Potential and Risks of Biological Control of Cactoblastis Cactorum (Lepidoptera: Pyralidae) in North America
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Pemberton & Cordo: Biological Control of Cactoblastis 513 POTENTIAL AND RISKS OF BIOLOGICAL CONTROL OF CACTOBLASTIS CACTORUM (LEPIDOPTERA: PYRALIDAE) IN NORTH AMERICA ROBERT W. PEMBERTON1 AND HUGO A. CORDO2 1USDA-ARS Invasive Plant Research Laboratory, Ft. Lauderdale, Florida 2USDA-ARS South American Biological Control Laboratory, Hurlingham, Argentina ABSTRACT Cactoblastis cactorum Berg, an invasive moth and famous biological control of weeds agent, threatens numerous native and economic prickly pear cacti (Opuntia) in the United States and Mexico. Biological control of the moth, using a variety of approaches, is considered in- cluding: introduction of parasitoids and pathogens from the moth’s native home in South America, introduction of parasitoids from related North American cactus moths (Pyralidae: Phycitnae), inundative releases of parasitoids known to attack the moth in Florida, and in- undative releases of mass reared generalists parasitoids. The primary risk of employing bi- ological control is the reduction of the many North American cactus moths, some of which probably regulate native Opuntia that can be weedy. The various biocontrol approaches are ranked according to their relative risk to the native cactus moths. The introduction of South American parasitoids or pathogens specific to the genus Cactoblastis (if they exist) may be the least risky approach. The introduction of South American parasitoids that can attack many cactus moths is the most risky approach because it could result in persistent “control” of these non-target native insects. Biological control probably can reduce the abundance of C. cactorum populations but is unlikely to prevent the spread of the moth. The relative ben- efits and risks of biological control need to be carefully assessed prior to any operational bio- logical control programs. It will be difficult to reach agreement on acceptable levels of risk, if the likely benefits can’t be predicted. Other management options need to be considered. Key Words: Opuntia, biological control risk, cactus moths, host specificity, parasitoids, insect pathogens RESUMEN Cactoblastis cactorum Berg, una polilla famosa como agente de control biológico de malezas, amenaza numerosas especies nativas y económicas de cactos del género Opuntia en los Es- tados Unidos de América y en México. Se considera en este trabajo el control biológico de la polilla, utilizando diversas alternativas: la introducción de parasitoides y patógenos de Sud América, el área nativa de la polilla; la introducción de parasitoides de polillas de cactos de Norte América (Pyralidae: Phycitinae); liberaciones inundativas de parasitoides que atacan a C. cactorum en la Florida, y liberaciones inundativas de parasitoides generalistas criados en forma masiva. El principal riesgo de la utilización del control biológico es el empobreci- miento de las muchas especies de polillas de cactos de Norte América, algunas de las cuales probablemente regulan Opuntia nativas que podrían ser malezas. Las distintas alternativas del control biológico son ordenadas de acuerdo al riesgo relativo hacia las polillas de cactos nativas. La introducción de parasitoides y patógenos específicos del género Cactoblastis (si existieran) en Sud América, sería la alternativa menos riesgosa. La introducción de parasi- toides sudamericanos que ataquen muchas polillas de cactos es la alternativa más riesgosa porque podría resultar en el “control” permanente de estos insectos que no son objetos del control biológico. El control biológico probablemente pueda reducir la abundancia de las po- blaciones de C. cactorum pero es poco probable que pueda prevenir la dispersión de la polilla. Los beneficios relativos y riesgos del control biológico necesitan ser cuidadosamente evalua- dos antes del comienzo de los programas de control. Será tal vez difícil lograr acuerdos sobre los niveles de riesgo aceptables si los beneficios esperados no pueden ser estimados. Otras opciones de manejo necesitan ser consideradas. Cactoblastis cactorum Berg has successfully Caribbean in 1957 to control native Opuntia spe- controlled pest prickly pear cacti (Opuntia spe- cies that were weeds of pasture (Simmons & Ben- cies) in Australia (Dodd 1940) and in many other nett 1966). In 1989, C. cactorum was found in places in the world (Moran & Zimmermann Florida (Habeck & Bennett 1990). The insect may 1984). The moth was introduced to Nevis in the have spread on its own from other places in the 514 Florida Entomologist 84(4) December 2001 Caribbean (Johnson & Stiling 1996) or may have tant to explore the potential use and implications been accidentally introduced by the nursery in- of various biological control options. dustry (Pemberton 1995). Since that time the moth has spread throughout the Florida penin- MATERIALS AND METHODS sula where it attacks five of the six Opuntia spe- cies native to the state, including the endangered Searches of the literature were made to detect Opuntia spinosissima Miller (see Stiling & Moon the known parasitoids and diseases of Cactoblas- this volume). There is considerable concern that tis species and other species of cactus moths the moth will continue to spread and attack addi- (Pyralidae: Phycitinae). Compilations of these or- tional Opuntia species. There are many native ganisms were created in different categories re- Opuntia in the southwestern U.S. and Mexico lated to various biological control options. Other that could be harmed by the moth (Strong & Pem- literature, primarily parasitoid catalogues, were berton 2000; Zimmermann et al. 2000). An esti- searched to detect records of other host insects of mated 79 Opuntia species native to Mexico and these natural enemies, to help judge their host the United States are at risk (Zimmermann et al. specificity. Criteria related to the potential benefit 2000). In addition, as many as 25 Opuntia species and risk of different biological control approaches in Mexico and three species in the United States were developed and then used to rank these ap- are used by people as food, animal fodder, and as proaches. the host of the cochineal dye producing scale (Zimmermann et al. 2000). RESULTS AND DISCUSSION Currently in Florida the primary host plant of C. cactorum is O. stricta (Haworth) Haworth Biological control using parasitoids of Cactoblastis which is distributed around the Gulf of Mexico cactorum from its native range in South America from Florida to Texas and Mexico. It appears likely that the moth will spread from Florida to The 8-9 parasitoids associated with the cactus Texas using this plant. If C. cactorum reaches moth in South America are shown in Table 1. Texas and Mexico, many other Opuntia species These include one braconid larval parasitoid, one could become hosts and the moth could continue chalcidid pupal parasitoid, 5-6 ichneumonid its spread via these new hosts. This would also wasps and one tachinid fly. Apparently no egg bring the moth into contact with endangered parasitoids are known. The chalcidid wasp, Bra- Opuntia species that could be harmed. The ability chymeria cactoblastidis Blanchard, is suspected of C. cactorum to quickly and completely control of being a hyperparasitoid (Zimmermann et al. many exotic weedy Opuntia in disparate parts of 1979). The braconid wasp, Apanteles alexanderi the world, and also native weedy Opuntia species Brethes, has been recorded to cause more than in the Caribbean, suggest that the moth could be 30% parasitism of the larvae and the ichneu- particularly dangerous in North America. monid, Temelucha sp., was recorded to cause 5- In addition to the ecological damage caused by 30% parasitism of the larvae (Zimmermmann et the moth, public confidence in biological control al. 1979). Parasitism rates of the other parasi- practice is being injured because of the moth’s toids were not recorded, but two of the ichneu- damage and threat to native Opuntia. Unfortu- monid wasps are rare. Apanteles alexanderi nately, this situation is occurring when biological attacks other cactus moths and at least three control, a critical tool in the fight against the many other genera of Lepidoptera, and probably others invasive species, is needed more than ever before. (DeSantis 1967; Mann 1969). The Temelucha sp. The possible use of biological control against and the tachinid, Epicoronimyia mundelli (Blan- C. cactorum in North America was first raised by chard), are known to use other genera of cactus Bennett and Habeck (1992). Biological control moths (Mann 1969; Blanchard 1975; Zimmer- has controlled many insects, including Lepi- mann et al. 1979). No information about other po- doptera that feed within plants. For example, the tential hosts of the remaining parasitoids, the European pine shoot borer, Rhyacionia buoliana four ichneumonid wasps, was found, but this is (Denis & Schiffermuller), and the European corn probably due to a lack of knowledge rather than a borer, Ostrinia nubialis (Hübner), have been suc- true absence of other hosts. cessfully reduced using biological control (Kogan Some of these wasps appear to have the poten- et al. 1999; Dahlsten and Mills 1999). In this pa- tial to reduce C. cactorum populations (e.g., A. al- per, we will consider the possibilities of various bi- exanderi and Temelucha sp.). If used in the ological control approaches that might be useful United States, they probably would be able to ori- to reduce existing populations of the moth in Flor- ent to the plants and locate C. cactoblastis inside ida and adjacent Georgia, and perhaps limit its the pads where they feed. It is, however, unlikely spread. The possible benefits and perceived risks that any of these parasitoids are monophagous, so of each approach will be discussed. We do not wish their introduction for C. cactorum control could to advocate the use of biological control for C. cac- result in use of and harm to non-target Lepi- torum in North America, but we think it is impor- doptera in North America, especially native cac- TABLE 1. KNOWN PARASITOIDS OF CACTOBLASTIS IN THEIR NATIVE SOUTH AMERICA. Degree of attack Presumed Parasitoid species Cactoblastis species Other hosts Stage attacked of Cactoblastis Reference specificity Hymenoptera Braconidae Apanteles alexanderi C.