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Journal of The Lepidopterists^ Society

1969                                          Number 4

BEHAVIORAL ADAPTATIONS OF CRYPTIC MOTHS. IV.

PRELIMINARY STUDIES ON SPECIES

RESEMBLING DEAD LEAVES

Ronald R. Keiper Dept. Biology, Pennsylvania State University, Mont Alto, Pennsylvania

A number of experimental studies have demonstrated that cryptic coloration conveys a selective advantage to animals by enabling them to avoid detection by predators (Young, 1916; Carrick, 1936; Turner, 1961). In addition to morphological adaptations, behavior of cryptic animals is also important. An animal, even if it is cryptically patterned, must be able to choose an appropriate background and to orient itself so that the cryptic pattern attains maximum effectiveness.

Several studies have shown that certain species of cryptic moths, which normally rest on tree trunks, are capable of selecting backgrounds which tend to match the reflectance of their forewings (Kettlewell, 1955; Sargent, 1966), and that these moths will adopt appropriate attitudes upon these backgrounds (Sargent, 1969). There are other moth species which rest in or on other substrates and which seem to be colored or patterned to match these substrates. This paper presents some early results from studies designed to examine the behavior of moths which resemble and rest in dead leaves.

Field studies

Two techniques were used in studying the natural resting habits of these moths. The first of these simply involved searching an area of forest floor covered with dead leaves. When a resting moth was located, a photograph was taken, along with notes concerning the resting attitude. Occasionally moths were flushed before being photographed. These were then followed to subsequent resting places and appropriate notes were taken.

The second technique involved releasing moths In wooded areas, and following them to their resting places. These moths had been captured

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Table 1. Field observations of some moths which rest in dead leaves

Species1                                                       Remarks

Geometridae:

l Numbers in parentheses: (previously undisturbed individuals, released individuals)

at lights or "sugar/7 kept overnight in experimental boxes, and released the following morning. Here, as with the undisturbed moths, photographs and notes were taken.

The two techniques produced similar results for a number of species and these observations are presented in Table 1. These results suggest that a number of brownish, leaf-like moths are able to select appropriate backgrounds and further, to orient with respect to these backgrounds so as to increase their crypsis.

Experimental studies Several species were released into an experimental box in an attempt to determine if the moths would exhibit preferences for certain test substrates. The experimental box (24 inches square by 19 inches high) was constructed of plywood. The floor of the box was equally divided into four quadrats (each 12 X 12 inches), and during these experiments,

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Table 2. Selection of substrates by moths in an experimental apparatus

* Denotes significant deviations from chance selections. Analysis by chi square tests, Probability less than 0.01

ns Denotes no significant deviation from chance selection. Probability greater than 0.05

each quadrat contained a different substrate. In these? experiments, the substrates used were: dead needles of white pine, dead grass stems, dead oak and maple leaves, and small twigs. Fresh substrate material was added nightly, and the box was rotated to eliminate any "position" effect. The box was covered with a pane of window glass and placed in a wooded area where a thick canopy excluded direct sunlight. Moths were introduced into the box by sliding the glass top to one side.

The moths were collected at lights or "sugar" bait and immediately introduced into the experimental box, generally 5-10 moths of the same species per night. The following morning, between 0600-0800 E.S.T., the box was checked and the substrate selection by moths noted.

The results of this experiment, which are summarized in Table 2, suggest that at least some of the species examined are capable of selecting appropriate substrates. However, the moths appear to fall into three groups with respect to their behavior in the box.

Moths in the first group never selected a substrate but instead were always found sitting either on the glass or on the sides of the box (e.g., the geometrids Abbotana clemataria Smith and Abbot and Nematocampa filamentaria Guenee).

The noctuids Parallelia bistriaris Hiibner and Zanclognatha cruralis Guenee are examples of moths which show the second type of behavior observed in the experimental box. Moths of this group select dead leaves, but also are frequently found resting on top of other substrates. From observation of both released and undisturbed moths, it appears that both species behave the same way in the wild, resting on top of leaves or other substrates if forced into areas where no dead leaves are present. Apparently these species choose any substrate which offers a relatively flat surface. P. bistriaris further enhances its crypsis by resting

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Table 3. Selection of differently colored substrates (3 X 3 in.

CARDBOARD SQUARES ) IN AN EXPERIMENTAL BOX

with the head burrowed into the substrate so that the moth is resting almost perpendicular to it. This posture allows the lighter-colored edge of the wing to stick up from the substrate and thus serves to break up the pattern of the moth.

On the other hand, the noctuids Epizeuxis lubricalis Geyer and Amphipyra pyramidoides Guenee did not rest on top of any substrate, but instead were found resting on the plywood floor of the box beneath the layer of dead leaves. This third type of behavior may not represent selection of dead leaves as such, but may only result from the moths choosing this substrate because it can be easily burrowed into and then effectively shields the moths from the light.

In an attempt to learn more about the mechanisms governing these choices, several additional experiments were devised. The same box was used, but cardboard squares (3x3 inches) were presented instead of the previous natural substrates in an attempt to keep the texture of the substrates constant.

In the first experiment, an attempt was made to determine the importance of the color of the substrate. Accordingly, squares of four different colors were used: black, chocolate brown, dark green, and bright yellow. The results of this experiment are shown in Table 3. For A. pyramidoides, there were sufficient numbers for a chi square test, but no significant selection tendency was noted. The sample sizes for the other species were too small to analyze separately, but the results were tested across species. In both cases however, the results suggested that the color of the substrate was not important to the moths in choosing a substrate.

In an attempt to determine the influence of the shapes of the substrate components on the choice of the moths, squares of white cardboard were used, but they were presented in four different shapes: flat squares ("flat"), squares folded in the middle and set on end ("tent"), squares folded in the middle and set on a side ("right angle"), and squares laid flat but set on top of a nail ("leaf") and thus raised off the floor of the

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Table 4. Selection of substrate components (3x3 in. cardboard squares) of different shapes in an experimental box

* Denotes significant deviations from chance selections. Analysis by chi square tests, probability less than 0.01

ns Denotes no significant deviation from chance selection. Probability greater than 0.05

box. Sufficient numbers were obtained for only three species, but fortunately these represent two of the previously discussed types. The results from this experiment are shown in Table 4. P. bistriaris was found about evenly distributed on all substrates, but was oriented somewhat differently on each. For example, on the "right angle" squares, this moth generally perched "head down" on the inside of the extended arm. However, when resting on the flat substrates, the moth lay flat on top of the cardboard. In the wild, this species shows a similar behavior, resting "head down" in substrates which permit burrowing (e.g., dead leaves, grass) but laying flat on substrates such as pine needles.

The other species, E. lubricalis and A. pyramidoides, were found to prefer the "tent" substrate (analysis by chi square, P < 0.01). Once again these data agree with the data obtained in the wild, for the former species rests beneath layers of dead leaves, while the latter species avoids light by resting in crevices.

Summary

The behavior of cryptic moths which resemble dead leaves was studied in central Massachusetts during the summers of 1967 and 1968. Both field observations and experiments were carried out.

Data obtained from undisturbed and released moths of the same species closely agree, suggesting that information gained from observing released moths is reliable.

The experiments involved the use of an experimental box in which the behavior of captured moths could be analyzed with respect to both natural and unnatural substrates. The results suggest that some cryptic moths, which resemble dead leaves, are capable of selecting this substrate when presented with a choice of substrates. Furthermore, it appears that the color of the substrate is not important to the moths when making selections, but that the shape or arrangement of substrate components may be the important factor. In general, two types of behavior

210                                        Cowan: The name Anthocharis                     Vol. 23, no. 4

were shown. Some moths which rest flat on top of substrates or burrow slightly into them in nature, choose those substrates which allow this resting attitude to be assumed. Other moths, which are apparently negatively phototactic, select those substrates which allow burrowing, and thus serve to shield the moths from light.

Acknowledgments Financial support for these studies was provided by a grant from the Theodore Roosevelt Memorial Fund of the American Museum of Natural History.

I would like to thank Dr. T. D. Sargent of the Department of Zoology, University of Massachusetts, for his assistance in planning and conducting this study.

Literature Cited

Carrick, R., 1936. Experiments to test the efficiency of protective adaptations.

Trans. Roy. ent. Soc. Lond., 85: 131-139. Kettlewell, H. B. D., 1955. Recognition of appropriate backgrounds by the

pale and black phases of Lepidoptera. Nature, 175: 943. Sargent, T. D., 1966. Background selections of geometrid and noctuid moths.

Science, 154: 1674-1675. Sargent, T. D., 1969. Behavioral adaptations of cryptic moths. III. Resting

attitudes of bark-like species. Anim. Behav. (in press) Turner, E. R. A., 1961. Survival value of different methods of camouflage as

shown in a model population. Proc. Zool. Soc. Lond., 136: 273-283. Young, R. T., 1916. Some experiments on protective coloration. J. exp. Zool., 20:

457-508.

THE NAME ANTHOCHARIS (PIEMDAE)

The generic name Anthocharis Boisduval, Rambur & Graslin, 18331 was published twice in quick succession, in consecutive livraisons of the same work; on 2 February on plate Papillonides 5, figs. 6, 7, and on 29 June on pages [35, 36]; in livraisons 12 and 13 respectively. On each occasion only one species was included, Anthocharis cardamines, i.e. Papilio cardamines Linnaeus, 1758, which is the type species by monotypy. The gender of the genus is feminine.

On the first occasion when it appeared, no authorship was indicated for the name. The heading of page [35] reads "Anthocharis cardamines Boisd.," suggesting that Boisduval claimed it as his own new combination. However, both technically and for clarity, it would seem best to credit the triple authorship.

These facts are published because it is noticed that some references are appearing to "Anthocaris," and once such an incorrect spelling gains currency it becomes increasingly difficult to eradicate. There is no doubt that Anthocharis is correct. Inevitably, misspellings followed, and in fact within two years "Anthocaris," "Antho-carix," and "Anthacaris" had all appeared. However, Boisduval himself, and all the nineteenth century authors were usually correct.—Charles F. Cowan, Little Gaddesden House, Berkhamsted, Herts., England.

i Boisduval, [J.B.A.de], Rambur, P., & Graslin, A. [de], 1832 [-1837]. Collection iconographique et historique des Chenilles, ou Description et Figures des Chenilles d'Europe, avec l'Histoire de leurs Metamorphoses, et des Applications a 1'Agriculture. pp. [1-5], 6, [7], 8-14, [15-496], pis. [126]. Paris.