Selected few insect pest questions and answers from the 2019 growing season
Q: Could the aerial applications for mosquito control due to the incidence of EEE in Massachusetts negatively impact the population of Cyzenis albicans released as a biological control of winter moth (Operophtera brumata)? (September 17, 2019)
A:. Cyzenis albicans is the parasitic fly that was released by Dr. Joseph Elkinton of UMass Amherst and his laboratory to manage winter moth caterpillars (defoliators of trees and shrubs in eastern Massachusetts). Aerial mosquito control applications that were made in August and September of 2019 in parts of eastern Massachusetts likely had little to no direct impact on C. albicans populations in these areas. First, given the life cycle and behavior of the parasitic fly, it was well protected during this time of year. Cyzenis albicans remains in its puparia inside the pupa of the winter moth, which is located in the upper layer of the soil or leaf litter once winter moth pupation occurs beginning in late-May/early-June. Parasitized winter moth pupae, containing the developing flies, will remain in this protected location until the following spring, when adult flies emerge to lay their eggs on foliage being fed upon by winter moth larvae. Dr. Elkinton agrees – the mosquito control applications and Cyzenis albicans missed each other not only in timing, but also in space. Additionally, the active ingredient used by the MA Department of Agricultural Resources for these applications, sumithrin, has a very short half-life (less than one day), which reduces the chance of unintended consequences for non-target insects. Half-life is the amount of time it takes for a certain amount of a pesticide to be reduced (broken down) by half. For more information about half-lives, visit: http://npic.orst.edu/factsheets/half-life.html. For more information about aerial applications for mosquitoes in Massachusetts, visit: https://www.mass.gov/service-details/mosquito-control-and-spraying.
Q: I hope you can help me ID this caterpillar (?) found on my client's Eastern red cedar in Bristol County, MA. Photos are attached. (August 12, 2019)
A: The species of insect included in your photos is likely Thyridopteryx ephemeraeformis or the common bagworm (also called the evergreen bagworm, eastern bagworm, or North American bagworm). These caterpillars develop into moths as adults. Their behaviors, life history, and appearance are interesting. The larvae (caterpillars) form “bags” or cases over themselves as they feed using assorted bits of plant foliage and debris tied together with silk. As the caterpillars feed and grow in size, so does their “bag”. Young, early instar caterpillars may feed with their bag oriented skyward, skeletonizing host plant leaves. As these caterpillars grow in size, they may dangle downward from their host plant, and if feeding on a deciduous host, they can consume the leaves down to the leaf veins. Pupation can occur in southern New England in late September or into October and this occurs within the “bag”. Typically, this means that the caterpillars could encounter a killing frost and die before mating could occur. However, in warmer areas of Massachusetts or if we experience a prolonged, warm autumn, it is possible for this insect to overwinter and again become a problem the following season.
If the larvae survive to pupation, adult male moths emerge and are winged, able to fly to their flightless female mates. The adult male is blackish in color with transparent wings. The female is worm-like; she lacks eyes, wings, functional legs, or mouthparts. The female never gets the chance to leave the bag she constructs as a larva. The male finds her, mates, and the female moth develops eggs inside her abdomen. These eggs (500-1000) overwinter inside the deceased female, inside her bag, and can hatch roughly around mid-June in southern New England. Like other insects with flightless females, the young larvae can disperse by ballooning (spinning a silken thread and catching the wind to blow them onto a new host).
While arborvitae and junipers can be some of the most commonly known host plants for this insect, the bagworm has a broad host range including both deciduous and coniferous hosts numbering over 130 different species. Bagworm has been observed on spruce, Canaan fir, honeylocust, oak, European hornbeam, rose, and London planetree among many others. This insect can be managed through physical removal, if they can be safely reached. Squeezing them within their bags or gathering them in a bucket full of soapy water (or to crush by some other means) can be effective ways to manage this insect on ornamental plants. Early instar bagworm caterpillars can be managed with Bacillus thuringiensis var. kurstaki (Btk) but this is most effective on young bagworms that are no larger than ¾ inch in length. As bagworms grow in size, they may also have behavioral mechanisms for avoiding chemical management. Management should seek to preserve any natural enemies that would be found attacking this insect, such as certain parasitic wasps. It is also important to note that the bags from dead bagworms will remain on the host plant, so check the viability of the bagworms by dissecting their bags to avoid unnecessary chemical applications. Historically in Massachusetts, bagworms have been mostly a problem coming in on infested nursery stock. With females laying 500-1000 eggs, if those eggs overwinter the population can grow quite large in a single season on an infested host. Typically, this insect becomes a problem on hedgerows or plantings nearby an infested host plant. Thyridopteryx ephemeraeformis is found from Massachusetts to Florida, and is typically a more significant pest in southern climates; however, this insect was problematic in many communities across Massachusetts during the 2019 season.
Q: Any tips for managing the viburnum leaf beetle (Pyrrhalta viburni; VLB)? I am noticing differences in feeding damage depending upon the species of viburnum involved. V. opulus is just decimated by the beetle. However, the V. acerifolium, not so much. V. carlesii, V. plicatum, and V. burkwoodii are fine. (June 14, 2019)
A: Viburnum opulus is known to be highly susceptible to VLB (viburnum leaf beetle) feeding. So your report about them being decimated unfortunately makes sense. V. acerifolium is thought to be “susceptible” (but perhaps not as favored as the aforementioned species). V. carlesii and V. plicatum are actually considered resistant to VLB. And finally, V. burkwoodii is only “moderately susceptible”, and in this ranking is just a step above those considered resistant. The following provides a good outline of susceptibility: http://www.hort.cornell.edu/vlb/suscept.html
For management, some options include, but are not limited to:
- Use resistant varieties. Viburnums in locations where they are constantly defoliated by this insect, and thus dieback occurs, should probably be removed and replaced with resistant varieties. Otherwise, management will be a constant battle. If you have plants that are not being completely stripped season to season, and are known to be perhaps only moderately susceptible, there are some things you can do:
- Mechanical management options: after the first frost or over the winter, in small plantings the terminal ends of twigs can be pruned off and destroyed if overwintering viburnum leaf beetle eggs are found. Look for the eggs (in capped pits created by the female beetle) and be sure to remove enough of the twig so that every egg site is removed. This will help reduce the overwintering population.
- Chemical management options: When larvae are still present and feeding on foliage, the reduced risk active ingredient (AI) spinosad can be sprayed on the foliage; but do so when the plant is not in bloom, as this AI is toxic to pollinators until it dries. Other active ingredient options include but are not limited to: acephate, acetamiprid, carbaryl, dinotefuran, horticultural oil, and imidacloprid. Read and follow all label instructions for safe and proper use. Each active ingredient can have different risks toward applicator health and the environment. The following fact sheet summarizes some of these risks, but should not be used as a replacement for reading the label: https://ag.umass.edu/landscape/fact-sheets/tree-shrub-insecticide-active-ingredients-risks-to-pollinators-other-non
Tawny Simisky, Extension Entomologist, UMass Extension Landscape, Nursery, & Urban Forestry Program
