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Based on laboratory observations and experiments, a larval behavior of gypsy moth, Lymantria dispar (L.), is documented that is used for climbing on a smooth vertical surface. Larvae on surfaces that do not provide structures that can be grasped by the crochets are able to climb vertically by spinning a “ladder of silk.” This use of silk apparently occurs more frequently in laboratory populations that are less fit (as measured by head capsule size, reduced pupal weight, and increased development time). It is suggested that the use of silk for climbing in the field may be associated with decreased larval fitness as a result of wound-induced plant defences.

In caged choice experiments, Lymantria dispar (L.) larvae strongly preferred Acer saccharum Marsh. and Fraxinus pennsylvanica Marsh. trunks (44.3 and 43.3% of larvae, respectively) to Betula papyrifera Marsh. trunks (5.7%). When larvae were allowed to choose among the foliage of live seedlings of the same species, they preferred B. papyrifera (71.0%) over A. saccharum (14.3%) and F. pennsylvanica (0.7%). Trunk sections of A. saccharum and B. papyrifera were wrapped around live seedlings of the same trees and F. pennsylvanica in six possible combinations of trunk and foliage species to evaluate the impact of trunk characteristics on host selection in the presence of foliage. The most preferred trunk-foliage combinations, in descending order of percentage larvae found on each, were as follows: A. saccharum-B. papyrifera (41.0%), B. papyrifera-B. papyrifera (19.0%), A. saccharum-A. saccharum (14.8%), B. papyrifera-A. saccharum (12.2%), A. saccharum-F. pennsylvanica (2.2%), and B. papyrifera-F. pennsylvanica (1.0%). Both trunk species and foliage species Significantly influenced larval choice. The effect of tree canopy size, as measured by leaf surface area, on the distribution of larvae was measured in a forest clearing where five replications of 17 tree species and cultivars were planted. The tree species ranged from highly susceptible ( Malus sp.) to highly resistant ( Gleditsia triacanthos L.). The number of larvae per tree was explained well by the size of the leaf canopy for the six most preferred tree species and cultivars. This relationship did not exist for the remaining 11 species and cultivars of less preferred trees. Apparently, the size of preferred trees influences the distribution of gypsy moth larvae among them.

Survival, development time, and pupal weights of larvae were determined for gypsy moth reared on foliage of red oak, sugar maple, white birch, trembling aspen, white spruce, black spruce, jack pine, and balsam fir. Mortality was >50% on sugar maple and balsam fir, 35% on jack pine, and ≤15% on the other species. Female larvae developed significantly faster on trembling aspen foliage (29 days at 21°C) than on that of other species. Larvae reared on foliage of trembling aspen, white birch, or a mixture of foliage of either species and that of other species produced larger pupae than did other foliage combinations. North. J. Appl. For. 8(3):126-128.

Summary. Theoretical calculations have been made for the idealized case in which an ocean is approximated by an infinitely long rectangular conducting sheet. The results indicate that even in the case of magnetic variations with periods as long as 24 hr one should expect a significant and easily observable enhancement in the vicinity of the edge of an ocean. When the inducing field is a function of local time only, it is found that the amplification of the variations is greater at the eastern edge of the ocean than at the western edge. Laboratory model studies have been used to investigate the effect of irregularities in the shape of a coastline. Results which have been obtained from a model of the Pacific Ocean in the neighbourhood of Japan indicate that it is reasonable to attribute at least a part of the anomalous diurnal variations observed in central Japan to electric currents induced in the ocean.

Summary The work of Bullard (1950) and Rochester (1960) on the geomagnetic westward drift and its effects on the Earth’s rotation is extended to investigate the effects of assuming various distributions of electrical conductivity in the mantle. By a proper choice of conductivities, one is able to increase the theoretical value for the tightness of the coupling by a factor of at least six over that afforded by Rochester’s model, without sacrificing agreement with observations on the rapidity with which changes in the secular variation are established at the Earth’s surface. It is shown that it is reasonable to attribute the observed random changes in the length of the day to perturbations in the electromagnetic coupling. I. Introduction . The most significant hypotheses brought forward to date for the explanation of the existence and maintenance of the terrestrial magnetic field have been reviewed by Jacobs (1956). Of these, only the electromagnetic dynamo theory is able to stand in the light of present information. Elsasser (1956) has reviewed the models suggested for a dynamo mechanism in the core capable of maintaining the dipole part of the field. The analytical details of dynamo operation in the core are irrelevant to the theoretical development in this paper. We need only assume, as did Rochester (1960), that toroidal fields of the correct character are produced in the deep interior and manifest themselves at the core boundary. Convective motion (more or less radial) in the fluid core is fundamental to the maintenance of dynamo action in all current theories. Where the velocity of the convective motion possesses a radial component, conservation of angular momentum requires that the inner fluid core rotate more rapidly than the outer layers. Evidence for this differential rate of rotation is given by observation of a westward drift of the non-dipole part of the field and of the centres of secular change (Bullard & others 1950). Since the high electrical conductivity of the core requires that the magnetic field lines be forced to move bodily with the fluid, the average value of the geomagnetic westward drift can be interpreted as the rate of rotation of the outer layers of the fluid core relative to an observer stationed on the mantle. The non-uniform rotation, together with the high electrical conductivity of the core, leads to the conclusion that a large toroidal field must be induced at the core boundary from the poloidal fields observed at the Earth’s surface. The toroidal fields leak into the conducting part of the mantle, vanishing at the boundary between the conducting and insulating parfs. The existence of a 361