Journal of the Lepidopterists' Society 40(3),1986,214-217

GROWTH OF THE BUCK MOTHS LUCINA AND H. MAlA () ON THEIR OWN AND ON EACH OTHER'S HOSTPLANTS

NANCY E. STAMP Department of Biological Sciences, State University of New York, Binghamton, New York 13901

AND

M. DEANE BOWERS Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138

ABSTRACT. We compared larval growth of Hemileuca lucina and H. maia on their own and on each other's hostplants. As expected, relative growth rate (RGR) of H. lucina was higher on its own host ( lati/olia) than on the non host (Quercus prinoides). Unexpectedly, RGR of H. maia on its own host (Q. prinoides) and on the nonhost (S. lati/olia) were low and similar.

Two species of buck moths, Hemileuca lucina Hy. Edw. and H. maia (Drury) (Saturniidae), occur in the northeastern United States. They overlap some in geographic range, but their hostplants are usually different. Hemileuca maia is widespread but uncommon in the eastern United States, occurring from Massachusetts and Michigan south to Texas and Florida, and west to Missouri and Illinois (Ferguson 1971). It is usually associated with scrub oak, Quercus ilicifolia Wang. (Fagaceae), al­ though it has been reported feeding on other oak species (Q. laevus, Q. rubra, Q. stellata and Q. velutina) (Tietz 1972). It also has been found on willow (Salix sp.), poplar (Populus sp.) and cherry (Prunus sp.) (Tietz 1972). Although Tietz (1972) reports H. maia on Spiraea salicifolia, this may have been a mistaken identification. In comparison to H. maia, H. lucina occurs in Massachusetts, south­ ern Maine and New Hampshire. Sometimes it is abundant, but popu­ lations are quite local and subject to large fluctuations in density. The hostplant, (Ait.) Borkh. (Rosaceae), is much more widespread than H. lucina. The reasons are unknown, but may be linked to thermal requirements of the larvae (Stamp & Bowers 1986a). Hemileuca lucina has been found occasionally on Betula populifolia, and Quercus sp. (Tietz 1972, Bowers & Stamp 1986). The moths' ranges overlap in some areas of Massachusetts. For ex­ ample, a population of H. maia occurs in pine barrens at Montague, Mass. (D. Schweitzer, pers. comm.), and populations of H. lucina are scattered throughout Leverett, Mass., in wet fields with S. latifolia. These areas are all in Franklin Co. VOLUME 40, NUMBER 3 215

As with many hemileucines, these species overwinter as eggs (Tuskes 1984). The larvae feed in the spring and pupate in the soil, where they aestivate until adult emergence in the fall. Phenologies in Massachu­ setts are offset slightly, with egg hatch and adult flight later in H. maia. The objective of this study was to compare the abilities of H. lucina and H. maia to grow on their own and on each other's hostplants. Oak leaves are relatively tough (Feeny 1970), especially compared to Spi­ raea leaves, although leaf toughness increases in Spiraea with leaf age (Stamp & Bowers 1986b). The leaves of these species probably differ in other important ways as well, such as in water content, and presence and amount of tannins and other allelochemicals. Because the moths are congeneric and have similar life history traits (Ferguson 1971), we expected that they could eat each other's hostplants but, because their food is different, that they would grow best on their own host species.

METHODS For the experiment, H. lucina larvae were reared from an egg clus­ ter collected on 14 April 1985 at Leverett, Mass., where the hostplant was S. latifolia. The egg cluster was kept in a refrigerator until 2 June; the larvae hatched on 6 June. Newly hatched H. maia larvae were collected from Quercus prinoides Willd. on 7 June 1985 at Barnard Valley (Nantucket), Mass. Caterpillars were kept in a growth chamber on a photoperiod of 16L:8D at 25°C during the day and 20°C at night, and were reared through the first instar on their own hostplants. At the beginning of the second instar, half of the larvae of each species were fed S. latifolia and half were fed Q. prinoides leaves. Larvae were given these diets throughout the second instar. At the beginning of the third instar, the growth tests were begun with larvae fed on the same diet they had during the second instar. For each treatment, 14 newly molted, unfed larvae were weighed and placed individually in Petri dishes, with a weighed sprig of S. latifolia or leaf of Q. prinoides. Sprigs of S. latifolia were used because indi­ vidual leaves were small and dried quickly. We used unlignified sprigs (leaves young and stems still green) because new leaves were primarily what H. lucina ate in the field. The larvae were given average sized Q. prinoides leaves. Each dish had a piece of wet toweling taped to its top to maintain humidity. Larvae fed freely for 48 h. Then they were weighed again, frozen, dried at 50°C for 72 h and reweighed to obtain wet-weight-to-dry-weight conversion factors to estimate initial dry weight. To compare the response of larvae to the two hostplants, a standard index of growth, relative growth rate (RGR), was used (Waldbauer 1968, Slansky & Feeny 1977). 216 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY

TABLE 1. Growth indices for third instar Hemileuca lucina and H. maia. Each treatment had 14 larvae. Means are indicated with ±1 SE. Means with the same letter in that column are not significantly different at the 0.05 level using the Newman-Keuls multiple range test.

Diet during second Mean dry weight per RGR Mean dry weight per larva instar and test period (mg) at beginning of test (mg/mg larva/ day) (mg) at end of test H. lucina Spiraea 5.1 ± 0.2a 0.45 ± 0.03 a 13.9 ± 1.0 a Quercus 3.8 ± 0.2 b 0.34 ± 0.01 b 7.8 ± 0.5 b H. maia Quercus 4.6 ± 0.2 a 0.17 ± 0.01 c 6.7 ± 0.4 b Spiraea 2.9 ± 0.3 c 0.18 ± 0.01 c 4.1 ± 0.4 c

RESULTS AND DISCUSSION After rearing through the second instar, H. lucina larvae fed Spiraea were heavier than those fed Quercus, but were similar in estimated dry weight to H. maia fed Quercus (Table 1). As expected, RGR of H. lucina fed Spiraea was higher than for those fed Quercus. But, unexpectedly, RGRs for H. maia on Spiraea and Quercus were both low and similar. Because H. maia growth on Quercus was so slow, those larvae did not gain much weight during the test (Table 1). Con­ sequently, H. lucina fed Spiraea weighed significantly more at the end of the test than larvae in the other treatments. The relative growth of H. lucina on Quercus was probably the same as that of third-instar H. lucina reared on old leaves of S. latifolia (0.34 ± 0.01 SE on Quercus, and 0.35 ± 0.01 SE on old Spiraea; two­ sample t-test, df = 26, P > 0.50, 1 - (3 = 0.31 at a = 0.05; data for old Spiraea leaves from Stamp & Bowers 1986b). Thus, Quercus and old Spiraea leaves were similar as food for H. lucina, but it was not clear why. Hemileuca maia did not exhibit such a pattern; it grew equally slowly on both its hostplant Quercus and non host Spiraea. This suggests that H. maia simply grow slowly in comparison to H . lucina. Alternately, Q. prinoides may be a less suitable host than Q. ilicifolia, the usual host of H. maia. However, in northern New York, H. maia used both oak species, and in one area used Q. prinoides predominantly even though the other oak species was present (Cryan & Dirig 1977). The end result (in this case, middle of the third instar) was quite different dry weights among the treatments (Table 1). Hemileuca lu­ cina fed on Quercus weighed but 56% of the weight attained by H. lucina reared on Spiraea. Even more striking, H. maia reared on its hostplant Quercus weighed only 49% of that attained by H. lucina on its host plant Spiraea. Because adults of these two buckmoths are similar VOLUME 40, NUMBER 3 217 in size (H. lucina somewhat smaller; Cryan & Dirig 1977), it seems likely that H. maia larvae may have a prolonged developmental period compared to that of H. lucina. Warrington (1985) found such an effect, with the combination of RGR and weight of prepupallarvae affecting the pupation date for four species of geometrids feeding on sycamore. Prolonged larval development in H. maia may have important ram­ ifications for exposure to abiotic conditions, predators and parasites and, consequently, for the means by which H. maia cope with those factors, especially compared with H. lucina.

ACKNOWLEDGMENTS We thank G. Puttick, F. Slansky Jr., and G. P. Waldbauer for comments on the manuscript, and G. Put tick for collecting H. maia and Q. prinoides for us. NES was supported by an award from the NYS-UUP Professional Development Committee. MDB was supported by the Clark Fund of Harvard University and NSF Grant BSR 8307353.

LITERA TURE CITED

BOWERS, M. D. & N. E. STAMP. 1986. Host plant exploitation by gregarious larvae: Effect of temperature and group size on buckmoths (Hemileuca lucina: Saturniidae). In review. CRYAN, J. F. & R. DIRIG. 1977. The moths of autumn: Buckmoths of the Pine Bush. Occ. Pub I. No.1. Pine Bush Historic Preservation Project, Albany, New York. 16 pp. FEENY, P. 1970. Seasonal changes in oak leaf tannins and nutrients as a cause of spring feeding by winter moth caterpillars. Ecology 15:565-581. FERGUSON, D. C. 1971. The moths of North America. Fascicle 20.2. Bombycoidea. E. W. Classey, Middlesex, England. SLANSKY, F., JR. & P. FEENY. 1977. Stabilization of the rate of nitrogen accumulation by larvae of the cabbage butterfly on wild and cultivated food plants. Ecol. Monogr. 47:209-228. STAMP, N. E. & M. D. BOWERS. 1986a. Hostplant exploitation by gregarious larvae: Thermal ecology of buckmoths (Hemileuca lucina: Saturniidae). In review. --- 1986b. Hostplant exploitation by gregarious larvae: Quality and availability of food and its effect on buckmoths (Hemileuca lucina: Saturniidae). In review. TIETZ, H. M. 1972. An index to the described life histories, early stages and hosts of the Macrolepidoptera of the continental United States and Canada. Vol. 1. A. C. Allyn, Sarasota, Florida. 536 pp. TUSKES, P. M. 1984. The biology and distribution of California Hemileucinae (Satur­ niidae). J. Lepid. Soc. 38:281-309. W ALDBAUER, G. P. 1968. The consumption and utilization of food by . Adv. Physiol. 5:229-288. WARRINGTON, S. 1985. Consumption rates and utilization efficiencies of four species of polyphagous feeding on sycamore leaves. Oecologia 67:460-463.

Received for publication 7 February 1986; accepted 23 May 1986.