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Journal of the Lepidopterists' Society

FEEDING AND SURVIVAL OF CECROPIA (SATURNIIDAE) LARVAE ON VARIOUS PLANT SPECIES

A. G. SCARBROUGH

Department of Biology, Towson State College, Baltimore, Maryland 21204

AND

G. P. Waldbauer and J. G. Sternburg Department of Entomology, University of Illinois, Urbana, Illinois 61801

During the course of our studies of the cecropia moth, Hyalophora cecropia (L.), we found a large proportion of cocoons in low shrubs. We suspected that many of these shrubs, particularly species of Juniperus and Taxus, do not support larval growth, and that the presence of cocoons on them is evidence that pre-spinning larvae wandered to them from the foodplant. Most of the shrubs in question are not included on published lists of the hostplants of cecropia, but since this does not prove that cecropia larvae could not feed on them, we made the feeding trials described below.

There is some doubt as to whether or not all of the species on the published "foodplant lists" of cecropia are actually eaten by cecropia larvae. Brodie's (1882) list is reliable since he included only plants on which larvae had been found feeding in the field. On the other hand, Marsh's (1937) list is of dubious value since he included plants on which he had found cocoons but had not seen larvae. Tietz (1958) compiled a long list, but, unfortunately, did not state the evidence upon which the plants were included.

Materials and Methods

Most cocoons were collected in residential areas, principally in the twin cities of Champaign and Urbana, Illinois, although a few were found in nearby small towns. A small number came from rural areas, mostly from ditch banks, railroad rights-of-way, roadsides and fence rows.

The larvae used in feeding trials were the progeny of wild parents which had been collected as described above. After mating in the laboratory, females were placed in large paper bags where they oviposited. Before hatching occurred, small bits of paper bearing the eggs were snipped out and transferred to petri dishes. The unfed first instars used in the first series of tests were indiscriminately selected within a

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half-hour of hatching. The partly grown larvae used in the second series were indiscriminately selected from groups of larvae reared in nylon mesh sleeves on apple trees (Malus pumila) essentially as described by Telfer (1967).

Plants of 118 species were tested for their ability to support the growth of first instar larvae. Each species was tested with at least three replicates. Species on which no larvae survived the first stadium in the initial test were retested with an additional three replicates. Each replicate consisted of ten larvae confined with foliage in a 10 cm petri dish lined with a disc of moist filter paper. The newly hatched larvae were weighed in groups of ten and immediately placed in the dishes. Undamaged foliage, collected daily from plants growing in full sunlight, was sealed in plastic bags and stored in a refrigerator until used later the same day. The dishes were kept under constant illumination and at a temperature of 23 ± 1° C. At least once a day fresh food was added, and dead larvae, left over food, and feces were removed. Feces were dried immediately, and eventually the aggregate for each replicate was redried to a constant weight at 100° C (see Waldbauer, 1964). This weight was divided by the sum of the number of larvae feeding on each test day to yield the mean dry weight of feces passed per larva per day. Larvae were weighed and considered to have survived the stadium as soon as they had spun a molting pad. Dishes with moist filter paper but no food, and dishes with Acer saccharinum foliage served as negative and positive controls respectively. A group of tests was started on each of three days. Each group had its own controls, but since the controls differed by very little they have been lumped in Table 2.

A few plants were also tested with two groups of partly grown larvae. Each group consisted of five larvae confined in a sleeve on a branch of a living plant in the field. They were transferred to the test plant from apple foliage, one group just before the molt to the fifth stadium and the other on the seventh day of the fifth stadium. Apple branches with leaves served as positive controls, and defoliated branches of the test plant as negative controls.

Results and Discussion

Table 1 lists the plants on which we found 1% or more of the cocoons collected during this study. Almost all of the cocoons from rural areas were on Salix interior, a shrubby willow which grows wild on ditch banks and in other moist places, but is not planted in urban areas. A few of the other listed species grow wild in this area, but with few

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Table 1. The location of cecropia cocoons found during the collecting seasons of 1967-68, 1968-69 and 1969-70. Only those plants on which 1% or more of the total was found are named. Species which do not serve as foodplants for cecropia are marked with an asterisk.

Cocoons Found

f See text.

exceptions we found cocoons only on cultivated specimens in urban areas.

The data of Table 1 do not reflect the importance to cecropia in this area of Rhamnus frangula and the two species of Cornus. In an earlier study (Waldbauer & Sternburg, 1967) we found cocoons abundantly on Cornus stolonifera and C. alba. However, during the present study we did little collecting from Cornus because most plants of these species in this area were included in another study of cecropia. R. frangula was formerly scarce in this area, but has become a popular hedge plant since we began our studies of cecropia in 1965; the great majority of cocoons from R. frangula were collected during the last year of the present study.

Over 12% of the cocoons were found on shrubby conifers, Juniperus spp. and Taxus media, but only if these conifers were close to trees, particularly Acer saccharinum and Betula spp., which are important foodplants of cecropia in this area. We hypothesized that the larvae do not feed on these conifers, but migrate to them from their foodplants when they are ready to spin cocoons. The observations recorded below

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Table 2. Survival, growth and feces production of first instar cecropia larvae on the leaves of various woody plants. All plants were tested with three replicates of ten larvae each except those marked with an asterisk, which were tested with six replicates of ten each, and A. saccharinum and moist filter paper which were tested with 9 replicates of ten each.

Others

Larix decidua Mill.

90.0 5.0 5.0-5.0 180 168-188 28.8 25.9-33.1

301 265-327

171 170-172

211

121 95-155

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show this hypothesis to be correct and, furthermore, show that the cocoons spun on certain angiosperms (see Table 1) are probably also spun by migrants from other plants.

We have found wild third to fifth instar larvae in the field feeding on the following plants: Acer platanoides, A. saccharinum; Betula papyrifera, B. pendula, B. populifolia; Cornus alba, C. stolonifera; Lonicera fragrantissima Linden and Paxton, L. tartarica L.; Malus pumila, Malus spp.; Paeonia officinalis L.; Prunus serotina; Rhamnus frangula; Rhus typhina; Salix interior; and Spirea alba. We have observed successful development to the adult stage on all of these except A. platanoides, B. populifolia, Malus spp. other than M. pumila, and S. alba. We have no reason to suspect that the latter would not support complete development.

Table 2 gives the results of some of the feeding trials with first instars. In the upper section of the table appear the plants on which most cocoons were found (see Table 1). In the lower section are listed other conifers, some of which, to our surprise, supported good growth.

Fifteen of the species on which we had found large numbers of cocoons supported apparently normal growth to the end of the first stadium; 83% or more of the test larvae survived the stadium, gained a fresh weight of 180 mg or more—usually in six days or less, and ate at a more or less normal rate as judged by the rate at which they passed feces. This does not prove that development could have been completed on these plants. However, we have found fifth instars feeding in the field on all of these plants except Acer rubrum and Platanus occidentalis. Thus there is almost no question that cecropia can complete development on thirteen of these plants, and there is no reason to assume that it cannot complete development on A. rubrum and P. occidentalis. It is, therefore, unlikely that cocoons found on these plants were spun by larvae which had wandered from some other species of plant.

The other plants on which large numbers of cocoons had been found, nine species of Euonymus, Juniperus, Ligustrum and Taxus, were usually eaten only in minute quantities and did not support growth or, at best, supported the slow growth of only one larva out of a group of 30 or 60 (see Table 2, /. chinensis and L. vulgare). The inability of these plants to support the growth of first instars proves that they are not usual food plants of cecropia. Therefore, cocoons found on them must have been spun by larvae which had moved from some other species of plant, the movement probably occurring only after growth had been completed.

It is possible that plants which do not support first instars may sup-

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Table 3. Survival of partly grown cecropia larvae transferred from Malus pumila to other plants. Each plant was tested with two groups of five larvae.

port the growth of partly grown larvae which may move to them from a more favorable plant. We have seen no evidence of such moves, and doubt that they are of more than rare occurrence. Furthermore, feeding tests with partly grown larvae (Table 3) indicate that although an occasional partly grown migrant might survive by eating the foliage of Ligustrum vulgare, there will be no survival on Juniperus or Taxus, even if the migrants feed on one of the usual foodplants until the middle of the last stadium. Taxus is probably toxic since larvae which ate small quantities died sooner than controls on a defoliated branch of Taxus. Three of the four species in the genus Hyalophora apparently feed only on non-conifers, while the remaining species, the northern H. Columbia (S. I. Smith), appears to feed exclusively on the tamarack, Larix laricina, (Ferguson, 1971). It is thus of more than passing interest that some conifers, most notably Larix laricina, L. decidua, and Tsuga canadensis, support good survival and growth by cecropia during the first stadium (Table 2). Furthermore, during the summer of 1973 we transferred five young third-instar cecropia from an apple to a small European larch (L. decidua) growing outdoors. Two disappeared from the sleeve, but the remaining three spun apparently normal cocoons. Whether or not they survive to emerge as adults remains to be seen since they are still in diapause. Recently Collins (1973) reported that the two western species can survive on some conifers. H. gloveri (Strecker) has been reared on L. decidua, L. laricina and Pseudotsuga menziesii (Mirb.). H. euryalus (Boisduval) has been found in the field feeding on P. menziesii and has been reared in captivity on the same

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plant. It would seem that all Hyalophora are potentially able to utilize conifers, but that this ability has been selected for only in H. Columbia. Many plants in addition to those listed in Table 2 were tested with first instars, but it would require too much space to list the data in detail. Plants on which over 70% of the larvae survived the first stadium are:

Acer platanoides Michx., A. negundo L.; Aesculus octandra Marsh.; Carya ovata (Mill.) K. Koch, C. illinoensis (Wangenh.) K. Koch; Castanea mollisima Bl.; Chaenomeles lagenaria Koidz.; Cornus florida L., C. racemosa Lam., C. sanguinea L.; Cotoneaster multiflora Bge.; Crataegus crus-gali L., C. molli Scheel.; Diospyros virginiana L.; Fraxinus pennsylvanica Marsh.; Hamamelis virginiana L.; Juglans nigra L.; Liquidambar styraciflua L.; Lonicera tartarica L.; Madura pomifera (Raf.) Schneid.; Nyssa sylvatica Marsh.; Populus deltoides Bartr., P. laurifolia Ledeb.; Prunus americana Marsh., P. serotina Ehrh.; Pyrus communis L.; Quercus alba L., Q. imhricaria Michx., Q. macrocarpa Michx., Q. muhlenbergii Engelm., Q. rubra L.; Rhus typhina L.; Robinia pseudoacacia L.; Salix babylonica L.; Sambucus canadensis L.; *Sanicula smallii Bicknell; Spirea alba Du Roi; Syringa chinensis Willd.; Tilia americana L., T. euchlora Koch., T. tomentosa Moench.; Viburnum dentatum L., V. tomentosum Thunb.

Plants on which there was survival, but less than 70% are:

Acer saccharum Marsh.; *Asclepias syriaca L.; Betula alleghaniensis Britton, B. nigra L.; Cotinus americana Nutt.; Deutzia lemoine Hort.; Elaeagnus angustifolia L.; Forsythia viridissima Lindl.; Fraxinus americana L.; Ginko biloba L.; Gleditsia triacanthos L.; Halesia Carolina L.; *Lactuca scariola L.; Lonicera japonica Thunb.; Morus alba L.; *Plantago rugelii L.; Rhus glabra L.; Salix nigra Marsh.; Syringa vulgaris L.; ^Taraxacum officinale Weber; Tilia platyphyllos Scop.; Ulmus americana L., U. carpinifolia Gleditsch., U. parvifolia Jacq.

Plants on which no larvae survived are:

*Adiantum pedatum L.; Ailanthus altissima (Mill.) Swingle; Asimina triloba Dunal.; Campsis radicans (L.) Seem.; Catalpa bignonioides Walt.; Celtis occidentalis L.; Cercis canadensis L.; *Chenopodium album L.; Kolkwitzia amabilis Graebn.; Liriodendron tulipifera L.; *Nicotiana tabacum L.; Philadelphus coronarius L.; Populus alba L.; *Sonchus asper (L.) Hill; *Verbascum thapsus L.; *Viola sp.; Vitis sp.; *Zea mays L.

In the above list herbaceous plants (as opposed to woody) are marked with an asterisk. Larvae survived on only five of the eleven non-woody plants tested. These were: Asclepias syriaca—30%, Lactuca scariola— 3%, Plantago rugelii—53%, Sanicula smallii—83% and Taraxacum officinale—63%. Almost without exception the recorded natural food-plants of cecropia are woody; the only indisputable exception is Paeonia officinalis (see above, and Waldbauer & Sternburg, 1967).

Table 2 shows considerable variation in response to the various species of acceptable plants, particularly in the duration of the instar, weight gained and the weight of feces passed per day. Large differences in the latter value (cf., for example, Malus pumila and Cornus alba) suggest large differences in the rates at which different plants are eaten.

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However, the weight of feces is only an approximate indication of the rate of intake since the former will vary not only with the weight of food ingested, but also with the proportion of the ingested food which is assimilated and expended for growth and the maintenance of metabolism (Waldbauer, 1964).

This study makes the following major points:

1.   It confirms past observations that cecropia larvae are able to feed and survive on a wide variety of woody angiosperms.

2.   It shows that neither first nor fifth instar larvae are able to survive on certain plants on which cocoons are commonly found, establishing that the larvae must have moved to them after completing their feeding on some other species of plant.

3.   It shows that first instars are able to survive on certain species of conifers, including Larix laricina, the foodplant of the closely related Hyalophora Columbia.

Literature Cited

Brodie, W. 1882. Food plants of Platysamia cecropia. Papilio 2: 32-33. Collins, M. M. 1973. Notes on the taxonomic status of Hyalophora Columbia

(Saturniidae). J. Lepid. Soc. 27:225-235. Ferguson, D. C. in Dominick, R. B. et al. 1972. The Moths of America North

of Mexico, Fascicle 20.2B, Bombycoidea (in part). Classey, London, p. 155-

275. Marsh, F. L. 1937. Ecological observations upon the enemies of Cecropia, with

particular reference to its hymenopterous parasites. Ecology 18: 106-112. Telfer, W. H. 1967. Cecropia, in F. H. Wilt and N. K. Wessels, eds., Methods

in Developmental Biology, p. 173-182. Crowell, New York. Tietz, H. M. 1959 (?). The Lepidoptera of Pennsylvania, a Manual. Pennsylvania

State Coll. Sch. Agr. & Agr. Exp. Sta. 194 p. Waldbauer, G. P. 1964. Quantitative relationships between the numbers of fecal

pellets, fecal weights and the weight of food eaten by tobacco hornworms,

Protoparce sexta (Johan.) (Lepidoptera: Sphingidae). Entomol. Exp. & Appl.

7:310-314. ----------. & J. G. Sternburg. 1967. Host plants and the locations of the baggy and

compact cocoons of Hyalophora cecropia (Lepidoptera: Saturniidae). Ann.

Entomol. Soc. Amer. 60: 97-101.

Note Added in Proof: The three pupae from larvae matured on Larix decidua produced three normal adult moths in 1974: 21 May, $; 29 June, $; 30 June, $.