The biting habits of Chrysops centurionis Austen and its distribution in Uganda are discussed. This species is everywhere arboreal and mainly crepuscular. The absence of loiasis in man in Uganda is, it is suggested, due to differences between the biting habits of this species and those of the known vectors, C. silacea Austen and C. dimidiata Wulp, which are closely allied to C. centurionis.

The peculiar biting-cycle of another Tabanid, Haematopota nefanda Edw., is described briefly.

Short notes on the biting habits and distribution of some other Uganda Tabanids are given.

Field trials in British Somaliland and in the Anglo-Egyptian Sudan showed that dry bran bait can be used for complete destruction of Desert Locust hoppers (Schistocerca gregaha). Wet bait was never found to be completely effective when dry bait was ineffective.

Failures of dry baiting were found which were attributable to several causes : hoppers not feeding just before moulting ; ground too hot for hoppers to remain on it ; too low or too patchy a deposit of bait ; adult locusts probably not making contact with bait. None of these failures could be attributed to the bait being dry.

The main constituent of standard bait, wheat bran, should not be replaced by barley husks or peanut flour, but dom flour could be used and dura and maize flours could be tried instead of bran.

The use of dry bait makes it convenient and practical for locust scouts who use camels, vehicles, etc. to destroy small bands of hoppers as soon as they find them.

Dry baiting against marching bands and ring baiting can be done very conveniently and speedily by means of the Shendi Funnel, designed to be tied to the back of a vehicle.

Area baiting can be done rapidly by blowing dry bait up from a dusting machine, so that the wind spreads it. An area-dosage of 25 lb./acre is recommended, and a rate of ½-acre/minute should be readily achieved.

The amount of labour required is reduced to about 25% by the use of dry bait instead of wet. Dry baiting by machine uses only 10 per cent. of the labour required for dry-baiting by hand, but the cost would not fall as much as this, because higher wages would have to be paid for the greater skill necessary.

Adults can be killed by baiting, but it is much more difficult than with hoppers to ensure that the locusts make contact with the bait.

The insecticides already in use against the Desert Locust, arsenic and benzene hexachloride, can completely destroy hoppers when applied in bait. An insecticide is required with a long persistence like that of arsenic and a low mammalian toxicity like that of BHC.

Tests of the acceptability of crushed dura (Sorghum millet) of various particle size composition suggested only small differences between any of them and wheaten bran. There seemed to be a slight advantage to dura passing a sieve of 20 meshes to the inch and stopped by 30, and a slight disadvantage to dura stopped by a 20-mesh sieve. There is certainly no reason to use wheaten bran in preference to crushed dura.

Maize bran containing 2·5 per cent. sodium arsenite was less acceptable than the other materials, but crushed maize was not. Nevertheless, this arsenic bait and also coarse dura with BHC produced a mortality apparently no lower than the most acceptable baits containing 0·5 per cent. BHC.

It is suggested that experiments with milling and separating machinery may produce a first-class dura bait and at the same time reserve the flour for human consumption.

Characters are given whereby the gall midges attacking St. John's Wort (Hypericum), a noxious weed, may be distinguished.

Four species, Dasyneura hyperici (Bremi), D. serotina (Winnertz), Macrolabis marteli Kieffer and Zeuxidiplosis giardi (Kieffer), inhabit leaf galls in Europe.

One species, Dasyneura toweri Felt, inhabits the flowers in the U.S.A. Three species, Contarinia hyperici, sp. n., Clinodiplosis hyperici, sp. n. and Lestodiplosis (Coprodiplosis) sp., live in the unopened flowers in Europe.

Two species, Lasioptera virginica Felt and Cecidomyia ? triadenii Beutenmüller, are recorded as attacking the stems in the U.S.A. The latter is a name given merely to a gall.

Four species, Geocrypta braueri (Handlirsch), G. hypericina (Tavares) (perhaps a synonym of G. braueri), Trisopsis hyperici Tavares and Lestodiplosis (Coprodiplosis) hyperici (Tavares), live in underground galls in Europe.

Descriptions of Contarinia hyperici, sp. n. and Clinodiplosis hyperici, sp. n. are given.

During a survey for whitegrub parasites, six Thynnid species were found in parts of western Patagonia and studied in varying degrees of detail.

Definite host records are established for Elaphroptera scoliaeformis (Hal.), E. (Paralycus) sp. near nigripennis (Smith) and Pseudelaphroptera brevipilosa Durán, which are solitary external parasites of the mature larvae of Aulacopalpus pilicollis (Fairm.) (Rutelinae), Macrosoma glacialis (F.) (Melolonthinae) and Adioristus acuminatus Hust. (Curculionidae), respectively.

No adult feeding was observed during the mating flight of E. scoliaeformis and E. sp. near nigripennis, but pairs of P. brevipilosa and Ornepetes semicincta Turner fed extensively on flower heads of Umbelliferae. Some evidence is presented suggesting that at the conclusion of the mating flight the winged males tend to return the apterous females to the sites where they picked them up.

Hosts are permanently paralysed and malaxated before eggs are laid on them. The eggs of the two Elaphroptera species are placed parallel to the longitudinal axis of the host, on the mid-ventral line of abdominal segments two to seven. In the case of P. brevipilosa, the egg is lightly cemented by its caudal end at an angle of about 45 degrees to the host surface, the attachment being near the spiracular line of the host and between the third thoracic and sixth abdominal segments.

There are five larval instars. The larvae do not normally move over the host surface. In the first four instars feeding is by suction, but the fifth-instar larva tears a hole in the host in the region of the earlier feeding punctures. The film of liquid with which the larva is bathed is produced from its posterior extremity and is not exuded from the feeding puncture. Cocoons of two types may be recognised, corresponding to the sexes, the female type being the shorter and of more rigid construction.

E. scoliaeformis, E. sp. near nigripennis, and P. brevipilosa have a single generation a year. The period from egg deposition to cocoon formation is generally covered in three weeks, and at least nine months are spent in the cocoon as a mature larva or prepupa. Adults probably live up to two months.

The only natural enemies observed were a Bombyliid of the genus Acrophthalmyda and a Carabid predator, Cnemacanthus sp., attacking the cocoon stages of E. sp. near nigripennis. The adult of this Thynnid is also attacked by a mimicking Asilid fly, Lycomya germainii Big.

The function of the mating flight and the economic value of members of the Thynnidae as controlling agents for Scarabaeid pests are briefly discussed.

The results of a series of catches of biting insects at human bait on platforms in the canopy of the forest at Mongiro, Bwamba, Uganda, are reported. The catches were designed to investigate differences in the numbers taken, due to platforms, season and weather, but mainly to study the short-term changes in the activity of biting insects near the time of sunset. Each catch lasted from 3 hours before to 3 hours after sunset, and was divided into 10-minute periods from 30 minutes before to 1 hour after sunset. The main analysis is of catches made on five platforms on each of 100 evenings which covered the end of the dry and beginning and end of the wet season, 1948, and the end of the dry season, 1949.

A list of the species of biting insects encountered is given. Eight species (Anopheles (M.) gambiae, Taeniorhynchus (C.) fuscopennatus, Taeniorhynchus (M.) africanus and uniformis, Aëdes (M.) nigerrimus, Aëdes (S.) apicoargenteus and africanus, and Chrysops centurionis) were found to be abundant and data relating to them has been subject to more or less detailed analysis. The remaining 27 species or groups of species are discussed shortly.

Six of the eight abundant species show statistically significant differences between the catches on the five separate platforms. Arrangement of the five platforms in order of the total numbers taken, for each of these six species, gives results which are practically identical in three species (Anopheles (M.) gambiae, T. (M.) africanus and uniformis) and in two others (Aëdes (S.) apicoargenteus and africanus) ; however, the arrangements in these two species groups differ widely from each other. The arrangement for C. centurionis differs again.

These ordinal arrangements are compared with the obvious characteristics of the platforms and no consistent relationship is found. It is pointed out that the first three species are derived, largely or even entirely, from breeding places outside the forest, in or associated with the adjacent extensive areas of open swamp, while the last three are likely to be completely confined to the forest for breeding ; both the latter two mosquito species breed in tree holes, and dense shade is characteristic of the breeding places of species of Chrysops closely allied to C. centurionis. It is considered most probable that these platform differences in the numbers yielded are due to local differences in the densities of the adult populations which in turn are related to the abundance and proximity of breeding places.

Seasonal variations in the numbers of the abundant species are also studied and are considered to be almost certainly related to the amount and distribution of rainfall affecting the profusion of breeding places at least as far as the mosquito species are concerned. The tree-hole breeding species, however, suffered a reduction in numbers before the end of the wet season, an effect also noted by Mattingly in West Africa.

The amount of the reduction of the numbers of A. (S.) africanus in the dry season is of importance in assessing the possibilities of the survival of yellow fever virus in that mosquito as a host. The estimated reduction in the dry season of 1949 was to less than one twenty-third of the population existing at the end of the previous wet season (November, 1948).

C. centurionis occurred during all the catch series but was extraordinarily abundant in late March and early April, 1948. It is considered probable that this time of increase represents a yearly period into which hatching from the pupa is compressed. This conclusion is supported by the finding that during this period the biting population was composed of two groups one of which tended to bite before, and the other after, sunset.

Evidence is produced to show that the biting activity of Anopheles (M.) gambiae was depressed by wind, that of Aëdes (S.) africanus by wind and rain but that that of C. centurionis was little affected by either of these factors.

Studies of the biting-activity changes in the nine ten-minute periods extending from 30 minutes before to one hour after, sunset are presented. Each of the species which were known to be mainly active by night and which were sufficiently abundant for study, show activity increasing about sunset, rising to a maximum shortly after, and thereafter declining again to moderate levels. This initial peak is very clearly marked in the cases of Anopheles (M.) gambiae, T. (C.) fuscopennatus, T. (M.) africanus, Aedes (S.) africanus and C. centurionis, less so, but still distinct, in T. (M.) uniformis and A. (M.) nigerrimus. Its position differs in different species being earliest in the case of C. centurionis (18.10–18.20 hours) and latest in that of T. (M.) africanus (18.40–18.50 hours). However, in any given species the peak period of biting activity was subject to only slight movement in time in relation to sunset; in analyses of the data by different platforms, by season, and by types of weather it was the exception to find the time of peak activity to be shifted more than one ten-minute period away from the position which it occupied over the whole series. Further, in studies of the curves of biting activity on individual nights, three consecutive ten-minute periods centred on the period which showed the peak over the whole series, included the peak in 21 of the 23 A. (M.) gambiae cases available, in all five of the T. (M.) africanus, in eight of the 11 A. (S.) africanus and in 15 of the 20 C. centurionis, cases. The regularity of the occurrence of the peak period of activity in any given species is considered to indicate that it is largely controlled by changes in light intensity about the time of sunset.

These findings are discussed in relation to the general problem of the mechanism controlling the rhythm of activity in insects biting by night and a hypothesis, which is based on the conception that different population groups may have different biting habits, is advanced to account for the different types of cycle commonly encountered.

1. Flies of 9–10 and 16–19 days old were more susceptible to DDT than 4–5-day-old flies. Female flies were less susceptible than males, and large flies less susceptible than small flies to residual deposits of DDT. It is clearly important that flies used in comparative toxicity tests should be standardised for age, sex and size.

2. The strain Torre in Pietra was 3·6 times more resistant to dry deposits of DDT on Essex board than the Roma strain, but this resistance declined after culturing the strain in the laboratory for 22 generations.

3. The DDT-resistant strain (Torre in Pietra) was as susceptible as the non-resistant (Roma) strain to deposits of γ BHC on Essex board but was slightly resistant to pyrethrins.

4. The DDT resistance of the Torre in Pietra strain was increased readily by selection, yet a similar selection with DDT on the Roma strain was unsuccessful. This failure in the Roma strain may be due to the purity of the stock.

The weights of insecticide picked up by mosquitos and tsetse flies in short contact periods on deposits from aqueous suspensions of DDT crystals of different sizes have been determined chemically and correlated with corresponding mortality rates.

The rate of action of DDT particles picked up by mosquitos increases as the size decreases.

Taking into account the weights of insecticide picked up, the median lethal dosage increases as the particle size increases. A further factor, that of retention on the body of the insects, has to be considered, however, for there is evidence that adherence of particles in the 0–10 and 10–20 micron ranges is greater than that of larger particles. Availability, and therefore effectiveness, of deposits from aqueous suspensions of insecticide particles is influenced considerably by the type of material to which they are applied.

An investigation on the taxonomy of A. stephensi and A. superpictus larvae in Iraq is reported upon.

As a result it is suggested that 90 per cent. of the larvae of these species can be separated on the relative length of the filaments of the abdominal palmate hairs.