Ground based thermographic screening of bagworm (Metisa plana Walker) infestation in oil palm and identification of their growth stages

Abstract

Bagworms (Lepidoptera: Psychidae) are one of the main species of vicious leaf-eating insect pests that affects oil palm plantations in Malaysia. A moderate bagworm attack of 10-50% leaf damage may cause 43% yield loss. In 2020, the economic loss due to the bagworm attack in Malaysia is estimated as RM 180 million. Hence, it is necessary to monitor closely the bagworm outbreak in infested areas. However, precise data collection with accuracy is a challenging task. In this context, we explored the possibility of using thermal infrared (TIR) cameras (T 440) for detection of bagworms and identification of bagworm growth stages at the infested areas for effective monitoring. The reflector method was applied to detect the reflected apparent temperature and emissivity of the bagworms using thermographic measurement techniques. The results have revealed that the bagworms from the 1st to 7th larval instar and pupal stages exhibit emissivity values ranging from 0.88 to 0.89. Two rounds of our observation have shown that the bagworms can be detected during evening and afternoon vision as compared to night, midnight and morning vision, with consideration of emissivity, solar radiation, and snapshot distance at a percentage accuracy of 74 and 85%, respectively. The classification of the larval and pupal stages was carried out by grouping the larval and pupal stages based on their real size; Group I: larval stage 1-3, Group II: larval stage 4-7; and Group III: pupal stage. Identification of the bagworm stages according to the classified group and the object led to differentiation between the larval stages from Gr. I, II, and III, with the per cent detection of 60, 84 and 89%, respectively. The results indicate that the thermographic imaging approach can be applied to detect bagworms, provided all conditions and time observation are taken into consideration. This thermographic technique deserves thorough testing and optimization for detection of bagworms in oil palm plantations.