Mole cricket
Invasive mole crickets and their biological control

Invasive species are those that cause harm in their newly occupied area, where biological control may be attempted. The first-detected invasive mole cricket species was Neoscapteriscus didactylus, a South American species reported as a pest in St. Vincent, West Indies, as early as 1837; by 1900, it was a major agricultural pest in Puerto Rico. It had probably slowly expanded its range northwards, island by island, from South America. The only biological control program against N. didactylus was in Puerto Rico, and it succeeded in establishing the parasitoid wasp Larra bicolor from Amazonian Brazil. In 2001, N. didactylus in Puerto Rico seemed to be a pest only in irrigated crops and turf. Small-scale experimental applications of the nematode Steinernema scapterisci were made in irrigated turf, but survival of the nematode was poor. Very much later, this same species was reported as a pest in Queensland, Australia, presumably arriving by ship or plane. The next-detected invasive species was in the late 19th century in Hawaii, probably by ship. It was named as Gryllotalpa africana, but much later as perhaps G. orientalis. It was not identified as Gryllotalpa krishnani until 2020. It attacked sugarcane and was targeted with Larra polita from the Philippines in 1925, apparently successfully.

The next detection was in Georgia, USA, and at that time was assumed to be N. didactylus from the West Indies. It was, in fact, three South American Neoscapteriscus species, N. abbreviatus, N. vicinus, and N. borellii, probably having arrived in ship ballast. They caused major problems for decades as they spread in the Southeastern USA. Scapteriscus mole cricket populations had built up since the early decades of the 20th century and damaged pastures, lawns, playing fields, and vegetable crops. From the late 1940s, chlordane had been the insecticide of choice to control them, but when chlordane was banned by the U.S. EPA in the 1970s, ranchers were left with no economic and effective control method. Especially to aid Florida ranchers, a project that became known as the UF/IFAS Mole Cricket Research Program was initiated in 1978. In 1985, a multiple-authored report was published on accomplishments. In 1988, an account was published on prospects for biological control, and in 1996 an account of promising results with biological control. The program ended in 2004 after 25 years of running monitoring stations, and in 2006 a summary publication announced success: a 95% reduction in mole cricket numbers in northern Florida, with biological control agents spreading potentially to all parts of Florida. Efforts to use Larra bicolor as a biological control agent in Florida began by importing a stock from Puerto Rico. It became established in a small area of southeastern Florida, but had little effect on Neoscapteriscus populations. A stock from Bolivia became established in northern Florida and spread widely (with some help) to most of the rest of the state and neighboring states. Its survival depends upon the availability of suitable nectar sources.

Once gravid female Ormia depleta flies were found to be attracted to the song of Neoscapteriscus males in South America, a path to trap these flies with synthetic mole cricket songs was opened. Experimentation then led to a rearing method. Laborious rearing of over 10,000 flies on mole cricket hosts allowed releases of living fly pupae at many sites in Florida from the far northwest to the far south, mainly on golf courses, and mainly in 1989-1991. Populations were established, began to spread, and were monitored by use of synthetic mole cricket song. Eventually, the flies were found to have a continuous population from about 29°N then south to Miami, but the flies failed to survive the winter north of about 29°N. Shipment and release of the flies to states north of Florida was thus a wasted effort. As the flies had been imported from 23°S in Brazil and could not overwinter north of 29°N, whether flies from 30°S in Brazil might survive better in northern Florida was investigated in 1999, but they did not.

The third biological control agent to target Neoscapteriscus in Florida was the South American nematode Steinernema scapterisci. Small-scale releases proved it could persist for years in mole cricket-infested sandy Florida soils. Its use as a biopesticide against Neoscapteriscus was patented, making it attractive to industry. Industrial-scale production on artificial diet allowed large-scale trial applications in pastures and on golf courses, which succeeded in establishing populations in several counties, and these populations spread, but sales were disappointing, and the product was withdrawn from the market in 2014. Although experimental application was made in states north of Florida, only in southern Georgia was establishment of the nematode verified, suggesting little interest in the other states.
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