- Scientific Name: Antonina graminis (Maskell). [Phylum Arthropoda: Class Insecta: Order Homoptera: Family Pseudococcidae]
- Common Names: rhodesgrass mealybug, rhodesgrass scale
- Climatic Zone: Tropical and subtropical
- Geographic Distribution: In the United States, rhodesgrass mealybugs have been found from South Carolina to southern California and south. It is found worldwide in tropical and subtropical regions of Africa, Australia, Central America, India, Japan, Pacific Islands and South China.
- Damaging Stage: nymphs and adults
- Hosts: This mealybug is known to attack over 70 species of grasses including range and weed grasses as well as warm season turfgrasses, especialy rhodesgrass, bermudagrass and St. Augustinegrass.
- Damage Symptoms: This mealybug does not commonly kill turf unless severe and prolonged drought stress occurs. This pest produces considerable honeydew that attracts ants or bees. The honeydew also promotes the growth of sooty molds that cause the turf to have a gray or sooty-black color.
- Description of Stages:
Though this pest is a type of mealybug, it resembles true scales by becoming immobile once settled.
Eggs: The eggs are elongate oval and cream colored, and they are retained inside the remains of the female and her waxy cover.
Crawlers: These are the first instar nymphs which are the only mobile form. The crawlers are flat, oval, cream colored insects with a median stripe tinged with purple. They have short legs, six segmented antennae and two waxy tail filaments.
Sessile Nymphs: The crawlers settle on grass crowns or at nodes, insert their mouthparts and begin secreting a waxy coat. After the first molt, the sessile nymph takes on a saclike form without legs. Only the thread like mouthparts and a tube like waxy anal filament emerge from the body. A second molt occurs while the waxy cover grows larger and the anal excretory tube elongates.
Adults: Only females are known and these reproduce asexually. The adult body is also saclike, broadly oval, dark purplish brown and 1/8 to 3/16 inch (1.5 3 mm) long. The fluffy waxy covering turns yellow with age and opens at the anterior and posterior ends to expose parts of the body. A very long, 3/16 to 1/2 inch (3 13 mm) waxy, tubular filament arises from the anus through which honeydew is excreted.
- Life Cycle and Habits:
This pest continues its life cycle year round but reproduction is considerably reduced during the winter while activity increases in the spring as the grass begins rapid growth. Peak populations are reached by July and populations again are reduced through July and August as summer stress is induced by heat and drought. In September and October the populations again surge until peaking in early November.
During the spring, females lay an average of 150 eggs over 50 days. As the crawlers hatch they remain under the waxy cover of the female for several hours before emerging. These crawlers tend to first walk to the tops of plants but eventually settle down by wedging themselves beneath a leaf sheath, usually at a node. Here the mouthparts are inserted and the excretory tube and waxy cover are started. In about 10 days, the first molt takes place, the walking legs disappear, and the antennae become much smaller. The excretory tube continues to elongate and the waxy cover becomes thicker and larger. Two more molts take place under the waxy cover and maturity is reached in 25 to 30 days.
During the summer, a generation averages two months but in cool weather, a cycle may take three-and-a-half to four months to complete. This mealybug apparently is spread by transportation of infested sod or sprigs. The crawlers may climb onto the legs of animals and "hitch a ride." High temperatures, especially near 100 °F, reduce mealybug development and may actually kill individuals. Exposure of the mealybug to 28 °F for 24 hours is fatal. Thus, winter cold limits northern movement and survival of this pest.
- Control Approaches:
This pest rarely kills turf unless the turf is poorly managed. Do not cut the turf too short and apply irrigation during prolonged periods of drought.
Cultural Control - Water and Fertilize - Frequent irrigation, fertilization of bermudagrass and St. Augustine as well as mowing no shorter than two inches helps prevent damage by this pest even when high populations are present.
Biological Control - Conserve Parasites - Two parasitic wasps have been successful in controlling rhodesgrass mealybug populations. A Hawaiian parasite, Anagyrus antoninae Timberlake, and an Indian parasite, Dusmetia sangwani Rao, have been established in the southern United States. Apparently, Dusmetia seems better adapted and can survive lower temperatures than Anagyrus. Both of these parasites, once established, should be conserved by not spraying some (refuge) areas known to have rhodesgrass mealybugs and the parasites. This area will serve as an refuge to supply parasites to other areas.
Chemical Control - Use of Contact Insecticides - Many contact pesticides do not effectively reach the protected stages of this mealybug, especially the eggs and protected crawlers. Repeated applications may be necessary if this strategy is used.
Chemical Control - Use Systemic Insecticides - Systemic insecticides are more efficient for controlling young feeding mealybugs. Some eggs may escape harm and may hatch after the insecticide’s reside disappears. Thus, a second application may be necessary to control newly emerged or settled crawlers.