We performed a trial at an urban site locally in New Plymouth last summer where wasps were feeding in a tree with no flowering and, therefore no floral nectar. The tree had in excess of 100 wasps at any one time during the day.

We analysed wasps approaching the property from 4-5 different directions and were a mixture of both common and German wasp species. From these numbers, we can estimate there were between 4-6 nests feeding at the tree.

The layout of the site and the direction in which the wasps were entering the property meant the usual wasp bait direction for use could not be followed. Usually, we recommend placing bait stations 5-10m from the point of feeding in the direction the wasps are coming from and >10-20m above ground. This could not be followed, therefore this trial was initiated to see whether a different approach to station placement would be successful in controlling and reducing wasp numbers.

(Hawkeye Wasp Station and Bait in action)

Stations were placed close to the point of feeding in orientations to try to capture the lines of approach by the wasps the the food source(tree). Three stations were placed in approximate north-south directions and two were approximate east-west directions.

Bait wells were approximately half filled with wasp bait, placed in the stations, checked periodically, and replaced with fresh bait when empty.

Recruitment to the stations took several days after bait placement and there was a fairly constant level of wasps at stations during daylight hours.

After two weeks no wasps could be observed in the tree, while low numbers of wasps remained consistent at the bait stations. For a further two weeks there were still no wasps present on the tree and wasp numbers in the stations fluctuated from 0 to 2-3 per station.
Over the next five weeks, a low number of wasps were present (0-1 per station) at most times after which 3 stations were removed to increase the numbers per station and better utilise the bait being used.

Table 1: Dates and observed numbers of wasps during the trial 

4th Feb 2023  Bait placed in 5 locations
28th Feb 2023  Wasp pressure low. No wasps in trees and 2-3 across all stations
2nd March 2023  3-5 wasps on/in stations. No wasps in tree
9th March 2023 Zero wasps visible
10th March 2023 10-15 wasps at times amongst stations. No wasps in trees
11th March 2023 onwards 3-5 wasps amongst stations  from this point forward. No wasps in trees
10th April 2023 3 stations removed. Occasional wasps visiting remainging stations. No wasps in trees
24th April 2023 All bait removed. No wasps visible

Seeing an increase in wasp numbers across the duration of a trial is likely due to the emergence of new wasps from larvae coming out from the (multiple) nests during this trial. It can also be due to changes in other availability of natural food sources over time.

Approximately 800mL of wasp bait was used over a period of 9 weeks during this trial to reduce numbers from >100 at a time to zero. Nest size, weather conditions, availability of other food sources, and percentages of foraging wasps feeding on bait and returning it to the nest all affect the amount of bait that is needed.

It is anticipated that the nests that were eliminated during this trial were the major ones in the local area and the time of elimination (eg April) would not allow for additional nests to be established in time for new queens to emerge before winter hibernation. Therefore, we expect fewer nests in the local area to establish in the next summer season and fewer wasps would be observed at the tress with non-floral nectar. This outcome is not expected to last longer than one season.