8 A. WATSON 



series of ultrasonic clicks when subjected to tactile stimulation, if restrained during 

 flight, or in response to recorded bat cries or artificially produced sound comparable 

 in frequency and pulse repetition rate to bat cries (Blest, Collett & Pye, 1963; 

 Blest, 1964; Dunning & Roeder, 1965; Dunning, 1968). Dunning (1968) has 

 commented on the probable aposematic nature of Arctiid sounds and the Mullerian 

 protection it confers. The palatability mentioned earlier, of Scaptius obscurata, 

 a nocturnal species with a well developed and apparently functional tymbal organ, 

 suggests the intriguing possibility that it may be a Batesian acoustic mimic as 

 well as a behavioural mimic. Dunning (1968) has cited the palatable North American 

 species Pyrrharctia Isabella J. E. Smith as a comparable acoustic mimic. 



All the species of the new genera and the type-species of most of the other Arctiid 

 genera referred to in the text have well developed tymbal organs (see plates). 

 These are typically globose, unsealed except posteriorly where there are often 

 several small, rounded scales, and with discernible microtymbals (transverse or 

 oblique corrugations of the tymbal); the tymbal organ is normally concealed by 

 the hind femur which may afford it some protection against damage. Recognisable 

 tymbal organs are lacking in Disconeura Bryk and Paranerita Hampson (type- 

 species) . In Echeta divisa Herrich-Schaff er the tymbal organ is irregularly grooved 

 and may represent a primitive condition (see PL 34, fig. 210). In most species 

 of Echeta the metepisternum is without microtymbals. The tymbal organ of 

 Glaucostola flavida (Schaus) (PL 34, fig. 208) is unusual in its microtymbal pattern. 

 The microtymbals in all the new genera typically possess a socket in each 

 groove but in only a few specimens were hair-scales found to be present (see, 

 for example PL 1, fig. 2). Pye (1973, personal communication) is currently 

 investigating the possible function of these hair-scales ; the short projection 

 anterior to the T-junction near their base apparently functions as an anchor 

 inhibiting lateral movement and tending to retain the hair-scale in its positions 

 along the groove. 



No sexual dimorphism of the tymbal organ has been detected in the Arctiidae 

 studied. Rothschild & Haskell (1966), summarizing the literature on Arctiid 

 sound emissions, have restated that the tymbal organ of the partly day-flying 

 European Cymbalophora Rambur is larger in the male than in the female, and suggest 

 that sound may have an epigamic function in this genus. The closely related 

 Nearctic genus Apantesis Walker lacks microtymbals but is still capable of sound 

 production from the metepisternum (Dunning, 1973, personal communication). 



With the exception of Glaucostola and Echeta, there is little variation in the 

 microtymbal pattern between the genera examined during the present study, 

 which suggests that the quality of their sound emissions will prove to be similar. 

 This can be expected from the experimental evidence that Arctiid tymbal sounds are 

 warning signals of Mullerian partners, although there appears to be no need for 

 exact replication of tymbal sounds between species as Dunning (1968) has found 

 that her bats reacted similarly to Halisidota tessellaris Smith and Haploa clymene 

 Brown clicks in spite of dominant frequency differences of as much as 20 kHz. 

 One experimental bat, however, learnt to distinguish between Pyrrharctia Isabella 

 clicks and those produced by tessellaris and clymene. 



