The life history and control of Pityophthorus juglandis Blackman on Juglans nigra L. in eastern Tennessee

In the last decade, western states have experienced an increasing mortality rate in Juglans nigra L., black walnut, as a result of the fungal species Geosmithia morbida Kolařík et al. that results in numerous cankers that girdle the branches, resulting in dieback and tree mortality. The only known vector of G. morbida is the walnut twig beetle (WTB), Pityophthorus juglandis Blackman. This newly recognized disease/insect complex has been named Thousand Cankers Disease (TCD) due to the quantity of cankers produced by G. morbida.

Recently, TCD was discovered in the eastern U.S. To limit the spread of TCD in eastern Tennessee, a better understanding of the life histories of G. morbida and P. juglandis is imperative.

The primary objective of this study was to determine the life history of WTB in eastern Tennessee using field-infested black walnuts bolts. From this data, it was determined that WTB has at least three larval instars. Gallery structures of the different WTB life stages were determined. Secondly, a survey was initiated to identify native predators and parasitoids for use as potential biological control agents of WTB. The consumption rates of WTB by the collected the predators were recorded and a potential listing of native predators was developed. From this survey, three clerid species were observed to feed on WTB. Nine additional coleopteran species and two parasitoid species were found in association with WTB infested logs. Concentration levels and translocation of two systemic insecticides (imidacloprid and dinotefuran) were studied in mature J. nigra and tissue types affected were identified. Concentrations of all the chemicals were determined using high pressure liquid chromatography (HPLC). Imidacloprid concentrations were detected in all tissue types tested including nutmeat. Dinotefuran was only detected in trace amounts in the first sampling period.