Joe’s Journal, Spring Edition – When Bugs Go Wrong: Eastern Tent Caterpillar

Malacosoma americanum (eastern tent caterpillar) is a member of the Order Lepidoptera. Moths and butterflies (perhaps more correctly, flutterbys?) both are members of this order. The name, Lepidoptera means “scale wings” which alludes to the scaly covering on otherwise clear wings.

Eastern tent caterpillar (ETC) form silk nests in the crotches of cherry and apple trees, both in the Rosaceae (rose) family.  Caterpillar hatch is early, about the time when trees break bud and start to form leaves.  The caterpillars have 6 instar stages, are hairy and have blue and white markings on each side of their body. The early instars feed early morning, afternoon and night.  The final instar spins silk to form a cocoon, from which an adult emerges.  The moths are active at night, mate and lay about 250 eggs in a single mass deposited on the tree.  The egg mass is dark in color, but also reflective in light.  Eggs are laid in late spring to early summer.

When Eastern Tent Caterpillar Goes Wrong

Eastern tent caterpillars defoliate trees if left untreated.  Trees generally recover from early spring defoliation, but repeat defoliations will have a negative impact on the health of the tree.  In addition, horses exposed to the setae (hairs) have aborted fetuses (mare reproductive loss syndrome) when populations of ETC explode. The first recorded incidence was in Kentucky, 2001.

Fig. 2 Eastern tent caterpillar

Management of Eastern Tent Caterpillar

In late winter, scout trees for the dark egg masses.  Scrape off or apply dormant oil to smother.  If practical, prune out small branches with tents early in spring.  This technique is not at all practical for tents in larger branches.  Spray the emerging foliage with an azadirachtin product such as AzaSol (6% azadirachtin SP).  Azadirachtin is the first go-to when treating fruit bearing cherry and apple trees.  It acts both as an anti-feedant and as an insect growth regulator.  Make applications early and repeat at 7 to 10-day intervals to protect foliage and to keep trees healthy.  Always follow label directions on use.

Join us next week when we talk about other things that can go wrong with your garden and trees.

~ Signing off for now, Joe