Control and Persistence of Native Opuntia on Nevis and St. Kitts 50 Years After the Introduction of Cactoblastis Cactorum
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Biological Control 41 (2007) 272–282 www.elsevier.com/locate/ybcon Control and persistence of native Opuntia on Nevis and St. Kitts 50 years after the introduction of Cactoblastis cactorum Robert W. Pemberton a,¤, Hong Liu b a USDA, ARS, Invasive Plant Research Lab, 3225 College Ave, Fort Lauderdale, FL 33314, USA b University of Florida, FLERC, C/O USDA, ARS Invasive Plant Research Lab, 3225 College Ave, Fort Lauderdale, FL 33314, USA Received 9 November 2006; accepted 2 February 2007 Available online 12 February 2007 Abstract Since Cactoblastis cactorum appeared in Florida in 1989, via importation of infested horticultural Opuntia plants and/or natural spread from the Caribbean, there has been a concern about the moth’s threat to native and economic North American and Mexican Opuntia. The moth’s occurrence in the Caribbean is due to its introduction to Nevis Island in 1957 for the control of native Opuntia that were pasture weeds. We assessed the abundance of C. cactorum in target and non-target Opuntia species and the persistence of these Opuntia species on the small islands of Nevis and St. Kitts 50 years after the moth’s introduction. C. cactorum occurred at 10/16 sites on the two islands and attacked 22.7% of total plants. Of the four Opuntia sensu lato species found, three were attacked, including the native targets Opuntia triacantha (with 15.6% of plants and 8.9% of pads attacked) and Opuntia stricta (with 44.4% plants and 8.1% pads attacked), and the non-target cultivated and naturalized Opuntia cochenillifera (with 19.1% plants and 1.2% pads attacked). The native nontarget tree pear, Consolea (D Opuntia) rubesens, was not attacked. Larger and wild plants had signiWcantly higher percentages of attack. Based upon our data, it appears that biological control of O. triacantha and O. stricta persists and these natives have survived 50 years of C. cactorum attack on these small islands, despite fears that the moth could have caused their extinction. Our analysis of this historical biological control eVort suggests that the potential impact of C. cactorum on native North American and Mexican Opuntia will be signiWcant and variable, but not necessarily catastrophic. Published by Elsevier Inc. Keywords: Biological control risk; Non-target eVects; Biological control safety; Cacti conservation; The Caribbean islands; Herbivory; Consolea rubescens; Opuntia cochenillifera; Opuntia stricta; Opuntia rubescens; Opuntia triacantha 1. Introduction from southern to northern Florida and then coastal South Carolina and west along the Gulf of Mexico to Alabama Since Cactoblastis cactorum (Berg) appeared in southern (Hight et al., 2002, S. Hight pers. com.). The larvae feed Florida in 1989 (Habeck and Bennett, 1990), there has been within the pads of virtually all pad bearing Opuntia sensu a growing concern about the moth’s impact and threat to lato (Subgenus Platyopuntia) in their native region (Zim- native North American and Mexican Opuntia (Pemberton, mermann et al., 2000). This moth has been a highly eVective 1995; Johnson and Stiling, 1998; Zimmermann et al., 2000; biological control agent of pest Opuntia in Australia and Mahr et al., 2001; Stiling, 2002; Louda et al., 2003). After its other parts of the world (Moran and Zimmermann, 1984). introduction to Florida via the importation of infested These factors, coupled with the great diversity, and eco- Opuntia from the Caribbean and/or natural spread from nomic and ecological value of Opuntia in North America the Caribbean (Pemberton, 1995), the moth has spread and Mexico, (Rebman and Pinkava, 2001; Soberon et al., 2001; Garrett, 2004) is the basis of the concern that C. cactorum could harm many of these species. The moth, * Corresponding author. Fax: +1 954 476 9169. which is originally from Argentina, could easily move along E-mail address: [email protected] (R.W. Pemberton). the Gulf of Mexico into Opuntia rich Texas and Mexico. 1049-9644/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.biocontrol.2007.02.002 R.W. Pemberton, H. Liu / Biological Control 41 (2007) 272–282 273 The threat is made worse by the current lack of control 3. To consider what these patterns of C. cactorum’s techniques that can be reasonably applied to the large, presence, use of, and impact to Opuntia in Nevis and St. diVuse and cryptic populations of C. cactorum larvae infest- Kitts may suggest for potential C. cactorum impacts to ing various low density Opuntia species in the Gulf coast Opuntia in North America and Mexico. corridor. Pesticides and mechanical control are unsuitable because it is diYcult to locate and treat the moths and lar- 2. Methods vae inside infested pads. Biological control is thought to be inappropriate because of the apparent lack of specialist Nevis was visited from December 15 to 20 and 24 to 25 enemies of the moth (Pemberton and Cordo, 2001). The and St. Kitts from December 21 to 23, 2002. This was 50 sterile insect technique (SIT) is seen as the best hope to stop years after Fred Bennett, Commonwealth Institute of Bio- the moth and both the US and Mexico are investing in logical Control (CIBC), Trinidad, visited Nevis (November research to develop the technique (Carpenter et al., 2001; 27, 1952) to assess the Opuntia pasture weeds at the request Hight et al., 2005). It will be very challenging to stop the of the colonial government administering the British West moth with SIT before it spreads west into Texas and Indies, and 45 years after the Institute introduced C. cacto- beyond possible containment. rum to Nevis in 1957 in an attempt to control the cacti bio- While not wanting to be unduely pessimistic about the logically. CIBC reports including Bennett’s trip reports and chances of containing the moth before it spreads into site photographs, and published literature aided the search Opuntia rich Texas and Mexico, we believe that there is for the original sites with targeted Opuntia infestations and merit in understanding what might happen to native other Opuntia species populations (Fig. 1B and C). Opuntia Opuntia should containment and control fail. One-way to species growing in residential and hotel gardens and town gain insight into this scenario is to examine the moth’s landscapes were also examined on both islands. The areas impact on native Opuntia where it has been an introduced intensively surveyed on Nevis were the arid southeastern herbivore for a relatively long time. An ideal place to and southern coasts and an area called Hurricane Hill on examine this association, and the area examined in this the northwest coast. On St. Kitts, the arid southern penin- study, is Nevis and St. Kitts in the Lesser Antilles, where sula, the only area recorded to have wild Opuntia species, C. cactorum was Wrst introduced into the West Indies. The was examined as were garden plants that were encountered moth was introduced to Nevis in 1957 as a biological con- (Fig. 1B). The use of herbicides against weedy or wild trol agent of Opuntia species, which were pasture weeds Opuntia on these islands is unlikely because the areas with (Simmonds and Bennett, 1966), and apparently overabun- cacti are impoverished and mostly highly eroded lands used dant because of selective grazing by goats. Examining the only for goat grazing. Goat grazing was evident on much of impact of the moth on Opuntia species in Nevis and St. these islands. Insecticide use against C. cactorum is also Kitts also has considerable merit independent of potential unlikely because the moth attacks undervalued plants, and extrapolations of the North American situation. Some neither the moth adults nor larvae are recognized by the workers (Bennett and Habek, 1992) have speculated that islanders (Zimmermann et al., 2004). C. cactorum may have exterminated one or more Opuntia At each site and population, the numbers of attacked on Nevis or other small islands such as Grand Caymen, and non-attacked plants were recorded, as were the num- where it has been introduced. Nevis is approximately 10 bers of pads per plant and the number of these attacked. by 12 km (100 km2) and St. Kitts is 43 by 12 km (170 km2). Infested pads were detected by the presence of holes from When Bennett assessed the degree of control on Nevis in which the larvae eject frass and from which the liqueWed 1960 and 1964, he found widespread collapse of the target pad contents ooze, the presence of larvae in the dissected Opuntia weed populations on Nevis, and on nearby St. pads, and by noting the opaque windows in the pads, indi- Kitts in 1964 to which the moth had spread (Simmonds cating hollowed out sections or pads. Pads with fresh dam- and Bennett, 1966). In 1964, Opuntia triacantha (Wilde- age were dissected to Wnd the larvae of C. cactorum, which now) Sweet had become scarce and only plants consisting are distinctively and uniquely colored yellow to orange of two to Wve pads could be found. Bennett visited again with black bands. Also sought were the moth’s unique egg in 1969 and took a photograph showing a man holding an sticks, comprised of single eggs laid end to end forming a O. triacantha plant with only seven pads, which he labeled spine-like stick usually laid on the areoles (the spine bearing “largest plant of O. triacantha found” (Fred Bennett areas) of the pads. Evidence of recent reproduction (pres- pers.com.). ence of Xowers and/or fruits) in the Opuntia populations The objectives of this study are as follows. was noted but degree of reproduction or reproductive suc- cess was not assessed. Two populations of O. stricta 1. To determine whether the target and non-target native (Haworth) Haworth were found consisting of large clonal and introduced Opuntia species have survived almost 50 masses instead of individual plants.