the life cycle of dircenna relata (ithomiidae) in costa...

258 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY

THE LIFE CYCLE OF DIRCENNA RELATA (ITHOMIIDAE)

IN COSTA RICA

ALLEN M. YOUNG

Department of Biology, Lawrence University, Appleton, Wisconsin 54911

This paper summarizes a variety of observations on the life cycle and natural history of the neotropical butterfly, Dircenna relata Butler & Druce, as studied in Costa Rica. While such studies of Brazilian members of the tribe Dircennini have been conducted (Brown & D'Almeida, 1970), the Central American ithomiid fauna generally remains to be studied in this respect. The excellent systematic studies of Central American Ithomiidae (Fox, 1968) provide a good basis for comparative studies on the biology of these butterflies and forms the foundation for examination of phylogenetic trends with respect to foodplant exploitation, behavior patterns, and a wealth of other factors underlying population biology. This paper represents an effort to study the biology of Costa Rican Ithomiidae, and supplements other similar reports (Young, 1972, in press).

METHODS

Field observations were carried out intermittently during JuneSeptember 1971 at Bajo la Hondura (San Jose Province), a montaine tropical forest locality (800-1000 m. elev.) in central Costa Rica. Observations were confined to a small breeding population of D. relata located at the bottom of the steep ravine at Bajo la Hondura; this population was discovered in exposed second-growth brush bordering the Rio Claro in the ravine.

Field studies or observations consisted of: ( 1) description of the life cycle, including estimation of developmental time and studies of larval hostplant specificity, (2) analysis of oviposition behavior, and (3) notes on larval behavior. Developmental time and larval hostplant specificity were studied in the laboratory. For these purposes, larvae at low densities were confined in tightly sealed plastic bags containing cuttings of hostplants.

RESULTS

Life Cycle and Developmental Time

The egg (Fig. 1,A) is barrel-shaped and truncated at the base. It bears several deep vertical ribs and many less distinct horizontal ribs. The egg (0.7 mm X 0.6 mm) is cream-colored when first laid but becomes deep yellow within a day. The vertical ribs remain cream-colored as the

VOLUME 27, NUMBER 4 259

egg changes color. The first ins tar larva is light green with three dorsal rows of yellow spots. The two outer rows appear continuous and the head is uniformly light green. The larva measures about 3.5 mm by the first molt. The second ins tar (Fig. I,B) is remarkably similar to the first but the central row of yellow spots now becomes interrupted with a complex patchwork of yellow and black spots. It is difficult to describe the body color pattern in terms of segments because these have become strongly subdivided in the Dircennini. The spots in the central row become square-shaped while the two outer rows continue to remain less distinct. The second instar is about 8 mm long by the second molt.

The third instar (Fig. 1, C) is very similar to the previous one, although now the general body color becomes dark green. The yellow patchwork and mottling of previous instars is retained in this instar. By the third molt the larva is about 13 mm long. The fourth ins tar (Fig. I,D) resembles the previous instar and measures about 19 mm long by the fourth molt. The fifth and final instar (Fig. I,E) is lighter green (like the second instar) and the yellow and black patchwork has become more diffuse. This instar attains a size of about 24 mm in length by 5 mm in width before changing into a truly mobile prepupa.

The prepupa is uniformly translucent light green with the yellow markings barely visible. It is an extremely active form but seldom crawls off the hostplant for pupation. The pupa measures about 11 mm in length and 7 mm in width (dorsoventrally in the thoracic region) and its coloration is somewhat variable; on light backgrounds the pupa is light green with gold markings (Fig. I,F) while on dark backgrounds the pupa is reddish-brown with gold markings (Fig. I,e). The gold markings in both forms are confined to rings around abdominal segments, legs, thorax, and wing veins. The cremaster in both cases is pink. To the human observer the pupae of this butterfly are very dazzling and reflective and when several are found together in the field they give the appearance of large drops of water reflecting sunlight.

Adults of both sexes are similar in size, having a forewing radius of about 31 mm (N = 23). There is very little sexual dimorphism in the delicate translucent orange ground coloration of the wings (Fig. I,H) . Descriptions of wing coloration are given by R. Haensch in Seitz (1924) and more recently in greater detail by Fox (1968).

Developmental time from egg to adult is summarized in Table 1. Despite a mean developmental time of 25 days, females take about a day

longer to complete ontogeny. In a total of 50 emergences, the sex ratio did not deviate significantly from unity, there being 28 males and 22 females.


Fig.!. Life cycle of Dircenna relata Butler & Druce: (A) eggs; (B-E) second, third, fourth, and fifth instars, respectively; (F -G) light and dark forms of pupa, respectively; and (H) adult female (above) and male (below).


TABLE 1. The developmental time' of Dircenna relata Butler & Druce (Ithomiinae) on its larval foodplant, Solanum hispidum (Solanaceae).

Statistics Egg 2

Mean (days) 5 2 2 ± S.E. 0.3 0.1 0.4 No. individuals studied 42 37 37 Died 0 6' 0

a Measured in the laboratory conditions (20-24 °C). b Includes an active prepupa which lasts about one day. , This mortality apparently due to handling effects.

Instars

3 4 5b

2 3 5 0.2 0.2 0.8d

37 34 34 0 3 0

d Females longer in development, by about 1 day, occurring in the fifth instar.

Larval Host Plant Specificity

Pupa

6 0.8

34 0

At Bajo la Hondura the major larval hostplant is Solanum hispidum Pers. (Solanaceae) which grows along the edges of the Rio Claro (Fig. 2) . This plant (see Standley, 1937 for description) is common in thickets of second-growth vegetation in central Costa Rica between 1300-2000 m elevation, and occurs as an armed shrub or small tree (1.5-3.0 m tall) (D.C. Wasshausen, pers. comm.). Geographically this species occurs northward to Mexico and perhaps southward into Panama. At the study site individual plants are highly scattered along the river edge (Fig. 2) and seldom occur in homogeneous patches.

Although this was the only hostplant I found for D. relata at Bajo la Hondura, caterpillars complete development successfully (with same developmental time) in the laboratory on several other species of Solanum. I tested the following species from various parts of Costa Rica: (1) S. laurefolium (from Vara Blanca, Heredia Province, 600 m elev.), and (2) S. orchraceo-ferrugineum (from San Miguel, Heredia Province, 100 m elev.). Both of these species appear very similar to S. hispidum both in life form and distribution of spines on leaves and stems. Neither one occurs at Bajo la Hondura, however.

Larval Behavior

Larvae devour their empty egg shells and always remain on the ventral surface of the leaf. Feeding may begin virtually anywhere on a leaf (i.e. first instars do not necessarily feed at the edge of a leaf). Although several caterpillars may be found on a single leaf of S. hispidum, they are never gregarious. This is in sharp contrast to the larvae of Mechanitis isthmia isthmia Bates (Ithomiidae), in which both feeding and resting are highly gregarious. But nongregarious larval behavior also occurs in other species of Costa Rican ithomiids such as Godyris caesiopicta


Fig. 2. Habitat and hostplant of Dircenna relata Butler & Druce at Bajo la Hondura, Costa Rica. Both adult D. relata and individuals of Solanum hispidum (large inset to the left), the major larval host plant, are distributed sparsely along the rocky edge of the Rio Claro (remainder of photo). The hostplant does not occur in the primary-growth forest lining the Rio Claro further back.

Niepett* (Young, in prep.), Napeogenes tolosa amara Godman (Young, in prep.), H ymenitis nero (Hewitson) (Young, 1972), and Pteronymia notilla Butler & Druce (Young, in press).

Larvae appear to be cryptically colored when on the undersides of the very hairy leaves of S. hispidum, and younger ins tars are especially difficult to find in the field. All instars are generally diurnal feeders, resting at night near major veins of leaves. In the field, larvae of all ins tars are most frequently encountered on the lowest leaves of S. hispidum, and mixed age groups are frequently seen. Larvae have never been found on apical leaves.

Neither predation nor parasitism on larvae have been observed in the field. Of a total of 37 additional larvae (of all ins tars ) collected in the field and reared in the laboratory, none gave rise to parasitic flies or wasps.

"This is the old name for this subspecies, and it was brought to my attention by Keith S. Brown, Jr., who encountered it in Lepidoptera Niepettialla (Vo1. 2); it was renamed by R. M. Fox as G. z. sorites.


Oviposition Behavior

Oviposition sequences were witnessed on several occasions, first on 11 July 1971 at 1220 (CST). A female patrols around the hostplant, lights on the ventral surface of a large, older leaf near the ground, and walks around, depositing several eggs. Eggs are loosely clustered (Fig. 1,A) and many are only loosely attached to the leaf by entwining hairs (i.e. there is no actual adhesion of eggs to the leaf). Eggs are not clustered in an orderly fashion as seen in other species of ithomiids (e.g. Mechanitis isthmia) but rather are scattered haphazardly on the leaf. It is possible that some eggs may become jarred loose, perhaps resulting in substantial mortality. However, it is equally possible that eggs are held securely by the very dense leaf hairs (Fig. 1,A).

Eggs frequently are laid on leaves where eggs had been desposited previously. The same female will often return to the same leaf to lay additional eggs over several successive oviposition sequences. Eggs are not laid on the younger apical leaves of the hostplant. An individual female, on the average lays between 1 and 14 eggs during a single visit to a leaf. Females always "drum" a leaf with the forelegs before laying an egg. Oviposition at Bajo la Hondura probably occurs throughout the day, although it is most frequent between 1130 and 1430.

Undoubtedly ovipositing females are quite vagile owing to the highly dispersed distribution of S. hispidum. A female ovipositing on a given individual hostplant will flyaway after several oviposition sequences (i.e. after about 10 minutes of interrupted patrolling) and may search for other individual plants on which to oviposit.

Courtship activity has never been observed in the immediate vicinity of hostplants. This behavior may occur in the understory of the primary growth forest that covers the sides of the ravine at Bajo la Hondura.

DISCUSSION

Although the Ithomiidae are generally solanaceous-feeding butterflies in the caterpillar stage, rendering at least one species unpalatable to some predators (Brower & Brower, 1964), it is apparent that this group has experienced several lines of phylogenetic diversification into several tribes differing substantially in morphology of both adults and immatures (Fox, 1940, 1967, 1968; Brown & D' Almeida, 1970). One of these tribes is the Dircennini, which contains several genera including Ceratinia, Dircenna, and Pteronymia (see Brown & D'Almeida, 1970, p . 14-15). Since these and other genera within this tribe presumably share some portion of their evolutionary history, it is interesting to discuss the life cycle and natural history data for D. relata in terms of similar studies of


other genera in the tribe, and genera in other tribes. It is realized, however, that contemporary differences in the biological properties of different species and genera in any animal group must not only be molded by evolutionary history, but also by simultaneous ecological factors operating on breeding populations (Birch & Ehrlich, 1967). The following comparisons are limited to a few illustrative examples that emphasize both similarities and divergences in life cycle and natural history.

Young (in press) found that Pteronymia notilla at Cuesta Angel in Costa Rica has an egg-adult developmental time of about 30 days on Cestrum megalophyllum (Solanaceae), which is about five days longer than the developmental time of D. relata on Solanum hispidum, under similar conditions. Brown & D' Almeida (1970) report a developmental time of about 45 days for Ceratiscada canaria on Solanum caavurana under presumably laboratory conditions in Rio de Janeiro. Young (1972) found the developmental time of Hymenitis nero (not in the Dircennini) on Cestrum standleyi (eggs from a Cuesta Angel population) to be about 30 days in the laboratory. Based on these very fragmentary records involving different foodplants, it is still not possible to assign generic or tribal differences in developmental time for these ithomiids. With respect to the duration of the egg stage, if we assume equal environmental conditions for the forementioned species, the genera Dircenna, Pteronymia, and H ymenitis (as represented by the species discussed) all have an incubation period of 4-5 days; but the incubation period of Ceratiscada is 9-10 days (Brown & D'Almeida 1970). It is very likely that there exists a wealth of unpublished measurements of egg-adult developmental in many genera and species of ithomiids on various foodplants by workers in Central and South America; I would like to make a plea to bring all of these data together and look for a phylogenetic pattern of developmental time (within tribes), especially where similar foodplants are involved. If more information is obtained regarding leaf toughness and secondary compounds for different genera of Solanaceae, such data would also shed light on developmental time differences resulting from foodplant differences rather than evolutionary history among the ithomiids. Since incubation period may be only indirectly influenced by foodplant (in cases where the female's foodplant affects egg duration), it may be best to examine differences in duration of the egg stage among genera and tribes.

Rather pronounced differences in external morphology of immatures are also evident among different genera of ithomiids. For example, the egg of D. relata is very different in appearance from that of Hymenitis nero, Pteronymia notilla, and Ceratiscada canaria. First, the egg of D.


relata is deep yellow, essentially spherical, and has a system of external horizontal and vertical ribs; the egg of P. notilla is white and more oblong in shape than the egg of D. relata (Young, in press). Furthermore, it lacks very definite horizontal ribs. While the egg of H. nero is also uniformly white, it's shape approaches that of D. relata and it has a similar array of vertical ribs as seen in P. notilla. Although the egg of C. canaria is white, the shape and distribution of vertical and horizontal ribs (grooves) are similar to that of D. relata (as determined from the egg description of C. canaria given in Brown & D'Almeida, 1970). The size of the egg of D. relata is closer to that of C. canaria while those of the other two genera (Pteronymia and Hymenitis) are smaller.

The coloration and extent of hair on body segments varies very strikingly when Dircenna (as seen by D. relata) caterpillars are compared to caterpillars of other genera such as Hymenitis, Pteronymia, and Ceratiscada. While it is not necessary to go into a detailed account of these differences here, the caterpillars of D. relata are hairy while those of H. nero, P. notilla, and C. canaria generally lack hairs on body segments in all ins tars (see larval descriptions in Brown & D' Almeida, 1970; Young, 1972, in press, and present report). Furthermore, the color patterns of the body in caterpillars of H. nero, P. notilla, and C. canaria consist of a dark green background color with lighter lateral stripes, usually yellow or light blue; the color pattern of the caterpillars of D. relata is very different, being a linear patchwork of yellow spots on a light green and speckled background color (Fig. 2, B-E).

The pupae of these genera are also different. The major difference is in the extent of reflective coloration on the external surfaces. The pupa of P. notilla is generally devoid of gold or silver markings, with the color being translucent yellowish-green (Young, in press). The pupae of both H. nero and C. canaria are remarkably similar in terms of the highly reflective silver cover on the wings (Young, 1972; Brown & D' Almeida, 1970). The network of reflective gold coloration on the pupa of D. relata (Fig. 2,F,G) is different from the previous two color patterns. It is interesting that there occurs considerable similarity between the pupae of Hymenitis and Ceratiscada since these genera belong to different tribes (Fox, 1940), while considerable divergence in appearance of the pupa occurs within the Dircennini, as typified by D. relata, P. notilla, and C. canaria.

Finally, it is interesting to consider some differences in larval and adult behavior among different genera. The ithomiid Mechanitis isthmia (see Fox, 1967) lays its eggs in tight clusters on the food plant (pers. obs., Costa Rica and EI Salvador), but most other ithomiids in other


genera do not show this type of oviposition behavior. For example, H. nero, P. notilla, C. canaria generally lay their eggs singly but D. relata exhibits loose clustering of eggs (Fig. 2,A). The size and orderliness of egg clusters in D. relata are very different from M. isthmia. From recent considerations (Labine, 1968) it would seem that marked differences in oviposition behavior accompany differences in egg productivity of individual females in different species, and differences in the spatial distribution of preferred foodplants (for egg-laying) in different species. It is therefore difficult to obtain phylogenetic correlations for egg-laying behavior in butterfly groups such as the Ithomiidae.

It follows from the oviposition behavior that different genera have different degrees of larval gregariousness on the foodplant. The caterpillars of M. isthmia form very tight and coordinated groups on leaves of the foodplant (pel's. obs.) in which there is group feeding and resting periods. This is very different from group organization in D. relata where each caterpillar is very individualistic for feeding, resting, and general locomotor activities. The more usually encountered situation, as seen in H. nero, P. notilla, and C. canaria, is where caterpillars occur singly on leaves and there is little or no evidence of group interaction of any sort when more than one individual is on the same leaf. For the ithomiids, it is clear that the degree of group interaction in caterpillars is a direct consequence of the type of oviposition.

SUMMARY

( 1) The life cycle of the itomiid butterfly, Dircenna relata Butler & Druce, is described for the first time.

(2) The egg-adult developmental time on a natural foodplant, Solanum hispidum Pers. (Solanaceae) is about 25 days under constant laboratory conditions. But caterpillars are capable of successfully completing development on several other species of Solanum.

( 3) The eggs are laid in loose clusters on leaves of the foodplant, and the number of eggs in each cluster is very variable. Eggs are generally laid on lower, older leaves and the caterpillars subsequently form loose, disorganized aggregations. There is no evidence of coordinated activity patterns (feeding, resting, etc.) among individuals within a "group." The loose association of the caterpillars is interpreted as a direct result of the loose clustering of eggs.

( 4) An attempt is made to compare morphology, developmental time, and behavior patterns among different genera of Ithomiidae within the tribe Dircennini and outside it. In the absence of further data on these species and others, it is difficult to separate phylogenetic from contempo-


rary ecological selective forces for the characteristics studied. A plea is made for the bringing together of unpublished data on developmental time and foodplants as gathered by different workers in Central and South America, so that a more grandiose attempt to look for phylogenetic trends in these characteristics underlying population biology and habitat selection can be made.

ACKNOWLEDGMENTS

This is a contribution from a College Science Improvement Grant (COSIP, GY-4711) awarded to Lawrence University. Research facilities in Costa Rica were provided by Dr. J. Robert Hunter of the Associated Colleges of the Midwest. Technical assistance in the field and laboratory was given by Patrick Eagan. Dr. D. C. Wasshausen (Smithsonian) identified all Solanaceae. Dr. Keith S. Brown, Jr. (Rio de Janeiro) also identified the species studied, and as a reviewer, made very helpful suggestions on the manuscript.

LITERATURE CITED

BIRCH, L. C. & P. R. EHRLICH. 1967. Evolutionary history and population biology. Nature (London) 214: 349-352.

BROWER, L. P. & J. V. Z. BROWER. 1964. Birds, butterflies, and plant poisons: a study in ecological chemistry. Zoologica 49: 137-159.

BROWN, K. S., JR. & R. F. D'ALMEIDA. 1970. The Ithomiinae of Brazil (Lepidoptera: Nymphalidae). II. A new genus and species of Ithomiinae with comments on the tribe Dircennini D'Almeida. Trans. Amer. Entomo!' Soc. 96: 1-17.

Fox, R. M. 1940. A generic review of the Ithomiinae. Trans. Amer. Entomo!' Soc. 66: 161-207.

1967. A monograph of the Ithomiidae (Lepidoptera). Part III. The tribe Mechanitini Fox. Mem. Amer. Entomo!. Soc. 22. 190 p.

1968. Ithomiidae (Lepidoptera: Nymphaloidea) of Central America. Trans. Amer. Entomol. Soc. 94: 155-208.

LABINE, P. A. 1968. The population biology of the butterfly, Euphydms editha. VIII. Oviposition and its relation to patterns of oviposition in other butterflies. Evolution 22: 799-805.

SEITZ, A. 1924 (ed. ). The Macrolepidoptera of the World. Vo!' 5. The American Rhopalocera. Stuttgart, A. Kernan Verlag. 1139 p.

YOUNG, A. M. 1972. On the life cycle and natural history of Hymenitis nero (Lepidoptera: Ithomiinae) in Costa Rica. Psyche 79: 284-294.

---. Notes on the biology of Pteronymia notilla (Ithomiidae) in a Costa Rican mountain forest. J. Lepid. Soc. (in press).

the life cycle of dircenna relata (ithomiidae) in costa...

Documents