increase in other invertebrate density in general with an increase in invertebrate size classes (Richards. 2010). This finding has potential significance for the survival of any insectivore on Christmas Island through feeding competition between them and YCA (starvation). The data from this study indicate that boric acid baits suppress YCA, without impacting negatively on other invertebrates, but rather allows for the re-colonisation of native insects in the trial site. Further the data show that there was a decrease of YCA numbers in all three baited sites with an absence of YCA in the Greta area from August 2010. With reference to the back-to-back sampling at South Point trial and Fipronil aerial baited sites the data to date indicates that the South Point boric acid trial site has a 2.3 fold more invertebrates than the control site and, to 5 to 6.2 times more invertebrates than either the Fipronil aerial baited sites. Analysis of the preliminary insect data collected at the two aerial baited areas compared to the trial and control areas at South Point trial site show that there may be evidence that Fipronil baited areas have a lag time for re-colonisation by native invertebrates of the area. The preliminary data from this trial also indicates that in the Fipronil aerial baited sites there is a significant lag in the time before re-colonisation of invertebrates after baiting has ceased. From the study of the two Fipronil aerial baited sites which were baited on 15 September 2009, the data (collected six months after the fipronil baiting) show that between 5 and 6.2 fold more invertebrates are found within the DOT baited trial site in South Point, compared to that baited with Fipronil. This could be caused by the residual adverse effect of Fipronil on invertebrates. This is a significant observation. If it is confirmed in subsequent sampling it would indicate that Fipronil baiting could be having an adverse effect on Christmas Island ecosystems. However according to a report commissioned by the Director of Parks Australia on monitoring of the aerial baiting using Fipronil in 2009 the conclusion was that there was no noticeable evidence of any impacts on non-target invertebrates (Weeks and McColl, 2011).
8. CONCLUSION
From the analysis of the trial data there is strong evidence that boric acid is aneffectivebait for the control of YCA, and that it is a safer and significantly more environmentally friendly approach to control YCA compared to the present Fipronil baiting regime on Christmas Island. Invertebrate counts show increases in numbers at all three trial sites, all sites showed a suppression or reduction in YCA density, with a total absence of YCA from the Greta Beach trial site. Observations of the Greta Beach baited site suggested that there has been a substantial decrease in scale insect numbers (including some trees showing mortality of the scale insect on branches) with an increase in leaf cover. This is assumed to be due to the removal of the YCAs from the area and the disruption of the primary mutualistic relationship (Davis
et al
, 2009; Von Holle, 2011) between YCA and scale insects