NOTE: this pest is not known to spread in or on firewood. It is included in the Gallery of Pests for general information purposes only.
The Harrisia cactus mealybug threatens columnar cacti in the subfamily Cactoideae from the Caribbean basin and possibly in the American Southwest and Mexico (Zimmerman et al. 2010).
Hypogeococcus pungens (Hemiptera: Pseudococcidae) is a species complex composed of at least five putative species, which are separated in part by the plants they use as hosts. Two of the undescribed species have apparently been introduced to Puerto Rico: H. pungens Hyp‑C feeds on cacti; H. pungens Hyp‑AP feeds on Amaranthaceae and Portulacaceae hosts. Both evolved from putative source populations in Brazil (Poveda-Martinez et al. 2022).
The species complex is native to northern Argentina and Chile, westernmost Brazil, Paraguay and southern Perú (USDA ARS). In South America, insects in this genus feed on many columnar cacti, including species in the genera Cereus, Echinopsis, Harrisia, Cleistocactus, Monvilea, and Parodia. Some of the mealybugs also feed on non-cacti in the families Portulacaceae, Amaranthaceae, and Euphorbiaceae species (USDA ARS; Zimmerman et al. 2010).
The taxonomic complexities and uncertainties have proved a difficult barrier to developing effective management strategies. [See https://scalenet.info/catalogue/Hypogeococcus%20pungens/ ]
The dry regions of the Caribbean Islands are home to about 100 native cacti, 75% of which are endemic. According to the Center for Plant Conservation, 20 species are listed as threatened by the IUCN.
The mealybug species temporarily designated as H. pungens Hyp‑C threatens seven of 14 native cactus species in Puerto Rico. The insect’s attack promotes abnormal gall-like growth on the stem and deformed flowers. These deformations severely affect infested plants’ reproduction and eventually survival (Poveda-Martinez et al. 2022) Three of the cacti are endemic; two are federally listed as endangered species: Harrisia portoricensis and Leptocereus grantianus (USDA ARS). Since the mealybug’s detection in Puerto Rico, it has caused extensive damage to Pilosocereus royenii (Royen’s tree cactus), Leptocereus qaudricostatus (pitaya), Melocactus intortus (turk’s cap), and an introduced cultivar, Cereus hexagonus. It has caused minor damage to Stenocereus fimbriatus (Zimmerman et al. 2010). These cacti provide food or shelter for endemic bats, birds, moths and other pollinators (Segarra and Ramirez; USDA ARS).
The mealybug is also killing native cacti on the U.S. Virgin Islands (Poland et al. 2019), although data on this invasion are scarce.
In the absence of control measures, scientists expect H. pungens Hyp-C to continue decimating Puerto Rican cactus diversity and threaten other cactus rich ecosystems across the Caribbean islands, Central America and, potentially, North America (see below) (Poveda-Martinez et al. 2022).
How and when the mealybug first invaded the Caribbean and North America is unknown. Genetic studies indicate that the two species each invaded Puerto Rico once, on separate occasions (Poveda-Martinez et al. 2022). The presence of the animal now known as H. pungens Hyp-C on Puerto Rico was detected in the Guánica Commonwealth Forest and Biosphere Reserve on the island’s southern coast in 2005 (Zimmerman et al. 2010). The introduction probably occurred in about 1996 (Poveda-Martinez et al. 2022).
The outbreak was soon determined to be widespread in the island’s dry districts. Every cactus within hundreds of acres had been killed by 2009. Cacti growing on the most favorable sites survived longer than those on rocky sites (Segarra pers. comm. August 2009). By 2010, it was estimated to be present on about 1,400 km2. Surveys found H. pungens Hyp-C in all 11 municipalities surveyed. At some locations, infestation levels were extremely high – e.g., 86% of stems surveyed were infested at Guánica (Segarra-Carmona et al. 2010). By 2014 – nine years after detection, the mealybug had reached the small island of Caja de Muertos. A later survey detected the mealybug on 268 out of 445 cactus plants examined (60%) in 12 out of 39 sites examined (Poveda-Martinez et al. 2022).
As noted, H. pungens Hyp-C has also spread to the U.S. Virgin Islands (Poland et al. 2019).
Genetic studies indicate that after its introduction to Puerto Rico in ~1996 H. pungens Hyp-C experienced a strong genetic bottleneck, causing reductions of more than 80% of the ancestral effective population size. This was followed by rapid population growth. As the insect spread across the Puerto Rico Archipelago, it rapidly evolved genetic differences. Three genetic clusters have been identified: in Cabo Rojo and Guánica, Petrona, and on Caja de Muertos island (Poveda-Martinez et al. 2022).
Several mealybugs in this species complex have been introduced to various locations. These introductions not only demonstrate the animals’ ability to take advantage of human transport (probably primarily through movement of infested plants) but also its ability to adapt to new conditions and rapidly expand their populations. Most worrying was the successful deployment of an undescribed mealybug in the H. pungens species complex as a biocontrol agent targeting invasive cacti in Australia and South Africa (Poveda-Martinez et al. 2022). Another troubling event has been multiple appearances of mealybugs that feed on cacti in southern California. Some pest populations were in the environment — on residential or recreational properties in Los Angeles and Orange County (present in 2010, 2012, 2014, and 2018). Other infestations were detected in several plant nurseries in three southern California counties and San Mateo County between 2004 and 2018. CDFA had intercepted the mealybug on alternanthera and ludwigia plants shipped from Florida in 2002 and 2004 (CDFA 2018). Another source (California Plant Pest and Disease Report. 2005) referred to a detection in San Obispo County in 2002.
Other introductions of mealybugs that are probably in this species complex have been recorded in California in 1951; Florida (1985 and 1996; reported to be in 16 counties in 2009) (Poveda-Martinez et al. 2022); and Dominican Republic (no date) (CDFA 2018); and in Hawai`i in 2005 (Hawaii Department of Agriculture new pest report). In at least some of these cases the mealybug fed on Amaranthaceae and Portulacaceae rather than cacti. A mealybug with this feeding habit was also detected in 2000 in San Juan, Puerto Rico (Poveda-Martinez et al. 2022). In most cases there is little information about the level of damage to the hosts, but it is generally thought to be minor.
Life Cycle
Mealybugs reach adulthood in a little less than a month. Females then lay 60 – 120 eggs over the course of the month. Eggs hatch within minutes and nymphs are probably dispersed by wind (Zimmerman et al. 2010).
Wider Threat
North America has more than 500 columnar cactus species in the Cactoideae (Zimmerman et al. 2010). Some of these cacti are already endangered, e.g., several Pediocactus. Others are totems of the desert, e.g., the saguaro (Carnegiea gigantea) and organ pipe (Stenocereus thurberi) cacti. The larger ones, particularly, play important ecological roles. It is not known how vulnerable individual species are to the mealybug (Golubov pers. comm. January 2011). In Mexico several mealybugs in the same genus are already present. The natural enemies of these mealybugs might be able to attack H. pungens Hyp-C if it invades the country (Zimmerman et al. 2010). Despite the well-founded concern, apparently no funds have been allocated by governments or conservation organizations to studying the vulnerability of these cacti to one or more mealybugs in the Hypogeococcus genus.
The most likely pathway by which the mealybug is spread is the trade in plants for planting (the horticultural trade) (Zimmerman et al. 2010). Mealybugs have been intercepted by USDA APHIS inspectors on cactus (primarily on roots) imported from Germany, Peru, and Puerto Rico. APHIS has also intercepted several other mealybugs in the same genus – on plants (including orchids and bromeliads as well as cacti) from Belize, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Panama, Peru, and Venezuela (USDA APHIS alert).
Climate Change
The two species H. pungens Hyp-C and Hyp-AP are currently separated on Puerto Rico by host preferences and climatic niches. They also occupy different geographic areas. Scientists fear that ongoing climate change could allow H. pungens Hyp-C to establish farther into the island’s interior and in a large area in the north. Such range expansion would end the geographic separation. Overlapping of the two species is likely to exacerbate the threat to Puerto Rico’s cacti. Most directly, it would complicate implementation of management strategies, especially biological control. Intermixing of the two species could also facilitate hybridization which might result in more vigorous attacks or a broadened host range. Hybridization is frequent in closely related species (Poveda-Martinez et al. 2022).
Biocontrol
Scientists at the USDA ARS laboratory in Argentina began the search for possible biocontrol agents in 2010. While no funds have ever been appropriated for this activity, for several years the U.S. Department of Agriculture supported the work by allocating funds from broader programs. The USDA Invasive Species Coordination Program and APHIS Eastern Region funded the search for biocontrol agents over six years (H. Diaz-Soltero pers. comm. August 2015). In fiscal years 2017 and 2019, grants under APHIS’ Plant Pest and Disease Management and Disaster Prevention Program Link provided ~ $208,000 and ~ $350,000, respectively, to fund testing of candidate biocontrol agents.
Scientists at the Center for Excellence in Quarantine and Invasive Species at the University of Puerto Rico devoted at least a decade to the search. As of February 2019, the Center was conducting host specificity tests on a parasitoid, Anagyrus cachamai, and continuing surveys for other primary and secondary parasitoids.
The search efforts have been complicated by the confusion over how many mealybug species are involved and which species attack which types of cacti. By ~ 2019 studies focused on two parasitoid wasps, Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae). Studies have revealed that the two behave differently in ways that might influence their efficacy. A. cachamai females attack more mealybugs as the number of hosts available rises. However, as the females age, they have fewer mature eggs so parasitize fewer mealybugs. In contrast, A. lapachosus females have two biological traits that give them greater flexibility: 1) older females produce more eggs; and 2) the females learn more effective host-finding methods over time. There appears to be no information about the status of these candidate biocontrol agents more recent than 2022.
Genetic Conservation
The USDA also partnered with the Naples (Florida) Botanical Garden to collect fruits and vegetative material for ex situ conservation. Only healthy plant material was collected, from areas outside the invaded regions. Rigorous phytosanitary procedures were followed to ensure the absence of the mealybug. 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 8 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. (These figures include Opuntia cacti that are hosts of a second invasive insect, Cactoblastis cactorum.)
Sources
Aguirre, M. G. Logarzo, S. Triapitsyn, H. Diaz-Soltero, S. Hight, O. Bruzzone. 2023? Effect of egg production dynamics on the functional response of parasitoids.
California Plant Pest and Disease Report. 2005. Vol. 22 No. 1. Covering Period from July 2002 through July 2005.
California Department of Food and Agriculture. 2018. California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A
Hawaii Department of Agriculture. 2006. https://hawaii.gov/hdoa/pi/ppc/2006-annual-report/new-pest-detections (accessed 11/1/10)
Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag.
Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. (2019) Prioritizing the conservation needs of US tree species: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/ << Project CAPTURE source
Poveda-Martinez, D. N.A. Salinas, M. Belen Aguirre, A.F. Sanchez-Restrepo, S. Hight, H. Diaz-Soltero, G. Logarzo, and E. Hasson. 2022 Geonomic & ecol evidence shed light on the recent demographic history of two related invasive insects. Scientific Reports.
Segarra-Carmona, A.E., A. Ramirez-Lluch. No date. Hypogeococcus pungens (Hemiptera: Pseudococcidae): A new threat to biodiversity in fragile dry tropical forests.
Segarra-Carmona, A.E., A. Ramírez-Lluch, I. Cabrera-Asencio and A.N. Jiménez-López. 2010. First Report of a New Invasive Mealybug, the Harrisia Cactus mealybug Hypogeococcus pungens (Hemiptera: Pseudococcidae). J. Agrie. Univ. RR. 94(1-2):183-187 (2010)
Srivastava, M., P. Srivastava, R. Karan, A. Jeyaprakash, L. Whilby, E. Rohrig, A.C. Howe, S.D. Hight, and L. Varone. 2019. Molecular detection method developed to track the koinobiont larval parasitoid Apanteles opuntiarum (Hymenoptera: Braconidae) imported from Argentina to control Cactoblastis cactorum (Lepidoptera: Pyralidae). Florida Entomologist 102(2): 329-335.
Triapitsyn, Aguirre, Logarzo, Hight, Ciomperlik, Rugman-Jones, Rodriguez. 2018. Complex of primary and secondary parasitoids (Hymenoptera: Encyrtidae and Signiphoridae) of Hypogeococcus species. mealybugs (Hemiptera: Pseudococcidae) in the New World. Florida Entomologist Volume 101, No. 3 411
USDA Agriculture Research Service, Research Project: Biological Control of the Harrisia Cactus Mealybug, Hypogeococcus pungens (Hemiptera:pseudococcidae) in Puerto Rico Project Number: 0211-22000-006-10 Project Type: Reimbursable
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Diaz-Soltero, Hilda. Then at the U.S. Department of Agriculture, personal communication.
Hight, Stephen. Then at the U.S. Department of Agriculture Agriculture Research Service, personal communication.