Rearing Cactoblastis cactorum (Lepidoptera: Pyralidae) on Artificial Diet and Opuntia Cladodes1 Orville G. Marti, Ronald E. Myers, and James E. Carpenter U.S. Department of Agriculture, Agricultural Research Service, Crop Protection and Management Research Laboratory, PG Box 748, Tifton, Georgia 31793 USA J. Entomol. Sd. 43(1): 95-106 (January 2008) Berg, is an invasive species that threatens Abstract The cactus moth, Cactob/astiS cactorum economically and ecologically important native cacti in Mexico and the U.S. Southwest. The insect presently occurs along the coastal U.S. from Charleston, SC, to Dauphin Island, south of Mobile, AL, and in the interior of Florida. Current control and eradication tactics include manual destruction of infested cactus and the Sterile Insect Technique (SIT), which involves the release of irradiated cactus moths to mate with wild moths and produce sterile offspring. The ability to rear the cactus moths in the laboratory has been crucial in research and development of survey and control techniques. Procedures for rearing the cactus moth in the laboratory on cactus cladodes and artificial diet are described and provide a foundation for the further development of mass-rearing protocols. Cactaceae, mass rearing, artificial Key Words CactoblastiS cactorum, Pyralidae, Opuntia, diet, invasive species, sterile insect technique The cactus moth, CactoblastiS cactorum Berg (Lepidoptera: Pyralidae: Phyciti- nae), is an invasive species first detected in the continental United States in Florida in 1989 (Habeck and Bennett 1990, Zimmerman et al. 2001). It has since been detected in the interior of the Florida peninsula, up the east coast of the US as far north as Charleston, SC, and along the coast of the Gulf of Mexico as far west as Dauphin Island, south of Mobile, AL, (Soils et al. 2004, Carpenter, pers. obs.). This insect is recognized as a serious threat to native Opuntia species in the US and particularly in Mexico (Perez-Sandi 2001, Stiling and Moon 2001), where Opuntia species are widely used as food, livestock fodder, medicine, dye production, and fencing (Vigueras and Portillo 2001). Most importantly, Opuntia and other cacti are major components of local ecosystems in Mexico and the US Southwest. To avert the economic and ecological consequences that C. cactorum could have in Mexico and the U. S. Southwest, the US Department of Agriculture, in cooperation with Mexico, has developed procedures for using the Sterile Insect Technique (SIT) is reared in large numbers on against C. cactorum. In the SIT program, C. cactorum artificial diet in the laboratory and adults are irradiated with Co 60 , which produces complete sterility in females and partial sterility in males. Irradiated insects are then released in large numbers at the leading edge of the invasive population and at times Received 18 June 2007; accepted for publication 16 July 2007. Mention of a product does not constitute an endorsement of its use by USDA. 2Address inquiries (email: Jim.Carpenter@ ars.usda.gov) 95 J 96 J. Entornol. Sci. Vol. 43, No. 1 (2008) which coincide with the presence of wild individuals available for mating. When irra- diated males mate with wild females, the Fl progeny of these matings are sterile. In order for the SIT program to succeed, large numbers of moths must be reared from egg to adult on artificial diet in a quarantined rearing facility (Carpenter et al. 2001). Mortality from disease in the rearing colony disrupts the SIT program by reducing the numbers of insects available for release. Disease problems have been more severe in insects reared on artificial diet than in those reared on Opuntia cladodes (Marti et al. 2007). Research is presently underway to develop an improved artificial diet which will be comparable to cactus cladodes in its ability to sustain the laboratory production of large numbers of C. cactorum for release in the SIT program. Until a satisfactory artificial diet has been fully developed and validated for several continuous genera - tions, we rely on Opuntia cladodes as the primary food source for Cactoblas f/s larvae. Here we provide a detailed description of the current procedures used at USDA- ARS Crop Protection and Management Research Unit (CPMRU) laboratory for rear- ing C. cactorum on artificial diet and on Opuntia cladodes. The components of the diet, its preparation, and the techniques for rearing and handling larvae and adults are the subject of ongoing research in an effort to develop the best procedures at lowest cost. The diet components in particular are subject to change and improvement. Rearing Protocol Mass-rearing of C. cactorum on Opun f/a cladodes and artificial diet are fundamen- tally similar, differing principally in the source of the diet, with the former collected from natural host plants in the field and the latter prepared in the laboratory from ingredi- ents purchased commercially. From the time that cocoons are gathered at the end of the larval period until hatch of eggs in the succeeding cycle, procedures and equip- ment for harvesting and handling of cocoons and pupae, management of adults, and incubation of eggsticks are identical, or nearly so. We have, therefore, provided parallel descriptions of the respective procedures for the cladode-reared and diet- reared colonies, and combined as much as possible the subsequent descriptions of similar or identical procedures. Rearing Cactoblastjs cactorum on Opuntia cladodes. Whereas artificial diet is prepared in the laboratory from commercially purchased components, the use of Opuntia cladodes (=pads) as food for C. cactorum larvae requires a reliable year- round source of suitable cladodes. Not all Opuntia species are a suitable food source for C. cactorum (Perez-Sandi 2001). Opuntia ficus-indica (L.) and 0. stricta (Haworth) are the most common and best-suited species in the vicinity of Tifton, GA, and can be located in the wild, usually along fence rows where they are often planted for orna- mental value. Old stands may be composed of many individual plants, either planted by property owners or propagated from seeds or fallen cladodes. The size of the laboratory colony should be scaled to the availability of wild plants and sites should be visited on a rotating basis to avoid overharvesting of cladodes and to allow time for new growth. Alternatives to harvesting of cladodes from the wild include farming of Opuntia locally or contracting with growers to have cladodes shipped from areas where the plants are more abundant. Before any new source of Opuntia is used in rearing the laboratory colony, tests should be conducted on a small portion of the colony to verify the acceptability and suitability of the cladodes. Collect mature ("2-year") cladodes as food for the colony. These are dark green and no thicker than -2 cm. The younger cladodes are thin and light green and a few 97 MARTI et al.: Rearing Cactob/astiS cactorum of these are collected to feed newly-hatched larvae. Cladodes are grasped with tongs, removed with a knife or pruning tool, and placed in a plastic tub for transport to the laboratory, where they may be stored up to several weeks in a cold room at 12 C. Remove spines from cladodes using scissors, heavy forceps, a scraper, or knife. Wash by soaking in cool or cold tap water with detergent, and scrub with a brush to remove all traces of dirt, rinse, then set them on the counter to dry. Avoid washing cladodes in hot water, as this may cook them. Cut large cladodes into two smaller pieces (-10 x 20 cm) and store them in the cold room until needed. Store young cladodes for neonates intact in a separate container in the cold room and cut them just before use. When eggs darken, place an eggstick with no more than -100 eggs into a 30-ml plastic cup with a 2 x 2 cm piece of young cladode so that food is immediately available to the neonates upon hatching. C. cactorum neonates will die within several hours if food is not available, but they may be held for several days in the cups as long as they have not completely consumed their food. We have recently begun placing only 1 eggstick per cup. In the event that disease problems arise later, the larvae from the entire container are discarded and the loss is limited to larvae developing from a single eggstick. Each container is provided with a 10 x 27 cm grid, made from hardware cloth, in which 2 cm at each of the long ends has been bent at right angles. This grid is used to support the cladode(s). Approximately 150 mL of a mixture of cat litter and sand is added to the bottom of the container to soak up excess moisture dripping from the cladode as the larvae develop. When containers have been prepared and neonates are ready, place a 2 x 2 cm piece of cladode containing approx. 70-100 C. cactorUm neonates on top of the cladode, secure the lid, label the container, and place the container in a chamber or incubator room at 26 C, 12:12 In photoperiod, and 70% or higher relative humidity (Fig. 1). Check the containers 10-14 d after inoculation and at least once weekly thereafter. Place a fresh cladode under the old one if larvae are still feeding inside it. As the old cladode is consumed, the larvae migrate to the fresh one and begin feeding. The larvae feed on the interior contents of the cladodes and do not consume the large fibers or the exterior cuticle. The remains of old cladodes should be checked for the presence of larvae and cocoons and discarded if none are present. Return any larvae to the container and remove and incubate the cocoons.