Environmental Engineering Reference
In-Depth Information
11.3.2.5 Trial of aerial baiting
The aims of the trial of aerial broadcast were threefold:
1)
To assess the effi cacy of Presto
®01 delivery by helicopter for controlling
supercolonies against a target of 99% knockdown.
To identify the lowest effective rate of Presto
2)
®
01 for supercolony control.
To assess the degree of bait penetration through the canopy to ground level.
3)
h e e
cacy of aerial bait delivery for supercolony control was assessed using a
before-after-control-impact design. h e CIGIS was used to delineate 6 plots (each
9-53 ha) in supercolonies, two for each application rate plus two untreated control
plots. In each plot YCA activity was monitored on cards (Abbott 2005) placed at
44 stations along four parallel transects (each 150 m long and 40 m apart), three
times before and eight times after aerial baiting.
Some aerial broadcast bait is likely to be intercepted by the forest canopy, redu-
cing the amount reaching the forest fl oor. Even though the YCA forages extensively
in the forest canopy (O'Dowd
et al
. 2003, Abbott and Green 2007) and would be
likely to collect suspended bait, decreased bait reaching the forest fl oor could com-
promise control. Penetration of bait dispersed through the canopy was estimated
with 30 one m
2
catch bags along the transects in each plot. Large plastic bags were
stapled to a circular wire hoop held up by wooden stakes. Catch bags were placed
in the plots 2-3 hours before aerial baiting and emptied 3-4 hours after treatment.
h e catch bags were emptied again 3-4 days later in case more pellets fell from the
canopy, and the catch dried and weighed.
Bait application rates averaged 5.9 kg/ha and 4.4 kg/ha on the high and low
application plots, respectively, very close to the target rates of 6-4 kg/ha. Eighty
percent of catch bags intercepted
>
90% of bait within 3-4 hours of application.
h e mean rate of bait penetration was 59.2% across all plots. Although a consid-
erable fraction of bait was intercepted by the canopy, YCA activity declined dra-
matically following aerial baiting. Aerially-dispersed Presto
®
01 had a signifi cant
negative impact on crazy ant activity within days of treatment, at both rates of
application. Ant activity on the control plots was high during the week preceding
treatment and remained so during the week after treatment. Conversely, on the
baited plots, ant activity in the week after aerial treatment declined by an average
of 91% of pre-treatment levels, and was essentially nil after 12 days, regardless of
application rate and su
cient to achieve
>
99% knockdown. Five days after the
trial, the Steering Committee endorsed the full treatment of all remaining super-
colonies on Christmas Island, at a nominal rate of 4 kg/ha.
11.3.2.6 Measuring the success of the island-wide operation
Success of aerial operations was assessed in terms of both the coverage and accuracy
of the baiting operations, and the impact on YCA activity. GPS downloads from
the helicopter indicated almost blanket coverage of all target supercolonies, more
than 2500 ha in just 8 days. The few mistakes included 3 ha that were baited in
