Overwintered eastern tent caterpillar (ETC) (Malacosoma americanum) moth eggs are hatching in southwest Ohio; a sure sign that spring has sprung. As their common name implies, the caterpillars are accomplished tent-makers displaying their silk handiwork in branch forks.
ETC spends the winter in shiny, blackish-brown egg masses wrapped around twigs on their host plants. A close examination will reveal that the eggs are encased in a structure that resembles bubble-wrap perhaps for winter protection.
The accumulated Growing Degree Days (GDD) that predicts ETC egg hatch is 92 and we've reached 112 in my part of Ohio. The full bloom of Corneliancherry dogwood (Cornus mas) is usually a pretty good phenological indicator for ETC egg hatch.
The caterpillars begin producing their highly visible silk nests immediately upon hatching. Indeed, egg-hatch may be revealed by observing the tiny, hairy first instar caterpillars clinging to small, silk nests that surround their egg mass.
The caterpillars prefer to feed on trees in the family Rosaceae, particularly those in the genus Prunus, such as cherry. They also occasionally feed on birch, maple, and oaks. Healthy large trees can handle the early season defoliation by producing a new flush of leaves. However, newly planted trees may not fare as well. Leaves lost to caterpillar feeding this spring must be replaced using energy stored from last season.
Small nests within reach from the ground can be eliminated digitally using five-fingered "smash and/or smear" techniques. Less hands-on methods include applications of the naturally occurring bacterium, Bacillus thuringiensis serotype kurstaki (Btk), applied to early instar stages, as well as standard insecticides labeled for general caterpillar control.
It's too early to assess the general population density of ETC in southwest Ohio. However, this native moth has a history of producing occasional outbreaks.
ETC is of particular interest to the thoroughbred horse industry because of the link between hairs on the caterpillars and Mare Reproductive Loss Syndrome (MRLS). The syndrome produced an estimated economic loss to the industry in Kentucky of $336-$500 million in 2001. The entire pathogenesis was untangled through diligent scientific sleuthing by scientists at the University of Kentucky. Many thoroughbred farms in the Lexington, KY, region took steps to reduce the risk by cutting down black cherry (Prunus serotina) which commonly grew in tree lines surrounding horse pastures.
Sweet Payment for Services
Nectar is the currency used by plants to pay insects and other animals to do their bidding such as carrying flower pollen from producer to recipient. And it costs plants nothing to photosynthesize this sweet medium of exchange. We can all breathe easier knowing that the only thing plants need is a little sunlight to rearrange the atoms in water (H2O) and carbon dioxide (CO2) to produce glucose (C6H12O6) and atmospheric oxygen (O2).
Of course, nectar is more complex than just glucose used by plants to satisfy their own energy needs. Plants raise the reimbursement by including a mix of nutrients essential to the needs of pollinators.
The recent rise in awareness of the importance of pollinators has highlighted this nectar-based economy. However, flowers are not the only place where nectar serves as coinage in exchange for services.
Extrafloral nectaries (EFNs) are plant glands that produce nectar but they are not associated with flowers. A good example is the EFNs found on the leaf petioles of trees in the genus Prunus. They were long used as handy identifiers of plants in the belonging to genus; particularly cherry, before research revealed their important ecological function.
The EFNs on cherries can vary considerably in size and shape from species to species. Some appear as small red or green "bumps" or even "dots" on the petiole at the base of the blade while others look like well-defined deep red donuts. Of course, a lot of things look like donuts to me, but that's another sweet story.
In 1978, the University of Minnesota ecologist Dave Tilman published a paper in the journal Ecology titled, "Cherries, Ants, and Tent Caterpillars: Timing of Nectar Production in Relation in Relation to Susceptibility of Caterpillars to Ant Predation." The title says it all.
Tilman found that the EFNs on black cherry commonly attract western thatching ants (Formica obscuripes) which are predaceous on many caterpillars including ETC. His research showed that the number of ants visiting the EFNs was directly correlated with the distance between ant colonies and cherry trees and ETC survivorship was positively related to those distances.
He also found that the highest number of ants visiting the trees occurred just after bud break and decreased as the number of active EFNs decreased. This time frame coincided with the development of ETC with caterpillars large enough to escape ant predation appearing after EFNs ceased their nectar-payment activity. He concluded that "… the ant-cherry relationship is a facultative mutualism and that nectar production is timed so as to maximize the chance of successful ant predation on tent-caterpillar colonies."
The term "myrmecophile" means "ant lover." It is derived from the Greek "myrmex" = ant, and "phlos" = loving. The term applies to the special relationship some plants and animals, including insects (e.g. aphids), have with ants. Obviously, many plants in the Prunus genus are myrmecophiles with their sweet love expressed through their EFNs.