterfly larval length and amount of feeding damage. In addition, there may be shade-related effects on Karner blue butterflies that are related to the density of wild lupine. Wild lupine are typically more abundant in open areas than in shade. Mildew infection of wild lupine may be increased in denser wild lupine patches. Lower mildew infection rates in shadier areas have been reported. However the implications of mildew infection on Karner blue butterfly are uncertain. It has also been suggested that the low density of wild lupine in shadier habitats could provide better larval habitat due to the increased search effort required by predators. This trade-off between lupine quality and quantity is another reason heterogeneous habitat is important for Karner blue butterfly.
On sites in Wisconsin and Minnesota, canopy cover did not have a significant effect on total numbers of ants, parasitoids, or predators. However, certain species did show trends across canopy cover categories. For instance the ant Formica nitidiventris was only seen in open areas, while another ant, Dolichoderus plagiatus was only observed in areas with a dense canopy. Parasitoids in the genera Phaeogenes and Orthostigma were all seen in closed habitats, while 90% of damsel bugs, a potential predator, were observed in open areas. Closed habitats had insignificantly more parasitoids on average than partial and closed habitats.
Nectar species
Nectar availability is likely to influence Karner blue butterfly abundance. In a right-of-way in west-central Wisconsin, the frequency that Karner blue butterflies stayed in an area between recaptures was significantly positively related to percent cover of nectar flowers such as Canadian horseweed and spotted beebalm. Preliminary results from a study in southeastern Minnesota suggest that openings where Karner blue butterflies were detected tended to have more flowering nectar species. In Michigan, more Karner blue butterflies were observed on sites with more nectaring plants, especially butterfly milkweed. As discussed in Canopy cover, nectar species increase in open habitats. For instance, at Fort McCoy in west-central Wisconsin, all the nectar species listed for Karner blue butterflies require either full or partial sun. In addition, treatments such as cutting with or without herbicides, herbicide application alone, or mowing at varying intervals resulted in a significant increase in the number and cover of nectar species. See section "Food habits" for species that Karner blue butterflies use as nectar sources.Other habitat characteristics: Although Schweitzer asserts that the presence of litter is important to Karner blue butterflies in some years, abundance in a right-of-way in west-central Wisconsin was negatively related with average litter cover.
In west-central Wisconsin, the amount of Karner blue butterfly larval feeding damage increased with grass cover. A review suggests that grass cover may provide roosting sites for Karner blue butterflies and that 5% cover of tall grass would most likely meet this need.