Vidensk. Meddr dansk naturh. Foren. (1972) 135: 37-59 ETHOLOGICAL AND AUTECOLOGICAL STUDIES ON CANARIAN VERMILEONINAE (DIPTERA BRACHYCERA, RHAGIONIDAE = LEPTIDAE) By J0RGEN FREDERIKSEN and AXEL M. HEMMINGSEN Strradam Biological Laboratory, 3400 Hillerrad, Denmark CONTENTS 1. Introduction ............... 37 3. Adult ñies o f Lampromyia fortunata 2. Larvae of Lamprotnyia canariensis Mac- Stuckenberg, 1971 ............ 52 quart, 1838, aitd Lampromyia fortutrata A. Emergence .............. 52 Stuckenberg, 1971 ............ 38 B. Oviposition .............. 53 A. Distribution of habitats. ...... 38 C. The question of specific preferred B. Distribution of larval pits in Cenó- temperatures ............. 56 bio de Valerón ............ 39 4. Additions and corrections to Hem- a. The influence of temperature . , 42 mingsen & Nielsen (1971). ....... 57 b. The influence of humidity.. .. 49 5. Summary ................ 57 c. The influence of light ...... 49 6. Ac kno wled gmen ts ............ 58 d. Correlations ........... 50 7. Re ferences ................ 59 e. Distribution of larval pits within caves.. .............. 51 1. INTRODUCTION Previous studies in this laboratory have analysed 1) the feeding instincts of the larvae, the so-called worm-lions, which construct pits in dust similar to those of ant-lions (Hemmingsen 1963, 1968) and 2) the feeding, mating and especially the ovipository instincts of the adult flies of a variety of species of Vermileoninae from Italy, Spain, Tunesia and the 7 major Canary Islands (Hemmingsen & Regner Nielsen 1971; hereafter abbr. H. & N.). We refer to these papers for references to earlier authors. This paper is based mainly on studies in the free on the two Canarian species, Lampromyia canariensis Macquart, 1838, on Tenerife and especially L.fortunata Stuckenberg, 1971, on Gran Canaria in April-May 1971. The object was to study the influence of various ecological factors on the distribution of the larvae and on the oviposition of the adult flies, and also to compare oviposition in the field with previous studies by H. & N. in the laboratory. 3 35 J0RGEN FREDERIKSEN & AXEL M. HEMMINGSEN The habitats of both imniature stages and ovipositing females are predomi- nantly dust in niches, crevices or open caves of many sizes. But the fact that larvae in their pits are also found in dust at the base of walls and foot of palms, indicates that the primary requireinents of the species are fulfilled wherever there is sufficient shelter against the wind for dust to collect; while shelter from sun and'rain appears to constitute secondary requirements. For the adult flies the presence of flowers in the neighbourhood from which to suck nectar, is also important. 2. LARVAE OF LAMPROMYIA CANARIENSIS MACQUART, 1838, AND LAMPROMYIA FORTUNATA STUCKENBERG, 1971 A. Distribution of habitats We found caves inhabited by worm-lions from near sea leve1 to about 930 m alti- tude (above Chio and above Aguamansa on Tenerife). Fig. 1 shows that there is no partiality for the opening of the caves inhabited by worm-lions to face any special points of the compass. Also more than 100 lar- val pits at the foot of Canarian palms (Plioenix canariensis Hort.) in the palm grove in El Charco at Maspalomas, Gran Canaria, were found to be situated independently of the points of the compass. It may not be amiss to state expressly that in al1 localities dealt with in this paper we have established with certainty that at least some of the pits found con- tained worm-lions. The worm-lion pits cannot at a mere glance in al1 cases be distinguished from ant-lion pits, though generally the former have steeper walls and occur in finer dust. Where the sun occasionally penetrates into the caves larvae may sometimes be found, yet as a rule exclusively in the shade. At the foot of palms larvae were found up to 1.5 m from the palm, yet always in its shade. Where the caves are facing North the substrate may at times be more or less humid causing the larvae to become more limp and sluggish at least at times. Substrates from caves inhabited by worm-lions on Tenerife (3) and Gran Canaria (5) were most obligingly examined by Mr. Henner Bahnson, Geological Survey of Denmark. Apparently largely resulting from rock disintegration these substrates consisted of poorly sorted sand, with no regular differences between the weight frequencies of grain sizes below 1/16, 1/16-1/8, 1/8-1/4, 1/4-1/2, 1/2-1, 1-2 and above 2 mm, some even apparently tending to be equally distributed over these groups. Still, some of the samples afford evidence of sorting by wind, the weights of grain sizes, which range from below 1/16 to above 2 mm, being log normally distributed with the peak of sizes between 1/4 and 1/2 mm. STUDIES ON CANARIAN VERMILEONINAE 39 Fig. 1. Orientation of worrn- N lion-inhabited caves in Tenerife and Gran Canaria. Each small square represents a cave or a cave complex facing the respec- tive point of the compass. GRAN CANARIA S We have collected larvae in a number of localities other than those listed by H. & N. (legend of fig. 1 on p. 151). Some of these are situated so near some of those already marked in the figure quoted (Nos. 17, 18, 24, 27 and 28), that they would in the map practically coincide with them. Others fill in the gaps left, viz. on Tenerife above San Juan de la Rambla and west of Garachico on the North coast, and Güimar on the South East coast, and on Gran Canaria Arguine- guin and between Playa de Mogán and Mogán in the South West part. The flies emerged at the time of writing were, as expected, from Tenerife L.canariensis and from Gran Canaria L.fortunafa; including, however, from the “gaps” so far only two from Garachico and one from the road between Playa de Mogán and Mogán. B. Distribution of larval pits in Cenóbio de Valerón An ideal locality for studying both larval and imagina1 biology of the Gran Canaria species Lainpromyia for.tunata was the remarkable prehistoric assem- blage of caves called Cenóbio de Valerón (Fig. 2) facing S.E. about 280 m above sea leve1 near Guia in Northwestern Gran Canaria; ideal but for the frequent visits of tourists. The aborigines, the guanches, are said to have elaborated these caves on the base of cavities already preformed by nature and to have used them for various piirposes; according to one version, as granaries; according to another version, as abodes for virgins to be fattened prior to marriage. Cenóbio 3* Number of Average number Distance Number of larvae in caves Number of larvae per of larvae per from of 4 different sizes larvae Storey storey (corr. cave (corr. to flowers per storey 1 1 11 1 111 1 IV to area of IV) area of IV) m * * O O O 28 3 2-0 O 5 8.7 2.2 26 1-8- 9 12.0 3.0 22 0-0 40- 17- 13 92 175.3 35.1 20 13-9 26 46-1 I- 169 190.8 34.7 18 33-19- 9-25 12 >lo0 >112 >116 > 58 15 17-19- 24-0t 60 96.0 32.0 10 ot-ot 10 >50 16 > 76 > 156 > 52 5 38-50 88 352.0 172.0 2 * Several large caves without pits. Disinfected cave. means cloister. Actually, the caves are like small rooms or cells rather than natural caves, Some are so low that one can only couch in them, others are so dark as to be fit only to sleep in. Many walls and roofs of the original 583 caves have collapsed and left 365 caves more or less intact (information by the guardian of the caves). Of some caves only the bottom is left. The present caves (when walls and ceiling are in- tact) measure from 3 (width) x 1 (length) x 1 (height) m to 3 x 33 x 2%m. One cave of intermediary size measured 13 x 13 x 14 m. Most caves are not visible in Fig. 2, being situated on both sides of a sort of high “corridor” extending deep into the dark rear to the right in the picture. Formerly, when there was no guardian, these more or less hidden, dark caves (as also a few in the front, see Table 1) were often polluted by visitors, but had now been disinfected, which is why they house no worm-lions. No ant-lion pits were found in Cenóbio de Valerón, and the worm-lions were usually directly visible at the bottom of the pits, as described and pictured e.g. by Hemmingsen (1963). The autecological studies of the larvae reported in the following pages were substantially planned and carried out by the junior author (J.F.). STUDIES ON CANARIAN VERMILEONINAE 41 Fig. 2. Cenobio de Valerón, Northwestern Gran Canaria. In the huge cave (a) the snialler caves or cells (examples in b) fornierly used by the aborigines and Hhich house nunierous larval pits of Ln/iipron-.iafortlr,rnro, are seen. There are a larger number further back to the right in the huge cave. Average size of the caves about if x if x l+ ni. A.H. phot. 42 J0RGEN FREDERIKSEN & AXEL M. HEMMINGSEN Table 1 shows the distribution of larva1 pits according to a rough estimate of proportional cave sizes (1-IV) and storeys (1-9). With rising storey number the caves in the front part of the whole complex are in general - though not very regularly - situated more and more to the rear, more or less like the arrange- ment of seats in an ainphitlieater. It will be seen from Table 1 that there is a relatively large number of pits in the louer storeys, especially in the lowest one, with a decrease throughout the storeys.