The influence of host deprivation and egg expenditure on the rate of dispersal of a parasitoid following field release

With a view of improving the establishment of Mastrus ridibundus, a potential candidate for the biological control of the codling moth in California, a series of studies were undertaken to investigate the effect of a pre-release treatment with or without hosts on different performance characteristics. The post-release dispersal of M. ridibundus females was investigated in this study, using mark-release-recapture experiments with immunological markers. The results suggest that, in general, M. ridibundus is high dispersive. In the absence of any host stimuli for at least 4 days before release, females showed a strong dispersal response with an average dispersal rate of 81.50 m2/h. In contrast, females continuously provided with hosts before release or deprived of hosts for only a short period of time (1–2 days), showed a lower rate of dispersal averaging 2.07 m2/h. These results suggest that to enhance local establishment in a fragmented environment parasitoids should be given access to hosts prior to release. In contrast, for regional establishment in a less fragmented environment, host deprivation could be used to encourage broader dispersal if large numbers can be released at each release site to counteract the dilution effect of dispersal.