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This article was downloaded by: [Lulea University of Technology] On: 05 September 2013, At: 02:46 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Natural History Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tnah20 A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae) J.R. Downie a , R.H.L. Disney b , L. Collins a & E.G. Hancock c a Department of Zoology, University of Glasgow, Glasgow, G12 8QQ, UK b University Department of Zoology, Cambridge, CB2 3EJ, UK c Department of Science, Museum and Art Gallery, Glasgow Kelvingrove, Glasgow, G3 8AG, UK Published online: 17 Feb 2007. To cite this article: J.R. Downie , R.H.L. Disney , L. Collins & E.G. Hancock (1995) A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae), Journal of Natural History, 29:4, 993-1003, DOI: 10.1080/00222939500770371 To link to this article: http://dx.doi.org/10.1080/00222939500770371 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms

A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae)

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Page 1: A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae)

This article was downloaded by: [Lulea University of Technology]On: 05 September 2013, At: 02:46Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Journal of Natural HistoryPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tnah20

A new species of Megaselia (Diptera,Phoridae) whose larvae prey upon theeggs of Leptodactylus fuscus (Anura,Leptodactylidae)J.R. Downie a , R.H.L. Disney b , L. Collins a & E.G. Hancock ca Department of Zoology, University of Glasgow, Glasgow, G128QQ, UKb University Department of Zoology, Cambridge, CB2 3EJ, UKc Department of Science, Museum and Art Gallery, GlasgowKelvingrove, Glasgow, G3 8AG, UKPublished online: 17 Feb 2007.

To cite this article: J.R. Downie , R.H.L. Disney , L. Collins & E.G. Hancock (1995) A new speciesof Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura,Leptodactylidae), Journal of Natural History, 29:4, 993-1003, DOI: 10.1080/00222939500770371

To link to this article: http://dx.doi.org/10.1080/00222939500770371

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms

Page 2: A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae)

& Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

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Page 3: A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae)

JOURNAL OF NATURAL HISTORY, 1995, 29, 9 9 3 - 1 0 0 3

A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylusfuscus (Anura, Leptodactyl idae)

J. R. DOWNIEr , R. H. L. DISNEY$, L. COLLINSt andE. G. HANCOCK§

~Department of Zoology, University of Glasgow, Glasgow G12 8QQ, UK "~Field Studies Council Research Fellow, University Department of Zoology, Cambridge CB2 3EJ, UK §Department of Science, Museum and Art Gallery, Glasgow Kelvingrove, Glasgow G3 8AG, UK

(Accepted 30 June 1994)

Megaselia nidanurae Disney sp. nov. is described from a series of males and females reared from larvae preying on the eggs of the foam-nesting frog Leptodactylus fuscus (Schneider) in Trinidad. The general biology of the association suggests that this is an obligate relationship for the fly. This is the first description of a 'frogfly' attacking foam-nests hidden in burrows.

KEYWORDS: Diptera, Phoridae, Leptodactylidae, foam-nest, 'frogfly', frog-fly association, new species, Neotropical.

Introduction Villa (1980) and Villa et al. (1982) have reviewed the literature on organisms

associated with amphibian eggs. Sometimes, these associations appear to be benign but, more often, amphibian eggs are used as a food source. In most cases, this use is opportunistic, with the amphibian eggs being only one of many available food sources. In a few cases, however, Villa suggests there is evidence for a close, possibly obligate association.

The best case for an obligate association can be made for the 'frogflies'. Villa (1977) coined the term 'frogfly' for a then unidentified drosophilid species, now believed to belong to the genus Zygothricha (Villa, 1980 and 1984), which lays its eggs in the egg clutches of the frog Centrolenella fleischmanni (Boettger) which oviposits on the underside of leaves overhanging streams. Villa 's search of the literature (Villa 1980; Villa et al., 1982) then revealed several further examples of dipterans from two families (Ephydridae; Drosophilidae) whose eggs are laid in frog-egg clutches and whose maggots feed on the eggs, as well as several other examples of maggots inhabiting frog-egg clutches without apparently killing eggs or tadpoles. Villa and Townsend (1983) then reported a third example, the phorid Megaselia scalaris (Loew) found laying eggs in clutches of Agalychnis annae (Duellman) in Costa Rica and Eleutherodactylus coqui Thomas in Puerto Rico. In this case, distinct from other reports of phorid associations with frog eggs, the maggots clearly consumed viable eggs. This however, is an example of facultative predatory behaviour, as M. scalaris is a well-known saprophage only rarely behaving as a facultative predator or parasitoid (Disney, 1994).

0022-2933/95 $10.00 © 1995 Taylor & Francis Ltd.

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994 J .R . Downie et al.

In all these cases, the frog egg clutches were laid out of water, either in the open attached to leaves or as foam nests. In all well-documented examples of 'frogfly' associations with foam nests, the nests were in the open [nests of a species of Physalaemus Fitzinger and Leptodactylus pentadactylus (Laurenti)] though Heyer (personal communication) did once find maggots in a foam nest of Leptodactylus bufonius Boulenger, a burrow-nesting species.

In this paper, we report on a 'frogfly' association with the burrow-nesting species Leptodactylusfuscus (Schneider), in Trinidad. The fly is a hitherto undescribed species of Megaselia Rondani, whose larvae appear to be obligate predators on L. fuscus eggs. L. fuscus like L. bufonius is a member of the ' fuscus' group of Leptodactylids (Heyer, 1978), all of which make foam-nests in burrows close to potential sites of temporary pools. In the case of L.fuscus, early development is rapid. Hatching into the foam occurs at stage 18-19 (Gosner, 1960) 2 full days after egg deposition. After one more day, tadpoles at stage 22-24 are found wriggling actively at the bottom of the foam mass. After a further day (stage 25) tadpoles start to make a new kind of foam which replaces the original nest foam, and they will remain in this foam for up to several weeks in a form of developmental arrest until heavy rains flush them out (Downie, 1984 and 1994a, b).

Materials and methods L. fuscus foam nests were collected over 6 seasons of fieldwork in Trinidad from

4 different sites. These were: (a) a temporarily flooded area on the University of West Indies (UWI) Campus at St August ine--seasons 1982, 1985, 1987 and 1989; (b) a drainage ditch at Carmody Road, St August ine--seasons 1989 and 1991; (c) a drainage ditch beside the road to Piarco Airport--seasons 1991 and 1993; (d) a drainage ditch beside the playing field at Lopinot vi l lage--season 1993.

Nests were normally found at the sides of ditches within a few cm of the ditch bottom. Normally, the entrance to the burrow was plugged with mud, and nests were located by pushing the handle of a teaspoon into the ditch side at favourable positions. However, at the Lopinot site, some nests were found with incompletely plugged burrows.

On finding a burrow with a foam nest, the plug was completely removed and the whole foam nest transferred, using the teaspoon, to a collecting pot for transfer to the laboratory. In the laboratory, any contaminating particles of mud were removed and each nest was placed separately on the surface of moist tissue paper in a 250ml polythene tub with a lid. Lids were fastened loosely enough to allow aeration, but tightly enough to avoid the foam drying out quickly and to prevent any insects entering the tubs in the laboratory. This precaution was certainly necessary; on 2 occasions foam nests were set up inadvertently in tubs with small holes punched in the sides. Within a few days, small flies had entered these nests and had produced larvae which attacked the already-hatched tadpoles, a situation first reported by Lutz (1946). In one of these cases, the larvae were fixed in 70% alcohol for identification.

Nests were incubated in the tubs in the laboratory (temperature: 27-28°C) and inspected daily. Nests were collected at all stages of development, from freshly-laid to foam-making tadpoles. Nests were collected mainly to study L. fuscus development but, after initial discovery of maggot infestation in 1982, any further maggot infestations were noted, and a full study of these was made in season 1993.

No attempt was made to search for insect eggs in the foam nests. Instead, we waited for signs of premature liquefaction of the nest foam and looked for maggots in these

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'Frogfly' maggots attack foam nests 995

FIG. 1. Foam-nest of Leptodactylus fuscus showing lower area liquefied by the activities of Megaselia nidanurae maggots. Scale bar = 10mm.

liquefying areas. In most cases, the 'healthy' part of the foam nest was then separated from the liquefying area to allow the remaining L. fuscus eggs to develop normally. By this stage, maggots were beginning to migrate out of the foam. Maggots were isolated from the nest debris and counted, then a proportion from each nest was preserved in 70% alcohol. The remainder were placed in glass tubes containing damp cotton wool and stoppered with gauze. Once the maggots had pupated, a proportion of these were also preserved in 70% alcohol, and the remainder allowed to incubate till flies emerged. The flies were then preserved in 70% alcohol.

Results

Natural history of maggot/L, fuscus interaction We were not able to observe fly eggs. The first sign of infestation was when maggots

were seen in a liquefying part of a foam nest (Fig. 1). This always occurred 2 days after foam-nest deposition, when L. fuscus eggs were around the stage of hatching (st. 18-19). Examination of liquefying areas demonstrated clearly that the maggots were feeding on the frog eggs. After one more day, maggots began to leave the foam nest, climbing up the sides of the polythene tubs. Some began to pupate that day and the remainder by the next day. Emergence of flies occurred 6--8 days later. If the liquefying area around the maggots was removed from the rest of the foam-nest, the eggs in the remainder of the nest were able to continue normal development, but if the maggot-infested nest was left intact, few if any tadpoles ever emerged. Data on infested nests are shown in Table 1.

Quantitative data on the number of nests infested are shown in Table 2. From 69 L. fuscus nests collected over 6 field seasons, 7 maggot-infested nests were found (Table 2). However, the biology of the infestation suggests that this underestimates its occurrence. Since we found that maggots leave the nest the day after tadpole hatching, and we never found maggots in nests of well-developed tadpoles, we should use only the nests collected at stages up to tadpole hatching in calculating infestation frequency: this gives 7 infested nests from a total of 31 collected during the first 2 days after egg deposition i.e. 22.6%. The data are too sparse to give any real impression of how

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996 J .R. Downie et al.

Table 1. Data on maggot-infested foam nests collected in 1993. Clutch number is from a series of 36 L.fuscus nests collected from Lopinot (except No. 1 at Piarco). All nests from which maggots emerged were collected at pre-hatching stages of L. fuscus development.

Number of Clutch Collection Appearance maggots/pupae Effect on Date of fly number date of maggots isolated foam nests emergence

4 12/7 14/7 9 Maggots removed; t many tadpoles survived

11 15/7 17/7 7 Maggots removed; t many tadpoles survived

15 15/7 17/7 119 All eggs destroyed ~" 25 20/7 21/7 33 Maggots removed; 27/7

many tadpoles survived

26 3/8 5/8 18 Maggots removed; 16/8 nest liquefied and eggs died

t Records of dates of emergence of clutches 4, 11 and 15 were lost in transit.

Table 2. Frequency of maggot-infested foam nests.

Frog development stager Number of nests Nest collection on collection and number infested with

Year site of nests (in brackets) maggots

1982 UWI Eggs (4) 2 Just hatched (1) 0 Tadpoles (4) 0

1983 UWI Eggs (2) 0 Tadpoles (4) 0

1987 UWI Tadpoles (1) 0 1989 UWI Tadpoles (1) 0

Carmody Rd Just hatched (1) 0 Tadpoles (1) 0

1991 Carmody Rd Eggs (1) 0 Piarco Rd Eggs (1) 0

Just hatched (6) 0 Tadpoles (7) 0

1993 Piarco Rd Tadpoles (1) 0 Lopinot Eggs (15) 5

Tadpoles (19) 0

t Frog development stage on collection of the nest given as: eggs = before Gosner stage 19; tadpoles = Gosner stage 20 or later.

widespread the infestation is, but maggots were found at 2 of the 4 sites sampled, and these 2 sites are a good distance apart, the UWI site being on the Caroni plain and Lopinot a valley in the Northern Range mountains.

The flies which attacked foam nests in the laboratory, by getting through holes in some tub walls, were also Phorids but of a different kind, though not Megaselia scalaris. Adults were not collected and their identification will require further fieldwork.

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'Frogfly' maggots attack foam nests 997

..." 1 _ _

FIG. 2. Megaselia nidanurae male, left face of hypopygium. Scale bar = 0-1 mm.

Taxonomy of the fly (by R. H. L. Disney) The fly species is described below from a series of reared specimens preserved in

alcohol. The type series includes a sample of 16 of these which have been mounted on slides.

Megaselia nidanurae Disney sp. nov. (Figs 2-6)

Material examined HOLOTYPE c~ : Trinidad, Lopinot, emerged in laboratory 16 VIII 1993, larvae having

been collected 3 VIII 1993 in nest of Leptodactylusfuscus (Schneider) (J. R. Downie) (In University Museum of Zoology, Cambridge, England).

PARAa~PES 7C~, 8 9 as holotype, except dates various VII-VIII 1993 and some deposited in the Art Gallery and Museum, Kelvingrove, Glasgow, Scotland. Also 62 c~, 54 9 (in alcohol) with same data as holotype or above paratypes.

Etymology The name refers to the breeding of this species in the nests of frogs.

Male Frons brown, to orange brown in parts, and microsetae dense (i.e. frons dull). Lower

supra-antennal bristles about half as long as upper pair, less robust, and about half as far apart. Antials approximately, but variably, half way between upper supra-antennals and antero-lateral bristles. Antials distinctly lower on frons than upper supra-antennals, but the antero-laterals a little higher than latter. Precellars further apart than upper supra-antennals and than either is from a medio-laterial. The latter a little higher on frons than preocellars. With 80-110 hairs on frons, which is slightly wider than long. Third antennal segment subglobose and pale brownish to greyish yellow. Second segment of arista about three times as long as greatest breadth and subequal in length to both first

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FIGS 3-4.

,

jill ............ ; . . . . . . . °

\° !' ,~ ..... ~ , o / k ~, ,T,~I~ 1 ~, /

4

Megaselia nidanurae female: (3) abdominal tergites 2-6: (4) Dufour's crop mechanism. Scale bars = 0-1 mm.

segment and swollen basal region of third. Palps pale brownish yellow, each with five strong dark bristles (two apical, a pre-apical and two behind these) and > 12 hairs below. Proboscis, including labrum, pale brownish yellow. Greatest breadth of labrum at most only 1.5 times greatest width of palp and only about two-thirds the greatest diameter of third antennal segment. Labella narrowing apically, with only a few short pale spines below, and with pale weak teeth on inner faces adjacent to glossa.

Prothorax brown dorsally; scutum pale brownish yellow, but a little darker on top especially behind. Scutellum brown. Two bristles on notopleuron, one on humerus (but situated behind anterior spiracle); an intra-alar, post-alar, 2 dorso-centrals, and at least one pre-scutellar acrostichal bristle (among the stronger hairs at rear of scutum) each side. Four strong subequal bristles on scutellum, or the anterior pair being a little longer than posterior pair. Pleural regions mainly pale dusky yellow, but a little browner dorsally. Mesopleuron with 4-9 hairs; but normally no differentiated bristles, but rarely there is a single short differentiated bristle near rear margin (at least on one side).

Abdomen with brown tergites, but 1 and 6 in particular may be partly yellow. Hairs of tergite 1 short, but longer ones on 2-6. Typically four strong hairs towards each side of 2, and some differentiated hairs postero-laterally on 3-5 and rear of 6. Venter greyish yellow, with hairs on segments 3-6. Hairs at rear of segment 5 conspicuous, and even more so at rear of 6. Hypopygium brown, with pale yellow cerci and apex of proctiger, and as Fig. 2. Posterior lobes of hypandrium markedly unequal, that of left side being much larger. Internally with four rectal papillae.

Legs dusky pale yellow, apart from brown apex of hind femur and dorsal face of hind tibia. Front metatarsus slender (7-8 times as long as broad) and a postero-dorsal hair palisade present on all five fore-tarsal segments. Mid tibia with longitudinal hair palisade extending > 0.75 of length, with clearly differentiated row of postero-

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'Frogfly' maggots attack foam nests 999

dorsal spine-like hairs below basal half clearly longer than those of antero-ventral row of outer half. Hind tibia with only simple spines in apical combs of posterior face, and a longitudinal row of 10, or fewer, spine-like postero-dorsal hairs and no differentiated antero-dorsals.

Wings 1-64-1.78 mm long. Costal index 0.58-0.61. Costal ratios 3-44--4.98: 2-53- 3.42 : 1. Costal cilia 0-06-0.07 mm long. No hair at base of vein 3. Axillary ridge with 4-5 bristles. Vein Sc ends just before reaching R1. Vein 4 originates at or, more usually, just beyond fork of vein 3. All veins brown and membrane greyish brown tinged. Haltere largely brown.

Female Head very similar to male; except labrum enlarged (with greatest breadth about 1.5

times greatest breadth of third antennal segment, and with stronger teeth on inner faces of labella. Thorax as male. Mesopleuron with 5-12 hairs.

Abdominal tergites as Fig. 3 and generally brown; but 1, anterior part of 2 and sometimes a narrow median stripe of tergites 3 and 5 yellow. Tergite 4 very variable in size (sometimes almost absent). Venter grey, with narrow intersegmental paler bands (as most of tergum of segment 4). Short hairs present on segments 3-6, but 2-6 more bristle-like hairs at rear of 5 and an extended row of such hairs at rear of 6. A narrow sternite on segment 7 and a pair of postero-lateral lobes, bearing bristles, at rear of ventral face of segment 8. Tergites 7 and 8 with bristle-like hairs but sclerotisation of tergites sometimes weak. Internally with four rectal papillae, a weakly sclerotised furcal ring (sternite 9) and Dufour's Crop mechanism as Fig. 4.

Legs similar to male. Wings 2.15-2.28 mm long. Costal index 0.59--0.64. Costal ratios 3.68-5.12: 2.57-3.93 : 1. Costal cilia 0.06-0.07 mm long. Vein 4 originates at level of fork of vein 3, or occasionally slightly before. Otherwise wing and haltere as male.

Larva (last instar) Pale creamy white and of typical Megaselia type (e.g. Fig. 4 in Disney, 1983,

Fig. 3.1 (b) in Disney, 1994, Fig. 104 in Peterson, 1987): except hairing of integument reduced (especially on anterior segments), spinose bands on anterior thirds of segments well developed and anal gills enlarged. Cephalo-pharyngeal skeleton as Fig.5. Pharyngeal ridges are present. This feature is normally associated with the ingestion of particles in suspension in a fluid (Disney, 1994).

Puparium Orange brown, with distinctly demarcated caudal region. The paired eclosion plates

(Fig. 6) and anterior cap detach when the adult emerges. The pupal respiratory horns are black.

Similar species In the primary key to Neotropical Megaselia species (Borgmeier, 1962)

M. nidanurae runs to couplets 15 and 16 on page 301, to the variable female of M. setigera (Brues). It differs in lacking the marked contrast between the long hairs at the rear of abdominal tergite 5 and short hairs at the rear of tergite 6. The male of M. setigera was subsequently described by Borgmeier (1969a). It also closely resembles M. nidanurae, but the latter has paler 3rd antennal segments, weaker bristles at the

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1000 J .R . Downie et al.

. - , . . • • •

• ~ • ? •

• • i

6 FIGS 5-6. Megaselia nidanurae pre-adult stages: (5) cephalo-pharyngeal skeleton of last instar

larva, viewed from left side; (6) right eclosion plate of puparium. Scale bars -- 0.1 ram.

rear of abdominal segments 5 and 6, and vein 4 originates a little beyond the fork of vein 3.

In supplementary keys to Neotropical Megaselia species M. nidanurae will key out as follows. In Borgmeier (1969a) it runs to couplet 3 on page 6, as M. setigera again. In Borgmeier (1969b) it runs to couplet 4 on page 80, to M. quartobsoleta Borgmeier. The female of the latter, however, has a yellow frons and abdominal tergite 5 clearly shorter than 6. Its male is unknown. In Borgmeier (1971) M. nidanurae runs to couplet 9 on page 8, to the female ofM. paraensis Borgmeier. The latter also has a yellow frons, and the hairs at the rear of abdominal segments 5 and 6 are much shorter than in M. nidanurae. The male of M. paraensis is unknown. I n t h e keys to Nearctic Megaselia species (Borgrneier, 1964) M. nidanurae runs to couplet 12 on page 263, to the male of M. melanderi Borgmeier. The latter, however, is immediately distinguished by its brown legs,

The occasional specimens with a short differentiated bristle on the mesopleuron will run to couplet 5 on page 301 of Borgmeier 's (1962) key, to 'M. caribbaea (Brues)'. This is a synonym of M. fasciiventris (Enderlein) (Borgmeier, 1969a). This species, however, has subequal supra-antennal bristles, shorter hairs below the basal half of hind femur, a generally yellow haltere knob and longer costal cilia, among other differences from M. nidanurae. Species formerly placed in Paraphiochaeta Malloch will also run to this couplet 5 (Disney, 1994). These are distinguished by a row of differentiated antero-dorsal hairs on the hind tibia. In the supplementary keys these specimens of M. nidanurae run to couplet 5 on page 8 of Borgmeier 's (1971) key, to the male of M. setipectus Borgmeier. The latter species has longer lower supra-antennals, a costal index < 0-5 and weaker postero-dorsals on hind tibia.

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'Frogfly' maggots attack foam nests 1001

Discuss ion Although the majority of anuran species lay their eggs in water as individuals,

strings or in jelly masses, a large number have evolved a variety of means of laying out of water-- in foam, in burrows, enclosed by leaves etc. There are likely to have been several selective forces behind these changes but a clearly demonstrated one is predation of eggs and hatchlings in water by other tadpoles and by a wide range of aquatic in'sects (Downie, 1988; Hodl, 1990; Magnusson and Hero, 1991). However, the escape from water makes the eggs available to a new range of potential predators. Villa (1980) and Villa et al. (1982) reviewed the range of arthropods that attack leptodactylid foam nests and other anuran egg clutches laid out of water, and Villa (1984) extensively documented the predatory associ~ition between a drosophilid fly and the eggs of a glass frog, laid on the undersides of leaves. In some cases, these associations seem essentially opportunistic but in others there is evidence of a closer more specific association between frog oviposition and predator behaviour. In the cases reviewed by Villa and his colleagues, the anuran eggs were laid in the open, making their discovery by potential predators relatively simple. In L. fuscus, on the other hand, eggs in foam are deposited in burrows which are then generally sealed by a mud plug when the mating adults leave. These hidden foam nests would seem to offer the best possible protection from predators: however, for any predator capable of penetrating the nest, it offers a food resource that can be utilised in seclusion.

The resource is considerable: nests contain around 100 large (1.8 mm diameter) pigmentless eggs (Downie, unpublished records, 1982, 1983) and these are unlikely to be protected by the toxins found in some pigmented eggs laid in the open (Duellman and Trueb, 1986). It will be of interest to discover how widespread 'frogflies' of the 'fuscus' group (Heyer, 1978) are, given that all these frog species make some kind of burrow nest, and whether the 'frogflies' show evolutionary signs of a long-term association with this group of amphibians. In particular, has there been a species radiation within the genus Megaselia? Probably the majority of phorid larvae are specialised predators of parasitoids of invertebrates (Disney, 1994).

The preliminary evidence presented here suggests a close dependence of the fly's life cycle on frog oviposition. In all cases, flies must have oviposited around the time of foam-nest construction, since maggots always appeared at the same stage of tadpole development, and the time of nest construction would be the best opportunity for locating the nest, since it is normally plugged on completion. (We hope in future work to test whether poorly-plugged nests--as found at Lopinot in 1993--suffer more predation than well-plugged ones). In addition, the emergence of the maggots from the foam a day after tadpole hatching is well correlated with the development of the frog: the original nest foam is stable and cohesive so that if the burrow is flooded by heavy rain soon after oviposition, the nest remains intact. However, the foam made by tadpoles soon after they hatch (Downie, 1984) is easily broken up by water, allowing the tadpoles to swim off into the stream; if maggots remained in the nest till this stage, they would risk drowning. These details contrast with those found by Villa (1977, 1984) in the Centrolenella (glass frog)-Zygothricha (drosophilid) relationship. Zygothricha oviposited on the day following Centrolenella mating, or even during the next few days, though the time to pupation (5-7 days) is not dissimilar to our findings forM. nidanurae.

Our data on frequency of nest predation and numbers of maggots per nest are clearly too preliminary for comment, but offer considerable scope for further investigation.

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Page 12: A new species of Megaselia (Diptera, Phoridae) whose larvae prey upon the eggs of Leptodactylus fuscus (Anura, Leptodactylidae)

1002 J .R . Downie et al.

A c k n o w l e d g e m e n t s JRD' s work on foam-nesting frogs in Trinidad was supported by the Royal Society

and the Carnegie Trust. RHLD' s work on Phoridae has been funded by the Isaac Newton Trust (Trinity College, Cambridge) and the Harold Hyam Wingate Foundation (London). Field-work done in Trinidad in 1993 was part of a University of Glasgow Expedition supported by many agencies. We are grateful for the laboratory facilities freely given by the Department of Zoology, University of the West Indies, St Augustine, to Tristan Hatton-Ellis for taking the photograph shown as Fig. 1 and to Patricia Johnston for typing the manuscript.

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BORGMEmR, T., 1964, Revision of the North American phorid flies Part II. The species of the genus Megaselia., subgenus Aphiochaeta (Diptera, Phoridae), Studia Entomologica, Petropolis, 7, 257-416.

BORGMEIER, T., 1969a, Bredin-Archbold-Smithsonian biological survey of Dominica: the Phoridae of Dominica (Diptera), Smithsonian Contributions Zoology,, 23, 1-69.

BORGMEIER, T., 1969b, New or little-known phorid flies, mainly of the Neotropical Region (Diptera, Phoridae), Studia Entomologica, Petropolis, 12, 33-132.

BORGMEIER, T., 1971, Further studies on phorid flies, mainly of the Neotropical Region (Diptera, Phoridae), Studia Entomologica, Petropolis, 14, 1-172.

DISNEY, R. H. L., 1983, Scuttle flies Diptera Phoridae (except Megaselia), Handbook for the Identification of British Insects, 10(6), 1-81.

DISNEY, R. H. L., 1994, Scuttle Flies: The Phoridae (London: Chapman & Hall). DOWNIE, J. R., 1984, How Leptodacrylusfuscus tadpoles make foam, and why, Copeia, 1984,

778-780. DOWNIE, J. R., 1988, Functions of the foam in the foam-nesting Leptodactylid Physalaemus

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dae) 1: descriptive analysis, Herpetological Journal, 4, 29-38. DOWME, J. R., 1994b, Developmental arrest in Leptodactylus fuscus tadpoles (Anura:

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DUELLMAN, W. E., and TRUEB, L., 1986, Biology of Amphibians (New York: McGraw- Hill). GOSNER K. L., 1960, A simplified table for staging anuran embryos and larvae with notes on

identification, Herpetologica, 16, 183-190. HE'~ER, W. R., 1978, Systematics of the fuscus group of the frog genus Leptodactylus (Amphibia,

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J. R. Vockeroth and D. M. Wood (eds), Manual of Nearctic Diptera, Vol. 2, Canada: Research Branch Agriculture Canada, Monograph 28, Chapter 51,689-712.

VmLA, J., 1977, A symbiotic relationship between frog (Amphibia, Anura, Centrolenidae) and fly larvae (Drosophilidae), Journal of Herpetology, 11, 3 l 7-322.

VmLA, J., 1980, 'Fmgflies' from Central and South America with notes on other organisms of the amphibian egg microhabitat, Brenesia, 17, 49-68.

VmLA, J., 1984, Biology of a neotropical glass frog, Centrolenellafleischmanni (Boettger), with special reference to its frogfly associates, Milwaukee Public Museum Contributions in Biology and Geology, 55, 1-60.

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'Frogfly' maggots attack foam nests 1003

VILLA, J., MCDIARMID, R. W., and GALLARDO, J. M., 1982, Arthropod predators of leptodactylid frog foam nests, Brenesia, 19/20, 577-589.

VILLA, J., and TOWNSEND, D. S., 1983, Viable frog eggs eaten by phorid fly larvae, Journal of Herpetology, 17, 278-281.

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