Gypsy moth update: friendly fungus at work

According to the Integrated Pest Management newsletter from Michigan State University, a friendly fungus called Entomophaga maimaiga is expected to slow down gypsy moth infestations next season:

"This fungus infects caterpillars, turning them into a mushroom in about a week. Fortunately, Entomophaga maimaiga is very host specific and only infects gypsy moth and not any other animals. The caterpillars die facing head down, the bodies becoming shriveled and rubbery in a few days. Eventually the dark-brown to black mushrooms, still in the shape of a shriveled caterpillar, fall to the ground around the base of the trees. In each mushroom are thousands of spores that will infect gypsy moth caterpillars next spring. When young caterpillars become infected next spring, they will die quickly, turn into mushrooms and sporulate immediately during wet weather, infecting other caterpillars. It is in this way that the fungus can spread quickly through a forest, infecting most of the gypsy moth caterpillars. The fungus in large caterpillar-mushrooms that are present now will not sporulate until next May when the next batch of gypsy moth larvae are active.

The outbreaks of gypsy moth that we are seeing around the state at this time may be due to two or three relatively dry springs in a row. Entomophaga cannot sporulate and infect caterpillars under dry weather conditions. However, the wet spring and early summer that we have had so far this year has allowed Entomophaga to spread quickly."

So how can you tell if the fungus is in your area? Here's what the MSU report says to look for:

"Take a look at the oak, birch, poplar or other infested trees on your property. You may find many dead caterpillars (mushrooms) on the trunks. If Entomophaga is active in your area, the gypsy moth population will naturally decline, so you may not see nearly as many caterpillars next year or the year after."

When I checked my trees recently, I saw exactly what they describe. Good news indeed. This fungus proliferates during moister, cooler conditions. (Though we are still a bit on the dry side, we've had more rain and cooler temperatures than last summer.)

For more information, see the newsletter and download a PowerPoint presentation on this fungus.

© Yvonne Cunnington, Country Gardener