Although many Lepidoptera species are highly specialized in the use of their hosts, some species are able to colonize exotic plants (Graves & Shapiro 2003, Bowers & Richardson 2013). In butterflies, this capacity may be predicted by the geographic range and the native diet breadth (Jahner et al. 2011). Native host range has also been mentioned as an important factor correlating with the use of exotic plants by geometrid moths (Fraser & Lawton 1994).

Host shifts have been acknowledged as extremely important for the survival of the populations of native butterflies in some human-modified environments (Shapiro 2002, Graves & Shapiro 2003, Bowers & Schmitt 2013). Furthermore, host shifts may have a number of effects on phytophagous populations (Bowers & Richardson 2013). The establishment of these new associations could be interesting from an evolutionary perspective, as they open an unexpected window for the understanding of the ecology and evolution of phytophagous insects (Tuda et al. 2014). Additionally, host shifts may have unexpected consequences at higher trophic levels, affecting, for instance, the behavior and physiology of parasitoids (Collatz & Dorn 2013).

Leucaena leucocephala (Fabaceae) (Fig. 1) is a tree species native in Central America the distributional range of which has been greatly expanded around the world mostly due to its cultivation (Rengsirikul et al. 2011, GISD 2014). This plant has become an invader in many localities where it has been introduced as a cultivar, and its presence may have severe effects on the native plant communities (Yoshida & Oka 2004). As a result, L. leucocephala has been listed among the world's 100 worst invasive species (Lowe et al. 2000). In some places, however, L. leucocephala has been classified only as a ruderal plant, not reaching the status of invasive (Costa & Durigan 2010).

The coastal valleys of the northern Chilean Atacama desert are characterized by a high level of human disturbance, mostly due to agricultural activities that have resulted in habitat loss. As a consequence, the original habitat has been turned into farmland and native vegetation has been widely replaced by exotic cultivars and introduced plants (Luebert & Pliscoff 2006). Within this context, some native lepidopteran species have been found to colonize adventive plants, with a few examples reported for butterflies (Vargas 2013) and moths (Vargas 2010, Vargas et al. 2013).

The Geometridae (Lepidoptera) is one of the most diverse moth families (Scoble 1995). Their larvae are generally phytophagous, and may be very important components of folivorous assemblages (Scoble 1995, Marconato et al. 2008, Bodner et al. 2010). Macaria mirthae Vargas, Parra & Hausmann, 2005 (Fig. 2–3) is a geometrid moth native to the northern Chilean Atacama Desert, where its oligophagous folivorous larvae have been found to be associated to three native Fabaceae species: Acacia macracantha, Geoffroea decorticans and Prosopis tamarugo. These were the only host plants recorded for this moth until now (Vargas et al. 2005).

In January 2013 six geometrid larvae were collected from the exotic L. leucocephala in the Azapa valley (18° 31′ S, 70° 10′ W), northern Chilean Atacama Desert. The larvae were brought to the laboratory in plastic containers. Additional leaves of this tree were provided each day until the last instar larvae completed their feeding activity, about seven days after collection. Pupae were periodically observed in order to verify the emergence of adults. Three males and three females were obtained about fourteen days after pupation. Based on the original description provided by Vargas et al. (2005), we identified the specimens as M. mirthae. Subsequently, five males and six females were obtained between March and September 2013 following the same procedure.

This is the first mention of L. leucocephala as a host plant for M. mirthae, which coincides with the previously mentioned association of this moth with host plants of the family Fabaceae. In the same way, this report represents the first record of an exotic host plant for M. mirthae, adding one more record of an association of a native moth species with an exotic host plant in the coastal valleys of the northern Chilean Atacama Desert (Vargas 2010, 2013, Vargas et al. 2013). Our finding is coincident with observations made for some other Neotropical species of Geometridae. Host shifts to exotic plants have already been reported for Iridopsis herse (Schaus, 1912) and Macaria abydata (Guenée, 1858), whose larvae have been associated with Glycine max in Honduras and Brazil, respectively (Lourenção et al. 1980, Passoa 1983). Furthermore, Thyrinteina arnobia (Stoll, 1782) has been described as a defoliator of Eucalyptus in Brazil (Oliveira et al. 2005).

Figs. 1–3.

Components of the new plant-phytophagous association in the northern Chilean Atacama Desert. 1. The exotic host plant Leucaena leucocephala in a human-modified habitat in the Azapa Valley. 2. Last instar larva of Macaria mirthae feeding on Leucaena leucocephala. 3. Male adult of Macaria mirthae reared from a larva on Leucaena leucocephala. Scale bars = 5.0 mm.

From an ecological perspective, an adequate knowledge of the larval host plant range of M. mirthae is extremely important in the study site, as the use of additional exotic hosts by M. mirthae could be an underlying factor shaping other ecological interactions in which this geometrid moth is involved (Collatz & Dorn 2013). Interestingly, besides the obvious ecological importance of M. mirthae due to the larval folivory on its host plants, its larvae have also been reported as an important prey item for the potter wasp Hypodynerus andeus (Packard, 1869) (Hymenoptera: Vespidae: Eumeninae) in the coastal valleys of the Atacama Desert (Méndez-Abarca et al. 2012). Additional studies should be performed to determine the importance of the association between M. mirthae and L. leucocephala in terms of the interaction between M. mirthae larvae and the potter wasp.

On the other hand, consequences of this new association could not be solely restricted to ecological interactions, but they should also involve a number of other life history traits of M. mirthae (Vanbergen et al. 2003, Oliveira et al. 2005). For instance, Jorge et al. (2011) and Mozzafarian et al. (2007) have shown wing phenotypic variation to be host-dependent for butterflies and moths, respectively. It should be interesting, then, to study the effects of the host shift here reported on the biology and evolution of this oligophagous phytophagous moth in the arid landscapes of northern Chile.

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. Three males and three females: Azapa, Arica, Chile, February 2013, H. A. Vargas coll., reared from larvae collected on Leucaena leucocephala, January 2013 (MNNC); four males and five females: Azapa, Arica, Chile, March 2013, H. A. Vargas coll., reared from larvae collected on Leucaena leucocephala, February 2013 (IDEA); one male and one female: Azapa, Arica, Chile, September 2013, H. A. Vargas coll., reared from larvae collected on Leucaena leucocephala, August 2013 (MNNC).