There are several harmful and yield decreasing arthropod pests, which live within plant tissues, causing almost unnoticeable damage, e.g. Ostrinia nubilalis Hbn., Cydia pomonella L., Acanthoscelides obtectus Say. Their ecological and biological features are rather known. The process leading to the damage is difficult to trace by means of conventional imaging tech- niques. In this review, optical techniques—X-ray, computer tomography, magnetic resonance imaging, confocal laser scan- ning microscopy, infrared thermography, near-infrared spectroscopy and luminescence spectroscopy—are described. Main results can contribute to the understanding of the covert pest life processes from the plant protection perspective. The use of these imaging technologies has greatly improved and facilitated the detailed investigation of injured plants. The results provided additional data on biological and ecological information as to the hidden lifestyles of covertly developing insects. Therefore, it can greatly contribute to the realisation of integrated pest management criteria in practical plant protection