Q. What is causing this feeding damage on my oak’s leaves?
A. Feeding damage similar to what is shown on these oak leaves was recently reported by the University of New Hampshire Cooperative Extension Forestry and Wildlife Program. They report having received “several reports of defoliated branches, dropped leaves, and the sound of frass (caterpillar droppings) falling from tree canopies”. In New Hampshire, the culprit is reportedly the saddled prominent, or Heterocampa guttivitta. The saddled prominent (or maple prominent) is a native moth whose caterpillars feed on apple, beech, birch, blueberry, buckeye, chestnut, dogwood, hazel, hickory, hop hornbeam, maple (especially sugar maple), oak, persimmon, sour gum, sumac, walnut, and many other woody plants. The saddled prominent is known as “irruptive”, meaning that populations sometimes can build to where defoliation of large forest tracks in northern New England and eastern Canada are possible. However, as a native species, the saddled prominent is normally controlled by native birds, mammals, and other insects including predators and parasitoids.
In Massachusetts, the cause of this feeding damage has not yet been confirmed by viewing samples of insects caught in the act, however some photographs of prominent moth-like caterpillars were also provided with images of this feeding in Ashburnham, MA. While the photos were clear enough to determine that the culprit in Massachusetts is likely another prominent moth, it is not certain if the activity can be blamed on the saddled prominent, or (what I’m leaning toward), the variable oakleaf caterpillar or Lochmaeus manteo. This is another prominent-type caterpillar in a different, but related genus. The variable oakleaf caterpillar has (as its name would suggest) a coloration and pattern that is highly variable in individuals. These caterpillars are mostly pale lime or blue-green with a back marked with green or with white or brick red saddles. (However, this species is very similar in appearance to the double-lined prominent, Lochmaeus bilineata and may need to be reared to adulthood to distinguish the two.) The variable oakleaf caterpillar feeds on beech, chestnut, and oak (preferred) but has also been reported on basswood, birch, elm, hawthorn, maple, walnut, and other trees (yet some of these records may be referring to the closely-resembled double-lined prominent).
So while a definitive identification of the culprit in this case has not yet been made, it would appear that native prominent moth caterpillars are having a good year in Massachusetts in 2020 as well as New Hampshire, and perhaps other parts of New England!
Q. I have two magnolia trees that have these all over them. Can you tell me what this is?
A. The insects pictured here are either one of the following: the magnolia scale or the tuliptree scale. The soft scale insects known as the magnolia scale (Neolecanium cornuparvum) and the tuliptree scale (Toumeyella liriodendri) can be difficult to differentiate in the field, depending upon the host they are found on. (On magnolia, it is very difficult to distinguish between the two species of soft scale.)
The magnolia scale is distributed throughout the eastern United States. The tuliptree scale is found east of the Mississippi River from Michigan to Alabama and from New York and Connecticut to Florida. It is also reported to be found in ornamental tuliptrees and magnolias in California and could be found wherever these trees are grown. Magnolia scale host plants include: Magnolia stellata (star magnolia), M. acuminata (cucumber magnolia), M. lilliflora ‘Nigra’ (lily Magnolia; formerly M. quinquepeta), and M. soulangeana (Chinese magnolia). Other species may be hosts for this scale, but attacked to a lesser degree. M. grandiflora (southern magnolia) may be such an example. Tuliptree scale host plants include: Liriodendron tulipifera (tuliptree or yellow poplar), Magnolia stellata (star magnolia), and M. soulangeana (Chinese magnolia). This insect has also been recorded on M. grandiflora (southern magnolia) and Tilia spp. (linden). The tuliptree scale has also, to a lesser extent, been reported on other ornamental trees and shrubs.
Mature individuals settle on a location on branches and twigs, then insert piercing-sucking mouthparts to feed. The insects feed on plant fluids and excrete large amounts of a sugary substance known as honeydew. Sooty mold, often black in color, will then grow on the honeydew that has coated branches and leaves. Repeated, heavy infestations can result in branch dieback and at times, death of the plant. Honeydew may also be very attractive to ants, wasps, and hornets. The life cycle of both of these species is similar and may have similar timing during the year, however subtle differences exist.
The life cycle of the magnolia scale is as follows: This scale overwinters as a young nymph (immature stage) which is elliptical in shape, mostly a dark-slate gray, except for a median ridge that is red/brown in color. These overwintering nymphs may be found on the undersides of 1st and 2nd year old twigs. The first molt (shedding of the exoskeleton to allow growth) can occur by late April or May in parts of this insect’s range and the second molt will occur in early June. At that time, the immature scales have turned a deep purple color. Stems of the host plant may appear purple in color and thickened – but this is a coating of nymphal magnolia scales, not the stem itself. Eventually, these immature scales secrete a white layer of wax over their bodies, looking as if they have been rolled in powdered sugar. By August, the adult female scale is fully developed, elliptical and convex in shape and ranging from a pinkish-orange to a dark brown color. Adult females may also be covered in a white, waxy coating. By that time, the females produce nymphs (living young; eggs are not “laid”) that wander the host before settling on the newest twigs to overwinter. In the Northeastern United States, this scale insect has a single generation per year.
The lifecycle of the tuliptree scale is as follows: The mature female tuliptree scale is hemispherical in shape. The color of the mature female varies in this species as well - a grayish-green to pink-orange insect mottled with black. Adult males emerge sometime in June and mate with the females. Like the magnolia scale, eggs develop within the body of the female tuliptree scale, leading to the “live birth” of immatures (crawlers) in late August and September. In the Northeast, one generation of tuliptree scales occurs per year. (However, in the southern-most portions of its range, this insect has been found in all stages of development during the winter, suggesting multiple generations per year.) A single female tuliptree scale may produce 3,000+ crawlers in one season. These crawlers are tiny (approximately the size of the head of a pin) and settle on host plant twigs in September. Past studies have shown that in addition to moving on their own with fully functional legs, the crawlers can be blown to new hosts on the wind, up to 100 feet away. (Being wind-blown to a new host, however, is a haphazard method of travel through which some less than 20% of these crawlers successfully make contact with a host plant, and fewer still attach to a suitable site on the plant.) The immature, crawler stage molts once prior to overwintering.
As two native scale insects in North America, the magnolia and tuliptree scales are hosts themselves for natural enemies that can impact their populations. Solitary parasitoid larvae have been collected from magnolia scales and have been identified as a syrphid fly species, Ocyptamus costatus. The natural enemies of the tuliptree scale have been studied to a greater degree and include certain lady beetle species [Hyperaspis signata, Adalia (formerly Hyperaspis) bipunctata, and Chilocorus stigma] which feed on nymphal scales, a number of parasitic wasps, and even an insect feeding moth caterpillar (Laetilia coccidivora). This particular moth species, also referred to as a type of snout moth, will consume the tuliptree scale underneath the protection of a silken web it spins over them! (The specific epithet coccidivora can be translated as “ones that eat soft scales” or Coccidae.) Unfortunately, in a landscape setting, it often seems that although these natural enemies may be common within the scale populations, they are seldom able to reduce the scale insect numbers below damaging levels. That being said, our management options should still seek to preserve these natural enemies.
Tawny Simisky, Extension Entomologist, UMass Extension Landscape, Nursery, & Urban Forestry Program