Effects of Anastrepha striata & Anastrepha ludens on Guava Cultures in Mexico: A Remote Sensing Approach

Remote sensing techniques have been incorporated for the detection of the presence of plagues affecting plants and animals for over two decades. The presence of Anastrepha striata and Anastrepha ludens in guava cultures is currently being detected in Mexico by catching the flies in properly placed traps. The goal of this research is to show that remote sensing may be used to discover locations where flies are present or absent, simplifying the typical method of detecting these plagues. In the field, groups of traps were selected where flies had been captured, as well as areas in which there was no capture in the traps. The radiometric signatures of complete trees and leaves were acquired, revealing substantial differences between plagued and unaffected species. Then we chose a SPOT5 image from 2007 that corresponded to the study region in Calvillo, Aguascalientes, Mexico, one of the major areas of guava cultures in the country. The location of guava cultures in the image was made possible via supervised classification. The guava culture areas obtained from this classification were validated comparing them to available maps of the cultured areas. The image data was used to create spectral signatures for each class. In order to maximise separation between classes, the separability of pairs of classes was also assessed. The IR/R (infrared to red ratio) ratio of the image bands was evaluated in 80 x 80 pixels around the locations of five traps where flies had been captured, and around five locations where the traps had not captured flies. Other forms of vegetation and soil coverage were eliminated, therefore only pixels with guava cultures were included in the analysis. The index distributions with flies taken and those without flies collected clustered into two distinct groups, according to our findings. We note that plotting the whole distribution of pixels around a trap yields a diagnostic view of the area, and individual index values do not provide such a view, since values with the flies’ presence and without these overlap to some extent. Further analysis of other trap locations supported this split and also identified a third group of intermediate values between the two above, that are interpreted as locations in which the guava cultures are affected by the plague at an early stage of development, where the flies are not captured by the traps since they do not yet hatch. We concluded that remote sensing techniques can be used to detect the presence of Anastrepha striata and Anastrepha ludens in Psidium guajava L. cultures, even at early stages of plague development. These results also suggest that a systematic analysis by means of satellite images is warranted in the detection of the presence of Anastrepha striata & Anastrepha ludens, which would complement the present techniques of physical capture of flies.