NEUROPTERA INTERNATIONAL 6 (1) - 1990 p. 51-56 THE PLANIPENNIA EYE USING MANTISPA STYRIAC4 (PODA, 1761) (MANTISPIDAE) AS AN EXAMPLE Karl KRAL Institut fiir Zoologie, Karl-Franzens-Universitat,Universitatsplatz 2, A-8010 Graz, Austria La revue presentbe ici porte sur la structure de l'oeil compost de Mantispa sfyriaca (Poda, 1761), prise comme exemple pour les Planipennia. La signification fonctionnelle en est discutke. Owing to their form and their powerful claws with which they capture insects as does the praying mantis, mantispids are spectacular representatives of the neuropteran family. Very few studies of these insects of prey are available and most of them are field studies (e.g. BRAUER, 1869 ; SCHREMMER,1959 ; NEW & HADDOW, 1973). We recently began systematic laboratory experiments to study the ontogenesis, anatomy, physiology and functional significance of the optical system of Mantispa styriaca (KRAL, 1989 ;EGGENREICH & KRAL, 1990 ;KRAL et al., 1990). The purpose of this review is to make available to entomologists preliminary interesting aspects of these works. Nocturnal insects have superposition eyes, which means that they have high sensitivity to light but less capacity for spatial resolution. The superposition eyes have an unpigmented space, the clear zone, between the lens apparatus and the retina (Fig. 1). The clear zone permits light to cross between ommatidia, so that the visual cells of one ommatidium receive light from a number of neighboring ommatidia. Planipennia also have superposition eyes (Chrysopa : HORRJDGE& @ 1990 Association Mondiale des N6vr~pt6ristes U.S. Copyright Clearance Center Code Statement : 0223-5137/90/010051-06 - $2.00/0. HENDERSON,1976 ;Ascalaphus : SCMNEIDERet al. 1978 ; Mantispa : EGGENREICH &, KRAL, 1990 ;KRAL et al., 1990 ; see also Am, 1920). As these insects are usually not just active in the twilight and night but also during day - RFcalaphus is only active by day - they require good spatial resolution for their usually predatory life style. And so these superposition eyes have become highly specialized in the course of evolution. A so-ded "functional double eye" developed. The eye of Mantispa styriaca works round the clock and is to be used here as an example of the principle of duplicity. The large, emerald-green, hemispherical eyes of Mantispa sfyn'aca are made up of some 3500 ommatidia whose dimensions and structure are uniform over the entire eye. A longitudinal section through the eye shows from outside to inside three distinctly different layers : dioptric apparatus, clear zone and retina (Fig. 1). The dioptric apparatus consists of a biconvex corneal lens whose surface is covered with nipples, as has been described for other lacewings (e.g. Ascalaphus : SCHNEIDERet al. 1978). In Mantispa styriaca, these nipples probably serve as an antireflection system for long-wave light. Below the dioptric apparatus there is a cone-shaped crystalline cone. The proximal part of the crystalline cone is surrounded by two principal pigment cells (iris cells). These serve as a pupil ;the higher the light intensity, the smaller the pupil. Between the dioptric apparatus and the retina there is a relatively wide dear zone. Fig. 1 : Rough schematic reproduction of a light-microscopic longitudinal section through the compound eye of Mantispa styriaca. CC = crystalline cone ;CL = corneal lens ;CZ = clear zone ; DA = dioptric apparatus ; RE = retina ;RH = rhabdom ;0 = ommatidium. species retina scotoplc photopic Chrysopa crepuscular 3 tiers RC1-6 RC7,E RC7=motion detector nocturnal Ascalaphus diurnal 3 tiers RC1-6 RC7,E RC7,8=detectors for polarized llght (3) Mantlspa dlurnal- 3 tlers RC1-6 RC7,E RC7=mot~ondetector nocturnal RCB=detector for polar~zed lrght (?I RC=retlnula cell. Table I The retina has one retinula per ommatidium. Each retinula has 8 retinula cells (visual cells), the photosensitive cells, which are arranged in three tiers, as in the common green lacewing Chrysopa (HORRIDGE& HENDERSON,1976) and Ascalaphus (SCHNEIDERet al., 1978) (Table 1). The retinula cells form a central fused rhabdom, which is the photosensitive structure (Figs 2 & 3). In the proximal part of the clear zone the small retinula cell 7 begins to form the rhabdom, which is surrounded by the distal processes of the retinula cells 1 to 6 (Fig. 2). This relatively short rhabdom goes on in the direction of the dioptric apparatus and joins the optically dense process of retinula cell 7. Owing to its ~ig~cantlyhigher refractive index as compared to that of the cytoplasm of the surrounding processes of retinula cells 1-6, this process probably has the task of serving as a light guide for the rhabdom of retinula cell 7. The rhabdom of retinula cell 7 is short and is pushed aside by the rhabdom of retinula cell 8 at the boundary between the clear zone and the retina. Finally, the large retinula cells 1-6 form a large central rhabdom ;cell 8 is pushed to the edge but its rhabdomere remains in the rhabdom unit (Fig. 3). There is a tapetal layer on the base of the retina, a sort of mirror made up of tracheoles, as is also found in other lacewings (e.g. Chrysopa : HORRIDGE& HENDERSON,1976) ; this makes the eyes reflect light. Superficial consideration of the optical and structural organization of the eyes of Mantispa styriaca shows that, as mentioned above, they are basically superposition eyes according to their anatomy. But the organization of the retina shows that this is an oversimplification of the case. Only the retinula cells 1-6 belong de facto to the superposition eye (skotopic system, light sensitive in the long-wave range) ; the small retinula cell 7 and possibly cell 8 as well apparently belong to the "apposition eye" (photopic system, light sensitive in the short-wave or ultraviolet (UV) range). The parallel rays from a number of adjacent ommatidia leaving their crystalline cones meet at the relatively large rhabdom of the retinula cells 1-6 of an ommatidium. The size of the superposition pupil is varied by possible longitudinal pigment movement in the accessory pigment cells, as has been seen in Ascalaphus (DRASLAR,pers. comm.). Every ommatidum is surrounded by 12 accessory pigment cells (see Fig. 2). The lesser the light intensity, the greater the superposition. However, the corneal anti- reflection system (corneal nipples) and the total reflection of light on the tapetal Figs 2 & 3. - Electron-microscopic cross section throu an ommatidium of the compound eye of Mantispa stytiaca in the rhabdom region (RH) op the retinula cells (RC). PG=pigment anules of accessory pigment cells. 2, retinula cell 7 ; 3, retinula cells 1-6 and 8. Scale bar Kg. 2 : 2.0 pm, Fig. 3 : 1.5 pm. layer at the base of the retina along with the voluminous rhabdom of retinula cells 1- 6 can provide an economical light yield and thus limit the superposition ; this would mean that the capacity for spatial resolution is retained in twilight or moonlight. On the one hand, this is important for binocularly controlled prey capture at twilight or on a clear night, and on the other hand, for seeking a mate or finding a place to lay eggs. Mantispa styriaca must often fly considerable distances to perform these activities. The optically dense distal process of retinula cell 7 directly contacts the crystalline cone. This lightguiding structure crosses the clear zone and so only axially incident light on the corresponding dioptric apparatus can fall onto retinula cell 7 ; a superposition of light beams of adjacent ommatidia is therefore not possible. In addition, the 3500 ommatidia with their relatively small diameters and the resultant relatively small interommatidial angles give the "apposition eye" excellent spatial resolution capacity. This system, however, can only function under sunlight. Retinula cell 8 may be a candidate for perception of the plane of vibration of linear polarized light from the sky ; this could be indicated by the orientation pattern of the rhabdomeres of cells No. 8. In summary, we may say that in Mantispa styriaca there is quasi an "apposition eye" within the superposition eye. The amient light determines which of the systems will be active at a given time. Further comparative studies on the eyes of representatives of Hemerobiidae (brown lacewings), Sisyridae, Osmylidae, Nemopteridae and Myrmeleonidae would be interesting in this context, whereby Coniopterygidae should also not be forgotten. ACKNOWLEDGMENTS The research on Mantispa styriaca was supported by Grant P6766 from the Austrian Science Foundation. Many thanks to DuSan DEVETAKof the University of Maribor for help with collecting mantispids in Premantura, Yugoslavia. Accepted : April 1990 Asr, F., 1920. aer den feineren Bau der Facettenaugen bei Neuropteren. Zoologische Jahrbiicher, Abt. Anat. 41 : 411-458. BRAUER,I?., 1869. Beschreibung der Verwandlungsgeschichte der Mantispa stynaca Poda und Betrachtungen iiber die sogenannte Hypermetamorphose Fabre's. Verhandlungen der kaisedich-koni lichen zoolo 'schen und botanischen Gesellschaft in Wen 19 : 831-840. EGGENREICH,U. & & IC, 198External design and field of view of the compound eyes in a raptorial neuropteran insect, Mantispa stytiaca. The Joumal of openmental Biology 148 : 353-365. HORRII~GE,GA. & HENDERSON,I., 1976. The ornmatidium of the lacewing Chrysopa (Neuroptera). Proceedings of the Royal Society of London B 192 : 259-271. KRAL, K, 1989. Fine structure of the larval eyes of Mantispa sp. (Neuroptera : Planipennia, Mantispidae). International Joumal of Insect Morphology & Embryology 18 : 135-143. KRAL, K., HERBST,K. & Pmsr, MA., 1990. The compound eye of Mantispa styriaca (Neuroptera : Planipennia). Zmlogische Jahrbiicher, Abt. Physiol. (in press). NEW,T.R. & HADDOW,A.J., 1973. Nocturnal flight activity of some African Mantispidae (Neuroptera).Joumal of Entomology (A)47 : 161-168. SCHNEIDER,L., GOGALA,M., DRASLAR,K, LANGER,H. & SCHLECHT,P., 1978. Feinstruktur und Schirmpigrnent-Eigenschaften der Omrnatidien des Doppelauges von Ascalaphus (Insecta : Neuroptera). Cytobiology 16 : 274307. SCHREMMER, F., 1959. Freilandbeobachtungen zur Eiablage von Mantispa pagana F.