258 the Life Cycle of Dircenna Relata

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 Ameri can Ithomiidae (Fox, 1968) provide a good basis for comparative studies on the biology of these butterflies and forms the foundation for examina tion of phylogenetic trends with respect to foodplant exploitation, be havior 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 June September 1971 at Bajo la Hondura (San Jose Province), a montaine tropical forest locality (800-1000 m. elev.) in central Costa Rica. Ob servations were confined to a small breeding population of D. relata located at the bottom of the steep ravine at Bajo la Hondura; this popula tion 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 host plants. 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 be come 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) re sembles 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 mark ings 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 colora tion 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. 260 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY 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). VOLUME 27, NUMBER 4 261 TABLE 1. The developmental time' of Dircenna relata Butler & Druce (Ithomiinae) on its larval foodplant, Solanum hispidum (Solanaceae). Instars Statistics Egg 2 3 4 5b Pupa Mean (days) 5 2 2 2 3 5 6 ± S.E. 0.3 0.1 0.4 0.2 0.2 0.8d 0.8 No. individuals studied 42 37 37 37 34 34 34 Died 0 6' 0 0 3 0 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. d Females longer in development, by about 1 day, occurring in the fifth instar. Larval Host Plant Specificity 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 262 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY 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 diffi cult 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. VOLUME 27, NUMBER 4 263 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.

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