Methods for Evaluating Treatment Success
Index of treatment success T
Criterion T indicates how much of the reduction in moth counts in pheromone
traps was caused by the treatment. In short, it is equal to the ratio:
1 - Moth Counts After Treatment / Moth Counts Before Treatment
If T > 0.67, then there is at least 3 times reduction in moth counts after
treatment. If the population was not treated, it would increase in numbers by
50-100% in the next year. Thus, 3 times reduction in moth counts corresponds to
mortality of 78 - 84% caused by the intervention activity. These levels of mortality
are usually considered satisfactory in field trials of pest control.
- Treatment was successful if T > 0.67
- Treatment was partially successful if 0.67 < T < 0.33
- Treatment failed if T < 0.33
Successful treatment does not necessarily mean that the colony has been eradicated.
If the initial population numbers were high, then several successful treatments
may be needed to complete the eradication.
The reduction of moth captures in the treatment block should be compared with
moth capture change in the 'control' area around it. The control area is set
within the 24 x 24 km area as shown in the picture below.
If the length or width of the treatment area is >12 km, then the control area
is enlarged so that its height and width are at least twice as large as the
treatment block. Then a 0.5-km grid is set over the treatment block and control
area. Cells that intersect with the treatment block are considered 'treatment
cells'. Neighboring cells (at a distance of 1.5 km) are 'buffer cells' and the
other cells are 'control cells'. Buffer cells are not used in the analysis.
If another treatment block appears in the control area, then the cells that
intersect with that block are discarded (they are not considered as control
Moth counts in pheromone traps are interpolated in the 0.5-km grid of cells using median indicator kriging with subsequent E-type estimation (Deutsch and Journel 1992). Then these interpolated values are averaged separately among treatment cells and control cells.
Index of treatment success is estimated using the equation:
T = 1 - [Nt/Nt-1]*[n
where Nt and nt are average moth counts in year t in the
treatment block and in the control area around it, respectively. Treatment is
assumed to be in year t. If treatment had no effect, then the change
in moth counts within the treatment block should be proportional to the change
in moth counts in the control area, i.e.,
Nt/Nt-1 = nt/nt-1
Then, T = 0. If T > 0, then treatment has reduced moth captures. In the
case of mating disruption or intensive trapping, evaluation is performed in
the following year t +1, and the equation for T becomes:
T = 1 - [Nt+1/Nt-1]*[n
If moth counts in the control area are too low, then the equations above are very
sensitive to the change of moth capture in a single trap. Thus, if average moth
captures in the control area are <0.05 per trap, then the equation for estimating
T is modified:
T = 1 - Nt/Nt-1
If this equation is used, then the value of T is marked with an asterisk in the table.
The final goal of managing isolated colonies in the STS project is to reduce population
numbers to the background level in the neighboring areas. In the areas far beyond
the population front, the background moth counts in pheromone traps are close
to zero. Thus, the colonies that are found in these areas should be eradicated,
i.e., moth captures should be reduced to the zero level. But in areas located
closer to the population front, the background moth counts may be 1-2 moths per
trap. There, the goal of colony management is not necessarily a complete eradication
but at least a reduction of moth counts to the background level.
Criterion C is used to evaluate how close we are to the goal of bringing
moth counts in the treatment block to the background level. It is estimated
as a ratio of average moth captures in treatment cells and control cells, i.e.,
C = Nt/nt
If C = 1, then moth counts in the treatment block are the same as in
the control area outside, i.e., the goal of colony management is reached. If
C > 1, then additional treatments may be necessary in the following year.
If the criterion C is high, it does not necessarily mean that treatment
was not successful, but it indicates that additional treatments are needed.
Colonies with a high initial density may require multiple successful treatments
to bring the criterion C to 1. Each successful treatment decreases the
value of C, and when C becomes equal to or less than 1, the goal
is reached and treatment is not applied in the following year. Thus, criterion
C should be viewed as an indicator of a long-term success in managing a colony.
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For more information, please contact Patrick Tobin or Andy Roberts
Maintained By Jiang Wu