Low frequency signal patterns for codling moth larvae activity in apples

Codling moth (CM) infestation poses a serious threat to agricultural export and import for apple growers and aggregators. The detection of infestation often requires destructive testing before export. Infestation detection is particularly problematic when the larva enters the apple through the calyx without apparent damage on the skin of the fruit. This work considers the use of low frequency (0.4 to 8 Hz) Lead zirconate titanate (PZT) sensors to enhance the detection of infestations non-destructively while monitoring larvae activities. This paper presents experimental results of a novel approach that correlate larvae's activities, such as chewing and body movements, with patterns in the vibro-acoustic signal transduced by contact PZT sensors. Experiments were performed to correlate various CM activities to specific signals. In these experiments, CM infested apples were sliced, and a digital camera was used to capture activities while simultaneously registering the signal patterns observed in the PZT signal. The chewing signals show a chewing rate of 1 to 2.3 times a second with internal movement signals showing large transient spikes at irregular intervals above the noise floor. In addition, results from uncut infested apples are also presented showing the occurrence of similar patterns in infested apples. These results suggest that CM activities (chewing and displacement) are mostly responsible for vibro-acoustic signals detected in infested apples. This understanding will enhance the use of acoustic signals in nondestructive detection of CM in apples. There is a need to expand this test to other varieties of apples and larvae at different stages.