Acoustic devices provide nondestructive, remote, automated detection, and monitoring of hidden insect infestations for pest managers, regulators, and researchers. In recent decades, acoustic devices of various kinds have been marketed for field use, and instrumented sample containers in sound-insulated chambers have been developed for commodity inspection. The efficacy of acoustic devices in detecting cryptic insects, estimating population density, and mapping distributions depends on many factors, including the sensor type and frequency range, the substrate structure, the interface between sensor and substrate, the assessment duration, the size and behavior of the insect, and the distance between the insects and the sensors. Considerable success has been achieved in detecting grain and wood insect pests. Microphones are useful sensors for airborne signals, but vibration sensors interface better with signals produced in solid substrates, such as soil, grain, or fibrous plant structures. Ultrasonic sensors are particularly effective for detecting wood-boring pests because background noise is negligible at > 20 kHz frequencies, and ultrasonic signals attenuate much less rapidly in wood than in air; grain, or soil. Problems in distinguishing sounds produced by target species from other sounds have hindered usage of acoustic devices, but new devices and signal processing methods have greatly increased the reliability of detection. One new method considers spectral and temporal pattern features that prominently appear in insect sounds but not in background noise, and vice versa. As reliability and ease of use increase and costs decrease, acoustic devices have considerable future promise as cryptic insect detection and monitoring tools.

Stored-product insects are a perennial problem in retail stores, where they damage and contaminate susceptible merchandise such as food products and

Acoustic technology provides information difficult to obtain about stored insect behavior, physiology, abundance, and distribution. For example, acoustic detection of immature insects feeding hidden within grain is helpful for accurate monitoring because they can be more abundant than adults and be present in samples without adults. Modern engineering and acoustics have been incorporated into decision support systems for stored product insect management, but with somewhat limited use due to device costs and the skills needed to interpret the data collected. However, inexpensive modern tools may facilitate further incorporation of acoustic technology into the mainstream of pest management and precision agriculture. One such system was tested herein to describe Sitophilus oryzae (Coleoptera: Curculionidae) adult and larval movement and feeding in stored grain. Development of improved methods to identify sounds of targeted pest insects, distinguishing them from each other and from background noise, is an active area of current research. The most powerful of the new methods may be machine learning. The methods have different strengths and weaknesses depending on the types of background noise and the signal characteristic of target insect sounds. It is likely that they will facilitate automation of detection and decrease costs of managing stored product insects in the future.

Accelerometer, electret microphone, and piezoelectric disk acoustic systems were evaluated for their potential to detect hidden insect infestations in soil and interior structures of plants. Coleopteran grubs (the scarabaeids Phyllophaga spp. and Cyclocephala spp.) and the curculionids Diaprepes abbreviatus (L.) and Otiorhynchus sulcatus (F.) weighing 50–300 mg were detected easily in the laboratory and in the field except under extremely windy or noisy conditions. Cephus cinctus Norton (Hymenoptera: Cephidae) larvae weighing 1–12 mg could be detected in small pots of wheat in the laboratory by taking moderate precautions to eliminate background noise. Insect sounds could be distinguished from background noises by differences in frequency and temporal patterns, but insects of similarly sized species could not be distinguished easily from each other. Insect activity was highly variable among individuals and species, although D. abbreviatus grubs tended to be more active than those of O. sulcatus. Tests were done to compare acoustically predicted infestations with the contents of soil samples taken at recording sites. Under laboratory or ideal field conditions, active insects within ≈30 cm were identified with nearly 100% reliability. In field tests under adverse conditions, the reliability decreased to ≈75%. These results indicate that acoustic systems with vibration sensors have considerable potential as activity monitors in the laboratory and as field tools for rapid, nondestructive scouting and mapping of soil insect populations.

We examined the substrate-borne vibrational signals used in communication between the sexes in Diaphorina citri Kuwayama (Hemiptera: Psyllidae), a vector of huanglongbing (an economically devastating disease of citrus), in an anechoic chamber and an olfactometer. Males and females both primarily produced simple, low-amplitude vibrational signals at multiples of 170-250 Hz, ranging in duration from 140 to 700 ms. The vibrational frequencies of males and females were negatively correlated with mass, but the correlation was statistically significant only for males. Females replied to male calls within an interval of 0.3-1.2 s. Such signals are within the ranges of signals observed for other psyllids. Female-female interactions were occasionally observed. Intervals between male calls were not significantly different whether or not females replied. In an olfactometer, calling rate did not differ between virgin males exposed to odors from virgin females on citrus versus those exposed only to clean air. However, the latent period for initialization of calling was significantly shorter for males exposed to clean air, suggesting that in the absence of olfactory cues psyllids might be more inclined to use acoustic signals to communicate with conspecifics. Moreover, calling rate and latency to initialization of calling were positively and negatively correlated, respectively, with male age, suggesting that males are more likely to call the longer they remain unmated.