Estimating the populations of three species of Volucella in an English woodland

1. Estimating the populations of three species of Volucella in an English woodland Roger Morris Stuart Ball

2. Volucella species studied V. inflata V. pellucens V. bombylans

3. Study site – Old Sulehay Forest, BCNP Wildlife Trust Reserve • 35 hectares of ancient semi-natural woodland • Managed as hazel coppice with oak/ash standards before 1940s • Main ride is well managed and open

4. Sampling sites in the wood 20 visitsfrom 7 June to 27 July 2003

5. Marking

6. Numbers marked and recaptured 160 out of 985 marked flies were recaptured at least once = 16.25%

7. Some practical lessons • The consistency of paint is important - too thin and the insect gets covered (and may be fatally damaged) • Species with hairy thoraxes are much harder to mark clearly • Constant effort is needed to ensure that new recruits to the population are marked before they displace existing members or disperse themselves

8. V. bombylans population estimates φ = 0.714 (0.244) φ = estimate of daily survival (standard error)

9. V. inflata population estimates φ = 0.853 (0.027)

10. V. pellucens population estimates  = 0.765 (0.013)

11. Summary of population estimates Estimate of the total population of each speciesusing Schnabel’s method, Krebs (1989)

12. Some emerging questions? • How big is the population of V. bombylans ? • The wood is only 35 hectares! It is difficult to believe: • There are sufficient sap runs large enough to support the larvae of 650 V. inflata • There are sufficient social wasps’ nests to support 2,000 V. pellucens

13. Longevity

14. Distance moved by recaptured individuals of V. bombylans

15. Behaviour of V. bombylans • Mating strategy well known: males perch on prominent foliage and dart out at passing insects • Our results suggest males are quite mobile. Therefore likely male does not return to the same perch each day • Males moved more than females

16. Distance moved by recaptured individuals of V. inflata

17. Behaviour of V. inflata • Both sexes mainly captured around flowers • Males make rapid flights around nectar sources (bramble & shrubs) • Only one observation of copulation: male flew high round dogwood (Cornus sanguinea) and briefly coupled with female in flight • Males moved much less than females • Some evidence that males held a territory

18. Distance moved by recaptured individuals of V. pellucens

19. Details of movements of male V. pellucens Consecutive captures of the same individual

20. Behaviour of maleV. pellucens

21. Behaviour of V. pellucens • Mating strategy well known: males hover and defend an air space, dart after passing insects • Male hovering extremely sensitive to sunshine: • When the sun goes in they rapidly perch in trees • When it comes out again, equally rapidly resume hovering • Copulation observed just once. Coupling appears to be very brief and in flight, like V. inflata

22. Behaviour of V. pellucens (2) • Both sexes visit flowers early during emergence and are fairly mobile • Later on males almost exclusively caught hovering and become very immobile • Some evidence that males hold a territory, sometimes over several days • As season progressed, it was much more likely an individual male would be found at the same hovering post • Suggests fierce competition for hovering posts early on leads to rapid turnover

23. Potential for further study • Our knowledge of V. bombylans population size is incomplete • Detailed survey for potential breeding sites is needed to better understand the population dynamics of V. inflata • Questions remain over the degree to which V. pellucens moves from breeding sites to suitable territories for mate-acquisition

24. ANYQUESTIONS?