Pyrgus warrenensis (Verity, 1928)

Host plants:
The caterpillar lives exclusively on Helianthemum alpestre (= Helianthemum oelandicum). Other Helianthemum species are not likely to be used in the field, but, however, easily accepted by the caterpillars in the breeding experiment.

Habitat:
Pyrgus warrenensis colonizes sunny, low-growing alpine meadows and pastures from about 1700m up to 2700m above sea level (peak between 2000-2400m above sea level) with occurrence of the larval host plant, often in southern exposition, but also in weak northern exposure, as long as the surface is still exposed to the sun.

Life cycle:
The life cycle is biennial. The first winter is passed as L1 (rarely also L2, a few observations in September 2009 along with numerous L1 above the Swiss Matter Valley near Zermatt), where the caterpillar constructs a small shelter in a shoot tip, so that the outer, larger leaves are woven together in upward direction and the larva is located centrally within the younger, smaller leaves that are wrapped onion-like. This creates a hermetically sealed hibernarium that protects the caterpillar from the rigors of alpine winter quite well (especially well against dehydration, at least 7 months are spent in it!). I found such caterpillars in the end of July 2005 and again on 30/10/2005 in the Swiss Valais on 2300m above sea level. I observed young caterpillars after the first winter there in June 2004. These began a repetitive hibernation, but were parasitized.

In 2005 Pyrgus warrenensis was studied in more detail in the Valais. Around mid-July many butterflies flew in 2300m above sea level. Important nectar plants were Thymus sp., Aster alpinus, Lotus alpinus, Trifolium sp. and Sempervivum sp., etc. Oviposition and caterpillar observations (also in May 2005, penultimate and final instar) succeeded only on Helianthemum alpestre, while the syntopic Pyrgus alveus, which flew slightly later in average (but with significant overlap) used no Helianthemum alpestre but Helianthemum nummularium grandiflorum. Pyrgus warrenensis has 6 larval instars according to the observations as it is the case with Pyrgus cirsii. But in this case this is so far based only on breeding and is not confirmed in the field. The second hibernation takes place in nature in penultimate instar in a ground-level shelter.

Endangerment factors:
In the German Alps Pyrgus warrenensis is very rare and local (Berchtesgaden, in the Allgäu region again observed by Karle-Fendt in 2008 and 2009). Overall, the butterfly is threatened by tourist development of all kinds. Helianthemum alpestre grows preferentially in summit and ridge areas which are especially affected by the massive mountain tourism.

In other regions of the Alps local populations can be endangered most likely by infrastructur and tourism development, too.

Remarks:
In breeding the two-year development can be shortened to three months. Moreover, it is possible to over-winter the caterpillars between L1 and the penultimate instar (apparently no longer in the last). Decisive are the breeding temperatures. In the field, hibernation is induced by the cold night temperatures as in the other alpine Pyrgus species. During the day, when the sun shines near the ground even over 20 degrees Celsius can still be reached in October.

Pyrgus warrenensis is distributed only very locally in the Alps from around 1700m above sea level upwards and supposedly according to literature also in the central Apennines.

Hints on determination:
Pyrgus warrenensis can be confused with some experience only with small, pale individuals of Pyrgus alveus (f. alticola). This is a case for genital section.