A lepidopteran saline: effects of inorganic cation concentrations on sensory, reflex and motor responses in a herbivorous insect.

Owing to the great variability in ionic composition of insect haemolymph (Bone", 1944; Duchateau, Florkin & Leclerq, 1953; Sutcliffe, 1963), it is probably desirable to use haemolymph itself as an experimental medium whenever this is possible. In the present studies of proprioception in Anthercea pernyi the long time spent in dissection and the necessity for aeration rendered the use of a simple synthetic medium essential. Certain phytophagous insects, among them the giant silkworms, possess haemolymph characterized by much lower Na concentrations and higher K and Mg concentrations than those found in the majority of other animals. Lockwood (1961) gave the composition of thirty-six different insect salines selected from published data, but of these only four were designed for such phytophagous insects with any reference to the cation concentrations present in their haemolymph. Previous electrophysiological work on Lepidoptera is very scanty. Finlayson & Lowenstein (1958) worked on Anthercea pupal muscle receptor organs (MRO) as part of a study of stretch receptors in various insect groups, but in their experimental work they used Ephrussi and Beadle's Drosophila saline, a high-Na type medium, which has also been widely used in studies on diapause in Hyahphora cecropia. Belton (1958), in a report on studies of the muscle physiology of adult Saturniidae of several species, described a saline supposedly based on the concentrations of inorganic cations present in the species studied, though probably with appreciable deviations from any one of them (their haemolymph compositions were not given). Van der Kloot (1958), in a study of diapause in Hyahphora with particular reference to the activity of the C.N.S. during diapause, and again in a study of pupal spiracular function in the same species (van der Kloot, 1963), used Ephrussi and Beadle's saline. The only experimental medium closely similar in inorganic cation concentration to the haemolymph of a lepidopteran was that used by Wyatt (1956) for ovarian tissue culture in Bombyx mori. Wyatt also analysed some of the organic constituents of haemolymph, including protein and amino acids, which among Holometabola largely replace chloride, the more usual major anion component (Sutcliffe, 1963). The work most relevant to the present problem has been done, not on Lepidoptera but on another phytophagous group, the Phasmidae. Carausius morosus, the representative of this group studied, has like the Saturniidae low Na, moderately high K