It has sparked concern the plant may have contained more than the one beetle, which was identified in the nearby grounds of Langham Primary School earlier this summer. The find was made during the Food & Environment Research Agency's (FERA) survey of the area within a 100m radius of the school.
FERA plant health team's Richard McIntosh said: "The plant had two exit holes, so we are working on the assumption that two beetles emerged. The one that was caught is a female, so the other one emerging could not be a mated female.
"Nevertheless, we will be completing the 100m survey as planned and inspectors will be carrying out a further survey in the autumn, when the leaves are off the trees and it is easier to check."
Inspectors have confirmed that the plant was one of a small batch sold by a local wholesaler and bought from an Italian supplier. It is not yet known whether the plants originated in Italy.
FERA is now tracking down the remaining plants from the same batch to carry out inspections and the Italian authorities are investigating the supplier.
McIntosh said two of the batch had been found at the wholesaler's nursery and had been checked by inspectors with no evidence of infestation.
He added: "We know the location of four others and these will be inspected this week. We will take a decision on what if any further action is needed in light of the results of these inspections."
European plant health authorities have been informed in case they have received plants from the same source. FERA continues to urge the trade to be vigilant.