Many butterflies are highly specialized in their use of host plants. Some are monophagous (Brückmann et al. 2011); at least at a local scale (Jordano et al. 1990, Vargas 2012). Despite this tendency towards specialization, however, oviposition by native butterflies on exotic plants, and the subsequent successful larval development, has been documented many times within the New World fauna and is probably a global phenomenon (Shapiro 2006). These host range shifts have been remarkably well studied in California, USA, where alien hosts are very important for the maintenance of the native butterfly fauna in both urban and suburban environments (Shapiro 2002, Graves & Shapiro 2003). Recently, Jahner et al. (2011) have shown that the use of exotic hosts is predicted by geographic range and native diet breadth, although the former is a stronger predictor.

Examples of associations among native butterflies and exotic plants have also been mentioned for the South American fauna (Shapiro 2006), including Chile (Shapiro 1997). For the Chilean butterfly fauna, the use of some exotic Malvaceae by the native Vanessa carye (Hübner, 1812) (Nymphalidae) is well known (Herrera 1987). This butterfly-host plant system is regularly used for teaching purposes at different levels of local educational programs. Moreover, the ability of V. carye to develop on exotic mallows is probably one of the reasons for its widespread occurrence in disturbed habitats in Chile, especially in urban and agricultural environments.

Pyrgus bocchoris (Hewitson, 1874) is a Neotropical skipper with three subspecies currently recognized along its geographic range (Mielke 2005), although some controversy exists concerning the synonymies (Shapiro 1991). Pyrgus bocchoris trisignatus (Mabille, 1875) is a little known skipper described from Valparaíso, Chile. Its geographic range along this country embraces a very long, narrow strip of about 2,000 km length, from the northern coastal desert south to the type locality (Herrera et al. 1957). However, Peña and Ugarte (1996) indicated that this skipper reaches the Bío Bío Region, increasing by about 500 km its range southward. Furthermore, its presence has been also reported in Peru (Herrera 1972, Warren et al. 2012).

In the northernmost part of Chile, P. b. trisignatus has been collected from near sea level, in the valleys of the coastal desert, up to the highlands of the Andes, exceeding 3,500 m. A number of environments are present along this elevational gradient, each characterized by a typical fauna and flora (Luebert & Pliscoff 2006). This skipper is one of the more frequently observed butterflies in many of these situations, including relatively pristine areas and also highly modified agricultural lands. Shapiro (1991) indicated that a Chilean representative of P. bocchoris (i.e.: trisignatus) is associated with weedy mallows (Malvaceae), but nothing more was published thereafter dealing with the field biology of this skipper. Thus, the objective of this paper is to document two Malvaceae host plants for P. b. trisignatus based on field collections performed in northern Chile.

In October 2008, some Hesperiidae larvae were collected on leaves of the exotic mallow Malva nicaeensis All. (Malvaceae) in the Azapa valley, located in the coastal desert of the Arica Province, near sea level. These larvae were brought to the lab in plastic vials with absorbent paper on the bottom. Leaves were changed daily until feeding was completed. Pupation occurred among fragments of leaves or absorbent paper. Nine adults were obtained in November 2008. Seven additional adults were reared from M. nicaeensis at the same locality from October 2011.

Between September 2011 and April 2012 additional skipper larvae were collected on leaves of the native Tarasa operculata (Cav.) Krapov. (Malvaceae) in the Cardones valley, located in the Precordillera of Arica Province, at about 2,000 m. Sixteen adults of P. b. trisignatus were obtained in the lab following the same procedures mentioned above.

Use of Malvaceae by P. b. trisignatus is consistent with the host plant relationships previously reported for this group of New World Pyrgus, Hübner, 1819 (Robinson et al. 2010), including the Neotropical representatives (Shapiro 1991, 2009). Exotic Malva L. species, including M. nicaeensis, are used as host plants by at least five species of native butterflies in California, including Vanessa annabella Field, the sister-species of the South American V. carye, Pyrgus communis (Grote) and its sibling species P. albescens Ploetz (Graves & Shapiro 2003).

The Azapa valley is a highly disturbed habitat, where much of the native vegetation has been eliminated by intensive agricultural practices. This is also the case for most of the coastal valleys of the northern Chilean Atacama Desert. Under these conditions, the presence of native Malvaceae is extremely low. Contrastingly, weedy mallows, as M. nicaeensis, are abundant. Moreover, in highly disturbed areas of Arica Province, at least two Gracillariidae micro-moths have also colonized exotic host plants: Acrocercops serrigera serrigera Meyrick, 1915 is associated with M. nicaeensis and the native Waltheria ovata Cav. (Malvaceae) (Vargas et al. 2013), while Angelabella tecomae Vargas & Parra, 2005 has been reared from the introduced tree Tecoma stans (L.) in addition to the native Tecoma fulva (Cav.) D. Don (Bignoniaceae) (Vargas 2010).

The Cardones valley is a relatively pristine place, where agricultural activities are not performed. One of the representatives of the native flora of this locality is T. operculata, which occurs frequently in many habitats throughout the Precordillera of the Parinacota Province, where exotic mallows are more or less restricted to small villages in which little agriculture is conducted.

The host plant relationships here recorded for P. b. trisignatus suggest that the abundance levels of this skipper in relatively pristine habitats of northern Chile are dependent on the populations of the native T. operculata, as was observed in Cardones valley, while in highly human modified environments the populations are dependent on the presence of the exotic M. nicaeensis, as detected in the Azapa valley. Thus, it constitutes another example of the importance of an alien plant for the maintenance of populations of a native butterfly in disturbed areas (Shapiro 2002).

In the future it would be interesting to survey for additional native or exotic Malvaceae as possible host plants for P. b. trisignatus in other localities throughout its complete Chilean range. It is hoped that other native Malvaceae will be associated in different pristine locals, while exotic mallows would be the larval substrate in disturbed landscapes.

Voucher specimens will be deposited in the “Museo Nacional de Historia Natural” (MNNC), Santiago, Chile, and in the “Colección Entomológica de la Universidad de Tarapacá” (IDEA), Arica, Chile.

Material examined. CHILE, Arica. Five ♂ and four ♀ Azapa, Arica, Chile, November 2008, H.A. Vargas coll., reared from Malva nicaeensis, October 2008; four ♂ and three ♀ Azapa, Arica, Chile, October 2011, H.A. Vargas coll., reared from Malva nicaeensis, September 2011; nine ♂ and three ♀ Cardones, Arica, Chile, October 2011, H.A: Vargas coll., reared from Tarasa operculata, September 2011; three ♂ and one ♀ Cardones, Arica, Chile, April 2012, H.A: Vargas coll., reared from Tarasa operculata, March 2012.