Entomophthora muscae is a fungus known for its unique interaction with flies. This organism transforms infected flies into “zombies” by orchestrating precise behavioral changes in its host, ultimately ensuring its own propagation. This intricate biological process offers a glimpse into the complex strategies employed by pathogens in the natural world.
Understanding Entomophthora muscae
Entomophthora muscae is an entomopathogenic fungus, meaning it causes disease in insects. It belongs to the Entomophthorales order, a group known for insect-specific parasitic lifestyles. The name Entomophthora muscae translates to “insect destroyer,” aptly describing its effect on flies, including common houseflies and fruit flies.
The fungus exists as microscopic spores in the environment. When these spores contact a suitable fly host, the infection process begins. While it may appear as a white fuzz on infected flies, the fungus’s development is primarily internal, involving sophisticated manipulation of its host.
The Infection Process
The infection cycle begins when airborne spores, called conidia, land on a fly’s outer surface. Within a few hours, these conidia germinate, producing a germ tube that penetrates the fly’s tough outer layer, the cuticle. This penetration occurs through mechanical force and digestive enzymes like chitinases and lipases.
Once inside the fly’s body cavity, or hemocoel, the fungal protoplast flows into the fly’s hemolymph, which is comparable to insect blood. The fungus then proliferates, growing as hyphal bodies that consume the fly’s internal tissues. Initially, it targets non-vital organs and fat reserves, allowing the fly to remain alive and active for several days while the fungus grows. This internal growth continues for approximately five to seven days in houseflies and four to five days in fruit flies, gradually depleting the host’s nutrients.
The “Zombie Fly” Behavior
As the fungal infection progresses and the fly’s internal resources deplete, Entomophthora muscae begins to control the fly’s behavior. The fungus manipulates the fly to climb to an elevated position, a behavior often called “summiting” or “summit disease.” This climbing typically occurs around sunset.
Once at a high vantage point, such as a plant stem, wall, or window, the infected fly extends its proboscis and secretes a sticky fluid, firmly attaching itself to the surface. The fly then raises its wings, assuming a characteristic posture that maximizes spore dispersal. This ensures the fly remains in an optimal position for the fungus to release its spores onto unsuspecting flies below, perpetuating the infection cycle.
Ecological Impact and Safety
Entomophthora muscae naturally regulates fly populations in various environments. Outbreaks of this fungal disease tend to occur in spring and autumn, particularly in cool, humid conditions where flies gather. In such conditions, a significant portion of a fly population, sometimes 60-80%, can become infected. This natural control mechanism highlights its potential as a biological control agent against pest flies.
Regarding safety for humans and other non-target organisms, Entomophthora muscae is highly host-specific, primarily targeting flies and other two-winged insects. There is no known threat to mammals, including humans and pets, or plants from this fungus. While research has explored its use in pest control, technical difficulties like its sensitivity to temperature and challenges in artificial culturing have limited widespread application.