The eggs of Locusta migratoria migratorioides, R. & F., increase in size during development. The increase is due to the absorption of water from the surrounding moist soil.

The wet weight of a freshly laid egg is 0·0063±0·0008 gms, and of a fully developed egg 0·014±0·002 gms. The dry weight of a freshly laid egg is 0·003± 0·0004 gms. and of a fully developed egg 0·0024±0·0002 gms. The water-content of an egg increases from 51·92±3·53 per cent, of the wet weight in the freshly laid egg to 82·36±2·14 per cent, in the fully developed egg.

The egg-wall consists of an exo- and endochorion and a thick vitelline membrane. The latter has a felt-like structure in the freshly laid egg, but as the egg develops, this membrane increases in thickness and acquires a laminated character.

The micropylar apparatus consists of a ring of about 35–43 oblique, funnelshaped canals arranged round the egg near its posterior end.

In common with the rest of southern-central Africa (Uvarov, 1933) the Nyasaland Protectorate was affected late in 1932 by the spread of the sixth generation of the red-winged locust. The course of the invasion, development of subsequent generations, and the damage done have been fully described in the Annual Reports of the Department of Agriculture for the years 1933 to 1934 (Smee, 1934, 1935).

1. An ecological description of the Red Sea coast of the Anglo-Egyptian Sudan is given, with special reference to the occurrence of the solitary phase of Schistocerca gregaria in its different parts and zones.

2. The greatest numbers of solitary Desert locusts were found amongst raingrown dukhn (Pennisetum typhoideum, Rich.) cultivated in the Suaeda belt of the coast, near the sea.

3. The factors responsible for the higher population of solitary locusts among the cultivation are probably the soil consisting of soft loose sand, and the more or less evergreen condition of the weeds on cultivated plots. It appears possible, however, that in some localities with naturally loose sandy soil all areas suitable for vegetation are cultivated, and in this case the cultivation in itself is not of primary importance.

4. Incipient outbreaks were observed in the type of cultivated areas described above in 1933–34, and again in 1934–35 winter seasons. Hoppers of the phase congregans were found mostly on a weed, Heliotropium undulatum, which is preferred by young hoppers to other food-plants, and seemed to act as a concentrating factor for the hoppers. No hoppers of the ph. congregans were found on clean cultivation where this weed was absent.

5. The chief factor determining the commencement of an outbreak seems to be heavy winter rains (over 240 mm. during the season), starting early (end of October) and continuing late (end of February), which allows for the development of two successive winter generations, as follows:—(a) Early maturation of old adults (November); (b) plentiful oviposition of old adults (November-December); (c) hoppers beginning to emerge (end of November); (d) hoppers beginning to become adult (early January); (e) majority of hoppers adult (end January); (f) these young adults remaining among dukhn in a fairly crowded condition (February); (g) young adults maturing (end February); (h) young adults ovipositing (March); (i) hoppers hatching (end of March-April); (j) young hoppers crowded on Heliotropium, assuming congregans coloration and later forming marching bands (April); (k) emigration of young flying swarms (May).

6. The exact cause of the rapid maturation of young adults of the first winter generation has not been discovered, although a short period of very high humidity seems to have some effect. There is no doubt that late rains are necessary for most adults to mature and oviposit in the field.

7. The Red Sea coast of the Sudan is distinguished from the interior of that country by its higher air humidity, by winter rains, and by the fact that the rainy season can extend for a longer time than the summer rainy period inland. The northern parts of the coast, north of the latitude 20°N., are less likely to produce outbreaks only because heavy and prolonged rains are unlikely to occur there.

8. General conditions in Eritrea, south of the Sudanese border, are such that some outbreak areas should be expected to exist there.

9. It appears probable that the Arabian coast of the Red Sea also contains some outbreak areas. As regards inland parts of Arabia, their climate, the distribution and the life-cycle of the solitary locusts there, are too little known to estimate the possibility of the existence of outbreak areas, until a special investigation is made.

10. The results of the investigations on the Red Sea coast put under suspicion of harbouring outbreak areas of the Desert locust all those parts of the sea-coasts of Africa and Asia which may obtain in some years winter rainfall of not less than 240 mm. extending for a period sufficiently long to allow for the development of two successive winter generations of the locust.

A short tour of northern Darfur was made by the author, on behalf of the Imperial Institute of Entomology, with the object of observing the solitary Schistocerca population, comparing it with that of northern Kordofan, and looking for any factors which might indicate the presence of potential outbreak centres of the desert locust.

1. All material was reared under constant conditions of temperature, light intensity and relative humidity. Two relative humidities were used—very wet and very dry. In some cases various coloured backgrounds were used. All material was solitaria, and was kept isolated.

2. Average weights were calculated from weighings made at all periods within the stadia, and thus represent the weights at the mid-points of the stadia.

3. The figures could not be fitted to the theory of a progression factor of 2.

4. Females are on the average 50 per cent, heavier than males even in the third instar; the sexes can probably be distinguished in this way much earlier.

5. The first three stadia are of about the same length; the fourth is longer, the fifth much longer.

6. The percentage rate of growth between the mid-points of successive stadia is of the same order for all pairs, though somewhat lower for the first and last pairs.

7. Hoppers kept in a very dry atmosphere are much lighter than those kept wet —proportionally more so in the later than in the earlier instars; on the other hand each stadium is lengthened—proportionally more so in the earlier than in the later stadia; the percentage rate of growth is just half that of hoppers kept wet.

8. The findings of Faure in regard to the causes of differences in coloration were fully confirmed.

9. The occurrence of a sixth instar in the females is due to an inherited factor.

10. This “ extra ” instar may represent an extra morphological third instar or an extra morphological fourth instar.

1. The Algerian race of Locusta migratoria, L., although never known to occur in the gregarious phase in nature can be transformed into almost typical ph. gregaria by breeding in crowded cages.

2. Biometric characters of such individuals indicate a relationship of the Algerian race to the subsp. migratoria, but the data are insufficient for a final decision on this point.

3. The rate of embryonic and hopper development in the Algerian race is the same as in the tropical African subsp. migratorioides when bred at the same temperature and relative humidity.

4. The rate of sexual maturation is very much slower in the Algerian race than in the tropical one bred under the same conditions.

The form of the Migratory Locust (Locusta migratoria, L.) appearing in swarms in south-eastern tropical Asia, the Malay Archipelago and the Philippine Islands, is usually referred to the subspecies migratorioides (Reiche & Fairmaire) which occurs in tropical Africa. However, even a superficial examination of series of specimens of the gregarious phase is sufficient to show that the Oriental locusts are somewhat different in their size and structure from the African ones. It was, therefore, of interest to compare the two forms biometrically and the results as described below have proved that the Oriental Migratory Locust should be regarded as a subspecies distinct from the African one, as well as from the three other subspecies of Locusta migratoria so far distinguished (Uvarov & Zolotarevsky, 1929).

The present paper is an account of a preliminary reconnaissance, undertaken during the wet season of 1932, of the suspected middle Niger outbreak area of the migratory locust, Locusta migratoria migratorioides, R. & F.