589 



time is spent in the larval stage, the parasite still being in an anomalous 

 stage, called by the author the feeding embryo, when the host is in the 

 pupal stage. 



A very large number of parasites succumb annually as a result of 

 the limited food supply, and for the same reason one caterpillar of 

 Hyphantfia may be attacked by several parasites, either of the same 

 or different species. As many as 22 parasitic larvae, belonging to four 

 species, have been found in one host. As the host larva is only sufficient 

 to maintain one parasite, whichever of these reaches the destructive 

 feeding stage first is likely to become the sole survivor ; Therion is 

 the most handicapped, as it is the last to reach this stage. The 

 struggle may take place between larvae of the same species, and 

 should several individuals reach this stage within a few hours of one 

 another none of them will be able to survive. Except under unusual 

 circumstances this interparasitic struggle does not appear seriously 

 to hinder the work of the parasites, the natural sequence of them 

 occurring in average years being sufficient to reduce it to unimport- 

 ance. The two great gaps in this sequence are the absence of 

 parasites of the egg and adult, which is probably due to the brevity 

 of these stages. 



In New Bninswick, Nova Scotia and British Columbia the absence 

 of hyperparasites of Hyphantvia is also very marked. This may be 

 explained by the fact that in these areas the primary parasites, like 

 the host, have only one generation a year, and the hyperparasites, 

 having at least two and sometimes four or five generations, would 

 have to support their spring and midsummer generations on parasites 

 of hosts other than Hyphantvia. This difficulty does not arise in the 

 transition zone, where Hyphantvia has two generations. 



An account is also given of some of the defensive measures of 

 Hyphantvia against its enemies, such as the armature of the larva, 

 the community web, phagocytosis and the habit of flying away from 

 parasites. 



Lafferty (H. a.), Rhyxehart (J. G.) & Pethybridge (G. H.). 

 Investigations on Flax Diseases. (Third Report.) — //. Dept. 

 Agvic. & Tech. Instv., Iveland, Dublin, xxii, no. 2, August 1922, 

 pp. 103-120, 11 figs. 



The investigations into flax diseases previously reported upon 

 [R.A.E., A, ix, 446] have been continued. Experiments in the trans- 

 mission of Browning disease (caused by the fungus Poly spot a lini), 

 showed that insects such as Longitavsns pavvtihis, Payk. (flax flea- 

 beetle) may, under natural conditions, act as mechanical carriers 

 in its early stages by spreading the fungus from below to the top 

 of the plant, whence it is rapidly disseminated to adjoining plants 

 by direct contact or through other agencies. 



A good deal of further data concerning L. pavviilus [R.A.E., 

 A, X, 339] has been obtained. Adults emerged in mid- July, one 

 month earlier than in the previous year. As the greatest damage is 

 done by those beetles that appear during July and August, and, 

 after hibernation, attack young flax during the following spring, it is 

 obvious that the seriousness of attack in any given season is dependent 

 on the weather conditions of two seasons. The maximum damage 

 may be expected when previous conditions have ensured the survival 

 of a large number of beetles, and present conditions are unfavourable 

 to the rapid growth of the flax brairds. Many experiments in remedial 

 measures are recorded, but the majority gave no successful results. 



