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THE MICROTYMBALS OF SOME ARCTIIDAE

M. B. FENTON

Deparhnent of Biology, Carleton University Ottawa, Ontario, Canada K1S 5B6

AND

K. D. ROEDER

Department of Biology, Tufts University, Medford, Massachusetts 02155

Acoustic communi8ation between moths and bats has provided biolo­gists with several intriguing examples of predator-prey interactions. Moths of some families, notably the Arctiidae, Ctenuchidae, Geometridae, and Noctuidae, possess tympanic organs capable of detecting the echolocating cries of bats (Eggers, 1928; Schaller & Timm, 1950; Haskell & Belton, 1956; Roeder & Treat, 1957). When presented with a source of ultrasonic pulses (cries of an echolocating bat or facsimiles thereof), restrained noctuid moths show changes in wingbeat and the same moths while flying free in the field pelform evasive maneuvers (Treat, 1955; Roeder, 1962, 1967 a, b).

When confronted with ultrasonic pulses, some arctiid and ctenuchid moths produce ultrasonic sounds usually consisting of a repeating sequence of brief, high-pitched, rapid clicks. These clicks are produced by a row of minute ridges or corrugations (= microtymbals or the 'striate band' of Forbes & Franclemont [1957J) in the cuticle of the meta thoracic episternite (Fig. 1). The basalar muscle inserts on the concave inner surface of the episternite, and its contraction cycle causes the microtymbals to buckle in sequence; each 'buckle' producing a click considerably less than one millisecond in duration and containing ultra­sonic frequencies (Blest et al., 1963; Blest, 1964). The contraction cycle of the basalar muscle determines the duration of the click cycle, and the number and form of the microtymbals on the episternite affects the number and acoustic nature of the clicks in each cycle.

Some arctiids and ctenuchids are not only noisy, but often distasteful (Beebe & Kenedy, 1957; Rothschild, 1961; Blest, 1964; Rothschild & Alpin, 1971). Some arctiids evert cervical glands when threatened (eg. Utethesia ornatrix bella (L.); Eisner, 1970, Fig. 6a), and this may be accompanied by noise (eg. Arctia caja (L.); Rothschild, 1965). Potential predators of these species may learn to associate the noise with an unpalatable taste and thus use the noise as a signal to leave the moths alone.

Captive Myotis lucifugus (LeConte) (Chiroptera: Vespertilionidae) avoided noisy Haploa clymene (Brown), Halysidota tessellaris (Abbot

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Fig. l. Diagram of left lateral wall of meso and meta thorax of a noctuid moth with the metathoracic episternite heavily outlined in black and the wing area indicated by lines (epm = epimaron; eps = episternite; sa = subalar plate; scu = scutum).

and Smith), and Pyrrharctia isabella (J. E. Smith), but bit into them if they were quiet. However, having tasted the moth, the bats spat out the H. tessellaris and H. clymene, and ate the P. isabella (Dunning, 1968), apparently a Batesian mimic of the other two species. Coutts et al. (1973) observed that captive M. lucifugus and Eptesicus fuscus (Palisot de Beauvois) (Chiroptera: Vespertilionidae) bit into and then rejected dead or quiet Cycnia tenera Hubner.

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Fig. 2. Scanning electron micrographs of the left (except d and g) meta thoracic episternites of: (a) Euthisanotia unio Hubner (Concord, Massachusetts); (b) Phragmatobia assimilans Newman and Donahue (Edmonton, Alberta); (c) Phragmatobia fuliginosa L. (Suisse Valias); (d) Hypoprepia fucosa Hubner (Con­cord, Massachusetts); (e) Hypoprepia cadaverosa Strecker (Greer Rd, White Mountains, Arizona); (f) HYPopl'epia miniata (Kirby) (Attons Lake, Saskatchewan); (g) Clemensia albata Packard (Bobcaygeon, Ontario); (h) Turuptiana permaculata Walker (Buena Vista, Colorado); (i) Spilosoma congrum (Walker) (Lac Mondor, Quebec). Scale indicates 1 mm.

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Dunning & Roeder (1965) showed that flying M. lucifugus veered away from their prey (moths or 'tossed mealworms') when confronted with tape-recorded microtymbal sounds as they closed with their prey. However, one of Dunning's (1968) captive bats learned to distinguish between the noises of P. isabella and H. clymene and H. tessellaris indi­cating that different moths produce different noises.

These behavioural considerations and the possibility of marked species differences in microtymbal systems of arctiids led us to make a pre­liminary survey to determine the incidence of microtymbals in this group. The following is a brief presentation of some of our anatomical findings which may be of interest to lepidopterists.

Figs. 2 and 3 are scanning electron micrographs of the meta thoracic episternites of specimens obtained from collections at the Entomology Research Institute, Canada Department of Agriculture, and Carleton University. It is evident from the micrographs that the details of the microtymbals vary considerably both within and between genera. Sexual dimorphism, if it occurs, was not investigated. The metathoracic episternite of a noctuid, Euthisanotia unio Hubner, is shown for com­parison (Fig. 2a).

Well developed microtymbals occur on the metathoracic episternites of the following species: Phragmatobia assimilans Newman and Donahue ( Fig. 2b), Phragmatobia fuliginosa L. ( Fig. 2c) , Phrag­matobia lineata Newman and Donahue, Hypoprepia fucosa Hubner (Fig. 2d) , H ypoprepia cadaverosa Strecker ( Fig. 2e ), H ypoprepia miniata (Kirby) (Fig. 2f), Clemensia albata Packard (Fig. 2g), Cisthene nexa Boisduval, Crambidia casta Sanborn, Crambidia pallida Packard, Halysidota tessellaris (Fig. 3a), Halysidota maculata (Harris) , Hemi­hyalea labecula Grote (Fig. 3d), Pyrrharctia isabella (Fig. 3f), Cycnia tenera (Fig. 3g), Euchaetias egle (Drury) (Fig. 3h), and Utethesia ornatrix bella (Fig. 3i).

The following species have poorly T uruptiana permaculata Walker (Fig. 2h),

developed microtymbals: Estigmene acrea (Drury),

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Fig. 3. Scanning electron micrographs of the left (except c, e, and h) metathoracic episternites of: (a) Halysidata tessellaris Abbot and Smith (Chaffey's Locks, Ontario); (b) Halysidota argentata Packard (Nanairno, British Columbia); (c) Halysidota caryae (Harris) (Normandale, Ontario); (d) Hemihyalea labecula Grote (Durango, Colorado); (e) Haploa clymene (Brown) (Arrowhead Lake, Myrtle Beach, South Carolina); (f) Pyrrharctia isabella (J. E. Smith) (Lac Mondor, Quebec); (g) Cycnia tenera Hubner (Chaffey's Locks, Ontario); (h) Euchaetias egle (Drury) (Concord, Massachusetts); (i) Utethesia ornatrix bella (L.) (Punta Gorda, Florida). Scale indicates 1 mm.

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Spilosoma eongrum (Walker) ( Fig. 2i), Araehnis maia Ottolengui, Spilosoma virginieum ( Fabricius), Aretia eaja, Plataretia parthenos ( Harris), and H alysidota earyae (Harris) (Fig. 3c), and in H olomelina ferruginosa (Walker) and H alysidota argentata Packard (Fig. 3b), they are absent.

The details of the surface of the microtymbals of U. o. bella (Fig. 3i) are strikingly different from those of the other arctiids mentioned.

Forbes & Franclemont (1957) considered using the 'striated band' of the Arctiidae as a taxonomic character but noted that it varied markedly in species considered on other grounds to be closely related. Their finding is strikingly confirmed by an examination of Figs. 2 and 3. Thus, the two species of Phragmatohia (Fig. 2b and c) and the three species of H alysidota (Fig. 3a, b, and c) show marked differences in the form and degree of development of the microtymbals. At the same time, the three species of H ypoprepia (Figs. 2d, e, and f) have micro­tymbals which are quite similar in form and arrangement. It will be interesting to see if microtymbalmorphology correlates closely with other characteristics used in the classification of arctiids.

ACKNOWLEDGMENTS

We thank Drs. E. G. Munroe and E. A. Amason for providing us with the specimens. We are especially grateful to Mr. L. E. C. Ling who took the micrographs of the uncoated specimens at low voltage using the techniques described by Howden & Ling (1973). Weare also grateful to Drs. E. G. Munroe and H. F. Howden for critically examining the manuscript and to Dr. E. C. Munroe and Rev. J. C. E. Riotte for en­couraging us in this survey. Rev. Riotte kindly checked and corrected the names of the moths. This study was supported by National Research Council of Canada Operating and Equipment Grants to MBF and by a Career Award from the National Institute of Health, United States of America, to KDR.

LITERATURE CITED

BEEBE, W. & R. KENEDY. 1957. Habits, palatability and mImIcry in thirteen ctenuchid moth species from Trinidad, B.W.I. Zoologica 42: 147-157.

BLEST, A. D. 1964. Protective display and sound production in some new world arctiid and ctenuchid moths. Zoologica 49: 161-181.

---, T. S. COLLET & J. D. PYE. 1963. The generation of ultrasonic signals by a New World arctiid moth. Proc. Roy. Soc., London (B) 158: 196-207.

COUTTS, R. A., M. B. FENTON & E. GLEN. 1973. Food intake by captive Myotis lUcifugus and Eptesicus fuscus (Chiroptera: Vespertilionidae). J. Mammal. 54: 985-990.

DUNNING, D. C. 1968. Warning sounds of moths. Z. Tierpsychol. 25: 129-138.

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---. & K. D. ROEDER. 1965. Moth sounds and the insect-catching behavior of bats. Science 147: 173-174.

EGGERS, F. 1928. Die Stiftfuhrenden Sinnesorgane, Morphologie und Physiologie der chordotonalen und der tympanalen Sinnesapparate der Insekten. Zool. Bausteine 2 (1 ), 354 p., Berlin.

EISNER, T. H. 1970. Chemical defense against predation in arthropods, in Chemical Ecology, E. Sondheimer & J. B. Simeone, eds., Academic, New York and London, p. 157-217.

FORBES, W. T. M. & J. G. FRANCLEMONT. 1957. The ,triated band (Lepidoptera chiefly Arctiidae) . Lepid. News 11: 147-150.

HASKELL, P. T. & P. BELTON. 1956. Electrical responses of certain lepidopterous tympanal organs. Nature 177; 139-140.

HOWDEN, H. F. & L. E. C. LING. 1973. Scanning electron microscopy; low magnification pictures of uncoated zoological specimens. Science 179: 386-388.

ROEDER, K. D. 1962. The behaviour of free flying moths in the presence of artificial ultrasonic pulses. Anim. Behav. 10; 300-304.

---. 1967a. Turning tendency of moths exposed to ultrasound while in sta­tionary flight. J. Insect Physiol. 13: 873-888.

---. 1967b. Nerve Cells and Insect Behavior. Harvard, Cambridge. revised edition.

---. & A. E. TREAT. 1957. Ultrasonic reception by the tympanic organ of noctuid moths. J. Exp. Zoo!. 134; 127-157.

ROTHSCHILD, M. 1961. Defensive odour and Mullerian mimicry among insects. Trans. Roy. Entomol. Soc. London 113: 101-121.

---. 1965. The stridulation of the garden tiger moth. Proc. Roy. Entomol. Soc. London (C) 30; 3.

---. & R. T. ALPIN. 1971. Toxins in tiger moths (Arctiidae; Lepidoptera), in Pesticide Chemistry, A. S. Tahori, ed., Gordon and Brech, London, p. 177-182.

SCHALLER, F. & c. TIMM. 1950. Das Horvermogen der Nachtschmeterlinge. Z. Vergl. Physiol. 32: 468-481.

TREAT, A. E. 1955. The response to sound in certain Lepidoptera. Ann. Entomol. Soc. Amer. 48; 272-284.

NEW STATE RECORDS FOR INDIANA AND ILLINOIS

On 22 July 1973, while collecting Lycaeides melissa samuelis (Edwards) in the vicinity of Griffith, Lake Co., Indiana, I took a pair of Problema byssus (Edwards), a slightly worn male and a fresh female, the first recorded from that state that I had knowledge of at the time. Identification was kindly verificd by Mr. Ernest M. Shull, co-author of an annotated list of the butterflies of Indiana (1972, J. Lep. Soc. 26; 13-24). According to Mr. Shull who, along with Mr. F. Sidney Badger, has carried out intensive collecting and study in Indiana, these are the first of­ficially recorded specimens for that state. Both specimens have been placed in the private collection of Mr. Shull.

On 24 June 1973, I took two fresh males of the color form pallida of Thymelicus lineola (Ochsenheimer) in Spears Woods Forest Preserve, Cook Co., Illinois. Ac­cording to word received from the Illinois Natural History Survey, these are the first records from Illinois. Both specimens have been placed in the permanent Survey collections.

IRWIN LEEUW, 1219 Crystal Lake Road, Cary, Illinois 60013.