P1: GDX Journal of Insect Behavior [joib] pp806-joir-462148 March 10, 2003 10:31 Style file version Feb 08, 2000 Journal of Insect Behavior, Vol. 16, No. 1, January 2003 (C 2003) Efficiency of Fruit Juice Feeding in Morpho peleides (Nymphalidae, Lepidoptera) M. C. N. Knopp1 and H. W. Krenn1,2 Accepted August 9, 2002; revised October 22, 2002 We have described the feeding behavior of the frugivorous butterfly Morpho peleides (Butler 1872) under various conditions and tested its ability to take up fluid from selected natural and artificial food sources in comparison with the nectarvorous Vanessa cardui (Linnaeus 1758). Both nymphalids showed similar probing behavior except for one particular proboscis movement and the fact that M. peleides was unable to feed from Lantana flowers. In 2-min feeding trials, M. peleides imbibed a greater amount of fluid from the food sources, with the most conspicuous difference on rotting banana. Without time restriction, M. peleides gained a significantly greater percentage of body weight from soaked plotting paper, whereas no significant difference occurred from tubular artificial flowers. The ability of M. peleides to feed more effi- ciently from wet surfaces than V. cardui is discussed in context with proboscis morphology. KEY WORDS: feeding behavior; fruit feeding; mouthparts; proboscis; butterfly; Morpho; Nymphalidae. INTRODUCTION Any tropical forest butterfly community can be divided into two adult feed- ing guilds. Members of the nectarvorous guild obtain the majority of their nutritional requirements from floral nectar and those of the frugivorous guild 1Institute of Zoology,Department of Evolutionary Biology,University of Vienna, Althanstrae 14, A-1090 Vienna, Austria. 2To whom correspondence should be addressed. e-mail: [email protected]. Fax: +43 1 42779544. 67 0892-7553/03/0100-0067/0 C 2003 Plenum Publishing Corporation P1: GDX Journal of Insect Behavior [joib] pp806-joir-462148 March 10, 2003 10:31 Style file version Feb 08, 2000 68 Knopp and Krenn feed primarily on juices of rotting fruit or fermenting tree sap (DeVries, 1987, 1988; DeVries et al., 1997). Species of the fruit-feeding guild all belong to the Nymphalidae, and in this context Morpho peleides is one of the best-studied representatives. This neotropical butterfly is a well-known fruit-feeder and observations clearly indicate that it virtually never visits flowers for nectar (Young, 1975; DeVries, 1983, 1987). Its food preferences and its resource exploitation in the habitat have been studied (Young, 1975, 1979; DeVries, 1983, 1988), however, detailed knowledge of the behavior during feeding and the amount of fluid imbibed is lacking. The proboscis of butterflies is adapted primarily for the uptake of nectar from flowers. A number of proboscis features and the patterns of proboscis movements could be functionally interpreted in context with the extraction of nectar from blossoms (Krenn, 1990, 1998; Paulus and Krenn, 1996). A comparison of the mouthparts between nymphalids of both feeding guilds re- vealed a characteristic proboscis morphology for the fruit-feeders including Morpho species. It was hypothesized that features of the proboscis tip might enhance the performance of fluid uptake from surfaces such as squashed fruit (Krenn et al., 2001). The aim of this paper is to describe the feeding behavior of Morpho peleides on rotting fruit and to compare this with the flower handling capa- bility of the proboscis in a nectarvorous nymphalid butterfly. A characteristic pattern of probing movements of the uncoiled proboscis and a distinct bend at one-third of the proboscis length have been described in nectarvorous butterflies (B¨anziger, 1971; Krenn, 1990, 1998; Penz and Krenn 2000). The analysis of the behavioral characters in fruit-feeding butterflies addresses the question if there is a specialized pattern of proboscis movements which could be interpreted in context with fluid uptake from a wet surface of rotting fruit. To investigate the efficiency of fluid uptake we experimentally tested the amount of fluid that can be imbibed from a variety of artifical nectar sources which mimic different conditions of fluid accessibility. MATERIALS AND METHODS Pupae from M. peleides were purchased from Worldwide Butterflies and Lullingstone Silk Farm (Dorset, UK) and reared in laboratories at the University of Vienna. A second generation was reared in the laboratory on Medicago x varia (Fabaceae). Eggs from V. cardui were purchased from Carolina Biological Supply Company (Burlington, N. C.). Larvae of the first generation were reared on artificial food (Carolina Biological Supply Company); larvae of the succeed- ing generations, on Cirsium arvense (Asteraceae). P1: GDX Journal of Insect Behavior [joib] pp806-joir-462148 March 10, 2003 10:31 Style file version Feb 08, 2000 Fruit Feeding in Morpho peleides 69 The experimental and behavioral studies were conducted in a green- house at the University of Vienna. Both natural and artificial food sources were used. Natural food sources included inflorescences of Lantana camara (Verbenaceae) and small amounts of squashed, rotting banana, presented on a petri dish. Inflorescences of L. camara are well known for their attrac- tiveness for a great variety of butterflies and have repeatedly been used in experimental observation of butterfly feeding behavior (Weiss, 1991; Penz and Krenn, 2000). Bananas were shown to be an attractive food for M. peleides in natural environments (Young, 1975). As artificial food sources we used cotton wool and plotting paper, both saturated with nectar mimics of L. camara, which contains a variety of sugars and amino acids (Alm et al., 1990), and presented them on a petri dish. In addition, for the experimental studies we used an artifical flower which consisted of a glass tube with a diameter of 1.5 mm, fixed in a polystyrene panel to serve as a landing site for the butterflies. The bottom of the tube was immersed in a glass of liquid nectar mimics, and by capillary action the glass tube became filled. Feeding behavior was recorded with a videocamera (Canon Canovision EX Hi8); the videotapes were analyzed on a TV monitor using the computer program The Observer Version 3.0. The butterflies were set on the food source and filmed until they left it or until 7 min had elapsed. More than 80% of the butterflies left the food source within 7 min. As the food source we used rotting squashed banana (for both species N = 7). The movements of the proboscis (coiled or uncoiled position, probing, and sucking) were measured as percentages of the observed time; the sequences of up-and- down movement were measured as events per minute. To study the efficiency of fluid uptake we measured the weight of the butterflies before and after feeding tests. For this purpose the butterflies were narcotized with CO2 and their weight was measured on a high-performance balance with a reading accuracy of 0.0001 g (Sartorius MC-1 Analytic AC 120S). The weight difference between before and after feeding represented the amount of fluid the butterflies had taken in. In the first feeding trial we tested the amount of fluid uptake during a 2-min period. The feeding sequence started with inflorescences of L. camara on the third day after emerging from pupae. The next feeding tests were carried out after a day of “rest” during which the butterflies were given only water to ensure a suffi- cient level of hunger. Tests proceeded in the following order: cotton wool, plotting paper, rotting banana, and tubular artificial flower (M. peleides, N = 9; V. cardui, N = 11). Two days after this feeding sequence one group of butterflies from each species was tested on plotting paper (M. peleides, N = 5; V. cardui, N = 16), and a second group on tubular artifical flower (M. peleides, N = 6; V. cardui, N = 8), without any time restriction (ad libitum). When the individuals P1: GDX Journal of Insect Behavior [joib] pp806-joir-462148 March 10, 2003 10:31 Style file version Feb 08, 2000 70 Knopp and Krenn ceased feeding they were stimulated with a drop of nectar on the midtarsi, which led to uncoiling of the proboscis and further feeding. The tests were stopped when the butterflies did not recommence feeding after having been given a stimulus twice. The proboscis length was measured in narcotized specimens using a Vernier caliper with a reading accuracy of 0.1 mm. Horizontal widths of the proboscis and of the food canal were measured in semithin cross sections at various distances from the base (M. peleides, N = 7; V. cardui, N = 5). For the preparation of semithin sections, heads were fixed in alcoholic Bouin solution and embedded in epoxy resin (Pernstich et al., 2003). RESULTS Feeding from Rotting Banana During food uptake the uncoiled proboscis bends distinctly at about one-third of its length. At this point, the proboscis is flexed downward and the tip region is sharply bent toward the body (Fig. 1). This results in a posture of the proboscis in which the proximal region is nearly horizontal, the distal region after the bending is held in a more or less vertical position, and the dorsal side of the tip region is positioned over the fruit (Fig. 1). Probing movements of the proboscis comprised (1) an up-and-down motion of the whole proboscis at its connection to the head, (2) an up-and-down motion of the whole proboscis produced by elevation and lowering of the head, (3) to-and-fro movements of the proboscis tip produced by flexion and extension of the bend, (4) a sideways motion produced by the turning head. These movements permit a range of action that included (a) maximal lateral movements in which the tip extends approximately to the tarsi of the legs, and (b) maximal forward movements in which the bend region is slightly stretched and the proboscis is fully extended in a forward sloping position so that only the apex touches the fruit.