Experiments were carried out in Kenya to find whether insecticidal smokes from “Swingfog” machines would remove tsetse flies, in this instance almost all Glossina longipennis Corti, carried by trains. Fogging was done by two operators, each with a machine, starting from opposite ends of trains halted at a station twenty miles inside a fly-infested area and assessment was by routine catches at a station twenty miles outside it. It was found that fogging reduced the number of flies found on trains by 60 to 70 per cent. As the trains had to pass through a light fly infestation after fogging, the real kill is likely to have been higher. The cost of such partial reduction is believed to be considerably higher than would be that of therapeutic control of trypanosomiasis in the affected region.

A DDT sol, prepared in glass dishes in the manner described, has a reproducible zeta potential of −25 mv. Electrophoretic measurements showed that DDT conditioned in cardboard cartons has a zeta potential of zero.

The zeta potential of the suspension behaves in a predictable and measurable manner in the presence of mono-, di-, tri-, and tetravalent ions.

Spectrographic analyses showed that there are two identifiable sources of ions: (1) the DDT, and (2) the cardboard container. A third source of ions was indicated as being, singly or together, the distilled water and/or the DDT solvent.

Spectrographic data showed that ions were associated with the conditioned DDT.

In glass containers, a poor source of ions, kill of larvae of Anopheles quadrimaculatus Say was higher than in paper containers, a good source of ions. These data are correlated with the zeta potential and flocculation behaviour of DDT suspensions.

A number of predacious mites of the PHYTOSEIINAE (family LAELAPTIDAE), found in south-eastern England, mostly in association with fruit trees, are listed. Certain measurements and other characters that are of value in separating species are given. The species found were: Typhlodromus tiliae Oudm., T. cucumeris Oudm., T. tiliarum Oudm., T. rhenanus (Oudm.), T. finlandicus (Oudm.), T. umbraticus Chant, T. massei Nesbitt, T. vitis Oudm., T. soleiger (Ribaga), Phytoseius macropilis (Banks) and two Amblyseius spp. Of these, T. tiliae, T. finlandicus and P. macropilis are normally abundant on apple trees, but only T. tiliae remains abundant on commercially-grown apple trees. For each species a list of plants on which it has been found is given.

Details of the life-history of laboratory-reared mites are given and these, together with counts of field populations, show that three generations a year is normal.

Predacious phytoseiine mites feed on several species of TETRANYCHIDAE, including Metatetranychus ulmi (Koch) and Tetranychus telarius (L.); when M. ulmi is supplied in adequate numbers, adults of T. tiliae consume 3 mites per day, the nymphs 2 mites per day, on an average. It is thought that they also feed on plant tissue, since individuals survived in the laboratory for a considerable length of time in the absence of phytophagous mites, though eggs were not laid.

In working out a collection of Heterocera made by J. D. Bradley in the Solomon Islands, preparations were made of the genitalia of specimens of Spodoptera mauritia (Boisd.) and they were found to differ from those of African specimens, with which they were compared. Subsequent study of the material in the British Museum has shown that two species have been confused under the one name; S. mauritia, which occurs in Madagascar, Mauritius, the Comoro Islands and from India to the Pacific and which is known from continental Africa from only a single female taken at Lindi on the coast of Tanganyika, and the second species, S. triturata (Wlk.), which occurs throughout continental Africa, south of the Sahara Desert. As both species are of economic importance, it has been decided to describe their differences in a separate paper rather than include them in the faunistic paper dealing with the Heterocera of Eennell Island.

The most important species of Pseudoeoccid transmitting the swollen-shoot virus disease in the Gold Coast is Pseudococcus njalensis Laing. It is almost always attended by ants of the genus Crematogaster. These ants usually build their nests in the cavities and galleries that have already been excavated by wood-boring insects in the dead branches of cacao trees. The only apparent advantage of this association to the ants is to imbibe the honeydew secreted from the anal orifice of the mealybugs; if this is allowed to accumulate it becomes a medium for bacteria and fungi which seems to kill the mealybugs eventually.

Attempts were made to break the link between the mealybugs and ants by spraying six cacao trees, not in contact with each other or any other trees, each with 3·5 litres of 0·2 per cent. DDT emulsion, twice at two-week intervals. All dead branches containing nests of ants were cut out, and a band of grease painted, on the trunk, one foot above the soil level to prevent the ants climbing up. Four weeks after the first application of spray, the population of mealybugs was brought down to 1·2 per cent, of its size before treatment. Unfortunately locating the ant nests, especially in the crevices and under the bark, is very difficult. Experiments were therefore carried out in which the trees were sprayed without previously eliminating all the sources of ants. The results were unsatisfactory, the size of the mealybug population, compared with that before treatment, after four, six and eight weeks was 16·9, 39·4 and 92·3 per cent., respectively, in the case of 0·2 per cent. DDT emulsion, and 11·6, 64·3 and 58·8 per cent., respectively, in the case of a treatment consisting of 3·5 litres per tree of a mixture of 0·2 per cent. DDT and 0·02 per cent, parathion active material. Cutting off the dead branches containing ant nests, followed by either painting the cut end of the dead branches with DDT (16·7 per cent, emulsion) or painting the trunk with a band of the same emulsion also gave poor results.

The unsatisfactory results obtained by spraying are attributed to the fact i that only the ants that happen to be exposed are affected by the application of ithe insecticide; the immature stages inside the nests are not touched.

The efficiency of dimefox when applied to the soil at 0·8 gm. active material per inch of tree girth was not increased when the ants had previously been partially eliminated.

Treated cacao trees could not in practice be completely isolated from forest jtrees and climbers containing nests of Crematogaster ants and these provide a continuous source of large populations. It is, therefore, considered that the icomplete elimination of ants is not possible.

It was also found that there is a relationship between the population of mealybugs and ants. Trees were usually free from mealybugs if no ants were found on them. The examination of isolated cacao trees with different sizes of dead branches containing nests of ants suggests that the number of mealybugs 38 in proportion to the size of the nests.

Field and laboratory studies on the rôle of oxygen concentration and speed of current on larvae of Simulium ornatum Mg. show that current speed is more important than oxygen concentration in governing their distribution.

The larvae prefer waters with a velocity range of 50 to 120 cm./sec., the greatest numbers occurring between 80 and 90 cm./sec.

Larvae move independently of oxygen in concentrations above 50 per cent, saturation level.

A systematic review of some species of the Coccid genus Saissetia occurring in East Africa led to the rediscovery of two species—S. persimilis (Newst.) and S. somereni (Newst.)—which although of economic importance have been almost completely neglected since they were first described. Both are redescribed in this paper. One new species recently collected in Kenya is described; this is S. pterolobina.

Seven species are dealt with in the paper, including the important and widely distributed S. oleae (Bern.). A provisional key for their separation is included, while one species—S. cuneiformis Leonardi—is sunk as a synonym of S. nigra (Nietn.).

Keys are provided for the larvae of 32 species of TINEIDAE, and detailed descriptions are given of 31 species. These include most of the species known to be of any economic importance. What is known of the biology of each is briefly summarised, but no attempt has been made to collate the available information on control measures.

No larvae have been available of four species of some economic importance nor of twelve others of doubtful status as pests. The literature on each of these species is noted.

The larvae of a few species of no known economic importance are described and are included in the keys. Most of these are very closely related to species known to be pests.

The keys and descriptions include 21 species which are indigenous to Britain or are established here, so that keys and descriptions are now provided for half of the British species of Tineidae.

Schizonycha larvae, of a species that cannot yet be named with certainty, are a serious pest of “lubia” (Dolichos lablab) and “dura” (Sorghum vulgare) in the Sudan Gezira. Damage from these grubs has seriously reduced lubia yields at the Gezira Research Farm during the 1946–52 seasons. Soil application of BHC, at rates between 10 and 40 gm. γ isomer per feddan (1·038 acre) give excellent control of this pest on lubia. Application with the seed at the time of sowing (in effect, by drilling) is, in general, more effective than broadcasting or applying the insecticide along the ridges. Seed dressings appear to be ineffective for control, with lubia.

Population estimates show that γ BHC does not kill Schizonycha larvae but repels them or prevents feeding. The larvae occur in the soil to a maximum depth of 60 cm., and are concentrated around the plant roots. The mean depth varies with time of year, and probably with type of plant, between 15 and 30 cm. The mean depth of the pupa is 15 cm.; this does not appear to be influenced by BHC.

Larvae are widely distributed in the Gezira but are most abundant in the South and Centre Groups of the Scheme. There is evidence that, where chafer larvae and termites are associated with groundnuts, the chafer larvae are responsible for initiating damage while the termites are secondary invaders. The beneficial effect of a good lubia crop (resulting from BHC application) is reflected in the cotton crop two years later.

It is known that the females of some species of parasites can distinguish hosts that have already been parasitised and refrain from ovipositing in them. A study was made of the extent to which Spalangia drosophilae Ashm. avoids superparasitism of the puparia of Drosophila melanogaster Mg. by means of these two steps, which are termed discrimination and restraint, respectively.

Host puparia 0–24 hours old were stuck on paper, with water, equidistant ¼ in. from each other and placed in 4½ in. × 1 in. glass vials into which females of Spalangia were introduced for different periods. A series of experiments was set up, in which 25, 10 and 5 puparia were exposed to attack by 1 unmated or 1, 2 and 5 mated parasites for 24, 48 and 72 hours. In this way a wide range was obtained of the parasite-host (P/H) ratio, computed as the ratio of the number of female parasites, multiplied by the number of 24-hour periods for which they were used, to the number of host puparia exposed. Each treatment was replicated ten times, thus entailing a total of 360 experiments. The sequence of events associated with oviposition consisted of examination of the puparium by the females, stinging, followed sometimes by feeding on the fluid that exuded, and finally, but not invariably, oviposition. At the end of the experiment each puparium was examined and the number of eggs present, or the occurrence of stinging only, was recorded. The chance of a puparium being attacked was unaffected by its position on the paper and there was no significant difference between the total number of eggs that virgin and mated females laid under the same conditions.

The results were assessed by comparing the observed distribution of parasite eggs amongst host puparia with the probable random distribution calculated from a formula that is given. The divergence between these distributions was greatest at the lower P/H values, and very little superparasitism occurred unless these exceeded 3/25, at which point total parasitism reached about 60–70 per cent. As the P/H value increased, so did the total parasitism and the degree of superparasitism, and the deviation of the observed from the random distribution of eggs diminished, although even amongst experiments in which parasitism reached 91–100 per cent., superparasitism was still avoided in 15·6 per cent, of them.

The degree to which females of Spalangia can restrain themselves from ovipositing in hosts that have been parasitised was estimated by plotting the percentage of experiments in which restraint was observed to break down, against the level of attack, and comparing the distribution of the points so obtained with the curves that would relate these two functions if the power of restraint was to break down when the female was confronted with 2, 3 or 4 successive puparia that had already been attacked. It is concluded that the assumption that restraint breaks down at about the third successive unsuitable encounter gives the best fit with the observed data.

Contributory evidence that females of Spalangia can distinguish parasitised hosts was obtained by direct observation of their behaviour, which indicated that, on the average, females took about 3½ minutes to examine an unparasitised host before deciding whether to attack or not, but, in the case of hosts already parasitised, either rejected them in half that time, or only accepted them after unduly prolonged examination.

When individual mated females were supplied daily for 16 days with a single puparium, then for 3 days with 25 puparia, then again for 8 days with a single puparium and finally for 8 days with 25 puparia, the number of eggs laid daily was restricted to less than two when only a single host was available, but rose to about 9–11 on the first day an excess of hosts was provided and then fell to a normal output. The females thus adapt their egg-laying to some extent to the number of hosts available.

It was hoped that this elucidation of the combination of perfect discrimination but imperfect restraint exhibited by Spalangia. when ovipositing, together with the data previously obtained on its biology, would make it possible to predict the fluctuations of a population of Spalangia in the field and its effect on the natural host, Oscinella frit (L.), but the factors involved, and their interactions, are too complex, particularly when weather effects are considered, and it is concluded that any predictions of population must be deduced empirically from field observations over a number of years.

The principal pest of sugar-cane in northern Tanganyika is the Red Cane Beetle, Cochliotis melolonthoides (Gerst.) (Melolonthidae). Descriptions of adults and larvae of Cochliotis and of allied beetles found in the same area are given.

The bionomics of Cochliotis have been studied in the field over two seasons. The life-cycle is annual with adult swarming in early October and a season of maximum larval damage in July–August.

The intensity of infestation and the nature of the losses are discussed, and the mortality factors which act upon Cochliotis in nature are reviewed.

Cultural control measures suggested include the deferment of planting until July to October, when larval activity has waned; introduction of quick-maturing varieties, mechanically cultivated so that long ratooning can be gradually eliminated; regulation of the water table by control of irrigation, and the trial of resistant varieties. The Mauritius varieties M. 134/32 and M. 165/38 are suggested in this connection.

Biological control is discussed and a review of the parasite species that might possibly be introduced is made largely from the writer's Mauritius work on Clemora smithi (Arr.).

Experiments in the chemical control of Cochliotis are described and the final recommendation is the application at planting of ½ lb. per 50 ft. of furrow of a BHC powder containing 2·5 per cent, of γ BHC. This practice has been adopted by the infested estate with successful results in virgins and first ratoons.

Further work is suggested on the chemical protection of second and later ratoons by surface application of BHC or aldrin.