The life cycle of this insect is still being studied by researchers. It occurs within the branches of black oak. Only an asexual twig-galling stage on black oak is currently known for this newly described species. Adult wasps have been observed to emerge from twigs in May following leaf expansion. Studies in the fall of 2013 and 2014 suggest that this wasp does not have a fall generation of adults that emerge from the twigs. Gall cavity development begins in late July to early August. Larval development was found to begin in August followed by pupal and adult development thereafter. This wasp was found to overwinter in multiple life stages within the twigs, including larval, pupal, and adult stages. From October to April, multiple life stages are present at the same time in twigs. So far, no evidence has been found for a sexual stage of this insect or alternate galls on black oak or an alternate host. Further research may be necessary. It is currently unknown whether or not this insect is an exotic or native species in New England.
Previous records may be under the scientific names: Bassettia ceropteroides or Callirhytis ceropteroides, however it was described as a new species, Zapatella davisae, in 2016 (Buffington et al, 2016).
Galled twigs may not be readily noticed or at times galled twigs may be obvious. Galled twigs often have pin-sized exit holes present, made by the adult wasps that have emerged. Removal of bark or outer wood from twigs will expose oval cells that the wasp creates. Often, adults, pupae, or larvae can be found within these cells. Symptoms of an infested tree include dieback, sparse growth in the spring, epicormic growth, flagging, and galled twigs. The galls may disrupt the vascular system of the tree and cause twig mortality or flagging. Infestations typically have been observed to begin in the upper crown of the tree and progress downward. Tree dieback may not occur until the 2nd or 3rd year of infestation. Very heavily infested trees may have almost 100% dieback. Outbreaks historically have been limited to the east coast of Massachusetts, including: Cape Cod, areas in the South Shore, Martha's Vineyard, and Nantucket. Parts of Rhode Island, coastal Connecticut, Long Island, New York, and potentially eastern New Jersey have also experienced outbreaks of this insect in the past.
Look for black oak with signs of dieback or flagging branches beginning in the upper canopy and continuing downward. Inspect flagged branches for slightly noticeable swelling and pin-sized exit holes from emerging adults. In very infested trees, extreme dieback may be observed along with epicormic shoots (water sprouts).
It has been suggested that selectively pruning galled twigs in the winter and early spring followed by burning those prunings may be an effective management option when the insect is at low densities. If gall wasp populations are too extensive and densities are too high, this method may not be successful.
Parasitoids of this insect exist and have been observed to emerge in June (Buffington et al, 2016). A recent study published in 2019 identified some of the parasitoids active in black oak gall wasp populations. They found that on Long Island in 2015 there was nearly 100% parasitism of the black oak gall wasp followed by a near total collapse of the population on Long Island in 2016. They also observed lower parasitism rates that remained consistent on Cape Cod between 2015 and 2016, when greater damage to black oak trees was observed at that time. Species of Sycophila were the dominant parasitoids found in the study, with one species Sycophila nr. novascotiae representing approximately 65% of reared parasitoids from black oak gall wasp populations on Long Island, and two species of Sycophila (S. nr. novascotiae and S. foliatae) appearing to be equally present in black oak gall wasp populations at the time on Cape Cod (Davis et al, 2019).
Carbaryl (L)
Dinotefuran (NL)
Emamectin benzoate (L)
Imidacloprid (L)
Pyrethrins+piperonyl butoxide (L)
Active ingredients that may be applied systemically include: dinotefuran (soil drench), emamectin benzoate (injection), and imidacloprid (soil drench).
A study in 2014 looked at the efficacy of two systemic insecticides (emamectin benzoate and imidacloprid) at managing the black oak gall wasp in 30 trees at a single site. On March 24, 2014 the 30 trees in Barnstable, MA were randomly assigned to one of three treatment options for a total of 10 trees per treatment. The three treatments were IMA-jet (5% imidacloprid) at 8 ml per 2.54 cm DBH, TREE-äge (4% emamectin benzoate) at 10 ml per 2.54 cm DBH, and an untreated control. Those conducting the study selected active ingredient rates based on rates used in previous studies. The number of injection sites for a given tree was calculated as the DBH (in centimeters) divided by five. Injection holes were drilled perpendicular to the surface of the bark and spaced 15–20 cm apart on the trunk’s circumference at a height of 20–40 cm above the ground. Insecticides were administered with either the QUIKjet or Tree I.V. system depending on each tree’s capacity to uptake product. There was a significant difference in branch mortality among the three treatments - the insecticides did not differ but both lowered branch mortality compared to the control. A single application of systemic insecticides emamectin benzoate and imidacloprid was found to reduce or prevent further accumulation of black oak gall wasp damage on infested black oak during a 1-yr trial (Davis and Elkinton, 2018).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
