چکیده :
Phenacoccus solenopsis Tinsley, a native of North America, is a widespread exotic mealybug infesting cotton,
Gossypium spp. in several countries. Monitoring of this pest is generally undertaken through regular
field surveys, which is labour intensive, time consuming and error prone. Alternately, radiometry is a reliable
technique for rapid and non-destructive assessment of plant health. Thus, a study was conducted to
characterize reflectance spectra of cotton plants with known mealybug infestation levels (grade-0 is
healthy and grade-4 is severe), and seek to identify specific narrow wavelengths sensitive to mealybug
damage. Reflectance measurements were made in the spectral range of 350–2500 nm using a hyperspectral
radiometer. Significant differences were found in green, near infrared and short wave infrared spectral
regions for plants with early stages of P. solenopsis infestation, and for plants showing higher grades
of infestation these differences extended to all the regions except blue. A significant reduction in total
chlorophyll (12.83–35.83%) and relative water content (1.93–23.49%) was observed in the infested plants.
Reflectance sensitivity analysis of the hyperspectral data revealed wavelengths centered at 492, 550, 674,
768 and 1454 nm as most sensitive to mealybug damage. Mealybug Stress Indices (MSIs) were developed
using two or three wavelengths, tested using multinomial logistic regression (MLR) analysis and compared
with other indices published earlier. Results showed that the MSIs were superior () to
all other spectral vegetation indices tested. Further, the proposed MLR models corresponding to each
MSIs were validated using two independent field data sets. The overall percent correct classification of
cotton plants into different mealybug damage severity grades was in the range of 38.3 and 54.9. High
classification accuracy for grade-1 (81.8%) showed that models are capable of early detection of mealybug
damage. Results of this study could suggest potential usage of remote sensing in monitoring spatial and
temporal distribution of the solenopsis mealybug, and thereby enable effective planning and implementation
of site-specific pest management practices.
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