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.

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 cells).

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 t-1/nt]

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 t-1/nt+1]

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.

Criterion C

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.

Back to the STS Decision-Support system

    For more information, please contact Patrick Tobin or Andy Roberts
    Maintained By Jiang Wu