1. The influence of atmospheric humidity on the various stages in the life-cycle of Microplectron fuscipennis, Zett., is examined. Both the longevity of the adults and the extent of oviposition are found to be proportional to the saturation deficiency of the atmosphere. Under favourable temperature conditions, functional activities are at their maximum in a moist climate, but a wide tolerance is exhibited so far as oviposition is concerned. At normal humidities no effect on the developmental period of the parasite is apparent when the humidity is varied, and this is shown to be due to the protection afforded by the host cocoon.

2. Temperature affects the parasite in a normal manner. The threshold of development is approximately at 8·3°C., and the zone of functional activity is from 15° to a little over 35°C. Optimum conditions for oviposition and development occur between 20° and 35°C. Death occurs at 40°C., while at the lower temperatures, near freezing point, starvation of adults takes place after a lengthy exposure. The hibernating parasite can withstand temperatures very much below freezing point, field records coming from countries where the winter temperature falls to so little as −37°C.

3. The relation of Microplectron to climate is discussed and an explanation is offered of the wide variation in natural parasitism occurring in European countries.

4. The actual and possible distributions of the parasite in Europe are discussed and a map is presented depicting the position as known at present.

5. The possible distribution of the parasite in North America, after liberations have been made, is dealt with and it is shown that the present trend of dispersal of Diprion polytomum is in the direction of climatic conditions that are more favourable to the parasite than are those in the area where the parasite has already become established.

Some of the problems involved in the estimation of parasitism in populations of Heliothis eggs are discussed:—

(a) Effective parasitism of the “active fraction” of eggs as laid in situ is denned.

(b) The habits of the egg-laying moth in point of the duration of oviposition on individual crops and diversion of moth activity from one host to another are discussed in relation to releases of Trichogramma lutea. Data are given on the distribution of bollworm eggs in a crop and associated factors.

(c) Investigations on the dispersion of liberated parasites are described. Dispersion was found to be rapid and widespread; concerted activity by large numbers in given areas did not apply.

Investigations in rain-grown crops are described and results are quoted from a typical experiment in maize, wherein the percentages of parasitism recorded in a large number of equal sections of the crop are regressed on proportionate larval survival. Although the egg parasitism ranged from 21·2 per cent, to 82·3 per cent., differences in larval populations were inappreciable. An explanation for this is offered in an analysis of the effect of various mortality factors.

The parasite was relatively ineffective in cotton crops. The low degrees of parasitism found are assigned to the growth-habit of the plant, the scattered manner of egg deposition thereon and the impediment offered to the insect by the dense hair processes of the plant at many sites where eggs are commonly placed.

Investigations on irrigated (cool season) market-garden crops and citrus orchards are described. These form the principal breeding sources of summer bollworm. Oviposition is extensive and sustained for three to four months on these crops, thereby affording opportunity for continuous parasite activity and the cumulative participation of progeny bred in the field. In nature Trichogramma lutea does not, however, appear until the latter end of the egg-laying by Heliothis and the authors were unable to establish laboratory-bred representatives at an earlier period.

Another egg parasite, Phanurus ullyetti, is prevalent before Trichogramma appears and accomplishes much that was hoped for from the attempted earlier introduction of Trichogramma. In effect, the latter, as seen from diagrams furnished with the paper, becomes substituted for Phanurus toward the close of the winter season. It is probable that temperature is a determining factor in the biology of both parasites, although other causes for the observed relations are suggested.

Further investigations are needed on the subject of exploiting T. lutea in the cool season.

A study of the variations of the population of Dysdercus fasciatus on cotton and on its wild host-plants is described.

The most important host of D. fasciatus in the Acacia savannah of Northern Rhodesia is Thespesia rogersii, and it is shown that at certain times a general flighting of stainer takes place from this host-plant caused by food shortage or defoliation. Generally a period of food shortage occurs during the earlier months of the year owing to rotting of the old crop and extensive destruction of the early new crop by the larvae of a Cossid moth. This causes an early influx into cotton, which leads to the establishment of a large population in the field at a critical period in the development of the bolls. When the early crop is retained on the trees a continuously increasing food supply is provided, and this first movement does not take place. A second movement from Thespesia, which is largely due to defoliation, begins generally in June. It has been shown that a second influx into cotton coincides with this later movement from Thespesia. A late influx such as this is of little practical importance since the greater part of the crop is picked in May and June.

The observations recorded indicate clearly that the movement of D. fasciatus into cotton is not due to any attraction exercised by the crop but is caused by a forced movement of stainers from Thespesia rogersii.

The genus Cicadulina was established in 1926 (Bull. Ent. Res. 17, p. 43) to hold a new species, C. zeae, China, injurious to maize in Kenya Colony. Later (Bull. Ent. Res., 19, 1928, p. 66) it was shown that Balclutha mbila, Naude, recorded as transmitting the virus of streak disease of maize in Natal, also belonged to this genus, and two new species C. arachidis and C. similis were described from the Gambia, where they were reported as injurious to ground-nut and suspected of transmitting the virus of the rosette disease of that plant. Since that time Dr. H. H. Storey of the Amani Research Station has been investigating the possibility of transmission of the streak virus of maize by C. zeae. In attempting to breed strains capable of transmission of the disease certain crosses were made which showed conclusively that he was dealing with two distinct species. These species he was able to separate on the colour pattern of the abdomen. Dr. Storey has now sent to me material of both these species and a study of the genitalia corroborates his finding. One, of course, proved to be C. zeae, the other is new and I therefore propose to dedicate it to the discoverer.

The types of the new species described below have been deposited in the British Museum.

An experiment is described in which G. tachinoides in an isolated secondary focus was marked with distinct colours during thirteen successive weeks and the fate of the groups studied by recaptures. The population was known to be declining from moderate density to great scarcity through the dry season and the wastage in the colour groups on the average proved to be 11½ per cent, per diem, rather more, probably, than the wastage in unmarked flies. Following Jackson's method of assessment the population is shown to fall from 6,000 at the end of October to 400 by mid-January. The ratio of the boy-hour rate to these numbers is worked out for each collection and it is found that when the boy-hour rate is above 50 it is not relative to population, but below 50 the rate falls as the population, allowing for the influence of weather on rate of catching.

It is shown that under the conditions of the experiment there is an almost complete change of fly population each 5 or 6 weeks, though an occasional fly may survive 11 weeks. The proportion of male flies in the catches fell with increasing age from an initial 57 per cent, to 23 per cent, in the 6th week and no male fly surviving this period was caught.

During a series of experiments at Rothamsted with the mechanical insect trap described by Williams & Milne (Bull. Ent. Res. 1935, 26, p. 543) it became necessary to make counts of large numbers of insects three or four times a day over periods of several weeks. The following is a description of a device which was designed to facilitate the handling of the insects and to increase the speed and accuracy of the counting.

1. There is considerable seasonal variation in the longevity of G. submorsitans and G. tachinoides, and these variations are negatively correlated with the fluctuations in the maximum temperature curve, i.e., as the temperature rises longevity decreases, as the temperature falls so longevity increases.

2. The cycle is as follows:—The rains commence and temperature falls, longevity increases and remains high throughout the rains. The wet season ends, temperature rises and longevity descreases. The cold spell intervenes and longevity becomes maximal. The cold weather ends, the temperature soars up and longevity becomes minimal, remaining low until the new rains commence.

3. Maximum temperature is considered to be the dominant factor; favourable humidity cannot increase longevity unless the maximum temperature is favourable.

4. The oldest individuals occur in the rains, but the average longevity is highest in the cold season, when both temperature and humidity are favourable.

5. In both species females tend to live longer than males.

6. In the field G. tachinoides males appear to live rather longer than the males of G. submorsitans.

7. It is doubtful whether wild flies of either species live much more than 2½ to 3 months under the most favourable conditions; it is probable that in the hottest weather longevity is curtailed to a month or less, and that the production of puparia is seriously affected when the rains are late and the hot weather is prolonged.

It is known that there is a high mortality in puparia of Glossina submorsitans and tachinoides if they are kept in air which is far from saturation; it seems anomalous that there is no evidence of mortality among puparia in nature at the end of the dry season when the soil in the thickets appears to be quite dry.

Experiments are described, showing that the soil of the thickets (unlike the more sandy soil of the open country) will take up large quantities of water; as its colloid content is high, this soil must also possess great power of retaining the water. Moreover even when the soil seems quite dry (water content 4 per cent.) the atmosphere in the soil spaces is very nearly saturated.

Oil has been used as a mosquito larvicide for about forty years, since L. O. Howard in 1892 first recommended its use, and a large literature has accumulated on the subject, but the physical and chemical properties which make an oil a suitable material for this work are very imperfectly understood. It is clear that the problem is one that can very favourably be studied in the laboratory, for it requires above all an answer to the question “How do larvae die under oil treatment?” which can only be answered by microscopic examination of the larvae.

1. Fifteen species of Chloropidae were taken in a survey of Jamaica.

2. H. pallipes, Loew, was found in greater numbers and in more localities than any other species.

3. H. peruanus, Becker, was readily attracted to traps baited with decaying dead animal matter whereas H. pallipes came but rarely to such traps.

4. H. pallipes was most prevalent at elevations ranging from 101 to 1,500 feet above sea-level. H. currani was frequent somewhat lower down, and H. pusio and H. illicis were most common quite close to the sea.

5. A key with explanatory diagrams has been prepared for identifying the adult Chloropid flies of Jamaica.

6. Also the distribution records of all species captured during the island survey have been tabulated.

7. Two new species of Hippelates flies have been described.

8. Three photomicrographs of the immature stages of H. pallipes which were taken are briefly discussed.

The Imperial Institute of Entomology has received from Mr. N. C. E. Miller, from Malaya, some interesting Chalcids, which have been bred from the eggs of Batocera rubus, L. Parasites of Cerambycidae are generally little known everywhere and only very-few egg-parasites of beetles have yet been described. Mr. Miller's breedings are therefore of special interest and importance. We understand that he has made some biological observations, which he intends to publish; therefore, although very few specimens of these parasites have been received so far, we venture to describe them here with the material at hand. One species belongs to the Cleonymidae and to a very striking new genus, which can be confused with no other known genera; the other is the first species of Ooencyrtus known to attack eggs of Coleoptera.

Oranges, and to a lesser extent grapefruit, have been exported from Jamaica for many years but to an extent considerably under the potentialities of production of the country. In order that the Colony may derive full benefit from natural conditions definitely propitious to the growth of these crops, as well as from the possibilities afforded by an exceptionally advantageous geographical position with regard to world markets and trade routes, the Department of Agriculture is at present organising and developing production of citrus fruits for export on a much larger scale.

1. It has been confirmed that the lower limit of the critical zone, for fly of medium age, is 102°F. for both species; this limit is probably even lower for very old G. tachinoides.

2. The adverse effect upon the fly community of a day when the maximum temperature enters the critical zone is continued among the older individuals for several days following, even though the maximum temperature on these days remains below the lower limit.

3. From the mean maximum temperatures recorded over 52 days in 9 microclimates, it would appear that sites on the ground are cooler than those above the surface; the difference is not very great, the mean for the four ground sites being only 4·4°F. lower than the mean for the five above-ground sites.

4. The evidence suggests that on very hot days only the ground within the true forest is safe for tsetse; in all other sites—above the ground in the true forest or on the ground in the intrusive and peripheral thickets—the temperature is liable to enter the critical zone, and may even reach the upper fatal limit.

5. The tsetse community is living very close to the critical zone in the late dry season. Even the coolest ground site yielded an absolute maximum that was only 3·5°F. below the lower limit.

6. Site no. 9 gives an indication of how severe the conditions might become in the true forest were the windbreaks of peripheral and intrusive thicket removed.

7. In ground sites a shower of rain produces about twice as great an initial drop in temperature, and temperature remains abnormally low for about twice as long, as it does for sites above the surface of the soil.

8. The duration of the period of dangerously high temperatures to which the fly community is subjected in the late dry season may be very varied; it depends upon the incidence of rain in April and May.