Southern Mole Cricket
- Scientific Name: Scapteriscus borelli Giglio-Tos, was know as S. acletus Rehn and Hebard until a recent revision of the genus was completed. [Phylum Arthropoda: Class Insecta: Order Orthoptera: Family Gryllotalpidae]
- Common Names: Southern mole cricket
- Climatic Zone: tropical and subtropical
- Geographic Distribution: Introduced into Georgia at the turn of the century; the southern mole cricket is found south of a line running from mid North Carolina through mid Louisiana and into eastern Texas; probably a native of South America where similar mole crickets have been found in northern Argentina, Uruguay, Paraguay, Bolivia and Brazil.
- Damaging Stage: nymphs and adults
- Hosts: Apparently this species prefers to prey on other insects and even each other. However, considerable feeding on plants occurs; 41% were found to have plant material in the gut. Often found in bahiagrass, bermudagrass and occasionally St. Augustinegrass. Rarely damages centipedegrass or zoysiagrass.
- Damage Symptoms: Produces typical mole cricket damage though most of the damage is due to tunneling. Nymphs and adults tunnel and throw up mounds of soil. Uprooted turf soon wilts and dies from desiccation.
- Description of Stages:
Mole crickets generally have one generation per year. Depending on the species, they may overwinter as nearly mature nymphs or adults.
Eggs: Rounded, barrel-shaped translucent amber eggs are placed in clusters of up to 35 in chambers under ground.
Nymphs: The nymphs look like small adults but do not have functional wings. The wings develop as pads which enlarge with each molt. This species can be identified by the U shaped space between the tibial dactyls. Some populations have mottled patterns on the pronotum while other populations have a dark background with four small pale spots.
Adults: Adults are generally smaller and thinner than tawny mole crickets. They are about 1 1/8 inch (32 mm) long by 1/4 inch (9 mm) wide. They are grey to dark brown and have either four distinct pale spots on the prothorax or mottling that has four pale areas. The forewings are shorter than the abdomen and the hindwings just extend beyond the tip of the abdomen. The U shaped area between the tibial dactyls is diagnostic of the species. Males also have a darker rasp and file mark on the forewing base.
- Life Cycle and Habits:
This species has a cycle much like the tawny mole cricket. Egg laying occurs from mid March into June but some adults continue laying eggs into September. The nymphs mature rapidly through the summer but only about 25% reach adulthood by winter. Some males call during the fall and mating at this time may occur. The nymphs complete development slowly during the winter with more adults appearing from February through April with a peak in May. Nymphs and adults of this species have been found during much of the year. Most activity is found after rain or irrigation and a spring flight period occurs during mating and oviposition. Males produce a bell like trill (2.8 kHz with 135 cycles/sec) for an hour or longer just after sunset. The southern mole cricket is more of an omnivore than the tawny mole cricket. Only 5% have been found with plant material alone in the gut while 59% had only animal material in the gut and the rest had a combination. Thus, it is suspected that turfgrass damage caused by the southern mole cricket is due to its tunneling and soil mounding rather than actual root feeding.
- Control Approaches:
The most difficult time to control mole crickets is late fall and early spring when the adults are flying to relocate and mate. These adults may move deep in the soil profile - below the zone where most controls can reach them - during cool or dry soil conditions and are less prone to feed which minimizes their exposure to control materials. There is little that the turf manager can do to prevent this movement and damage.
Cultural Control - Habitat Modification - Mole crickets generally prefer moist soil conditions and populations are generally concentrated near wetlands or waterways. Allowing turf to dry, especially in the spring egg laying period can help discourage females from laying eggs in such areas.
Biological Controls - Encouragement of Natural Agents - Mole crickets are cannibalistic and many young nymphs perish in this manner. Predacious insects, birds and mammals prey on mole crickets but may dig up turf in the effort. The parasitic wasp, Larra bicolor Fab. (Hymenoptera: Sphecidae), has been introduced and new strains have become established in Florida, Georgia and Alabama. A tachinid fly, called the red-eyed fly, has also been established in northern Florida but it appears to have a rather restricted range. Fire ants are major predators of mole crickets, but these are not deemed acceptable in well managed turf.
Biological Controls - Insect Parasitic Nematodes - The insect parasitic nematodes, Steinernema scapterisci and S. riobravos have been touted as providing permanent, long term preventive control of mole crickets. However, it appears that while often becoming permanently established in an area, these nematodes do not produce the desired level of control expected by golf course managers, especially in high maintenance, irrigated turf. These nematodes may be useful in roughs, wetland sites and other lower maintenance turf areas.
Chemical Control - Insecticides -
Targeted Treatments. A targeted strategy to control mole crickets with surface insecticide uses a preventive approach “mind set” though the process is technically a curative approach. In this strategy, insecticides that have short residual efficacy against mole cricket nymphs are applied to areas that were mapped and determined to have considerable adult activity in April and early May. The insecticide is applied at egg hatch and every three weeks thereafter until egg hatching stops (usually after two to three applications).
Curative Treatments. The Curative Approach involves broadcast applications of sprays or granules and baiting. Broadcast Application of contact/stomach pesticides are made when the mole cricket eggs are hatching and again when nymphs are about half grown (no more than one inch long). To achieve maximum effect, the turf to be treated should be irrigated for several days before application to ensure that the soil is moist and mole cricket nymphs are near the surface. When rainfall has been sufficient to move nymphs near the surface, pre-irrigation is not needed. To determine whether nymphs are near the surface, apply a light sprinkling (water can) of soapy water. If present, the small nymphs will “pop” out immediately. If it takes several minutes for them to surface, irrigate before making the pesticide application. After application, irrigate lightly to move the pesticide to the nymphs. Inspect treated areas at dawn the following morning to determine treatment effectiveness. Affected nymphs will surface after being exposed to the pesticide. If few or no nymphs are found on the surface, recheck treated areas with a soap flush. If numerous nymphs surface after the recheck, retreat with a different insecticide. Bait-formulated insecticides are usually more effective once the nymphs are longer than one inch. Areas remaining moderate to highly infested after application to control earlier small-nymphs are candidates for treatment with bait. Again, irrigate application to move the nymphs to the surface, but DO NOT IRRIGATE after applying the bait. Baits are most attractive when they are fresh and not subjected to rainfall or irrigation. Also avoid applying the bait if rainfall is expected the night after application. Stopping turf damage from fall or spring migrating adults is difficult to achieve. The turf manager can do little to PREVENT migration or damage. Baits are also suggested when control of adults is deemed necessary.
Preventive Treatments. Insecticides with moderately long residual activity against mole cricket nymphs can be applied to high risk areas at the beginning of mole cricket egg hatch (usually late May to early June). Mapping of mole cricket activity or knowledge of chronic mole cricket damage areas are prime candidate areas for preventive treatments. Both surface and subsurface applications of certain long residual insecticides have been effective for preventive control.
At sporadic times, usually associated with warm and rainy weather, adults move to the surface, tunnel extensively, fly in mass and mate. Research has shown that moist but not saturated sites with dense turf or weed growth is highly attractive to spring-active adults. These sites are where eggs will be concentrated. Mole cricket Activity Mapping has been adopted by many golf course superintendents to identify areas at highest risk of having damaging mole cricket nymph populations.
Mole Cricket Activity Mapping. In the spring, areas where mole crickets are most actively tunneling, emerging and digging back into the soil are where most of the eggs will be laid. A visual inspection of each fairway, wetland margin, and even managed roughs should allow for easy detection of mole cricket “hot spots.” It will take time for the turf manager to differentiate between light, moderate and extensive mole cricket activity.
Detecting Mole Cricket Nymphs and Evaluating Control Efficacy. If in doubt as to whether mole cricket nymphs are active in an area, especially when they are small, use of a soap solution drench can rapidly cause the nymphs and even adults to surface. Use one tablespoonful of a household dishwashing detergent per gallon of water (Joy™ and Ivory Clear™ have shown no evidence of phytotoxicity) and apply 2 to 4 gallons of this solution through a sprinkling can over a one square yard of turf suspected of being infested. During dryer conditions, two soakings may be needed to bring mole crickets to the surface. This drench applied after a control application can help evaluate the efficacy of the application.