# Near-Real-Time Detection of Insect Outbreaks in Urban Trees Using a PlanetScope Time Series
## 4 Discussion
Correlating these periods with the vegetative cycle of _Pinus pinea_ highlights the concomitance between vegetative stress and the insect's infestation, which significantly affects the plant's vitality compared to a non-infested tree (Figure 4). A further element that supports the consistency of the results and the usability of the proposed approach for monitoring activities is the supplementation of remote-sensing data with in situ surveys. These surveys are useful for focusing the analysis on areas where infestation presence is known with certainty, thus allowing the spectral behavior of those areas to be studied in a targeted and limited way. This is particularly important in an urban context, where there is great heterogeneity in land cover and variability even within the tree cover, both in terms of plant placement and species diversity [64; 65]. This can be problematic in areas with complex vegetation structures, where the signal from non-target species or underlying substrates (e.g., buildings, roads, or other ground cover) can overlap with the spectral signal from _P. pinea_. Through the georeferencing of trees using ground surveys, it was possible to accurately identify the pixels relating to _P. pinea_[32], enabling a deeper analysis of their spectral behavior. Another confounding factor is the great variability in the size and health status of pine canopies. Age, tree size, crown density, and environmental stressors can cause significant differences in spectral reflectance, even within a single species. For this reason, georeferenced pixel values were preferred over average canopy value, as the latter could introduce more noise into the remote sensing-data extraction [66]. Comparing the normal distributions of the RDVI\({}_{\text{sua}}\) for the infested areas and the control area (with trees free of infestation and in good health), it was possible to define a threshold value of RDVI of 33.1, which can be used as a reliable criterion for separating damaged areas from intact ones. In this sense, the index can be useful in supporting monitoring activities, providing preliminary information for identifying diseased trees with low implementation costs and high timeliness. Considering this value, it is possible to discriminate between healthy and diseased areas with an overall accuracy of over 99%. In any case, healthy trees belong to a natural and protected area (i.e., Parco Regionale Migliarino, San Rossore, and Massaciuccoli), and, consequently, the photosynthetic activity of these plants may already be better than that of plants in an urban area [67]. This result showed consistency not only due to the long observation period but also due to the size and heterogeneity of the study area considered, which goes beyond homogeneous pine forests in the natural environment [68] to focus on trees in the urban area [63]. Potential and New ChallengesAs [PERSON] et al. [69] observed in their review, field data constitute a crucial element in the study of forest insect disturbances, particularly in the context of remote sensing. For this reason, it is important to evaluate the efficacy of the treatments employed to control insect spread. Unfortunately, no comprehensive information on these treatments was available for this study. The municipality of Rome has conducted and continues to conduct endotherapy cycles in the most affected areas. However, complete information regarding the timing and modalities of these cycles is currently unavailable. Consequently, the interpretation of the results was also influenced by this deficiency. In addition to endotherapy, the _T. parvicornis_ treatment guidelines [70] recommend crown thinning. This technique is employed to mitigate the proliferation of _T. parvicornis_. It is therefore pertinent to highlight that in instances where maintenance has been conducted appropriately, the trees in question have undergone a significant degree of thinning. In the absence of the insect, ordinary pruning would have been carried out and not extraordinary pruning, as was the case [71].