The cactus moth, Cactoblastis cactorum (Berg), is native to Argentina, Uruguay, Paraguay and southern Brazil (Mann 1969). Larvae feed gregariously inside the cladodes of many species of Opuntia (Cactaceae), often facilitating secondary pathogenic infections and, eventually, death of the plant (Starmer et al. 1988). In the 1920s, this moth was successfully used for the biological control of invasive Opuntia spp. in Australia and southern Africa, where no native cacti occur. This program represented one of the most spectacular cases of successful biological control of weeds. In 1957 the cactus moth was introduced into Nevis, an island in the Caribbean Sea, to control native Opuntia. The moth spread throughout the Caribbean, either naturally or by human-assisted introductions (García-Turudi et al. 1971), and in 1989 was found in the Florida Keys (Habeck & Bennet 1990). The northward geographical expansion of the cactus moth along the Atlantic and Gulf coasts of Florida was monitored intermittently (Hight et al. 2002) and estimated to be approximately 160 km/yr (Solis et al. 2004); the westward movement of the moth reached Louisiana in 2009 (Hight & Carpenter 2009). The cactus moth was detected on the Mexican islands of Mujeres in 2006 and Contoy in 2007, probably originating from islands in the Caribbean such as Cuba (Bloem et al. 2007; Hight & Carpenter 2009). Establishment of the moth represents a potential threat to the diversity of both wild and cultivated Opuntia species in North America (Strong & Pemberton 2000; Perez-Sandi C. 2001; Soberón et al. 2001). Bioclimatic models have been used to predict the ultimate geographical range and the potential impact of the cactus moth in North America (Soberon et al. 2001). In these models the ecological requirements of the cactus moth have been based upon the locations from which the moth has been collected. Unless the full extent of the indigenous geographical range of the cactus moth is known, bioclimatic models may under-estimate the potential invasion and impact of the moth in North America.

The native host range and the geographical distribution (Fig. 1) of the cactus moth have been reported in many studies (Heinrich 1939; Dodd 1940; Mann 1969; Zimmermann et al. 2000, 2007). However, recent detailed host range studies of C. cactorum populations in Argentina (unpublished data) and the discovery of its high genetic diversity (Marsico et al. 2011) have altered some of the earlier findings. For example, C. cactorum from central Argentina were consistently successful in attacking plants up to 8 yr old of the native species O. quimilo K. Schum. at high enough levels for this cactus species to be used in developmental and life table studies on C. cactorum. Earlier reports identified O. quimilo as a non-suitable host plant for C. cactorum, citing only occasional records of the moth attacking the youngest of plants (Dodd 1940; Mann 1969; Zimmermann et al. 1979; Zimmermann et al. 2000, 2007).

In addition, the systematics of Opuntia is complex and accurate identifications difficult to obtain (Kiesling 1999; Anderson 2001). Consequently, misidentifications of Opuntia species are common, making the cactus moth field host range not yet fully characterized. For example, O. longispina How. var. corrugata (Salm-Dyck) Backeb., reported as a non-host by Zimmermann et al. (1979, 2000), was first transferred to the genus Tunilla as T. corrugata (Salm-Dyck) Hunt and Iliff (Hunt & Iliff 2000) and finally to the genus Airampoa as A.corrugata (Salm-Dyck) Doweld (Doweld 2002). Opuntia delaetiana (F. A. C. Weber) Vaupel, reported as one of the cactus moth hosts by Dodd (1940) and Mann (1969) is now identified as O. elata Link & Otto var. cardiosperma (Schum.) Kiesling (Kiesling 2005). Even the identification of the original host plants, O. monacantha (Willd.) Haw., from which the cactus moth source population was collected for shipment to Australia (Dodd 1940) has now come under scrutiny; because this species is now considered native to Brazil (Taylor et al. 2002; Lenzi 2008) and not naturalized in Argentina, where it occurs only as an ornamental.

The known southern boundary of the C. cactorum distribution in Argentina was reported to be the area of La Plata (Fig. 1; 34° 56′ S, 57° 56′ W) in northeastern Buenos Aires province (Heinrich 1939; Dodd 1940; Mann 1969). However, recent collections of this moth indicated its presence further south. To confirm the moth's distribution and to identify potential new hosts, a field exploration for the presence of the cactus moth was conducted in May 2011 in the provinces of Buenos Aires, La Pampa, San Luis, Mendoza and Río Negro (Fig. 1). A total of 1,000 Opuntia plants was examined at 62 roadside sites arbitrarily selected by the occurrence of host plant patches, between coordinates 32° 53′ and 40° 48′ S, and 58° 38′ and 64° 10′ W. At sites with large patches (more than 150 plants), at least 50 plants were visually inspected for the presence of moth damage on the cladodes. In small patches of less than 50 plants, all plants were inspected. Cladodes exhibiting damage from larval feeding were dissected and examined for the presence of C. cactorum larvae. Host plants were tentatively identified in the field and voucher specimens were collected for identification and confirmation by Fabián Font (School of Pharmacy and Biochemistry, Herbario Museo de Farmacobotánica Juan Domínguez, Buenos Aires, Argentina). Opuntia species names were assigned according to Zuloaga et al. (2008).

Fig. 1.

Partial map of Argentina showing: (1) Known distribution (shaded area) of Cactoblastis cactorum, and (2) New localities surveyed: white small circles represent negative localities and black crosses (numbered) show the positive localities listed in Table 2.

Eleven Opuntia species were observed in the area surveyed (Table 1). Larvae of C. cactorum were found in the southern provinces of Buenos Aires at 6 of 26 sites, La Pampa at 1 of 11 sites, and Río Negro at 2 of 8 sites (Fig. 1). Of the 53 plants attacked, 64% were O. megapotamica Arechav., 34% O. flcus-indica L., and 2% O. penicilligera Speg. This is the first record of C. cactorum collected on the endemic species O. penicilligera (Table 2, Fig. 1, site #1). The southernmost collection of C. cactorum was in Stroeder, Buenos Aires province (Table 2, Fig. 1, site #6), on the exotic species O. ficus-indica and the westernmost collection was at Santa Isabel, La Pampa province (Table 2, Fig. 1, site #9), on O. megapotamica.

Although a survey of natural enemies was not the main purpose of this work, the parasitoid Apanteles sp. (Hymenoptera: Braconidae) was found in Villa Arias, Buenos Aires province on C. cactorum collected on O. megapotamica. In addition, a total of 37 larvae of different sizes collected at 7 sites within the area surveyed were examined for the presence of microsporidia. Larvae were ground individually with a homogenizer (Tissuemizer®, Tekmar Co., Cincinnati, Ohio) and a drop of the aqueous extract was examined under a phase-contrast microscope (400×) for the presence of spores. Several cactus moth larvae were found infected with abundant numbers of spores of a microsporidium, tentatively identified as Nosema cactorum Fantham. Infected larvae were collected in Villa Arias, Stroeder, and Buratovich, all in southern Buenos Aires province. These natural enemies should be given further attention as potential biocontrol agents.

Our findings represent an important southern extension of the geographic distribution of C. cactorum in its native land, approximately 800 km further south of the original limit, and should be useful in improving bioclimatic models to predict the potential geographic range in North America. Surveys further south and southwestern of the new distribution range are now advisable given the new occurrences identified here. Also, O. penicilligera was found to be a new native host plant of C. cactorum.

SUMMARY

A field exploration was conducted to confirm the southern distribution of Cactoblastis cactorum in Argentina. The distribution of the moth was found to be extended to the south (40° 10′S) and west (66° 56′W). The native species Opuntia penicilligera was recorded as a host for the first time. These findings should be useful in improving bioclimatic models to predict the potential geographic range of C. cactorum in North America.

TABLE 1.

SURVEY AT 62 ROADSIDE SITES FOR CACTOBLASTIS CACTORUM ON OPUNTIA SPP. IN THE PROVINCES OF BUENOS AIRES, LA PAMPA, SAN LUIS, MENDOZA, AND RÍO NEGRO, ARGENTINA.

TABLE 2.

WEATHER INFORMATION AT THE 9 LOCALITIES WITH CACTOBLASTIS CACTORUM ON OPUNTIA SPP. IN THE PROVINCES OF BUENOS AIRES, LA PAMPA, AND RÍO NEGRO, ARGENTINA.