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Mole crickets can be serious pests of vegetable crops through feeding and tunnelling, which can cause considerable losses in vegetable production. They cause the most severe damage to seedbeds and newly transplanted seedlings. Tunnelling through the soil around the plant's root system will desiccate the surrounding soil, and the plants will be water stressed and eventually die. The mole crickets that feed do so on the roots and during warm, wet nights they may feed on the stems and occasionally the leaves at the soil surface. Those crops producing marketable products below ground, such as potato (Solanum tuberosum) and radish (Raphanus spp.), are also at risk because mole crickets will feed on these plant parts as well. Entire plants have been pulled beneath the soil surface. The feeding damage is commonly referred to as cutworm-like in appearance and this damage will increase the probability of introducing plant pathogens onto the seedlings (Frank et al., 2004).
Evidence of mole crickets in turf is the presence of galleries at the soil surface. Extensive digging by mole crickets to form galleries loosens the soil (Frank et al., 2004).
Cultural Control and Sanitary Methods
Control measures include deep digging in autumn to destroy the overwintering insects; loosening the soil in the spaces between rows to a depth of 10 to 15 cm, two to three times in late May to June; destroying the eggs and larvae; and the application of kerosene (Arkhipov, 1984).
Sometimes the nests in the soil can be found and destroyed, and the effect is considerable because each may contain 300 to 400 insects (Reznik, 1977).
The nymphs and young adults overwinter, and in the autumn they are attracted to baits of horse manure in containers or holes in the soil. In the winter, the manure is removed and the collected insects can be destroyed or they die under the frost (Volkov, 1978).
Mole crickets are commonly found around the perimeter of vegetable fields and will migrate into the field as the soil fumigants dissipate and as the growing season progresses. Therefore, if a field of young seedlings is adjacent to a field or pasture that is infested with mole crickets it will be largely at risk. The mole crickets directly feed on the crop or on the weeds between the crop. Smaller vegetable seedlings appear to be very susceptible to feeding damage and soil disruption caused by the tunnelling activity of the mole crickets. Larger plants appear to be more tolerant. To decrease the likelihood of substantial damage, large rather than small seedlings should be planted, and these may be more tolerant to mole cricket damage. Reducing the occurrence of weeds that may colonize in fields and act as an alternate food source, may also limit population growth (Frank et al., 2004).
G. gryllotalpa is polyphagous and can damage all agricultural crops, thus it is too difficult to discover resistant plants and varieties, although some plants are more tolerant to the damage.
The relative susceptibility of 17 potato cultivars to infestation by Phthorimaea operculella (potato moth), Euzophera osseatella (Indian meal moth) and G. gryllotalpa was studied in tubers at harvest in Kalubia and Minia governorates, Egypt. The cultivar 'Spunta' was the only one resistant to all three species; others least susceptible to the pests were 'Diamond' for P. operculella, 'King Edward' for G. gryllotalpa and 'Grata', 'Draga' and 'Claudia' for E. osseatella (Doss, 1984).
In general, among grass species, bahia grass (Paspalum notatum) is heavily damaged, closely followed by Bermuda grass (Cynodon dactylon), whereas St Augustine grass (Stenotaphrum secundatum), zoysia grass (Zoysia spp.), and centipede grass (Eremochloa ophiuroides) suffer less damage. Selected cultivars within these grass species may exhibit more or less damage than is typical of the species. Some grass species (and cultivars) seem to be preferred, which means that mole crickets, when given a choice, will more readily feed on one grass species than on another. Without a choice, they will feed on whatever grass is available. Some grasses suffer less damage when exposed to equal numbers of mole crickets, which means that feeding and tunnelling by mole crickets has less effect on these due to their growth characteristics (Frank et al., 2004).
In the laboratory, the antifeedant and moult disruption effects of 0.3% azadirachtin applied once per week for 4 weeks were evaluated for G. gryllotalpa. The highest concentration of formulated product (5 ml extract/50 ml distilled water/25 g crushed corn seeds) resulted in 98% mortality. The crickets surviving treatment grew slower and tunnelled less compared to their untreated counterparts (Sanaa, 2002).
According to Pfiffner (1997), studying Steinernema carpocapsae, mole cricket population density in tomatoes grown under plastic tunnels was reduced to approximately 84% at 60 cm deep.
In the USA, G. gryllotalpa is a minor pest and three biological control agents are currently used against other species of mole cricket (mainly Scapteriscus spp.) in Florida. These are classical biological control agents: the sphecid, Larra bicolor, the Brazilian red-eye fly, Ormia depleta [Euphasiopteryx depleta], and the nematode, Steinernema scapterisci, which functions as a biopesticide with residual activity. Trials of O. depleta and S. scapterisci have been and are being conducted in other southeastern states. Trials of other Steinernema spp. have been conducted, but are considered to be inferior because no residual activity has so far been noted. L. bicolor is used in Puerto Rico, and Larra polita is used in Hawaii; both as classical biological control agents. S. scapterisci or O. depleta, or both, may prove useful in Puerto Rico. Other potential biological control agents such as bombardier beetles, and fungal, protozoan, viral, and bacterial pathogens have received various levels of attention and, if there is funding for research and development, may reach the point of usefulness in the field (Frank et al., 2004).
The larvae of Stenaptinus spp. have been known for some decades as specialized predators of G. gryllotalpa eggs. Studies in Japan and China showed that the adult beetles prey on various insects, but the larvae enter mole cricket egg chambers to feed on the eggs. Pheropsophus aequinoctialis is widely distributed in various countries, and inhabits river banks and other wet places. Its diet was unknown until living specimens were imported from Uruguay, Brazil and Bolivia, into a quarantine facility in Gainesville, USA, where the adults were found to be generalist feeders. However, the larvae only developed when provided with a diet of mole cricket eggs. Improvements in methods for rearing the beetles are necessary before tests can be completed (Frank et al., 2004).
Fungal, protozoan, viral, and bacterial pathogens have been found associated with mole crickets in North and South America. Beauveria bassiana and Metarhizium anisopliae have received most attention by researchers. Both have been found as pathogens of many insects in nature, but normally they kill few because of their low concentration in nature. These pathogens are industrially produced and marketed as biopesticides. When applied at high concentrations, they kill a high proportion of insects in the area of application. The number of target pests killed can be improved by:
- Method of application. Application methods for some insect pests have been devised, but methods for subterranean insect pests, such as mole crickets, still need development. Broadcast application on the soil surface is likely to be prohibitively expensive and may lead to the rapid demise of the pathogen when it encounters bright sunlight. Alternative methods include injection into the soil, or incorporation of the pathogen into bait.
- Strain differences. Each fungal pathogen has been collected from various insect species and various places. The capabilities of these strains differ. Under laboratory conditions using Scapteriscus spp., some strains killed all mole crickets contacted, whereas others killed a much smaller proportion. The speed of kill by these various strains also differs, although in general, all are slower than chemical pesticides now in use (Frank et al., 2004).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
G. gryllotalpa is a very important polyphagous pest in Europe and western Asia. All vegetables grown in hotbeds, forcing-houses, greenhouses and open fields are at risk. It also damages field crops, floriculture, turf grass and many other plants (Grigorov, 1976; Anon., 2004b). Sometimes up to 50% of seedlings in hotbeds and young plants in the field can be destroyed (Gulii and Pamuzak, 1992).
In the Stavropol region of the USSR, G. gryllotalpa infests tulip (Tulipa spp.) and Gladiolus spp. fields. Up to 30% of production was regularly lost to bulb damage and subsequent rotting (Denisenko, 1986).
During 3 to 4 years in cotton (Gossypium spp.) fields in Azerbaidzhan, G. gryllotalpa caused heavy damage, where as many as 30 burrows per square metre were observed (although the usual number was lower). The burrows were most numerous in fields bordering vegetables or other crops (Ismailov and Rustamova, 1981).
In the USA, G. gryllotalpa is at most a minor pest. Damage to golf course greens has been recorded; galleries excavated by mole crickets may cause a rolling golf ball to deflect (Frank et al., 2004).
In Italy, there are approximately ten insect species that repeatedly infest turf grass in golf courses, football fields, and green areas in general. The most important is G. gryllotalpa. The damage caused by these insects is often made worse by the presence of Corvus cornix [Corvus corone cornix]. This bird was observed damaging the turf of golf courses by tunnelling in search of the phytophagous larvae (Alma, 2001; Lozzia et al., 2001).