Harrisia cactus mealybug

Hypogeococcus pungens

Last updated by: 
Faith Campbell

A second South American insect in addition to cactus moth threatens cacti from the Caribbean basin to the Southwest and Mexico: the Harrisia cactus mealybug, Hypogeococcus pungens. This insect threatens columnar cacti in the subfamily Cactoideae (Zimmerman et al. 2010)

Determining the level of threat to various columnar cacti is complicated. First, H. pungens and a closely related species - H. festerianus have been confused in the past (Golubov pers. comm. January 2011) - raising questions about the host range. H. pungens has a wider host range.

The Harrisia cactus mealybug is native to northern Argentina and Chile, westernmost Brazil, Paraguay and southern Perú (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. H. pungens has also been observed feeding on some non-cacti, including Portulaca spp. (Portulacaceae), Althernathera (Amaranthaceae) and Acalypha (Euphorbiaceae) species (USDA ARS; Zimmerman et al. 2010).

The Harrisia cactus mealybug was detected in the Guanica Forest Reserve on the southern coast of Puerto Rico in 2005 (Zimmerman et al. 2010). In the dry forests of Puerto Rico there are 13 native and three endemic species of columnar cacti; two are listed by the U.S. Fish & Wildlife Service as endangered: Harrisia portoricensis and Leptocereus grantianus (USDA ARS). These cacti play important roles in the ecosystem, including as important food sources or shelter for endemic bats, birds, moths and other pollinators (Segarra & Ramirez; USDA ARS).

In the 5 years since the mealybug’s detection in Puerto Rico, it has caused extensive damage to Pilosocereus royenii (Royen’s tree cactus), as well as to Leptocereus qaudricostatus (pitaya), Melocactus intortus (turk’s cap), and Cereus hexagonus. It has caused minor damage to Stenocereus fimbriatus (Zimmerman et al. 2010). The mealybug has spread to a large area in the southern coast region and continues to spread rapidly (Zimmerman et al. 2010; Segarra & Ramirez). In Guanica Commonwealth Forest, every cactus within hundreds of acres has been killed. Cacti growing on the most favorable sites survive longer than those on rocky sites (Segarra pers. comm. August 2009).

In Florida, as of 2009, a mealybug usually thought to be H. pungens occurs in the following counties: Brevard, Broward, Charlotte, Clay, Collier, Dade, Escambia, Hendry, Highlands, Hillsborough, Lake, Lee, Leon, Manatee, Miami-Dade, Monroe, Okaloosa, Orange, Palm Beach, Pasco, Pinellas, Polk, Sarasota, Seminole, St. Lucie and Volusia . Since the insect is rarely found on cacti in Florida (University of Florida fact sheet), Segarra suspects it is actually a different species (Segarra pers. comm. August 2009). The mealybug is not causing economically important damage in Florida (University of Florida fact sheet). Harrisia cactus mealybug has also been detected in Hawai`i – on hibiscus in 2005 (Hawaii Department of Agriculture new pest report)

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 quite likely dispersed by wind. Damage to the cactus host is usually found as malformations and gall-like structures. Growth is usually arrested, flowering prevented, and some specimens are eventually killed (Zimmerman et al. 2010).

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 gigantean) 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). Furthermore, Mexico already has several mealybugs in the same genus, and specialized natural enemies of these mealybugs might switch hosts in the event that H. pungens invades Mexico and so prevent population explosions (Zimmerman et al. 2010). Still, concern appears warranted.

The most likely pathway by which the mealybug might cross the considerable distance between the Caribbean and the American Southwest is the trade in plants for planting (the horticultural trade) (Zimmerman et al. 2010). The species has been intercepted by USDA APHIS inspectors on cactus (primarily on roots) imported from Germany, Peru, and Puerto Rico. The Harrisia cactus mealybug has been collected in Europe and the Mediterranean, primarily in greenhouses. APHIS has also intercepted several other mealybugs in the same genus – on plants (including orchids and bromeliads as well as on cacti) from Belize, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Panama, Peru, and Venezuela(APHIS alert).

Once established in the region, it could spread rapidly on the wind (Zimmerman et al. 2010).

It is thus of considerable concern that the Harrisia cactus mealybug has been detected in California. One such detection was in 2002 in San Obispo County (California Plant Pest and Disease Report. 2005). The second detection was in Beverly Hills (Los Angeles County) in 2010 (Zimmerman et al. 2010; Leavitt pers. comm. November 2010). In the Beverly Hills case, only one mealybug was found despite a survey of the surrounding 400 meters (Leavitt pers. comm. November 2010). Officials do not know how the mealybug reached the area (Leavitt pers. comm. November 2010).

Meanwhile, scientists at the USDA ARS laboratory in Argentina have begun the search for possible biocontrol agents.

Sources

California Plant Pest and Disease Report. 2005. Vol. 22 No. 1. Covering Period from July 2002 through July 2005.

Hawaii Department of Agriculture. 2006. http://hawaii.gov/hdoa/pi/ppc/2006-annual-report/new-pest-detections (accessed 11/1/10)

Leavitt, Robert. Director, Plant Administration, California Department of Food and Agriculture, personal communication November 2010.

Segarra-Carmona, A.E., A. Ramirez-Lluch. No date. Hypogeococcus pungens (Hemiptera: Pseudococcidae): A new threat to biodiversity in fragile dry tropical forests. {title/org/other identifying information for Segarra-Carmona plus an entry for the pers. comm.}

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

Zimmermann, H.G., M.P.S. Cuen, M.C. Mandujano, and J. Golubov. 2010. The South American mealybug that threatens North American cacti. Cactus and Succulent Journal. 2010 Volume 82 Number 3

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