The Argentine cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), an invasive pest native to South America that feeds on prickly pear cactus (Opuntia spp.), has been used as an effective biological control agent against exotic Opuntia cacti around the world, including several Caribbean islands, Hawaii and Australia. However, the unintentional introduction of the moth to the Florida Keys in 1989 was recognized by scientists and conservationists as a serious threat to the rich flora and biodiversity of the native desert ecosystems in North America. Opuntia cacti are a key component in these arid areas, minimizing soil erosion and providing food, water, shade and shelter for a wide variety of vertebrate and invertebrate species. Researchers have identified the parasitic wasp Apanteles opuntiarum Martinez & Bertha as a strong candidate for release as a biological control agent to manage the Argentine cactus moth in the U.S. The Florida Department of Agriculture and Consumer Services (FDACS) is currently awaiting approval from the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) to release the wasps.
Argentine Cactus Moth
The larvae of the Argentine cactus moth feed inside the thick green pads or "cladodes" of the prickly pear cactus (Opuntia sp.).
Argentine cactus moth was originally detected in the Florida Keys in 1989. Since then, it has spread as far north as North Carolina and as far west as mid-Texas.
Adult moths have a wingspan up to 1¼ inches (3 cm) and are grayish brown, with whiter margins and distinctive black lines on their forewings. Females lay their eggs 50 to 80 at a time, stacked coin-like to form an egg-stick usually attached to a cactus spine.
The eggs hatch and the larvae enter the cladode, feeding gregariously and moving to a new cladode as the food supply is exhausted. The larvae grow to 1 inch (2.5 cm) in length and are a bright orange with dark transverse bands. The red and black banding pattern, coupled with finding the larvae feeding inside cactus, is diagnostic for Argentine cactus moth. Native cactus-feeding larvae are not red and black.
Fully developed larvae usually leave the plant and spin white cocoons in leaf litter or crevices of nearby trees. The entire life cycle takes approximately 90 days.
Research
No satisfactory method of chemical control has been found because of the larvae’s internal host feeding, as well as the sensitivity and expanse of the cacti ecosystem.
The combination of releasing sterile cactus moths (Sterile Insect Technique, SIT) and removing infested plants has been used to slow the moths’ geographic expansion. SIT has proven effective in controlling many lepidopteran pests and is unparalleled in its specificity and safety because only the target species is affected. It relies on the mass production and release of large numbers of sterilized or partially sterilized insects that will mate with wild insects. When sterile and wild insects mate, reproduction does not occur. For several years SIT was used to suppress the cactus moth populations in the Florida Panhandle and the Mississippi barrier islands, preventing their westward expansion. Unfortunately, the tactic was abandoned in 2012 due to expense and difficulty of application in the coastal wetlands of Louisiana.
The current area-wide management program focuses on the development of a more sustainable mitigation option, using a biocontrol agent to minimize the impact of Argentine cactus moth on native desert ecosystems and commercial cactus production areas. Over the years several natural enemies have been identified in South America attacking the cactus moth. However, these potential biological control agents lack the specificity to prevent impacts on native non-target insects, especially the many native cactus-feeding moths in North America. A newly described braconid wasp, Apanteles opuntiarum Martinez & Bertha, was observed exclusively attacking C. cactorum larvae in field conditions in Argentina.
Since March 2013, the FDACS Division of Plant Industry's Bureau of Methods Development and Biological Control has maintained a colony of the wasp in the Invertebrate Research and Containment Laboratory and has been improving mass-rearing techniques. Host-specificity testing on numerous native moth species is now complete. An application for a permit to release was submitted to APHIS in July 2023. On approval, we will likely employ a cooperative mass-rearing and multi-state release program.
Rearing
Argentine cactus moth artificial diet preparation
Cactus Moth Rearing
A kidney-bean based artificial diet was developed to rear cactus moth more efficiently. Blocks of artificial diet are coated with beeswax to simulate the cuticle of a cactus pad, encouraging the larvae to burrow in and to prevent the diet from desiccating. Approximately 60 eggs are placed onto a diet block. The larvae are incubated at 84 degrees F for up to eight weeks with monitoring and venting of the container to keep the relative humidity optimized based on the larvae’s size and metabolism. If the container gets too dry, larval growth rate will be severely hindered; too moist, and mold will develop. The diet block is replaced as necessary and pupae collected as they complete their development.
Parasitoid Wasp Rearing
Cactus moth larvae used for rearing A. opuntiarum are approximately third or fourth instar (3 weeks old). Mated parasitoid wasps are added to a jar with a cactus pad infested with 20 cactus moth larvae. The parasitoids are allowed five days to oviposit in the larvae. Larvae are then maintained with fresh cactus as needed until pupation of the moths or wasps. Parasitized pupae are moved to a petri dish and watched for adult wasp emergence.
