Tawny Mole Cricket
- Scientific Name: Scapteriscus vicinus Scudder, was originally called the Changa or Puerto Rican mole cricket but this is another species not currently found in the Continental United States. [Phylum Arthropoda: Class Insecta: Order Orthoptera: Family Gryllotalpidae]
- Common Names: Tawny Mole Cricket
- Climatic Zone: Tropical and Subtropical
- Geographic Distribution: This species is a native of coastal South America from northern Argentina through Brazil and in Columbia, Panama and Costa Rica. The tawny mole cricket was introduced into Georgia around 1899, but is now found throughout Florida and south of a line running from the southern half of North Carolina, across Georgia and to the coastal areas of southern Alabama.
- Damaging Stage: Nymphs and adults feed on plant roots and plant parts.
- Hosts: Most turfgrasses are attacked as well as several vegetable plants.
- Damage Symptoms: Turf can be generally thinned, but extensive tunneling by the nymphs and adult mole crickets can kill the turf by dislodging the root-to-soil contact necessary for healthy turf.
- Description of Stages: Mole crickets have incomplete life cycles with egg, nymphal and adult stages.
Eggs: Round, barrel-shaped translucent white eggs are placed in clusters in chambers three to 10 inches below the soil surface.
Nymphs: Nymphs look like miniature adults. Early instars do not have visible wing pads while later instars develop visible wing pads. The nymphs molt 6-8 times, the exact number is not known. Nymphs can be identified by the shape of the tibial dactyls.
Adults: Fully grown adults are about 1 1/4 inch (30 - 34 mm) long and 3/8 inch (8 - 10 mm) wide. They are a light tawny brown and have the obviously modified front legs and enlarged thorax typical of mole crickets. The forewings are shorter than the abdomen and males have the darker rasp at the forewing base. The V-shaped space between the tibial dactyls is species characteristic.
- Life Cycle and Habits:
Male mole crickets locate preferred habitats in the spring and call with their toad-like trill (3.3 kHz with 60 cycles/sec at 77°F) from the entrance of their burrows. This occurs for about an hour shortly after sunset. Mole crickets can fly more than six miles in a night and may fly more than once. Females are attracted to the calls of males in the spring when temperature and moisture allow easy movement and flight. Egg laying may begin in March but 75% of the eggs are laid between May 1 and June 15. During the mating and oviposition periods, the adults are extremely active, emerging from the soil at dusk to crawl about, tunnel and fly. Flight in mass commonly occurs after rainfall and adults are attracted to lights.
Mated females dig down a few inches into suitable soil and construct an egg chamber in which they lay an average of 35 eggs. Females may construct three to five chambers and lay 100-150 eggs total. The eggs hatch in about 20 days and the young nymphs dig upward to seek out food. These nymphs prefer to feed on plant roots but will eat small insects and can be cannibalistic. Larger nymphs will often attack smaller nymphs and eggs. Only 10-15% of the adults and nymphs have been found with insect parts in the gut. The nymphs continue to feed, molt and grow through the summer months.
By the end of October, 85% of the nymphs have reached adulthood. The remaining nymphs continue development very slowly and most mature by the following spring. Adult and nymphal behavior are highly regulated by temperature and soil moisture. Most feeding occurs at night, especially after rain showers or irrigation during warm weather. These insects may tunnel 20 feet per night in moist soil. During the day, individuals tend to return to a permanent burrow which is deeper in the ground. The crickets may remain in these permanent burrows for considerable periods during cool winter temperatures or dry spells.
- 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.