Safeguarding the genetic diversity of cacti threatened by the Harrisia Cactus Mealybug in Puerto Rico

Within the Caribbean Islands, the cactus family (Cactaceae) comprises about 100 native taxa (75% endemic), mainly from subtropical dry forests. While some taxonomic discrepancies exist and new species are being discovered, the IUCN Red List considers only 20 Caribbean cacti species as threatened. Invasive insects deliberatively introduced as a biocontrol in Australia and South Africa, have found their way into the Caribbean and are one of the main factors threatening cacti species. The Harrisia Cactus Mealybug [HCM] (Hypogeococcus pungens s.s.), recorded in the Caribbean since 1986, is now killing cacti in the Cactoideae subfamily in Puerto Rico. Another pest, the Cactus moth (Cactoblastis cactorum), deliberately introduced in the Caribbean in 1957, continues to threaten cacti in the Opuntioideae. Puerto Rico has 17 native cacti species, many of which are island or regional endemics, including 11 threatened by these two invasive pests.
The USDA and collaborators are working on a long-term biocontrol research program to control HCM. Effective Environmental Restoration conducted a field collection for ex situ conservation through a USDA-funded project in partnership with the Naples Botanical Garden (NBG). In 2021, fruits and vegetative material were collected in non-infected areas, securing 13 of the 17 native cacti species. Only healthy plant material was collected, and a rigorous phytosanitation protocol was implemented throughout the process. Collections of fruits and vegetative material provided 1,298 cacti samples from 13 species, representing 1,173 maternal lines from 91 sites throughout Puerto Rico. A total of 90,720 seeds representing eight species are banked at the NBG for long-term storage. Propagation of the vegetative material has 56% success, and plants are incorporated into the NBG’s living collections. Through this ex situ approach, plant material is secured with a genetic representation of each species from some of the most important dry forests of Puerto Rico.