Prey Recognition in Larvae of the Antlion Euroleon Nostras (Neuroptera, Myrrneleontidae)

Home , Antlion, Euroleon, Euroleon nostras, Neuroptera, Neuropterida

Acta Zool. Fennica 209: 157-161 ISBN 95 1-9481-54-0 ISSN 0001-7299 Helsinki 6 May 1998 O Finnish Zoological and Botanical Publishing Board 1998

Prey recognition in larvae of the antlion Euroleon nostras (Neuroptera, Myrrneleontidae)

Bojana Mencinger

Mencinger, B., Department of Biology, University ofMaribor, Koro&a 160, SLO-2000 Maribor, Slovenia Received 14 July 1997

The behavioural responses of the antlion larva Euroleon nostras to substrate vibrational stimuli from three species of prey (Tenebrio molitor, Trachelipus sp., Pyrrhocoris apterus) were studied. The larva reacted to the prey with several behavioural patterns. The larva recognized its prey at a distance of 3 to 15 cm from the rim of the pit without seeing it, and was able to determine the target angle. The greatest distance of sand tossing was 6 cm. Responsiveness to the substrate vibration caused by the bug Pyrrhocoris apterus was very low.

1. Introduction efficient motion for antlion is to toss sand over its back (Lucas 1989). When the angle between the The larvae of the European antlion Euroleon head in resting position and the head during sand nostras are predators as well as the adults. In loose tossing is 4S0, the section of the sand tossing is substrate, such as dry sand, they construct coni- 30" (Koch 1981, Koch & Bongers 1981). cal pits. At the bottom of the pit they wait for the Sensitivity to vibration in sand has been stud- prey, which slides into the trap. Only the head ied in a few arthropods, e.g. in the nocturnal scor- and sometimes the pronotum of the larva are vis- pion Paruroctonus mesaensis and the fiddler crab ible; the other parts of the body are covered with Uca pugilator. They can determine the direction grains of substrate. They feed on small arthro- and the distance of a vibration source (Brownell pods such as insects, isopodes, mites, spiders, & Farley 1979, Aicher & Tautz 1990). diplopods and chilopods (Koch & Bongers 1981, Sand as a medium attenuates substrate vi- Gepp & Holzel 1989). bration. Propagation velocity in sand depends on The antlions exhibit certain behavioural pat- frequency. The propagation of disturbances in terns when trying to capture the prey: tossing the sand also depends on the size of the particles and sand at the escaping prey, openinglclosing their on the moisture content, and the amount of damp- jaws and occasionally traveling short distances in ing varies with the frequency (Aicher & Tautz the direction of the prey (Devetak 1985, Lucas 1990). 1989, Mencinger 1995). The aim of this study was to determine the The antlions are not equally efficient in toss- cues for prey recognition when the prey is moving sand in all directions. The easiest and the most ing on the surface of the sand. Mencinger ACTA ZOOL. FENNICA Vol. 209

Fig. 1. The measured parameters when the antlion larva reacted to the presence of the prey. cx = target angle, 0 = sand tossing angle, a = target distance, b = sand tossing distance.

2. Materials and methods angle between the antlion's long axis and the end point of the sand tossing (Fig. 1). The depth and diameter of the pit Third instar larvae of Euroleon nostras were collected in were also determined. NE Slovenia. All experiments were carried out dunng the In the second part of the experiment the eyes of the daytime at a temperature range from 18 to 29OC, and a hu- antlions were covered with a paint EDIGS to exclude visual stimuli. The reactions of the antlions to the presence of the midity range from45 to 80%. Each individual was kept in a prey were recorded. plashc contalner (50 X 50 X 240 mm, tilled w~thsand to the height of 40 mm, the grain diameter < 500 pm). Vibrations Results of the experiments were analyzed with the com- of the environment were excluded wlth 2 layers of styrofoam puter program Videoanalyse made by Michael Poteser, and a car tyre below each container. University of Graz, Austria, Institute for Zoology. The antlions were fed wlth one ant Formica sp. per day. Behavioural responses of the antlion larva were re- 3. Results corded with a Sony video camera CCD-TR750E. The following prey species were used in the experiments: mealworms Tenebno molitor, tsopodes Tracheltpus The antlion larvae reacted to the presence of the sp. and bugs Pyrrhocoris apterus. prey in the container with the following behav- The prey was dropped onto the sandsurface 18 cm away ioural patterns: greater locomotory activity, anten- from the antlion Trials were evaluated only if the antlion nal movement, openinglclosing of jaws, sand toss- responded to the stimuh within 2 minutes. ing, and snappinglgrasping. At the moment when the larva reacted to the presence The intact larvae recognized their prey - a of the prey with sand tossing we measured the distance he- tween the prey and the centre of the plt, the distance be- mealworm Tenebrio molitor and an isopode tween the centre of the pit and the end of sand tossing, the Trachelipus sp. at a distance of 3 to 15 cm from angle between the anthon's long axis and the prey, and the the rim of the pit (Fig. 2). They tossed sand in the ACTA ZOOL. FENNICA Vol. 209 Prey recc 7gnition in antlion larva Euroleon nostras 159

-180 -90 0 9 0 180 a Fig. 3. Sand tossing angle P as a funct~onof target angle a. - A: lntact antlion, target Tenebrio molitor. 0 30 60 90 120 150 - B: Blind antlion, target Tenebrio molitor. -C: lntact Distance (mm) antlion, target Trachelipus sp. Fig. 2. Frequency of the behavioural responses at different distances (In mm) of the target from the centre In a few cases, the larvae travelled up from of the pit (a). - A: lntact antlion, target Tenebrio molitor. - B: Blind antlion, target Tenebrio molitor. - the bottom of the pit to the surface in the direction C: lntact antlion, target Trachelipus sp. of the prey, or they oriented so that the prey was posterior to the antlion's body, in order to throw sand directIy at their prey. direction of the vibrational signals caused by the One day before the antlion larvae pupated they moving prey (Fig. 3). The distance of the sand did not react to the presence of prey. tossing was from 0.7 to 6 cm (Fig. 4). Responsiveness to the substrate vibration The error angle between the position of the caused by the bug Pyrrhocoris apterus was very prey and the sand tossed was dependent on the low. The antlion larvae reacted to the presence of position of the moving prey. When the prey was the bug only in five cases out of 30. on the posterior side of the antlion the error angle was smallest (Table 1). There are no statistical differences between 4. Discussion intact larvae and blind larvae in detection of vibrational signals in sand caused by the prey (Ftest, Propagation of vibrational signals through a solid 0.3 < P < 0.7). substrate, water or air has an important role for 160 Mencinger ACTA ZOOL. FENNICA Vol. 209

6 0 communication in arthropods, for recogni~inga 50 mate, an enemy, or a prey (Wiese 1974, Michel- et & h sen al. 1982, Mark1 1983, Bleckmann Barth U 40 1984, Bleckmann & Rovner 1984, Gogala 1985, d Dambach 1989). Pit-digging antlion larvae are 8 30 W semi-sessile predators and thus dependent on 20 6-I prey activity for their food supply (Griffiths 1991). 10 The antlion larva Euroleon nostras can per- o ceive vibrational signals over a certain distance. The greatest responses were when the prey was the mealworm Tenebrio molitor. During locomotory activity it beats with the abdomen on the surface of sand. Thus it produces additional vibrational signals in sand. The distance depends on the direction of transmission. The predators recognize their victims at a distance of 3 to 15 cm from the rim of the pit without seeing them. The greatest distance of the sand tossing was 6 cm. In sand, artificial vibrational signals (Brownell 1977, Devetak 1985, Aicher & Tautz 1990) or signals resulting from the animal's activity (Aicher & Tautz 1990) are considerably attenu- ated. In complex environments certain sound fre- quencies are less damped than others (Michelsen 1985). Detection of the prey increases with the body weight of the prey (Mencinger 1995). Prey recognition in the antlion larva involves many elements consisting of visual, tactile and vibratory stimuli caused by its potential prey.

Di S tance (mm) Acknowledgements. Thanks are due to Dr. D. Devetak, Fig. 4. The frequency of the distances (in mm) of the Department of Biology, Univers~tyof Maribor, Slovenia, sand toss~ng(b). - A: Intact antlion, target Tenebrio for advice and reading the manuscript, and to Michael rnolitor. - B: Blind antlion, target Tenebrio molitor. - Poteser, Insbtute for Zoology, University of Graz, Austria, C: Intact antlion, target Trachelipus sp. for help with a computer program.

Table 1. Error angle (mean k S.E.) of the antlion Euroleon nostrasas a function of target angle and sand tossing angle. 0" is directly ahead, 180" directly behind the antlion; n refers to the number of responses of the antlions.

Target angle: 0-45" 45-90" 90-1 35" 135-1 80" lntact antlion Target Tenebr~o n Target Trachelipus n Blinded antlion Target Tenebrio n ACTA ZOOL. FENNICA Vol. 209 Prey recognition inantlion larva Euroleon nostras 161

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Reference Citation: Mencinger, B. 1998 [1998.??.??]. Prey recognition in larvae of the antlion Euroleon nostras (Neuroptera, Myrmeleontidae). in Panelius, S. P. (ed.). Neuropterology 1997. Proceedings of the Sixth International Symposium on Neuropterology (13-16 July 1997, Helsinki, Finland). Acta Zoologica Fennica 209:157-161.

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