"Maimaiga" is the Japanese word for "Gypsy Moth".
In 1908, shortly after classical efforts began to control Gypsy Moth populations, North American researchers studied cadavers of Japanese gypsy moths which had been killed by an entomophthoralean fungus. The fungus was released in the Boston area between 1910–11. By 1912, they summarized their work, stating that extensive releases had never established this fungal pathogen, which they referred to as "gypsy fungus".
In the early 1980s, another attempt was made to introduce Entomophaga maimaiga into the wild. They obtained the sample from the western coast of Honshu. The fungus was determined to belong to the genus Entomophaga in the fungal order Entomophthorales and was given the name maimaiga based on geographical distribution.
In 1985 and 1986 were made small-scale releases of laboratory Gypsy Moth larvae injected with fungal cells. The locations were New York State and Shenandoah National Park respectively. At the time these releases were not considered to be successful.
In 1989, cadavers of gypsy moths found hanging on tree trunks revealed large resting spores characteristic of entomophthoralean fungi. The fungus found appeared to be the same species as released in 1910, 1911, 1985 and 1986.
The fungus spread across Gypsy Moth populations over the next several years.
Method of dispersion
The fungus spreads through aerial dispersion of actively ejected asexual spores from cadavers of Gypsy Moth larvae it has killed. It can also be spread unwittingly by humans.
The fungus persists in the top layer of soil as resting spores. These have been shown to persist for at least 11 or 12 years, probably longer.
Effect on Gypsy Moths
The fungus causes high levels of infection among gypsy moths in both low and high density populations, leading to population crashes.
Effect on non-target Lepidoptera
E.Entomophaga maimaiga can only potentially effect Lepidopteran larvae that are present in the spring, when Gypsy Moth larvae are present. 78 species which fit this criteria were tested. Only about one third were able to be infected under optimal conditions. Infection was only consistently high among three species of tussock moths and one colony of a hawk moth. However, field studies showed that rates achieved in the laboratory are far higher than found in the field. Overall the pathogen is considered highly host-specific.
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