Genetic and Ecological Data Shed New Clues on the Invasion History of  Cactus Mealybug Pests in Puerto Rico

By Belen Aguirre and Guillermo Logarzo, Foundation for the Study of Invasive Species (FuEDEI)

The Harrisia Cactus Mealybug (HCM) has been causing extreme damage and death to cacti in dry forests of the island of Puerto Rico (Figure 1, a, b), making it urgent to protect cacti species affected by the pest. HCM was considered to be a single species, Hypogeococcus pungens, widely distributed in South America, but it turned out to be several different species. Scientists from the Foundation for the Study of Invasive Species (FuEDEI) have recently published a paper revealing the invasion history of two of these species that invaded Puerto Rico, one that feeds on plants in the amaranth and purslane families, and another, known as the Puerto Rican cactus mealybug pest (Figure 1, b, c, d), which is the one threatening cactus conservation in the Caribbean, and in Central and North America.

The study was based on DNA sequencing, measurements of the extent of the attack on host plants in the field, the geographic distribution of both invasive mealybugs, and climatic data. Both species showed footprints of severe past population bottlenecks (when a species’ population is so reduced that its genetic diversity is greatly reduced), suggesting very few specimens of each species arrived in the island, but later evolved rapidly as they spread across the island, achieving relatively high genetic variability again. In addition, the plants that the invasive insects attack in Puerto Rico varied between the Hypogeococcus species, and even among populations within each species, which indicates they can easily adapt to new plant hosts. Geographical models also suggest that under future climatic scenarios both species could expand the distribution range in Puerto Rico, posing an even greater threat for cactus conservation. It is also predicted that the mealybugs could easily spread across the region and into neighboring areas. Efficient management and control strategies of the Puerto Rican cactus pest will likely demand the release of natural enemies in regions with high incidence of host infestation. Two parasitoid species from Argentina and Paraguay, Anagyrus cachamai and A. lapachosus, are currently in quarantine in Puerto Rico completing specificity tests to confirm they are safe for release on the island. These tests, performed on five populations of mealybugs of the same genus as the Puerto Rico cacti pest, plus two mealybug species from other genera, indicate that both parasitoid species are restricted to the cacti pest genus, Hypogeococcus, suggesting, so far, that they may be safe for release. Tests are expected to be completed within a few months.

For more details:

Poveda-Martínez, D., Salinas N. A., Aguirre, M. B., Logarzo, G., Sanchez-Restrepo A.F., Hight, S., Diaz-Sotero H., & Hasson, E. Genomic and ecological evidence shed light on the recent demographic history of two related invasive insects. Scientific Reports 12, 19629 (2022). https://doi.org/10.1038/s41598-022-21548-y

Figure 1. Adult females and host plant damage of both Hypogeococcus species invading Puerto Rico. Hypogeococcus sp. on a cactus (a) and the typical damage caused by the insect (b). Hypogeococcus sp. feeding on purslane (c) and the infestation produced on amaranth (d)

Contact: Belen Aguirre

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.