Colour matching for recognition of Spodoptera litura larvae infected with baculavirus

Biopesticide is one of the most promising biological insecticides for insect pest control to date. Spodoptera litura Nucleopolyhedrovirus (SpHNPV), a member of the family Baculoviridae, has been used for the control of army worm, Spodoptera litura. To commercialize NPV as a biopesticide product, the harvesting of SpHNPV-infected Spodoptera litura is done manually by screening the external symptom. This process is currently done by human expert and time-consuming. Therefore, an image processing system based on color-matching technology to identify SpHNPV-infected Spodoptera litura larvae is proposed. The present study was conducted to construct a color matching system for recognition of SpHNPV infected Spodoptera litura larvae. Third instar larvae were inoculated with NPV at a dosage of 10 sup 6 occlusion bodies using leaf disc method. The leaf disc treated with distilled water was served as control. Both categories of larvae were fed with leaf diet. Three parts of the larval body were identified showing significant color changes at the initial stage. The three parts were at the side beside the yellow lines at dorsal, the middle of the dark patch on the mesothorax at ventral and the middle of the last proleg at ventral. R (red), G (green) and B (blue) color coordinate data was collected from all parts and the levels of infection were developed based on the color range of each part. The levels of infection consisted of post infection level, intermediate infection level and serious infection level. Among the three parts, only RGB color coordinate at the side beside the yellow lines at dorsal showed a significant difference among control and diseased larvae at respective level of infection. The validation of samples using color matching recognition method based on the side beside the yellow lines at dorsal gave the best matching percentage up to 100%. Therefore, the color matching for recognition of SpHNPV-infected Spodoptera litura larva can be done based on the side beside the yellow lines at dorsal.