Ryo Nakano, Akio Ito, and Susumu Tokumaru

PNAS October 10, 2022; 119 (43) e2211007119

Significance

Global warming probably increases occurrence and migration levels of agricultural pests (e.g., armyworms and desert locusts), which are typically regulated with chemical insecticides; however, minimizing the unwanted effects of such chemicals on nontarget organisms and the environment is a priority for sustainable crop production. Here, we show the implementation of synthetic ultrasounds in plant protection against moth pests, which have evolved ultrasound-sensitive ears and evade predatory bats that emit ultrasonic echolocation calls. The intrusion of eared moths into crop-producing fields was suppressed where ultrasound-equipment repelling major moth pests without leading to auditory adaptation was active. Synthetic ultrasounds reduce the need to apply insecticides to target moths, which contribute to mitigate damage to agroecosystems and development of insecticide-resistant pests.

Abstract

Nocturnal moths evolved ultrasound-triggered escape maneuvers for avoiding predatory bats emitting ultrasonic echolocation calls. Using ultrasound for pest control is not a novel concept, but the technique has not been systemized because of the moths’ habituation to sounds and the narrow directionality of conventional ultrasound speakers. Here, we report the use of pulsed ultrasonic white noise, which contributes to achieving ecologically concordant plant protection. An ultrasonic pulse, which is temporal mimicry of the search-phase pulse in the echolocation calls of a sympatric bat, was identified using neuroethological screening of eared moth–repelling ultrasounds; these pulses elicit flight-stopping reactions in moths but have no or little auditory adaptation. Such repellent ultrasounds broadcast from the cylindrical omni-azimuth ultrasound emitters suppressed the intrusion of gravid females of pest moths into cultivation fields. Thus, egg numbers and plant damage by hatched larvae were drastically reduced, enabling farmers to substantially skip applications of chemical insecticides for controlling moth pests.

See https://www.pnas.org/doi/10.1073/pnas.2211007119

Figure 1: Auditory characteristics in Spodoptera moths. (A) Tympanic ears of S. litura located on the lateral metathorax (denoted by a circle). Inset: Magnified SEM image of the right tympanic membrane. (B) Frequency tuning curves in S. litura (Left; n = 3 males and 2 females) and S. exigua (Right; n = 3 males and 3 females). Auditory thresholds differed among sound frequencies within species (P < 0.0001), but differences were not found between sexes in each species (P = 0.93 for S. litura and P = 0.25 for S. exigua). The shape of tuning curves did not differ between the two species (P = 0.44). Circles, lines, and shaded areas around the lines denote individual data, estimated mean response curves, and 95% confidence intervals of the mean, respectively. (C) Power spectrum of the sound stimulus, i.e., broadband ultrasonic white noise, used in the laboratory experiments. (D) Auditory thresholds to the broadband ultrasound stimuli in S. litura (n = 4 males and 4 females) and S. exigua (n = 5 males and 4 females). There were no differences between species (P = 0.11) or sexes (P = 0.48). Small circles, bold circles, and bars denote individual data, estimated mean values, and 95% confidence intervals of the mean, respectively.