Spread of the Wasp Parasitoid Sphecophaga Vesparum Vesparum following Its Release in New Zealand

If one or more parasitised nests were found in an annulus which had few nests dug in total, the results were pooled with those of an adjacent annulus in order to give a total of at least 10 nests before calculating the dispersal distance. The annuli were 0.2 km wide up to 2 km from the release site then 0.5 km wide thereafter (see Table 1). Aggregating the data and annuli into fewer groups with larger total numbers of nests in each had little effect on the resulting estimates of mean displacement. Percentage parasitism is analogous to recaptured insects per trap in Southwood’s (1981) description of the method, so long as the density of wasp nests within each annulus is constant. In the absence of evidence to the contrary and in view of the broadly similar densities found throughout Nothofagus forests in the area (Barlow, Moller and Beggs, 1996), this was assumed to be the case. The other major caveat is that the full outward displacement of the parasitoid is encompassed within the annuli searched, since recoveries in the furthest annuli contribute particularly significantly to the weighted average distance (Southwood, 1981). It is unlikely that this condition was met, particularly in the last few years of the study, so estimates of mean parasitoid dispersal distances will be conservative. Introduction