In an earlier paper (Woodroffe, 1953) full details were given of the results of a survey, the purpose of which was to study the insects and mites which inhabit certain birds' nests in Britain. Since then further work has been carried out on certain species, and, as a result, one or two statements made in the earlier publication now require correction or modification.

A microburette made from glass capillary tubing is mounted on the mechanical stage of a microscope and filled with insecticide solution to a point at which the meniscus is in the field of the microscope. The magnified images of the meniscus and a calibrated micrometer scale in the eyepiece are projected on to a small screen mounted close to the tip of the microburette so that the scale and the insect being dosed can be seen simultaneously. This feature renders the apparatus particularly suitable for topical application work in which accurate positioning of the dose on the insect is required. When an insect, held in a suction device described, is applied to the tip of the burette, the solution flows out unaided, and stops immediately the insect is removed. With the microburette described, doses from 0.005 to 0.035 μl. can be dispensed to within ±0.00035 μl. The apparatus can be made to cover several other dosage ranges, either lower or higher, by simple modifications which are discussed.

Experiments were carried out in Syria with parathion dusts for the control of Eurygaster integriceps Put. on wheat to ascertain the best time to apply the dust and the most suitable rate of application using a 6 h.p. dusting machine mounted on a “ jeep ”.

A field experiment is described in which a dust containing 0·75 per cent. parathion was applied under a drag-sheet to three plots of wheat at rates of 40, 20 and 10 kg. per hectare, respectively. The insects onthe wheat were mostly in the first three instars and the population was assessed by making 100 hand sweeps with a net at both 60 hours and 70 hours after treatment on each plot. The effect of treatment when compared with a control plot was to reduce the insect population in the three plots by 98·4 per cent., 83 per cent. and 65 per cent., respectively.

A further field experiment on a larger scale was carried out in an area in which plots of wheat were interplanted with plots of barley. In this case, the great majority of the insects were fourth-stage nymphs or adults. Five plots of wheat were treated with a dust containing 0·8 per cent. parathion at a rate of 35 kg. per hectare without using a drag-sheet. In two of the plots which were dusted in calm weather, about 89 per cent. control was obtained, in the other plots the effectiveness of the dusting was appreciably reduced by wind.

A cage containing 1,406 live specimens was placed, prior to dusting, in one of the plots of the latter experiment (dusted under calm conditions) and 6¾ hours after treatment all were dead. In the control only two specimens out of a total of 239 originally caged were found dead 24 hours later.

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.

Glossina brevipalpis Newst. is recorded for the first time in Ruanda-Urundi, where it has been found in the riverine forest of the upper Malagarasi river in the south-east of the territory.

Resting places of both male and female flies have been found to be on tree trunks, between six and twelve feet up, in heavily shaded riverine thickets.

The species is clearly crepuscular. It is suggested that the male's habit of resting on paths toward sunset is due to thermotropism rather than to phototropism, or that it may be related to passage of game.

Numerous puparia have been found in a late-dry-season breeding ground; these have hatched readily.

The animals encountered near the habitat of G. brevipalpis.

Infections by trypanosomes have been found in proboscis, gut and salivary glands, but experiments on transmission of these trypanosomes from the wild flies to goat, guineapig and rabbit have thus far failed. Research is at present being carried on to determine the nature of the trypanosomes, of which there are probably several.

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.

Three volatile solid insecticides (DFDT, γ BHC and aldrin) were tested against two species (Oryzaephilus surinamensis and Tribolium castaneum) at two temperatures (30°C. and 11°C.) in simple laboratory fumigation tests. DFDT killed both species faster at 11°C. than 30°C.; γ BHC killed O. surinamensis faster at 11°C. than 30°C., but T. castaneum faster at 30°C. than 11°C.; aldrin killed both species faster at 30°C. than 11°C.

DDT in odourless distillate was topically applied to individual males and females of the Rothamated wild type of Drosophila melanogaster Mg. The lines for the regression of mortality in probits on log. dosage of DDT for males and females, five days old, were parallel, and males were 1·86 times as susceptible as females. Susceptibility was high in young flies, but rapidly decreased with age, to a minimum at about five days, thereafter increasing rapidly in males and not significantly in females. The need for sexing and standardising age in flies used for toxicological investigations was thus demonstrated.

Respiration rate in untreated flies was measured by a modified Barcroft method. In males it increased with age up to five days, and then decreased; in females it increased with age up to nine days. Variations with age in respiration rate and susceptibility to DDT were negatively correlated.

The Makueni fly belt is chiefly infested with Glossina pallidipes Aust. and lies between 4,000 and 2,600 feet above sea level. The climate is hot and dry with two wet and two dry seasons, annually. The dry period during January and February is hot with bright sunlight while during the June to September dry period the temperatures are lower and with dull cloudy periods. The vegetation is Acacia-Commiphora dry grassland association with the Commiphora especially predominating at the lower altitudes in the east. The non-riverine deciduous bushland and thickets show two leafless periods in the year, corresponding with the dry seasons. A system of regular fly patrols has been in operation in this area since January 1949. The total flies caught show a regular seasonal increase during February-March each year and less regular and smaller increases during June-July and October-November. The same seasonal increases in the fly-populations are shown by the average number of old male flies caught per patrol.

Flies caught during 1951 were fewer than in 1950 in the settled areas and at Thwake camp, but at Kikumeni in the dense Commiphora-Acacia thickets the catches in 1951 were at least as numerous as in 1950.

Laboratory investigations with the mosquito AËdes aegypti (L.) have shown that air pressure has the following effects on flight activity:

The effects of pressure changes are consistently large enough to constitute an important factor in determining activity provided the mosquitos are acclimatised first to a particular pressure level.

The period of constant conditions necessary for complete acclimatisation was between three and six hours for all pressure conditions investigated.

When the period of acclimatisation had been fulfilled, the flight activity was approximately the same at all levels of static pressure investigated between 550 mm. and 800 mm. Hg.

After complete acclimatisation the activity following a moderate decrease in pressure was 1·5 to 2·4 times that following a similar increase in pressure when the general pressure level exceeded 735 mm. Hg.

When the general pressure level was less than 735 mm. Hg., the activity following a decrease in pressure was less than that following an increase; it would appear that 735 mm. is a critical pressure level for the stock of A. aegypti employed.

The activity during a uniform rise in pressure from 530 mm. to 730 mm. at 7·7 mm. /min. was at least 10 times that during a reverse fall in pressure fall in pressure at the same uniform rate.

Provided the rate of change was not greater than 1 mm./sec., the maximum flight activity for falling pressures was observed at 780 mm. while the maximumfor rising pressures was observed at 735 mm.

Using mainly the overwintering prepupae of a “ slug caterpiller ”, Cnidocampa flavescens (Walk.), the mechanism for the frost-resistance in insects was investigated.

Though the freezing point of the blood shows the value of about −2°C. the prepupae are very readily supercooled. When cooled below −20°C., however, the insect body suddenly congeals hard. Insects frozen thus, even for a long period of 100 days, usually withstand the solidification of their bodies without any harmful effect upon either the further development or upon the next generation.

Judging from the shape of the freezing curves of the prepupae and the freezing processes of the blood and isolated tissues, it is inferred that the most probable freezing process of the caterpillar is as follows. At first, the blood freezes rapidly, and consequently the grade of supercooling of the tissue cells is very much lessened by the latent heat of fusion of ice. Extra-cellular freezing of the tissue cells then takes place, in which case the properties of the blood as well as some property of the plasmic surface layer of the cells may play an important role in the prevention of the transmission of freezing into the cell. With the advance of the blood freezing, the tissue cells undergo dehydration and contraction; neverthless, they usually withstand such a condition for a long period, provided that the freezing temperature is not too low. Consequently, the so-called anabiotic state of a frozen insect does not necessarily mean the destruction of the cell structure.

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.

Experiments were designed to determine the criteria by which an ovipositing female of Spalangia drosophilae Ashm. is attracted to an environment where suitable hosts may be found, and by which these hosts are selected.

The results obtained indicate that ovipositing female Spalangia are attracted to and maintained in areas where suitable host puparia may occur by their reaction to sensory impressions. Thus females tend to be attracted to dampness and to soil level where, in grasses, host material is likely to be found. In such an area searching for hosts appears to be at random, but once an object that is a possible host is located there follows a careful examination and, if the object is “ considered ” a suitable host, oviposition follows. It appears that there are several definite criteria by which an object is accepted as a host suitable for oviposition. In general the hosts selected by the parasite are those which are suitable for the development of her progeny.

Laemophloeus minutus (Ol.) has been reared on six food materials of a type with which the genus, Laemophloeus, is commonly associated in the field. Consideration of the length of egg to adult development, together with the mortality, recorded from each medium indicates that Manitoba wheat and whole-meal flour are equally favourable for the development of the species, followed in order of precedence by Plate maize, English wheat and, finally, National (85 per cent. extraction) and Canadian (70–75 per cent. extraction) flour which proved equally unfavourable.

The stage of the life-history at which mortality mainly occurred varied with the diet. The high death-rate on English wheat was caused by the inability of newly hatched larvae to enter grains undamaged in the germ region. Mortality on National and Canadian flour occurred chiefly in the fourth instar.

There were indications of cannibalism in both larval and adult stages, at any rate when the diet was unfavourable.

The germ of wheat was attacked in preference to any other part of the grain. Maize germ was also consumed but whether it was preferred to the same extent as that of wheat was not established.

Pupation was mainly, but not exclusively, intergranular in wheat. Normal cocoons were formed in National and Canadian flours but some larvae pupated in loose webbing or in flour free from webbing and freshly emerged adults were observed in unwebbed National and Canadian flour.

A breeding-place of Glossina pallidipes Aust., in evergreen shrubs of Craibia sp. on the Kiangine river, Makueni, Kenya, was studied by means of hand-searching for puparia in conjunction with records of rainfall and temperature. A fly-patrol was also operated. The country away from the river was thorn-scrub, with Acacia and Commiphora trees predominating.

Three sites, each of 200 sq. yards, divided into 50 squares, were marked out, and two of them were searched monthly and the third quarterly.

Site “ A ” was searched nearly every month between April 1949 and June 1952, and full puparia were nearly always found. Numbers varied very widely; and it was noted that few could be found in rainy seasons during the months of November to January and April to May, though 1950 was an abnormal year. A consistently large increase in numbers was observed in February, the hottest and driest month, and a rather less marked increase towards the end of the long dry season in September and October. Large numbers of full puparia also tended to coincide with times of low average minimum temperature.

The numbers of flies caught on the fly-patrol did not appear to bear any close relation to the numbers of full puparia discovered.

Testing for efficiency of searching by means of marked puparia showed that about 40 per cent. of puparia were recovered, so that results must be taken as relative.

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.

1. Disappearance of Simulium neavei after DDT-treatment of rivers in Kodera, Kenya, is still manifest after seven years, and the species seems to have been eradicated from the district.

2. Skin microfilaria rates have dropped from something under 7 per cent. to nil in the under 4 years age group; from 37 to 5 per cent. or less in the 4–8 years; and from 70 per cent. to 50 per cent. in adults.

3. The length of life of the adult worm can be at least seven years.

Experiment showed that all developmental stages of Lacemophloeus minutus (Ol.) can survive exposure to a temperature of + 2°C. for a limited period which varies with the instar.

The egg was more susceptible to such exposure than any other stage, followed by the first, second and third larval instars and the adult, which did not differ significantly from each other, and then by the fourth-instar larva and pupa which can also be grouped together.

The adult male proved 1·21 times more susceptible than the female to the effects of exposure.

Atmospheric humidity did not influence the mortality of eggs or adults. Previous starvation did not affect the mortality of adults subsequently exposed to + 2°C.

The weight of fresh grass eaten by Schistocerca gregaria (Forsk.) on each day of its development from hatching until maturation of the adults was investigated. Hoppers in all instars ate on the average about one gram per gram body-weight per day on the middle days of the instars and the adults ate approximately half-a-gram per gram body-weight each day. The percentage of food assimilated, calculated from the dry faeces and estimated dry weight of food eaten, falls from about 78 in the first to 35 in the fifth instar. There were some indication that the food consumption per hopper increases with the number of hoppers per cage.

The weight of wheat bran eaten by hoppers was also investigated. The amount eaten by hoppers on the middle day of the first instar is approximately the same, in relation to their body weight, as that eaten per day just before and just after moulting by those in the fourth and fifth instars. More is eaten in the middle of these instars.

Measurements of weights and lengths of males and females in the hopper instars and of the weights of adults showed that in the course of their development females become progressively heavier and larger than males. The weight of a newly-hatched hopper is about 10 mg.; a female fledgling weighs about 2 gm. and a male 1·5 gm. Hoppers are approximately 1 cm. long on hatching, and males on reaching maturity are about 4·5 cm. long and females about 5.0 cm.