The following method was developed over 6 weeks and does need improvements. It is offered without guarantee of success but if it works for you and you find ways to improve it.
Don’t keep it to yourself; after all, they didn’t.
In 2017, Jersey experienced its first serious encounter with the yellow legged hornet, Vespa velutina nigrithorax(Vv), from the first sighting in mid-July they were studied intensively and by late August a successful method of tracking secondary nests had been developed. This was used to find 7 of the 10 nests destroyed. The 3 remaining nest were discovered by members of the public.
It is simple and effective method, requiring some patience and standard beekeeping equipment, a watch or phone, a compass, a plate and some kitchen paper + A. The method is a little crude but will be improve.
An attractant is vital to this method. We were lucky with the first sighting of Vv as they were feeding on the sap of an oak tree. It was observations at this and another damaged oak that led us to the assumption that they habituate to a food source. This method has subsequently proved this assumption.
Moving a tree is very difficult but after experiments with a range of suggested and proprietary attractants we had a reliable mobile attractant. As it outperformed all the others, the attractant chosen in 2017 was Suttera Wasp Attractant®. N.B. It should not be assumed that the attractant will be the same everywhere so constant testing should be undertaken.
No observation of individuals is possible unless they are recognisable. Marking is therefore necessary and to be marked they need to be held still. For Vv, using an insect marking cage with plunger is recommended. Vv are easy to trap on a flat surface, such as a plate, as they are docile on the attractant and while aggressive with the plunger, in our experience, do not attempt to sting the applier on release.
Beekeepers regularly mark their queens to distinguish them in a hive of bees, they also colour code them to record their year of accession. A marking cage with plunger is standard equipment as are the 5 coloured year marking pens or paints. Colour markers were used on Vv’s thoraxes for the initial phase of research, however, Vv has a hairy thorax and markings quickly wore off and the limited colours available restricted the number we could mark. To widen our scope a queen marking kit consisting of 5 x 100 coloured and numbered discs plus glue and applicator was purchased which increased flexibility and enabled individual marking at multiple sites.
Once there were identifiable individuals, the possible areas for research broadened considerably. One of which was the recording the length of time Vv were away from the bait. From these timings it was possible to estimate the approximate distance to a nest. The distance then determines how you track them, for instance, a very long interval time such as 15 minutes+ might indicates that a nest is over 1k away (an accurate time over long distances has not yet been determined) and the trajectory is not always accurate over that distance. Whereas, an interval of less 2 minutes means that the nest is close enough to call for backup.
NB It has been our experience that Vv from 1 bait station do not visit other station outside an, as yet, undefined, sector, that is why differentiation between sites using different disc colours and/or numbers is important.
Bait stations in open area are best for tracking as the trajectory to the nest will be observable over some distance. This not always possible, however, if Vv are visiting regularly, an offset in 10-15 metre jumps to reach an open site can be successful; providing the Vv re-establish between moves; i.e. are no longer returning to the previous site, this takes between 1 & 2 hours.
Having established the trajectory, you can start to track. To save time use a long distance between baits, but be prepared to back track if you lose contact. It is good practice to keep the previous station active until the new one is established This can be problematic as marked Vv tend to return to their familiar site, however, marking new individuals before removing the previous bait gives you some peace of mind. When an interval time of less than 5 minutes is recorded smaller but more frequent moves (1-2 hours) are possible until the magic time of 2 minutes is reached.
As the data becomes more plentiful and accurate we will be better equipped to calculate distances from the times. It is possible to triangulate by placing baits around an assumed focal point. This was not tested last year as by the time the method had been developed,to a reasonable accuracy, foundress queens were likely to be developing.
However close the nest is thought to be, don’t assume that it will be easy to find, it could be anywhere from the top of a tall tree to a hole in the ground. Of the 10 secondary nests found in Jersey in 2017, 2 were in tall sycamore trees, in full leaf, 2 in medium sized oaks, 1 birch and 1 apple tree,1 in a cavity wall, 2 in hedges at heights below3 m and 1 in a bramble patch almost at ground level.
Until we have developed other tools such as infra-red and electronic tracking, the more eyes the better, keep watching and following Vv (using a bait can help) and if what you think you see is unbelievable, it isn’t.
Caution! Please take care. This is the time of greatest risk to you and your team. If any Vv come to investigate you this close to the nest, retreat to a safe distance.
The advice is that Vv will defend an area up to 5 metres from the nest. You have been warned.
Celebrate away from the nest.
As 2018 progresses we will assess whether this method has had any effect on the Jersey population. Watch this space.