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Saving Prickly Pear Populations from the Cactus Moth

Prickly Pear
Prickly pear plant attacked by the cactus moth. (Photo courtesy of Foundation for the Study of Invasive Species (FuEDEI))

Opuntia cacti, commonly known as prickly pears, are a group of flowering plants in the cactus family. Like most true cactus species, prickly pears are native only to the Americas. Prickly pear species are abundant in the arid, semiarid and drought-prone western and south central United States and Mexico, especially in the central and western regions, as well as in the Caribbean islands (West Indies).

Prickly pears are valued as forage, food, and to raise cochineal, a scale insect from which a natural dye, called carmine, is derived. Above all, however, prickly pears are of great conservation concern in North America because of the number of endemic species, and their role as chief primary producers in many arid ecosystems. Many desert animals depend on prickly pears for sustainment, such as rock iguanas and arid-land birds.

cactus moth catepillars
Cactus moth caterpillars feeding inside a cactus. (Photo courtesy of Foundation for the Study of Invasive Species (FuEDEI))

The invasive cactus moth, native to South America, physically damages prickly pears by consuming inner tissue during larval development. It can decrease plant longevity, impact fruit production both in North and South America, and threaten cactus diversity in North America. In 2003, the USDA Agricultural Research Service initiated a control program to slow the spread of the cactus moth in the United States by sanitation and the implementation of the sterile insect technique.

These control tactics proved insufficient. As a result, a classical biological control program was then initiated in the moth’s native range in Argentina. Foundation for the Study of Invasive Species (FuEDEI) researchers are studying the ecology and biology of this pest, with the aim of identifying the natural enemies that may be promising candidates as biological control agents.

Parasitoid wasp of cactus moth caterpillars (a). Wasps waiting for caterpillars to emerge to parasitize (b). Older wasp larvae finishing off a cactus moth caterpillar (c). Parasitoid cocoons (d). (Photo courtesy of Foundation for the Study of Invasive Species (FuEDEI))

A small wasp that lays its eggs in cactus moth caterpillars was identified that showed high specificity and attack rates. This wasp, Apanteles opuntiarum, was repeatedly exported to the United States, and is currently being mass reared in quarantine at the Division of Plant Industry, Florida Department of Agriculture and Consumer Services, in Gainesville, Florida. The petition for its release is in development and should be submitted before end of 2021.

Contact: Guillermo Cabrera Walsh

The Foundation for the Study of Invasive Species (FuEDEI), formerly known as the South American Biological Control Laboratory (SABCL), is located in Hurlingham, Argentina, near Buenos Aires. The SABCL/FuEDEI plays a crucial role collecting and providing candidate biological control agents for South American weeds and pest insects for federal and state cooperators, several U.S. universities, and research collaborators worldwide since 1962. FuEDEI’ s main mission includes exploring for natural enemies of target insects and weeds in Argentina and neighboring countries and conducting host-specificity testing to determine their safety for eventual release in the U.S. In addition, complementary research that investigates the ecology, behavior, taxonomy, and genetic differences based on geographic distribution is conducted on both targets and potential agents. Performing these studies in the region of origin of the target pest serves as an efficient prescreening process that reduces the number of biocontrol agent candidates shipped. This reduces the amount of quarantine work and valuable quarantine space occupation, the expenses related to permitting processes, the risks of escapes, and the release of maladapted or wrongly identified agents to a minimum, saving in costs and hazards. On some occasions these complementary studies help us understand why an exotic organism becomes invasive, which can, in turn, lead to determining novel strategies for their management.