1. For the purposes of this paper a suitable host is defined as one on which the parasitoid can generally reproduce fertile offspring.

2. To be suitable for Trichogramma, a host must satisfy conditions required by two generations of the parasite: it must be such that it can be actually parasitized by the adult parasitoid; and it must provide an environment in which the parasite offspring can develop.

3. Some hosts prevent the attack of Trichogramma leading to parasitization by the physical resistance of their chorion; others by inhibiting the impulse to oviposition.

4. Five physical characteristics of the hosts of Trichogramma are investigated: the permeability, rigidity, and hardness of the egg-shell; and the fluidity and quantity of the egg-contents (pp. 226 to 231).

5. Eggs of Sialis lutaria, Tenebrio molitor, and Bruchus obtectus are chemically unsuitable for Trichogramma evanescens as food.

6. Two biological characteristics of the host, its viability and its age, do not directly affect its suitability for Trichogramma; a third, the ability of the embryo to move, is of some importance.

7. The various known factors of host unsuitability are given in tabular form (p. 239).

8. In spite of numerous attempts during several years it has not been possible to develop a strain of Trichogramma evanescens which could use Bruchus obtectus as a host.

9. The host list of most groups of parasites is greatly limited by the inaccessibility of many species; it is further restricted in some groups (e.g., the parasitoid Hymenoptera) by the selection exercised by the parasite; it is finally limited in all groups (and especially the parasitoid Diptera) by the unsuitability of many infected animals.

10. The division of the problem of host specificity into the three parts, host finding, host selection, and host suitability, is fundamental.

Apanteles carposinae, sp. n.

♀. Black; the front legs entirely (save for the black feet and for some occasional slight darkening on femora above and below, on tibiae above, and on coxae and tarsi), middle legs entirely (save for the black feet and for femora darkened above and below and for some occasional slight darkening on tibiae and coxae), hind coxae at apex below, hind trochanters and trochantines, hind femora (save above and below extensively), hind tibiae, hind tarsi (save for black feet and some darkening), and palpi, red testaceous; tibial spurs pale; wings infumated evenly throughout and the setae coloured; stigma, metacarp, and all veins, brown; stigma uniformly opaque.

♂. Black; front coxae (save at base), front trochanters and trochantines, front femora (save for darkening above and below, which is sometimes strong), front tibiae (save for strong darkening above), front tarsi (save for some darkening and the black feet), middle coxae (save at base or even basal half), middle trochanters and trochantines largely, middle femora (save for extensive strong darkening above and below), hind coxae at apex below to some extent in the lighter but not in the darker examples, hind femora (save for extensive strong darkening above and below), and palpi, red testaceous; the four posterior tibiae and tarsi, and the hind trochanters and trochantines, largely darkened throughout save perhaps in an occasional lighter example; tibial spurs pale; wings infumated evenly throughout and the setae coloured; stigma, metacarp, and all veins, brown; stigma uniformly opaque.

The following mosquitos should be added to the list given in my earlier paper on this subject (Bull. Ent. Res. 28, 1937, pp. 405—407).

1. Anopheles elutus, Edwards.

The larvae are found in the same habitats as those of A. maculipennis, but seem to show a greater preference for waters near the sea-shore. A. elutus appears to be considerably rarer in Corfu than A. maculipennis, but sufficient data are not yet to hand to settle this question.

2. Anopheles plumbeus, Stephens.

Not common. I have obtained the larvae from the rot-holes of oak, elm and white poplar, but never so far from those of olive-trees. They favour deep holes containing plenty of rotting material.

3. Aëdes (Ochlerotatus) caspius, Pallas.

The larvae are sometimes present in fresh, but more frequently in slightly brackish waters. They are often gregarious with the larvae of O. detritus, Hal., but are much less abundant than the latter.

4. Aëdes (Ochlerotatus) pulchritarsis, Rondani.

The larvae live in rot-holes of oak, elm and white poplar, and are sometimes met with in considerable numbers in the same hole. They prefer holes in which the collected water has become thick and very dark amber in colour owing to the presence of decaying wood debris.

5. Orthopodomyia pulchripalpis, Rondani.

The larvae are found in the same habitats as those of O. pulchritarsis and are often gregarious with the latter. They are less plentiful, on the whole, than O. pulchritarsis and prefer somewhat clearer water.

Note.—In my paper referred to above I mentioned that Finlaya echinus, Edw., is commoner in Corfu than F. geniculatus, Oliv. This statement is due to an error of determination arising from the fact that in many of the Corfu larvae of F. geniculatus the bristles of the abdominal tufts are somewhat more developed than those described in some text-books.

The results of the present investigation can be summarized as follows:—

1. Cold-hardiness in insects depends on the physiological state of the organism; the most resistant are the phases in diapause (prepupae of Croesus septentrionalis, eggs of Lymantria dispar, pupae of Acronyctinae); not so hardy are the caterpillars of Lasiocampa quercus stopped in their development and prepupae of Agrotis segetum; practically non cold-hardy are developing (or growing) insects, viz., the full-grown larvae of Calliphora erythrocephala, the growing caterpillars of Loxostege sticticalis and Agrotis segetum.

2. The difference in the cold-hardiness of these three groups depends on the specificity of their cellular respiration. Growing insects show in their cellular respiration the prevalence of oxydases, the activity of which is connected with characteristics of their cellular structures; in cold-hardy insects the cellular respiration is closely connected with the anoxybiotic processes caused by the dehydrases; their activity is not bound up with the structural elements of the cells, but is closely connected with the presence of non-saturated fat-acids (Dixon, 1929; Meldrum, 1934) peculiar to insect fats.

3. The respiration of growing or developing insects is entirely and rapidly destroyed by narcotics, cyanide and low temperatures; the effect of these agents is due to the destruction of the cellular structures. The respiration of cold-hardy insects is characterised by its definite thermostable part and is also resistant to narcotics (or cyanide, Bodine, 1934). Destroying the cellular structures does not affect that respiration. Cold-hardiness increases with the increase of the percentage of thermostable respiration.

4. Freezing of the protoplasmic water causes the death of an insect only in the absence of thermostable respiration. Many insects in diapause (characterised by a high percentage of thermostable respiration) can be frozen without any lethal effect (Pyrausta nubilalis, Croesus septentrionalis, Lasiocampa quercus). It is clear that the freezing of the free protoplasmic water cannot be considered as an obligatory cause of “ anabiosis.”

5. The quantity of fat does not show any direct connection with thermostable respiration and cold-hardiness in insects. It is probable that the important factor is the quality of the fats, namely, the rôle of non-saturated fat-acids. The increase of cold-hardiness in insects after dehydration can be connected with the changes in cellular respiration; the same can be said regarding the general connection of the water content of the protoplasm and cold-hardiness.

The life-history of Blatta orientalis has been studied from the time of the deposition of the ootheca by the female till the nymphs of the third generation emerge, viz., through two embryonic and one post-embryonic lives.

The cockroach passes through one pronymphal and six nymphal stages and moults seven times after its exit from the ootheca.

The post-embryonic growth, including the increase of the antennal and cercal joints, and the modification of the external genitalia, is described. It has been shown that nymphs of various instars and their sexes can be distinguished, especially with the help of the genitalia, the number of cercal joints, and the growth of the wing-rudiments.

The average time taken by 27 nymphs to mature at 27·5C. is 279 days. The males mature earlier than the females and also die before the latter.

The formation and structure of the spermatophore are described and also the exact mode of copulation, including the use of various parts of the male genitalia.

The ootheca is deposited with special care by the female in that she digs a pit with the help of her mandibles and the fore legs and covers the ootheca afterwards. The nymphs emerge without the help of the female and the latter does not take any care of the ootheca after it has been safely deposited.

1. The moth—Cydia nigricana—whose larvae bore into the pods of developing peas and render most of the contained seeds unfit for human consumption is considered by some authorities to be one of the principal insect pests of agriculture in Canada. It is particularly destructive in the Maritime Provinces and British Columbia, while in Ontario it increased to such proportions that the farmers of that province had to give up growing mid-season peas altogether.

2. This state of affairs is attributed to the fact that the pea moth was accidentally introduced from Europe in 1893 without the insect parasites which attack and check it in its native home. At any rate no parasites have emerged from the representative collections of pea moth material made by the Canadian entomologists in the affected areas, while three species with a combined parasitism of up to 60 per cent. have been reared by the writer from cocoons of the moth in England. Furthermore, in Canada, where parasites of this particular pest are absent, 10–50 per cent. of the pea crop and sometimes as much as 75 per cent. or more, is said to be destroyed annually by the moth larvae, whereas in England, where they are present, the attack is usually comparatively slight.

3. The paper opens with a general account of the biology of the pea moth including systematic descriptions of the adult and developmental stages, and notes on the host-plants and distribution of the insect.

The Encyrtidae reported upon in this paper are mostly Coccid-inhabiting species, received by the Imperial Institute of Entomology from various collectors in Africa and forwarded by Dr. C. Ferrière for identification. The species of Microterys, Metaphycus, and Anicetus will be reported upon in separate papers at a later date, All holotypes and allotypes are deposited in the British Museum; paratypes will be deposited in the United States National Museum.