Societies and Academies

Abstract

LONDON Royal Society, February 8. G. SALT: Experimental studies in insect parasitism. (1) Introduction and technique. (2) Superparasitism. Statistical analysis of field data relating to natural parasitism by Collyria calcitrator, Ibalia leucospoides and Lim-nerium validum shows that the parasites were not distributed at random among their hosts. A female of Trichogramma evanescens placed on a group of hosts can be observed to avoid ovipositing in hosts already attacked. Females of Trichogramma are able, at least for a time, to retain their eggs rather than deposit them in parasitised hosts. This restraint leads to the deposition of fewer eggs than the parasites are actually capable of laying. Females of Trichogramma are able to distinguish between large and small hosts and, when the number of hosts is limited, lay two, three or even four eggs in some of the larger ones. The hypothesis that the progeny of parasitoids are distributed at random, without reference to the previous parasitisation of the host, is untenable for the species considered. Miss D. E. SLADDEN: Transference of induced food habit from parent to offspring (1). Previous experiments with the stick-insect (Carausius morousu) in 1912-15 tended to indicate the inheritance of an induced food-habit. With the object of testing this possibility a series of experiments was devised. In the first generation few insects took ivy at all readily, only 10 per cent at the first presentation, 32 per cent at the second, 21 per cent at the third, 12 per cent at the fourth and so on for as many as ten presentations before the whole 125 insects being tested were induced to accept ivy. These insects were then grouped according to the presentation at which ivy was taken and reared to maturity on that food-plant. In the next generation 78 per cent took ivy at the first presentation. Other insects of the second generation were tested for preference. An insect on hatching was given both privet and ivy, being required to show its preference at three successive feeds. Some insects took only privet, others only ivy and yet others showed no preference. These were regarded as neutral. Offspring of privet-fed parents, 44 per cent privet, 35 per cent neutral, 21 per cent ivy. Offspring of ivy-fed parents, 28 per cent privet, 37 per cent neutral, 35 per cent ivy. Miss P. A. CLAPHAM: Experimental studies on the transmission of gapeworm (Syngamus trachea) by earthworms. Eisenia fctida, an earthworm commonly found in contaminated soil, is an important intermediate host of Syngamus trachea, the common gape-worm of birds. Lumbricus terrestris, another earthworm, may also act as intermediate host, but is much less efficient. The third stage larva of S. trachea, which hatches from the egg, is ingested by the earthworm; it migrates to the muscles of the body wall, where a thin hyaline cyst is developed around it. It remains dormant in this position, undergoing no further morphological development, until the earthworm is taken in by a chicken or other suitable host. The Syngamus larva then hatches, finds it ways to the lungs and trachea, where it settles down and grows to an adult gapeworm. Syngamus merulce, the gapeworm of blackbirds; has been transmitted to chickens by means of infected Eisenia fcetida.