Dispersing Rice-Associated Arthropods Ignore a Phantom Ultrasonic Insect Chorus

The acoustic environment can provide fitness-enhancing information to dispersing animals. Tropical irrigated rice ecosystems host an exceptionally rich assemblage of sound-producing animals, including meadow katydids (Tettigoniidae, Conocephalinae, Conocephalini) which produce ultrasonic choruses. We aimed to test whether aerial arthropods were attracted to, deterred by, or indifferent to an experimental ultrasonic katydid chorus.

A 100-speaker array installed in a newly planted Philippine rice paddy served as a “phantom chorus” and was turned on and off hourly for 2-4 hours on 30 nights during the first half of the growing cycle which is naturally katydid-free. Aerial arthropods were sampled hourly using three passive intercept traps: one nested within the speaker array paddy, one in a paddy with poles and lines but no speakers, and one in an empty paddy. Arthropods were subsequently identified and sorted by functional guild and family.

We captured 2078 arthropods representing 158 species. Detritivores comprised 34% of captured arthropods and decreased significantly in abundance with days after planting. Alternatively, (aquatic and general) predators and herbivores both increased over time and represented 48% and 8% of captures, respectively. None of the analyzed arthropod functional guilds or taxonomic families exhibited a statistically significant response to the phantom chorus.

Our results suggest that meadow katydid choruses may neither attract nor deter arthropods characteristic of early-stage rice. We recommend further experiments deploying a more robust ultrasonic playback system at sites and during rice stages with more herbivorous rice pests.

Ultrasonic noise treatments applied during early rice growth stages may have a neutral effect on non-pest species; however, we encourage further studies to test whether ultrasonic katydid choruses serve as natural pest repellents in tropical irrigated rice.