## 3 Results and Discussion  
### Qualitative Description of Biospeckle Activity  
The example graphical outcomes obtained by the AD and GD methods is presented in Figure 4. The dark blue colour represents regions with low BA, whereas the dark red colour corresponds to the highest BA. Images show the whole area illuminated by the laser, so circular boundaries of the beam may be noticeable. In the late stage of infestation, fruits started to deform; thus the irregular shape of the illuminated region. The left column of Figure 4 contains activity maps of the uninfested sample. Results obtained by both methods clearly indicated that the tested fruits had very low biospeckle activity. Highbush blueberry is a climacteric fruit, which means that after harvesting, processes related to respiration and transpiration take place, but its rate of ethylene production was much lower than in other typical climacteric fruits, e.g., apples, with activity maps showing higher values [16].  
The middle column in Figure 4 shows activity maps of a fruit with visible signs of puncture on its skin.  
Since fruits were positioned with scar or scars facing the camera lens, it would be expected that the oviposition site, or its near location, would show a different (higher) biospeckle activity, because scars are often attacked by other pathogens, most often fungi. Activity maps obtained by the GD method revealed regions wherein biospeckle activity slightly increased. An example map in Figure 4 contains two brighter areas, one on the upper left side of the fruit and the other slightly lower on the right edge of the illuminated area. On activity maps generated by [PERSON]'s method, these areas were not visible or were barely visible, as shown in Figure 4. The rightmost column of Figure 4 presents biospeckle activity of a sample inspected 48 h after removing it from the rearing container. By this time, larvae started feeding inside the flesh, and skin at the puncture site collapsed. Results obtained with the [PERSON]'s method contained areas of increased activity, which were a little more visible than in the previous phase. Their contours, however, appeared blurred as shown in Figure 4. Such a result may indicate that the dynamics of intensity transitions were low. [PERSON]'s method analyses only consecutive frames in the sequence, which provides temporal information [28,29]; thus, the low frequency of changes resulted in poor representation on the activity map. This effect may also be related to the frame rate being too high in relation to the frequency of speckle intensity changes. Activity maps generated by the GD method resulted in much better contours of regions of heightened biospeckle activity and, in some cases, pipe-like shapes occurred as shown in Figure 4. Given previous considerations, as well as the shape of the active areas discovered by the GD method, it cannot be ruled out that not only destruction of the fruit flesh caused by the larvae feeding may be the source  
Figure 4: Example maps of biospeckle activity generated by the average difference method (**a–c**) and generalized difference method (**d–f**). Maps from left to right show stages F0 (uninfested sample), F24 (24 h after exposure), and F72 (72 h after exposure) of example fruit No. 03. Dark blue and red colours correspond to the lowest and the highest values respectively. ‘Max’ stands for the maximum value of general differences.  
of BA, but also the larvae themselves. Better representation of BA by GD outcomes results from a different calculation protocol that incorporates intensity differences between all frames including nonconsecutive ones [16]. Since analysis of BA of highbush blueberry aim mostly at detection of a pest, the information about the temporal variability in pixel brightness is ultimately less essential. Therefore, the GD method may prove more useful for detecting BA especially if it is not uniform within the investigated area [39], as for samples from F24 or F72 series.