Observations on Feeding Behavior of Newly-Hatched Larvae in Two Luehdorfia Species (Papilionidae)

Abstract

The author noticed that the newly-hatched larvae of Luehdorfia japonica (hereafter referred to as LJ) and Luehdorfia puziloi (LP) behave differently when they start their very first meal. He then observed a number of egg batches of these species both in the wild and in captivity for comparison of patterns of behavior of newly-hatched larvae until they start feeding. 1. After hatching from the eggs normally deposited on the underside of a fresh leaf of the foodplant, LJ larvae crawl away to the basal margin of the leaf and start feeding near the petiole, while LP larvae take their first meal without wandering away from the site of oviposition, showing no preference for the basal margin. LP larvae from eggs experimentally transferred to LJ's local foodplant, Asarum takaoi, did not crawl to the basal margin but behaved as if on their natural foodplant, Asarum Sieboldii; the opposite experiment, however, brought divergent results, with some groups of LJ larvae behaving normally and others feeding in the normal LP fashion. LJ larvae, newly hatched or otherwise transferred to a new leaf, mostly chose the basal margin close to the petiole as the site of initial feeding. Thus, the difference in the choice of the initial feeding site between the two species appears to be due to a hereditary factor. 2. Both species lay eggs in batches, and the larvae lead a gregarious life so long as possible. In LJ, it is usually the first to hatch that plays the role of a leader to guide the others in the clutch to the initial feeding site. The second to hatch can occasionally be the leader. In either case, the leader crawls on until it comes across a vein, which is ridged on the underside. This the larva follows and ultimately reaches, by trial and error, the basal margin. It crawls about the petiole and descends a little along it, but returns to the basal margin and start feeding. The leader spins his way throughout, and the larvae to follow evidently take the same silk trail, strengthening it while walking. It is possible that the larvae's silk carries some pheromone that helps in their gregarious behavior. Once the first few larvae have established a feeding site, those hatching later in the same egg batch go to the feeding site without hesitation. 3. Why the newly-hatched LJ larvae are attracted to the basal margin of the leaf close to the petiole is not quite clear. One of the reasons may be that the larvae, through wandering near or on the petiole, confirm the route by which to reach another suitable food leaf.