Simultaneous percussion by the larvae of a stem-nesting solitary bee – a collaborative defence strategy against parasitoid wasps?

Andreas Müller,Martin K Obrist

doi:10.3897/jhr.81.61067

Abstract

Disturbance sounds to deter antagonists are widespread among insects but have never been recorded for the larvae of bees. Here, we report on the production of disturbance sounds by the postdefecating larva (“prepupa”) of the Palaearctic osmiine bee Hoplitis (Alcidamea) tridentata, which constructs linear series of brood cells in excavated burrows in pithy plant stems. Upon disturbance, the prepupa produces two types of sounds, one of which can be heard up to a distance of 2–3 m (“stroking sounds”), whereas the other is scarcely audible by bare ear (“tapping sounds”). To produce the stroking sounds, the prepupa rapidly pulls a horseshoe-shaped callosity around the anus one to five times in quick succession over the cocoon wall before it starts to produce tapping sounds by knocking a triangularly shaped callosity on the clypeus against the cocoon wall in long uninterrupted series of one to four knocks per second. Sound analysis revealed that the stroking sounds consist of several syllables, which are very similar to the single syllables of the tapping sounds: both last about 0.5 ms and spread over 40 kHz bandwidth from the audible far into the ultrasonic range. The production of stroking sounds by a prepupa induces other prepupae of the same nest to stroke and/or to tap resulting in a long-lasting and simultaneous albeit unsynchronized percussion by numerous prepupae along the whole nest stem. We hypothesize that these disturbance sounds serve an anti-antagonist function and that they have evolved to disturb the reflectance signals that parasitoid wasps use to localize concealed hosts during vibrational sounding.

Highlights

Innumerable insects from many different taxa produce vibrational signals (“sounds” hereafter), which are propagated through air, water or solids and perceived by the recipients with tympanal ears or near-field receptors including sensory sensillae, subgenual organs or the antennae (Gullan and Cranston 2000; Yack and Hoy 2003; Drosopoulos and Claridge 2005)
Hoplitis tridentata is a 10–12 mm long Palaearctic osmiine bee (Megachilidae, Osmiini), which has a vast distribution ranging from Europe and northern Africa eastwards to Western Siberia and Central Asia (Müller 2020)
To address the question whether the prepupae of other osmiine bees are equipped with similar sound producing structures like Hoplitis tridentata, we examined the prepupae of the following eleven Central European species belonging to four genera and ten subgenera obtained from nests collected by the first author in 2020 and by P

Summary

Introduction

Innumerable insects from many different taxa produce vibrational signals (“sounds” hereafter), which are propagated through air, water or solids and perceived by the recipients with tympanal ears or near-field receptors including sensory sensillae, subgenual organs or the antennae (Gullan and Cranston 2000; Yack and Hoy 2003; Drosopoulos and Claridge 2005). Depending on the insect taxon, these sounds are produced in very different ways encompassing i) vibration of thorax, abdomen or wings, ii) percussion of body parts against each other or against a substrate, iii) deformation of modified cuticular areas by contraction and relaxation of special musculature, iv) expulsion of air through spiracles or proboscis, v) stick-slip movements of adjacent body segments and vi) true stridulation, which involves the movement of two specialized body parts against each other in a regular patterned manner (Ewing 1989; Claridge 2005; Dolle et al 2018) The majority of these air-, water- or substrate-born insect sounds serve for intraspecific communication, such as species recognition, mate finding, courtship, male competition, recruitment to feeding sites or warning against antagonists. Disturbance sounds are widespread among insects and known for example from i) larvae of Blattodea (Blaberidae, Ectobiidae) and Coleoptera (Cerambycidae), ii) pupae of Coleoptera (Scarabaeidae) and Lepidoptera (Arctiidae, Callidulidae, Hesperiidae, Lycaenidae, Lymantriidae, Noctuidae, Notodontidae, Nymphalidae, Phalaenidae, Pyralidae, Riodinidae, Sphingidae, Zygaenidae) and iii) imagines of Auchenorrhyncha (Cicadidae), Blattodea (Blaberidae), Coleoptera (Cerambycidae, Cicindelidae, Scarabaeidae, Silphidae), Heteroptera (Cydnidae, Reduviidae), Hymenoptera (Apidae, Bradynobaenidae, Mutillidae, Crabronidae, Formicidae, Rhopalosomatidae) and Lepidoptera (Nymphalidae) (Hinton 1945, 1955; Downey 1966; Nelson 1979; Schal et al 1982; Tremevan 1985; Tschuch and Brothers 2000; Drosopoulos and Claridge 2005; Kočárek 2009; Olofsson et al 2012; Dolle et al 2018)

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