Non-consumptive Effects Of Bat Echolocation Calls On Spodoptera Exigua

Predation risk shapes the density and traits of prey.Bat-moth interactions are a classic model for studying predator-prey relationships.Nocturnal moths have evolved auditory receptors for early perception of bat echolocation calls and escape from the source under strong predation pressure from echolocating bats,which greatly reduces the chance of eared moth being predated by bats.Even so,moths as prey are induced to undergo density and trait regulation by ultrasound waves emitted by bats,and such effects will continue throughout the life history of the pest.To quantify the non-consumptive effects of the bat soundscape of fear to eared moth,we assessed differences in moth response to calls of different spectral features and clarified the indirect ecosystem services provided by bats in agroecosystems.We selected a cosmopolitan crop pest,the beet armyworm,Spodoptera exigua(Lepidoptera,Noctuidae),as the subject of our study.We recorded three species of bats in the field: two species of bat,Rhinolophus pusillus and Rhinolophus macrotis that prey on the S.exigua;an echolocation calls of a bat Eptesicus pachyomus,which is co-dominantly with S.exigua.The moth was exposed to the echolocation calls of each of these bats under laboratory conditions.We divided the three echolocation calls into two CF calls which the main frequencie of two species were 58 k Hz and110 k Hz,and one FM call.We used the echolocation calls of these three bats to represent the spectral characteristics of the majority of bat echolocation calls,and used ultrasonic playback technology to systematically investigate the effects of different types and frequencies of echolocation calls on the feeding behavior,reproductive behavior and life history of S.exigua throughout their life histories,and to investigate the repellent effects of FM calls on adult moths.The results showed that: 1).The FM echolocation call playback group showed significantly lower frequency of flight,movement,courtship,and mating than the silent control and were most strongly subjected to acoustic stress.Among the two CF playback groups,calls of R.macrotis with a dominant frequency of 58 k Hz had a greater effect on adult reproduction and activity levels,and calls of R.pusillus with a dominant frequency of about 110 k Hz had no significant effect on adult behavior.All echolocation call treatment had no significant effect on female egg production.There was no significant difference in activity frequency and egg laying between the white noise control and the silent control.In addition,compared with the silent control,adults showed a strong negative tendency to exhibit a distribution away from the sound source under FM call stimulation,which indicated that bat echolocation call stimulation produced a strong repellent effect on the moth.2).Compared to the silent and noisy controls,FM calls significantly inhibited the feeding behavior of larvae while significantly increasing larval body weight;both CF calls did not significantly affect S.exigua larval feeding behaviour and fresh weight at all ages,except for the pupal stage of the R.macrotis call playback group with the dominant frequency at 58 k Hz.Adult longevity was significantly lower in the echolocation acoustic playback group of the E.pachyomus and R.macrotis compared to the control groups.In summary,this research investigated the non-consumptive effects of ultrasound with different acoustic characteristics of three insectivorous bats on S.exigua,including reduced activity frequency,reduced feeding,increased body weight,and reduced survival rate,and the intensity of the non-consumptive effects varied with frequency.The sensitivity of S.exigua to the FM calls of the codominant bat,the E.pachyomus,was higher than that of the CF calls emitted by the other two predators.The results of this study also imply that some insectivorous bats that emit sound frequencies within the hearing threshold of moths can produce significant non-consumptive effects on moths by the echolocation calls emitted by them,even though they cannot directly prey on moths.This study is of great scientific significance for understanding the bat-pest interrelationship,and will provide new ideas for green control technology of "bat-to-pest".