INTRODUCTION AND SPREAD OF THE FUNGAL PATHOGEN ENTOMOPHAGA-MAIMAIGA (ZYGOMYCETES, ENTOMOPHTHORALES) ALONG THE LEADING-EDGE OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) SPREAD
Ae. Hajek et al., INTRODUCTION AND SPREAD OF THE FUNGAL PATHOGEN ENTOMOPHAGA-MAIMAIGA (ZYGOMYCETES, ENTOMOPHTHORALES) ALONG THE LEADING-EDGE OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) SPREAD, Environmental entomology, 25(5), 1996, pp. 1235-1247
The gypsy moth fungal pathogen Entomophaga maimaiga Humber, Shimazu, &
Soper was first reported in North America in 1989 but did not occur i
n areas more recently colonized by gypsy moth, Lymantria dispar (L.).
To establish this pathogen along the leading edge of spreading gypsy m
oth populations, 6 x 10(5) E. maimaiga resting spores were released ar
ound the bases of oaks in 0.01-ha plots in Maryland, Pennsylvania, Vir
ginia, and West Virginia. E. maimaiga was released in 34 plots in 1991
and 7 plots in 1992, with 15 control sites in 1991 and 3 control site
s in 1992. During 1991, E. maimaiga infections were found in 28 plots,
with infection levels >40% in 6 plots (17.6%). Infection levels were
greater in plots where E. maimaiga resting spores were watered weekly.
Low levels of infection were found in 4 of the 15 control plots. In 1
992, E. maimaiga infections were detected in 40 of the 41 release plot
s as well as in the majority of control plots. Infection levels in 199
2 E. maimaiga release plots averaged 72.4 +/- 10.7% (mean +/- SE) and
were associated with declining egg mass densities. In 1991 fungal rele
ase plots resampled in 1992, disease prevalence in 1992 was greater in
plots with higher levels of infection during 1991. During 1992, epizo
otics (>70% infection) occurred in 24 of the 28 1991 release plots. Th
roughout this study, levels of E. maimaiga infection were never associ
ated with gypsy moth egg mass density at the beginning of the season.
May rainfall was positively associated with infection for each year, a
nd optimal average temperatures for infection were approximate to 13-1
9 degrees C during May and June. During 1991, E. maimaiga spread up to
350 m from centers of release plots, and in 1992, E. maimaiga was abu
ndant 1,000 m from release plots. Because of the abundance of E. maima
iga in 1992 control plots and at 1,000 m from 1992 release plots, 228
sites were surveyed to reevaluate the distribution of this fungus. E.
maimaiga was found at all sites sampled in Virginia and Maryland and i
n the majority of West Virginia sites, demonstrating spectacular sprea
d by this pathogen to the south and west; E. maimaiga now occurred at
the southern limit of the gypsy moth distribution in the northeastern
United States. Such rapid spread was completely unexpected and has nev
er before been documented for an entomopathogenic fungus. We hypothesi
ze that both our E. maimaiga release sites and preexisting E. maimaiga
populations to the north and east may have been sources for the funga
l inoculum that spread.