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common name: ground pearls
scientific name: Margarodes spp. (Insecta: Hemiptera: Margarodidae)

Introduction - Distribution - Life Cycle - Dispersal - Economic Importance - Management - Selected References

Introduction (Back to Top)

Ground pearls, Margarodes spp., are primitive, subterrestrial relatives of the widely recognized, above ground armored scale insect (family Diaspididae). They are also sometimes referred to as earth pearls or pearl scale. While retaining well-developed fossorial legs with numerous setae (which scale insects do not have), ground pearls cannot secrete scales similar to their scale relatives (Beardsley and Gonzalez 1975). Instead, ground pearls excrete a waxy covering that totally surrounds their body with the exception of their piercing- sucking mouthparts. The voided, waxy, spherical covering of the insect is the most likely structure to be encountered. The sphere is pink to yellowish-brown in color and measures from 1/6 of an inch in diameter to as small as a grain of sand (Buss 2008). The exposed mouthparts are used to feed and attach to the roots of plants.

Immature ground pearls

Figure 1. Immature ground pearls, Margarodes spp., in centipede grass. Photograph by David Shetlar, Ohio State University.

 

Distribution (Back to Top)

Reports of ground pearls as pests occur in Australia, and the southern USA (Allsopp et al. 2000, Buss 2009, Hoffman and Smith 1991). However, the distribution is further-reaching than its pest status. A revision (Foldi 2005) of the family, reported species of Margarodes present in North America, South America, the Caribbean region, Africa, and Southwest Asia.

In Florida, ground pearl populations are believed to be restricted from the panhandle to north central Florida (Alachua county) (Buss 2009).

Life Cycle (Back to Top)

During late spring or early summer adult female ground pearls, which are pink in color, emerge from their pearl cysts, migrate, and then lay up to 100 eggs into a chamber consisting of a wax-like filament. During favorable conditions, a female may have several egg-laying episodes in a single year. The eggs hatch several days after being laid. The first instars (called crawlers) leave their encasement and seek out a healthy root on which to feed. Once established, the nymphs begin to secrete their outer covering and develop into "ground pearls." During the summer and into the fall the nymphs continue to develop. By late fall or early winter the insects are adults and overwinter in the cys (pearl) surrounding them. The life cycle appears to be predominately parthenogenic (Hoffman and Smith 1991).

Mature female ground scales

Figure 2. Mature female ground scales, Margarodes spp., found in soil sample. Photograph by David Shetlar, Ohio State University.

 

Various life stages of ground pearls

Figure 3. Various life stages of ground pearls, Margarodes spp. Photograph by University of Florida.

Dispersal (Back to Top)

The small size and below soil-surface habitat of Margarodes spp, limit their ability to move very far by natural means. Ground pearls must dig through the soil to locate a new feeding site. Migration rates through continuous patches of turf have been calculated at the maximum rate of 4 to 6 inches per year (Hoffman and Smith 1991). The expansion of a ground pearl population occurs in an irregular circular shape.

As a result of this extremely slow dispersal rate, the long distance movement of ground pearls is attributed to anthropogenic causes. Examples of human-induced, ground pearl introduction into uninfected sites include movement of infested organic material on tools, farming implements and tractors, and the sale or introduction of infested plants.

Economic Importance (Back to Top)

Ground pearls are chiefly restricted to grasses. Centipedegrass is highly prone to ground pearl attacks, but St. Augustinegrass, bermudagrass, bahiagrass, carpetgrass, and zoysiagrass can also be infested (Buss 2009, 2008; Hoffman and Smith 1991).

Reports from Australia identify sugarcane as a potential host (Allsopp et al. 2000). In addition, grape roots are also reported to incur damage from ground pearl species in California (Barnes et al. 1954). Exact impact, measured in dollars, is unavailable for sugarcane and grapes. In turf, the acceptable damage level will largely depend on an individual's preference and the utility of the turf (e.g., athletic professional turf versus public playing fields). Turf damage is characterized by yellowing of the grass followed by browning and death. If a plant is experiencing stressful conditions (e.g., over-watering, very low mowing heights, etc.) large expanding brown or dead patches of grass may appear (Buss 2008).

Management (Back to Top)

No insecticides or other chemicals are recommended for control of ground pearls. In addition, there are no biological control management techniques currently available for ground pearls. The best solution is to reduce plant stress by following recommended fertility and irrigation recommendations to enable turfgrass tolerate the damage (Buss 2008.) However, non-specific predators, such as ants, may be useful in reducing populations of ground pearls. Applying broad-spectrum insecticides, not needed to control other turfgrass pests, could eliminate these natural enemies (Brandenberg 2003).

The ground pearls' ability to avoid insecticides is believed to be the result of their long encysted "pearl" stage and their depth in soil (up to 12 in.) (Hoffman and Smith 1991). Since the organisms move slowly and reside only as deep as the root zone, manual removal of infested areas with a generous buffer zone may alleviate the problem, but this remains to be verified (Buss 2008).

In agricultural situations, fallow periods with regular tillage or crop rotation with a non-grass crop may reduce population levels. The life cycle of some species of ground pearls is two or more years (Allsopp et al. 2000). The multiyear life span should be taken into account when planning pest control strategies. All equipment used in affected areas should be properly cleaned before leaving a ground pearl-infested area.

Selected References (Back to Top)