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Gypsy Moth Caterpillar Feeding Finished For 2018

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 Three adult female gypsy moths laying masses of eggs on a tree trunk in Amherst, MA on 7/10/18. Note that the female moths are white in color with black, thread-like antennae. Female gypsy moths (those present in MA) do not fly. (Photo: T. Simisky)
July 13, 2018

Gypsy Moth (Lymantria dispar) caterpillar feeding for 2018 is officially over! Pupation has occurred, and many across the state are noticing gypsy moth adult male flight activity. Adult moths were reported to UMass Extension by landscape practitioners and homeowners in Amherst and Millis, MA on 7/2/18, Holliston, MA on 7/3/18, Natick, MA on 7/4/18, and many male moths (estimated hundreds) could be seen flying outside of French Hall on the UMass Amherst campus on 7/5/18. On 7/10/18 at a location in Amherst, MA, gypsy moth males are still fluttering around, mating with females, and many female gypsy moths are seen laying eggs on tree trunks and branches.

Adult male gypsy moths are generally brown in color with feathered antennae and can fly. They can often be seen flying across the landscape with a jumpy, almost erratic pattern. The males are searching for flightless females with which they will mate. The males can sense pheromones (sexually attractive chemicals) released by the females and they use these pheromone signals to locate a mate. Females, although they have wings, cannot fly and are white in color with thread-like, black antennae. Female moths may be seen at this time resting on tree trunks and branches and actively laying the spongey, tan-brown colored egg masses, which can contain 500-1000 eggs. These egg masses will overwinter on tree trunks, branches, picnic tables and other outdoor furniture, the sides of buildings, and any other flat surface the female moth lays them on and provide the gypsy moth population for 2019. For activity in areas closer to you, please see the full Landscape Message.

On average, when thinking about the entire state of Massachusetts as a whole, the 2018 gypsy moth population did decrease when compared to the population in 2017. While MA experienced over 923,000 acres of defoliation in 2017, the hope is that this number will be much less in 2018. The MA Department of Conservation and Recreation is currently conducting their aerial survey of the state, and will have the estimated 2018 acreage available in the near future. That being said, this experience of a decrease in the gypsy moth population did not hold true for every individual community and neighborhood across MA in 2018. UMass Extension has received many reports of communities dealing with what they describe as just as bad, if not worse, gypsy moth caterpillar populations this year. It certainly seems that this is the case for areas in Amherst and Belchertown, MA (where female gypsy moths are now healthy and laying eggs and previously much defoliation occurred due to the caterpillars).

We can hope that the gypsy moth population size will continue to trend downward, but in certain locations in MA – noticeable populations could still exist in 2019. This seems true for Amherst and Belchertown, where (unfortunately) it does not look like Entomophaga maimaiga (the caterpillar killing fungus) had as large of an impact on the gypsy moth population in 2018 as it did in 2017. In the coming weeks, it will be important to monitor the adult females and get a sense of how many total egg masses are being laid in your area, or on individual properties, to aid in management decisions for next season.

A note about gypsy moth management: at this time, it is not recommended to manage the adult moths, as feeding has stopped for the season. Homeowners frequently ask about scraping egg masses from trees, to help decrease next year’s population. This can be done on individual properties, when egg masses can be safely reached, but this is time consuming and undoubtedly, plenty of egg masses (particularly those high up in the canopy) will be missed. If you decide to scrape off egg masses, do so into a can of soapy water (do not just brush them to the ground, as the eggs may still survive). Use a gloved hand, or a soft brush to remove the egg mass from the bark or other surface. Avoid any actions that remove bark from host plants, while attempting to remove egg masses. Others ask about using horticultural oils on the egg masses. This may only be as effective as the coverage of the horticultural oil on the eggs themselves is thorough. Each egg must be thoroughly coated, which again presents problems on egg masses located high up in trees and even eggs further away from the top of an individual mass. Do not coat gypsy moth egg masses with anything that is not explicitly labelled for such a use (ex. WD-40, used motor oil, etc. is not the answer). The best action at this time may be to scout your property and get an idea of how many egg masses are being laid by female moths. If there are many egg masses, consider speaking with a MA licensed pesticide applicator and professional about reduced risk options for managing the caterpillars when they hatch from the eggs next spring.

Reported by Tawny Simisky, UMass Extension Entomologist

Topics: 
Commercial Horticulture