Observations on the Early Larval Activities of Nymphula Maculalis Clemens* (Lepidoptera).

Abstract

In a previous paper dealing with the biology of certain aquatic Lepidoptera, the writer pointed out (1916, pp. 173-174) that while it was possible to force a few first instar larvae of Nymphula maculalis Clemens to feed upon the tissue of the floating, green leaf of the yellow water-lily in small aquaria, the normal field habits of the younger instars were not determined and that in rearing such larvae in aquaria difficulty was experienced in securing the second larval instar and in preventing a very high mortality among those which hatched from egg-masses. It was also pointed out in the same connection that certain circumstantial evidence suggested that possibly the larvae, on hatching, “settle to the bottom and after one or two ecdyses, approach the surface of the water on the petioles of the water-lily.” Field observations and breeding work in aquaria subsequent to that on which the above mentioned paper was based repeatedly confirmed the following points from which the inference concerning some form of bottom life for early instars was derived: (1) Recently hatched larvae tend to drop to the bottom of aquaria and wander restlessly about, manifesting no interest in fresh tissue from floating leaves of the normal food plant (2) The first and second instars are not found, in the field, on the floating leaves of the yellow water-lily, although such leaves are the bearers of the egg-masses; (3) Only well advanced larvae occur on the floating leaves, but somewhat younger larvae are to be found on the submerged, green leaves which have not yet reached the surface; and (4) Pupae are absent on submerged leaves. It therefore became reasonably certain that a study of the bottom of the lily beds was necessary in order to understand the early larval development of this species. Forbes (1910, p. 225) had also reported that in his work on Nymphula gyralis Hulst the larvae, just hatched from the eggs, “all died without eating, though provided with leaves of Nymphaea and Limnanthemum (laid on the latter), but they gathered on the Nymphaea leaf in numbers. Possibly in the first stage they may feed on the submerged stems.” Apparently circumstances attending the early larval history of Nymphula gyralis resemble somewhat those of NymPhula maculalis , and it may be that results described herein will yield some clue as to their nature.