| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 186 March 10, 1998 | aceska@victoria.tc.ca |
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[This article was compiled from published and unpublished papers that Dr. Ann E. Hajek (Cornell University) kindly sent to me for use in BEN. - Adolf Ceska]
The gypsy moth, Lymantria dispar (L.), is a serious defoliator of broadleaved forests in eastern North America. The gypsy moth is indigenous to temperate Eurasia and was introduced into Boston area of Massachusetts in 1869. In eastern North America, populations of this insect pest undergo periodic outbreaks increasing to high densities that result in widespread defoliation to an average 2.0 million forested hectares per year. In British Columbia we experienced periodic gypsy moth infestations on Saltspring Island, around Victoria and Vancouver, and in Kelowna.
In eastern North America, the gypsy moth is subject to a variety of naturally occurring infectious diseases caused by several kinds of bacteria, fungi, and a nucleopolyhedrosis virus (NPV), which was inadvertently introduced with gypsy moth or its parasites. There are six species of entomopathogenic (causing disease in insects) fungi known to infect the gypsy moth.
The fungal class Zygomycetes, which includes the bread molds, is a primitive group of fungi with no species native to North America known to infect gypsy moth. Species in one zygomycete order, the Entomophthorales, are predominantly insect pathogens. Many entomophthoralean pathogens are known to cause dramatic epizootics (disease outbreaks) in insect populations.
In 1984, researchers isolated this entomophthoralean fungus from the Asian gypsy moth in Japan and brought isolates to the United States. Stages of this fungus now could be maintained year round in the laboratory using several different culture media, rather than having to be perpetuated on gypsy moth larvae. The name Entomophaga maimaiga was given to the Japanese isolates of this fungus. The specific name for this new species, "maimaiga," was based on the Japanese common name for the gypsy moth. Host range studies have shown that E. maimaiga does not infect insect other than Lepidoptera.
Laboratory bioassays were conducted over two years to maximize the diversity of species that were tested. These laboratory tests optimized chances for E. maimaiga to cause infections, yielding information about an idealized host range for this pathogen. Out of a total of 78 species tested from 10 different superfamilies, cadavers of 35.6 percent of the species produced E. maimaiga spores. Infections occurred in 7 of the 10 super-families tested although infection levels were 50 percent within both the Bombycoidea (Malacosoma disstria) and Sphingoidea (Manduca sexta). In the Noctuoidea, >50 percent infection was only found within the Lymantriidae.
However, laboratory bioassays optimize chances for infection and frequently do not agree with field observations. Therefore, during 1995, Linda Butler, Dick Reardon, and Ann Hajek continued their studies by investigating the host range of E. maimaiga under field conditions. With the help of Steve Talley (Rockbridge County, Virginia), they sampled larvae of gypsy moth and non-target Lepidoptera in seven plots in Virginia where E. maimaiga was present and active. The moderate density gypsy moth populations in these plots experienced 40.8 - 97.5 percent infection by E. maimaiga during the field season.
A total of 1421 larvae from 53 species belonging to 7 lepidopteran families and 4 subfamilies were collected and reared. Only two individuals, one of 296 Malacosoma disstria (Bombycoidea: Lasiocampidae) and one of 96 Catocala ilia (Noctuodea: Noctuidae) became infected by E. maimaiga. (Unfortunately C. ilia had not been tested during laboratory bioassays.) In summary, laboratory studies demonstrated infection by E. maimaiga over a greater diversity of species compared with field studies, and for those species infected in both the laboratory and field, the percent of infection was much higher in the lab studies than findings from the field.
There is general consensus among scientists and pest managers that E. maimaiga is probably responsible for the decline in gypsy moth outbreaks and damage over the last few years. However, we do not know if this level of fungus activity will continue because E. maimaiga has been highly variable and unpredictable. This poses a dilemma for pest managers because treatment projects must be planned and carried forward well before it is known how active the fungus might be during the next gypsy moth season. Consequently, the use of environmentally safe and effective insecticides will continue to be important tools to reduce damage caused by gypsy moth outbreaks.
Entomophaga maimaiga is effective in both high- and low-density gypsy moth populations, unlike the nucleopolyhedrosis virus, which is only effective at high-density moth populations. The fungus could play a significant role in the natural control of gypsy moth, especially in years with a wet spring. Only time will tell whether increasing the area where E. maimaiga is established will lead to constant lower populations of the gypsy moth in North America.
Acknowledgements. I would like to thank Dr. Ann Hajek for sending me her published and unpublished papers on Entomophaga maimaiga and for her permission to use them in BEN. Some information used in this article was previously posted in the Gypsy Moth News that can be reached on the following web site:
Further reading:
There are several on line guides to species identification. Here are several that should be of interest, especially for those in North America:
New HTML and Intkey versions of "Grass Genera of the World" and "Families of Flowering Plants" were posted recently, at
Both have been edited and improved in various ways, and for the first time, they incorporate extensive character illustrations for use with Intkey. The "Families" character illustrations have been adapted from the range of taxon images presented with earlier versions, but the Poaceae package now includes (for example) numerous character and taxon photomicrographs illustrating leaf blade anatomy and spikelet details, many of which which have never been published before.
The Intkey versions are freely available for downloading, but can be run directly from the Web using the Windows95/NT version of the program.
A modest contribution but there is a key to the Parmelias of Great Britain and Ireland on the British Lichen Society's web site at
Karl Urban of Umatilla National Forest has developed a series of line drawings designed for children to color. They are available, copyright free, from
The print version will look much better than the drawing on your monitor.
Submissions, subscriptions, etc.: aceska@victoria.tc.ca. BEN is archived at http://www.ou.edu/cas/botany-micro/ben/