Home • Entomophaga maimaiga ARSEF 7190 v1.0
Entomophaga maimaiga Humber, Shimazu & R.S. Soper 1. Late instar Lymantria dispar larva killed by E. maimaiga and containing resting spores, 2. Resting spores (average 32 µm diameter), 3. Early instar Lymantria dispar larva killed by E. maimaiga gripping twig with prolegs. Dark setae appear white because they are covered with conidia that have been ejected, 4. Appressoria (arrows) produced from germinated conidia at the base of a seta on L. dispar larval cuticle, 5. Pyriform conidia with large oil droplets, averaging 21 x 26 µm (stained with aceto-orcein). Images by Ann Elizabeth Hajek.
Entomophaga maimaiga Humber, Shimazu & R.S. Soper 1. Late instar Lymantria dispar larva killed by E. maimaiga and containing resting spores, 2. Resting spores (average 32 µm diameter), 3. Early instar Lymantria dispar larva killed by E. maimaiga gripping twig with prolegs. Dark setae appear white because they are covered with conidia that have been ejected, 4. Appressoria (arrows) produced from germinated conidia at the base of a seta on L. dispar larval cuticle, 5. Pyriform conidia with large oil droplets, averaging 21 x 26 µm (stained with aceto-orcein). Images by Ann Elizabeth Hajek.

Entomophaga maimaiga Humber, Shimazu & R.S. Soper 1988, strain ARSEF 7190

Entomophaga maimaiga is an obligate pathogen of a limited number of lepidopteran species, only infecting larval stages and producing two types of spores: conidia or resting spores. This species grows well as protoplasts in liquid Grace’s insect medium (modified) plus fetal bovine serum (GFBS) as well as in some serum-free insect cell culture media. Resting spores have also been produced in GFBS by some isolates. Entomophaga maimaiga grows as hyphae on egg yolk Sabouraud maltose agar (EYSMA) media. When mature cultures on EYSMA are starved, E. maimaiga produces forcibly discharged multi-nucleate conidia. Conidia germinate to form either germ tubes that may lead to vegetative growth, or they can form a short conidiophore from which a secondary conidium is forcibly discharged. If a secondary conidium lands on a substrate unsuitable for germ tube development but still retains enough internal reserves, it may make and discharge still another forcibly discharged (tertiary) conidium. When the conidia of this fungus land on the cuticle of susceptible larvae the germ tube produces an appressorium from which the fungus grows into and through the host cuticle.

Once within a susceptible insect, E. maimaiga first grows as protoplasts and after a few days switches to growing as hyphal bodies. Infected larvae die once fungal cells are abundant throughout the body. After host death, E. maimaiga either 1. grows out through the cuticle, forming conidiophores from which conidia are actively ejected, 2. forms putatively asexual resting spores (azygospores) that mature within the larval body, or 3. produces both types of spores from one larval body. There is a trend for conidial production from cadavers of younger larvae and resting spore production within cadavers of older larvae. Younger larvae dying from infections are generally found in the tree canopy near where they had been feeding but tightly gripping a petiole or twig with the prolegs and often the anterior half of the body is extended at a 90o angle. Cadavers of older larvae containing resting spores are generally found vertically oriented on tree trunks with prolegs extended at 90o from the body holding the cadaver in place.

This species is principally known as a pathogen of the erebid Lymantria dispar, which in many areas can increase to defoliating outbreak densities. E. maimaiga is well known as causing epizootics in either high or low density populations of L. dispar (and, in the former case, controlling outbreak populations). E. maimaiga has also been collected infecting a limited number of other lepidopteran species in nature but never at high prevalence. Entomophaga maimaiga is native to Japan, northeastern China, and far eastern Russia but has been introduced to northeastern and midwestern North America and central Europe for long-term control of L. dispar.