Experiments were conducted to investigate oviposition and host selection by Stenobracon deesae (Cam.), a Braconid parasite of certain Lepidoperous borers of sugar-cane, maize and sorghum in India. The fecundity and sex-ratio of this parasite and the duration of its life-cycle were also studied.

Chilo zonellus (Swinh.) and Corcyra cephalonica (Staint.) were used as hosts. The former is one of the principal hosts in the field, but the latter is not normally a host of this parasite.

The femal Stenobracon normally avoids laying eggs on hosts that are already parasitised by its own kind when unparasitised hosts are available; but in the absence of healthy hosts or when these are too crowded, parasitised hosts are attacked by it.

At a temperature of 26°C. and relative humidity of 75 per cent., the life-cycle of the parasite was completed, on an average, in 23·3 days, but under laboratory conditions at Delhi it took 14·1 days in June-July and 43·7 days in November-December. The average duration of adult life of females in June-February, mainly in ordinary laboratory conditions, was 35·7 days, and single females lived as long as 122 and 128 days. The adult male lived for 42·7 days on the average.

In the laboratory, the female lays about 24 eggs on an average, but only about one-third of them yield adults.

Males predominate. The sex-ratio appears to vary according to the host; among adults reared on Chilo larvae, 28·8 per cent. were females, but among others reared on Corcyra larvae, only 6·2 per cent. were females.

The phenomena of discrimination between parasitised and unparasitised hosts and of the change of sex-ratio with change of host are discussed. It is suggested that the ovipositor enables the parasite to recognise the host and that the stimuli received by the ovipositor from the host influence the functioning of the spermatheca which in turn controls fertilisation and finally the sex of the progeny.

The red bollworm attacking cotton in Nigeria has recently been shown to be Diparopsis watersi (Roths.), distinct from D. castanea Hmps., the southern African species previously assumed to be that occurring on cotton throughout Africa. Earlier work on cotton pests, including Diparopsis, in southern Nigeria (1664) is briefly reviewed, and the discovery and definition of the problems of cotton pests in northern Nigeria is outlined, and the climatic and agricultural background of the northern areas described.

The main object of the present work, centred at Samaru, was to determine; the annual cycle of activity of Diparopsis in northern Nigeria. The methods employed are described. The insect passes the dry season in diapause as a pupa in the soil. In late May or June, emergence from these pupae commences, but this is completely interrupted during July-September. In October, after the end of the rains, emergence recommences, and the main attack occurs on the crop during October and November. The proportion of pupae entering diapause rises rapidly from mid-October onwards, and activity ceases in early December.

When diapause pupae were incubated at controlled (86°F.) or indoor air (74–86°F.) temperatures, emergence was unimodal, extending from June to October, with the peak in July or August, respectively. It is concluded that the bimodal emergence in the field is caused by waterlogging, or some other factor restricting aeration of the soil during July-September, when the emergence from diapause pupae is interrupted

Trials of dates of sowing laid down at Samaru and Daudawa showed that early sowings, made in mid-June or early July, may suffer heavier bollworm attack than those made in mid- or late July. The earlier sowings nevertheless outyielded later ones. It is suggested that this results from their benefiting from a longer growing season, in which a greater production of fruiting points more than offsets greater losses from bollworms and other insects.

Elimination of ratoon and standover cotton would prevent breeding by the early emergence of moths from diapause pupae, and consequent red-bollworm attack on early sowings of cotton.

The possibility of producing a unimodal emergence from diapause pupae is worth further attention. This might be achieved by altering the soil conditions during July-September, and if successful would result in the main crop escaping almost entirely any attack by Diparopsis.

There appear to be no fundamental differences biologically between Diparopsis castanea and D. watersi, as illustrated by previous work reported from South Africa and Nyasaland, and the observations recorded here.

The work described in this paper has been carried out with two proprietary samples, designated Systox 50 emulsion and E 1059, of a systemic insecticide of which the active ingredient, subsequently referred to throughout as Systox, is a mixture of O,O-diethyl O-ethylmercaptoethyl thiophosphate and its isomer, O,O-diethyl S-ethylmercaptoethyl thiophosphate.

The samples were tested against Aphids for contact and systemic action.

It is concluded that, as a contact insecticide against Aphis fabae Scop, on broad beans, Systox is about equitoxic with paraoxon and so more toxic than schradan and dimefox.

Systox is readily absorbed by the roots of broad bean and cabbage plants from soil, sand and aqueous solutions and the translocated material is very effective as an insecticide against A. fabae on broad bean, and Myzus persicae (Sulz.) and Brevicoryne brassicae (L.) on cabbage.

Applied in this way, Systox is more effective than schradan, dimefox and paraoxon, and about equal to the most toxic compound previously tested, sodium fluoroacetate.

An experiment by the cut tap-root technique confirms these conclusions. A dose of 1 mg. of Systox per kg. of fresh bean-plant tissue gave a complete kill of A. fabae by the 10th day. The same amount of sodium fluoroacetate had previously been shown to give a complete kill in three days.

The plants were carefully watched for signs of damage during the tests. It was concluded that there was a considerable margin between the insecticidally effective and the phytotoxic concentrations.

Systox is also translocated from older to younger leaves of bean and cabbage plants and it may reach concentrations sufficient to kill the Aphids feeding on the untreated leaves. This effect was more consistently obtained in the broad bean than in cabbage plants. In both cases, however, the results were variable.

Solutions of Systox exert a direct fumigant action on Aphids, but there is little evidence that toxic material is transpired by treated plants.

The mixture of O, O-diethyl O-ethlmercaptoethyl thiophosphate and O, O-diethyl S-ethylmercaptoethyl thiophosphate, known as Systox, which has been previously tested against Aphids, has now been tested as a systemic insecticide against the eggs and larvae of Pieris brassicae (L.) and the eggs, larvae and adults of Phaedon cochleariae (F.).

Systox is toxic by direct contact to all stages of these insects but is much less effective in this way than diethyl p-nitrophenyl phosphate (paraoxon).

As a systemic insecticide applied to the roots of teh host-plant, Systox again acts on all stages of the insects (except the eggs of Phaedom), but, compared with the dose which killed Aphids, about twice as much is required to kill Phaedon larvae and between 20 and 100 times as much to kill Pieris larvae, depending on the method employed.

When applied systemically Systox, like paraoxon, can prevent the emergence of Pieris larvae from the eggs.

Specimens of the first of the new species here described were received by the Commonwealth Institute of Entomology from Mr. G. Swaine, Entomologist to the Department of Agriculture, Tanganyika Territory, who reported it as injurious to shoots and young fruits of the cashew nut, Anacardium occidentale L., and of the second through the British Museum (Natural History) from Mr. G. S. Dun, Senior Entomologist, Division of Plant Industry, New Guinea.

Xylebrous morstatti Hag. is a shot-hole borer which is well known as a pest of coffee. It has also been recorded from avocado pear (Persea americana) in Fiji, and is here reported attacking the same tree in the Seychelles, where it appears to be too scarce so far to do any serious damage.

The infestations and nature of the damage on avocado pear are described and illustrated, and the recorded geographical distribution of the insect is summarised.

A method of insecticidal control is described which, on the small scale on which it was carried out, appears to have been successful.

The anatomy of the tarsi and pretarsi of Phormia (Protophormia) terraenovae (R.-D.); Glossina palpalis (R.-D.) and Musca domestica L. is described with particular reference to structures possibly concerned in the action of deposits of contact insecticides. The numerous setae which cover the tarsal segments are distributed in a pattern which is common to all three species. Long spines situated at the distal extremity of each segment are the points of contact with which a fly engages a surface, and which take the thrust as the fly walks. Proximal to the primary spines are two ventral rows of chemoreceptors, protected from mechanical damage by smaller spines. In addition there are lateral and dorsal rows of bristles.

Contact chemoreceptors, which have been identified by experiment, are present in large numbers on the tarsi of P. terraenovae and M. domestica. Each chemoreceptor is a differentiated hollow seta possessing an extremely thin frontal membrane of cuticle, in which a lipoid layer appears to be incorporated and through which a lipoid-soluble insecticide might readily penetrate to the sensory neurocytes.

Receptors of this type are also present on the tarsi of G. palpalis, though tsetse flies have not been reported to possess a tarsal gustatory sense.

The pulvilli of all three species are entirely filled with viscous endocuticle and possess neither nerves, sense organs nor gland cells. The pulvilli are probably less important sites of penetration of insecticide from deposits than are the tarsel chemoreceptors, articulating membranes of setae, and intersegmental joint membranes.

Measurements of nerve diameters at different parts of the tarsi are used to interpret the results of Fisher (1952) concerning the action of DDT applied to limited areas of M. domestica. It is concluded that the relative toxicity of DDT at different parts of the body may be correlated with the number of sensory nerve fibres passing close to the site of penetration, but not with the number of sensory end organs directly affected.

For both of the important cacao Mirids, Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), there is a well-marked annual population cycle. Numbers are at their lowest in March and, although showing fluctuations from month to month, remain low until July. After this period, there is an increase in numbers to a peak level which may be bimodal, an earlier peak corresponding with the maximum numbers on pods and a later peak on stems alone in January or February. This is followed by an abrupt drop in the dry season to the minimum values of March.

The period of increasing numbers is, at first, associated with the presence of more cacao pods but evidence is given to prove that Mirid increase is nor determined by pod increase but that both reflect the action of some common cause. The final peak population is associated with the symptoms of seasonal blast, but although Mirid numbers beneath the canopy are at their maximum at this time, there is no corresponding increase in the resident canopy population, the blast symptoms being produced by a transient population of adults from the sub-canopy levels.

Even at their highest the numbers of Mirids are small compared with most crop pests, the normal maximum being of the order of 1,000 per acre in mature stands of cacao.

Such aspects of mortality as could be studied from field observations are described. There is a steady loss during nymphal life, more dying during the later stages because these last longer. Parasitism, food supply and predation appear to be the main controlling factors, but, of these, only predation is examined quantitatively. Mantids, ants and Reduviids kill between 16 per cent. and 21 per cent. of the nymphs with which they are associated and the proportion of Mirids killed by such predators increases as the number of Mirids increases. Predation plays an important part in the natural controla of Mirid populations but, although optimum conditions for predation exist in Mirid pockets, economic control is not effected.

The use of ants as a Mirid control measure is examined and rejected. Infestation of healthy trees by ants does not protect nearby attacked trees and the association between ants and healthy trees is due to the colonisation of such trees as the only ones suitable in an area subject to Mirid damage. A single instance is quoted where Oecophylla longinoda (Latr.) appeared to exert a control but only at a level where the ants were so numerous as to constitute a hazard to humans in the plot.

A final discussion of the three papers of the series is included to focus attention upon those aspects of Mirid biology which need immediate investigation. These include an evaluation of the loss caused by Mirids and the need for experimental work to determine the effect of physical factors on Mirids. Suggestions are made for sampling which could be employed in any future field observations.

Further experiments have been carried out to investigate how a coarse aerosol, released from a low-flying aircraft, is deposited upon the ground in open country. The aerosol had a mass median diameter of approximately 80 microns, and was produced by a boom-and-nozzle apparatus.

The aircraft height was 65 ft. It is shown that the rate of deposition is related to the degree of atmospheric turbulence, of which a simple and easily measured parameter is given. The rate of deposition is greatest when there is a large temperature inversion and a low wind speed.

A comparison is made with previous work where the aircraft height was 30 ft. Within the limits investigated, an increase in aircraft height reduces the deposits near the line of emission, but does not greatly affect the total amount that deposits within 150–200 seconds of production of the aerosol.

A method for estimating population changes of Aphis fabae Scop. on bean plots is described. This involved the classification of bean stems in the field according to five arbitary classes of infestation and the removal to the laboratory of ten samples of each class of infested stem for the estimation of their Aphid numbers. A simple volumetric method for counting large numbers of A. fabae is described and the results obtained from three bean plots are presented.

A series of field observations and rearing experiments were carrried out in Florida to gain information on the duration of the larval stage and the time of day of pupation and emergence of the salt-marsh mosquito, Aëdes taeniorhynchus (Wied.).

The technique adopted in a series of experiments is described.

It was found that the duration of the larvel stage is dependent on several factors of which water temperature is probably the main factor. Hunger was also shown to be important either through lack of food or overcrowding. Larvae which later became male adults pupated before those which became female imagines.

The period of maximum pupation is determined by the distribution of light and darkness, 83 per cent. of all pupation taking place during the evening periods, 15 to 24 hours after experimental midnight, and 48 per cent. in the period just after sunset, 18 to 21 after experimental midnight. The tendency to pupate around sunset is thought to have just as much accelerating as retarding effect on the larval development.

Temperature is considered to be the only factor of importance in determining the duration of the pupal stage which varies from 61 hours at 20·8°C. to 45 hours at 25·5° and 37 hours at 29°.

Both in nature as well as under controlled conditions in the laboratory it was found that, for a large number of larvae hatched simultaneously, the emergence of adults usually lasts three or fours days, with a maximum at the same hour on each of these days. The period of emergence is proportional to the duration of the post-embryonic development and may under unfavourable conditions last weeks.

Maximum emergence of imagines has been found to occur at various times of the day. This is as should be expected since the hour of pupation is fixed to a certain period of the day, and the duration of the pupal stage is solely dependent on the temperature.

The difference in the duration of pupation in males and females is very small but owing to the rather marked sexual difference in the duration of the larval stage, 129 hours for males against 145 for females at 29°, there is a preponderance of males during the first emergence maxima and of females in the last.

It is concluded that if the temperature of the water in which the larvae are living in the field is known, it should be possible to predict at what hour of the day the emergence maxima will take place.

A review of the available information concerning gall midges as endoparasites shows that only three species in two genera have been described.

Endaphis perfidus Kieffer is a parasite of apterous Drepanosiphum platanoides (Schr.) (Aphididae) in Lorraine and England. Although on several occasions larvae of Endaphis sp. have been found in England, the Netherlands and Germany parasitising other Aphids, practically no information additional to that supplied by Kieffer has beeen published. In only one instance besides E. perfidus has the adult midge been reared and figured, i.e., Endaphis (cf. perfidus Kieffer) in Macrosiphum jaceae (L.) on Carduus in Germany.

Endopsylla agilis de Meijere is a parasite of winges Psylla foersteri Flor (Psyllidae) in the Netherlands. The bionomics of what is almost certainly the same species, parasitising P. mali race peregrina Foerst. on hawthorn (also P. pyricola Foerst. and P. melanoneura Foerst.) and P. mali (Schmidb.) on apple, respectively, have been studied in Scotland and Germany.

Endopsylla endogena (Kieffer) was found parasitising the larva of Stephanitis pyri (F.) (Tingidae) in Portugal but has not been recorded again.

A fourth species, Pseudendaphis maculans, gen. et sp. n., that parasitises various Aphids in Trinidad, has now been described.

Indications are given of the whereabouts of any existing types or other specimens of all the known endoparasitic gall midges.

An account is given of the life-history of Pseudendaphis maculans Barnes, a common and widely distributed endoparsite of Aphids, especially of Toxoptera aurantii (Boy.), in Trinidad. Alates are parasitised to a much smaller extent than apterae : it is thought that this is due to the parasite larva inhibiting wing development. Nymphs appear to be attacked usually during the first stadium; the parasite larva is fully fed after 6 to 7 days. Shortly before the larve leaves its host the latter assumes a characteristic spotty appearance, due to numerous granules of dark matter that are readily visible through the integument, which has become paler and more transparent than normal. Pupation takes place in the soil: 9–10 days after leaving the host the adult emerges, invaribaly during the early afternoon.

The general distribution of the Muscidae (other than Glossina) of medical interest in the Sudan is discussed, and brief notes are given on some Muscids in relation to trypanosmiasis.

Eighty-six species of some medical interest, belonging to 22 genera, are listed, with records of their distribution and notes on the habits of several of them.

Observations were made in Sierra Leone from September 1949 to November 1951 on the incidence of trypanosomes in Glossina palpalis (R.-D.), in continuation of those previously reported that began in September 1948. Flies were dissected; trypanosomes found to be restricted to the proboscis were classed as Trypanosoma vivax and those found also or only in the mid-gut as T. congolense. None of the flies had infected labial glands. The whole data are presented for the sexes separately by months.

The existence of a marked seasonal variation in the incidence of T. vivax in G. palpalis is confirmed. The highest rates of infection occured in the months of heavy rain, and there was a significant inverse correlation between the monthly means of infection rate and of hours of sunshine. The cause is unknown, but possible explanations are discussed.

The older the fly, as judged by its appearance, the greater the rate of infection by both species of trypanosme; the virtual absence of infection in the youngest group of flies does not support the theory that they can only be infected when very young.

In the case of T. vivax, but not in that of T. congolense, females flies were more heavily infected than males. This may be due to larger food intake by the females, or to males, because of their more active life, appearing to be older than they are.