This paper presents further observations on the continued persistence of larvicidal treatments applied to small plots (10 yd. × 10 yd.) on Soutra Hill, Midlothian, to control larvae of the biting midge, Culicoides impunctatus Goetgh. Before doing so, consideration is given to the nature of the observed fluctuations in larval population encountered in the untreated plots. Evidence is produced which indicates that this is not due either to delayed hatching of eggs (this, if it occurs, is of minor importance), to change in technique or to the application of insecticide to neighbouring plots, but is due to the larvae responding to an oscillating factor (or factors) in the breeding site. It is suggested that one such factor might be soil water level. Therefore, it follows that changes in the untreated larval population must be taken into account when assessing the degree of control achieved by treatments, especially when the larval population is declining.

As regards insecticidal persistence three years after application: —

(i) Nine of the eleven DDT treatments (wettable powder, water-miscible concentrate and dust at 12, 50 and 200 mg. p,p′DDT/sq. ft.) gave 100 per cent. control. The other two (both wettable powder at 12 mg./sq. ft.) produced 75 and 22 per cent. reduction.

(ii) Only one of seven γ BHC treatments (wettable powder at 50 mg. γ BHC/sq. ft.) gave complete control and one treatment (w.p. 12 mg./ sq. ft.) was completely ineffective.

(iii) DDT retained its superiority to γ BHC as a larvicide against Culicoides, achieving 93 per cent. control compared with 55 per cent. for γ BHC.

(iv) The lowest dosages of dieldrin (3 mg./sq. ft.) and chlordane (6 mg./ sq. ft.) had begun to lose their larvicidal power, control declining from 76 to 53 per cent. and 67 to 29 per cent., respectively. There was no change at 6 mg. dieldrin/sq. ft. but the other treatments (12 and 25 mg. dieldrin and 12, 25 and 50 mg. chlordane/sq. ft.) had improved. Dieldrin at 12 and 25 mg./sq. ft. and chlordane at 50 mg./sq. ft. attained complete control.

The spray-volume treatments, now in their second year, showed an increase in activity. This was most marked in the wettable-powder treatments at 25 mg. p.p′DDT/sq. ft. which a year ago were completely ineffective and now five out of six trials gave complete control and the other 97 per cent. Improvement in the treatments at 50 mg./sq. ft. was less (from 43 to 83%) due in the main to the complete failure of one treatment (10 gal./acre).

It is confirmed that spray volume in itself is unimportant in larvicidal applications providing the coverage is adequate.

Sugar-cane is subject to the attack of a number of insect pests of which the moth borers—Diatraea sticticraspis, Hmps., D. venosata, Walk., Scirpophaga auriflua, Zell. and S. rhodoproctalis Hmps.—are the most serious. During the course of our investigations on Scirpophaga, seven larval parasites, viz., Elasmus zehntneri, Ferr., Stenobracon nicevillei, Bingh., S. deesae, Cam., Iphiaulax famulus, Bingh., Goniozus sp. n., Rhaconotus scirpophagae, Wilkn., and a new species of Rhaconotus have been noted. A paper on “ Studies on Elasmus zehntneri, Ferr., a parasite of the sugar-cane moth borer (Scirpophaga) ” by the authors has already been published. The present paper gives detailed information on the habits and life-history of Stenobracon nicevillei and its efficacy in controlling the pest.

(a) Small field experiments (not attempts at control) are described with DDT in emulsion and in solution in mineral oils, 5 per cent, pure DDT in each material. These were tested on mosquito larvae (mainly A. funestus) under conditions that provided good opportunities for repetition and measurement of dose per unit area. Considerable day to day fluctuations were observed in numbers of larvae obtained by dipping, before the insecticide was applied.

(b) Preliminary work showed that kerosene, or dieseline without DDT, were not larvicidal in doses up to 0·5 cc./sq. yard. The dose of oil that was harmful was not determined.

(c) It is clear that DDT, either in oil or as an emulsion, is a very effective larvicide, as is well known from work (mostly unpublished) in many parts of the world.

(d) One may compare the effectiveness of DDT as an emulsion (Mixture A) and in solution in dieseline, as follows:—

It is clear that, under these rather precise conditions of testing, the dieseline solution is more effective than the emulsion both in the minimum amount required to kill, and in lasting effect.

(e) Field tests seem to indicate that DDT dissolves from oil into water, so as to make a larvicidal solution, at least when the water is shallow.

(f) Even if one puts down a relatively high dose (say 0·10 cc. of 5 per cent. DDT per sq. yard, at least ten times the quantity that will kill all larvae) the effect passes off in a few days, even on stagnant waters. It is not known what happens to the DDT, and difficult to know why it disappears.

(g) A heavy dose of DDT (0·50 cc. as above) gives a period of complete kill, followed by a period of partial irregular control. This was more often observed with solutions of DDT than with emulsions and might last as much as four weeks. No explanation of this irregular effect is put forward. It seems most difficult to understand how an insecticide, applied over an area of only a few square yards, can continue to kill some but not all larvae for a period of weeks.

(h) Except in one experiment, in which emulsion destroyed small fish, there was no evidence that creatures which prey on mosquito larvae were destroyed. There was no reason for thinking that after the population of mosquito larvae got back to normal it rose to exceptionally high figures (as it might have, had the predators been decimated).

Pine beauty moth, Panolis flammea (Denis & Schiffermüller), is a recent but persistent pest of lodgepole pine plantations in Scotland, but exists naturally at low levels within remnants and plantations of Scots pine. To test whether separate host races occur in lodgepole and Scots pine stands and to examine colonization dynamics, allozyme, randomly amplified polymorphic DNA (RAPD) and mitochondrial variation were screened within a range of Scottish samples. RAPD analysis indicated limited long distance dispersal (FST = 0.099), and significant isolation by distance (P < 0.05); but that colonization between more proximate populations was often variable, from extensive to limited exchange. When compared with material from Germany, Scottish samples were found to be more diverse and significantly differentiated for all markers. For mtDNA, two highly divergent groups of haplotypes were evident, one group contained both German and Scottish samples and the other was predominantly Scottish. No genetic differentiation was evident between P. flammea populations sampled from different hosts, and no diversity bottleneck was observed in the lodgepole group. Indeed, lodgepole stands appear to have been colonized on multiple occasions from Scots pine sources and neighbouring populations on different hosts are close to panmixia.

Laboratory experiments showed that the mated status of male sheep blowflies (Lucilia sericata (Mg.)) can be reliably detected a week after mating, but subsequently the test is less accurate. Injection of 4–36 Ϝg tepa/male fly induced approximately 95% sterility. Tepa-injected flies mated freely, and the treatment did not interfere with the mated status test subsequently performed. The test has potential value in sterile male release studies.

The paper describes the construction, calibration and performance of an electrolytic hygrometer based on the principle of the “Gregory” hygrometer, but considerably smaller. Its dimensions are about 6×6×10 mm.

The element consists of two platinum-clad nickel-iron electrodes, holding a spiral of continuous fibre-glass wool yarn which is impregnated with a solution of calcium chloride. The water content of this hygroscopic salt varies with humidity, so that the resistance between the two electrodes also varies. In order to measure this resistance, alternating current of a known voltage is used, and the current is measured in terms of micro-amperes. A suitable circuit is described. Air temperature is measured by a fine thermocouple permanently attached to each element.

Long exposure to air above acid and water mixtures damages the elements so that calibration is best carried out without acid. An apparatus in which this can be done is described. A stream of air with a high water vapour content is cooled to a precisely known temperature which is below its saturation point, and then raised to the temperature required for calibration, so that its relative humidity is known as it passes over the element being calibrated. Finally the dew-point is again found as a check. Temperature affects the resistance of the elements, and calibration must therefore be carried out at three different constant temperatures.

Curves obtained by means of this apparatus show that one element will give readings from 50 to 98 per cent. R.H. within ±2 per cent. Another element with more hygroscopic salt must be used for humidities between 60 and 10 per cent. R.H.

There is an ageing process whereby the resistance of each element increases for some time after it has been constructed. This period can be shortened by exposing the elements to alternating high and low humidities for a few days. Elements which have received this treatment can be calibrated and used after six weeks, and will remain in calibration for at least a fortnight.

Subsequent calibrations can be made in a simple apparatus (which is described) involving acid-and-water mixtures, but the use of filters and exposure of the elements for no more than 15 minutes avoids damage.

The hygrometer equilibrates in a new humidity within ten minutes.

The instruments possess certain advantages: they are small, they can be read or recorded at a distance, and they do not depend upon evaporation of water, so that disturbance of the natural environment is minimised. The main disadvantages are that they cannot be exposed to saturated air without going out of calibration and that each instrument must be calibrated individually—they cannot easily be standardised for mass production.

On initiating this investigation my first aim was to discover a small isolated fly area, such as those described as “ primary fly centres ” by Dr. Shircore (Bull. Ent. Res., v., pt. 1, p. 87), with a view to carrying out experiments in the clearing of bush and endeavouring to reduce the numbers of the fly by systematic capture on a large scale.

A recent extension of the fly-belt in Songea, southern Tanganyika, has been delimited.

The preferred habitat of the tsetse in this region is constituted by open, short-grassed glades, representing old village sites, in well-grown Brachystegia woodland, with a double-canopied interzone between glade and woodland.

Destruction of this interzone by clearing of the upper canopy will undoubtedly prove effective in causing eradication of the fly.

An incomplete ring of electric nets was evaluated as a means of estimating trap efficiency for Glossina spp. This methodology assumes flies approach the trap directly, and then enter, or leave directly in random directions. These results showed that the ratio of the number of flies intercepted on the outside of the electric nets to the number on the inside was lower than predicted by this single-approach behavioural model. Moreover, an incomplete ring of nets around a trap reduced trap catch more than the model predicted. These inconsistencies were greater early in the day, and greater for females than for males. It is suggested that flies may make several approaches to a trap before entering or departing. This mixes arriving and departing flies on each side of the electric nets. Use of a complete ring of nets around a trap to estimate trap efficiency entails fewer behavioural assumptions. Catches at a complete ring around a trap were compared to catches in a trap without nets, replicated in a cross-over design. The efficiency of an odour baited NG2G trap was estimated to be 58% for males and 37% for females. Biconical traps were much less efficient. Both trap types were less efficient in the early morning, suggesting entry response is temperature dependent. The NG2G trap was more efficient for non-teneral nulliparous females than for other ages. For both trap types there was little difference between mean fat content of approaching and trapped males, but the mean fat content of trapped females was lower than that of approaching females.

Daily observations were made of the developmental stages of Pachydiplosis oryzae (Wood-Mason) on laboratory-infested IR8 and W1263 rice seedlings at Peradeniya, Ceylon. The previously observed resistance of W1263 was attributed to the inhibition of moulting of first-instar larvae in 40% of the terminal shoot apices. In comparisons of the two varieties, differences in the following parameters were not significant or of no importance: the numbers of P. oryzae eggs laid and their hatching time, the mortality rates of the developmental stages, the number, body length and activity of the larvae and pupae at the terminal apices, and gall length.

Clean summer fallow is often recommended for reducing wireworm and white-grub infestations, but our investigations on this subject, conducted during the years 1933–35 at the Ukrainian Rubber Plants Experimental Station (near Kremenchug) showed that in arable fertile “ chernozem ” soil there is no significant decrease in the number of these pests after a clean summer fallow. These divergent results led us to suppose that the reaction of various species of wireworms and white-grubs to soil cultivation and fallow may be different.

A continuous method is described of separating adult Silvanus surinamensis from infested tea by means of an apparatus involving three behaviour stimuli, namely, light, heat and mechanical activation.

Large electrocuting nets were used at different seasons near a big tree in Zimbabwe to capture tsetse flies at different heights, distances from the bole and times of day. Some differences were found between species and sexes, but most flies were caught within 3·3 m of the ground and in the late afternoon. In the cool and wet seasons, Glossina pallidipes Aust. was less confined to lower levels than was G. morsitans morsitans Westw. Flies, especially fed males of G. pallidipes near the bole of the tree, were recorded in the greatest numbers in the midday period. Diurnal variations occurred in the relative proportions of females of the two species caught at different points. Releasing ox odour through an electrocuting net suspended at different heights confirmed that most flies were flying near the ground, especially in the hot dry season. Comparison of samples from the large electrocuting nets with those caught by other methods operated contemporaneously showed that the large nets gave samples which compared well with those from an electrocuting screen used in conjunction with a ventilated pit. Methods involving fly-capture by people gave very distorted results for all catch parameters examined. No method used gave consistently representative samples of replete flies or of newly emerged flies.

The internal reproductive system of adult males of Spodoptera littoralis (Boisd.) is described, and changes in colour of a secretion in the ductus ejaculatorius simplex with age and mated status are noted. Virgin males 0–7 days old and mated males 0–7 days after mating were killed and the colour of the secretion in the simplex compared with colour chips in the Munsell book of color (1929–1942). The results showed that the simplex of newly emerged males was colourless or pale yellow, but after two days an orange pigmented secretion had begun to accumulate in 61·3% of males examined. By four days this pigment had darkened to deep red in 96·4% of virgin males. On mating, a portion of this secretion was incorporated into the spermatophore while the rest was passed into the bursa copulatrix of the female, leaving the simplex of newly mated males colourless. There was. however, a gradual re-accumulation of the pigmented secretion after mating through yellow, orange and finally to deep red. This accumulation of the red pigment was slightly slower in the mated males than in virgins, and three days after mating only 29·6% of the males had a red simplex compared with 78·8% of three-day-old virgin males. The potential use of these changes in colour to determine the mated status of field-caught males is discussed.

Early in 1959, observations on the farm Tayside, in the East London district of South Africa, suggested that populations of the ‘two-host’ red tick, Rhipicephalns evertsi Neum., were more difficult to control with toxaphene preparations than they had been in the past. Resistance to toxaphene was suspected, and both field and laboratory experiments were carried out to investigate this possibility. Field trials indicated an increase in tolerance by Tayside populations of the tick to toxaphene, γ BHC and dieldrin, but showed no increased tolerance to sodium arsenite or DDT. Similar results were obtained in laboratory experiments where Tayside adults were compared with those of other populations of the tick known to be sensitive to insecticides. Laboratory experiments with larvae indicated a high degree of resistance to toxaphene and γ BHC in the Tayside population, but no increased tolerance to sodium arsenite, Delnav, Sevin or DDT could be detected. This pattern of cross-resistance is similar to that occurring in resistant populations of Boophilus dccoloratus(Koch).

The new age determination technique for tsetse flies based on the accumulation of fluorescent pigments in the head capsule has the minor problem that it is not possible to accurately identify very young flies. In this paper we describe a technique for the identification of very young Glossina morsitans morsitans Westwood based on their high levels of abdominal fluorescence. Under our holding conditions these fall back in a linear fashion to a minimum at five days post-emergence. The variability in the levels of head fluorescence at eclosion is mainly influenced by the size of the emerging fly, with the number of blood meals taken by the female parent, and intra-uterine larval and puparial periods of the emerging flies also playing a part.

Field screening experiments for resistance of faba bean (Vicia faba) to Bruchus dentipes Baudi in Syria between 1982 and 1985 involved about 1000 accessions and indicated that only phenological resistance was present. Two accessions were chosen, on the basis of seed infestation with larvae, for further study. The two accessions (BPL33 and ILB1814) were tested against natural infestations as well as under four levels of bruchid infestation and at two different times of release of adults. BPL 33 maintained its resistance (about 50%) in relation to ILB1814 under these different conditions, except when adults were released at a time when both accessions carried pods simultaneously. This confirms that the resistance of BPL33 was phenological, related to late flowering and late pod setting. An intergrated control approach is there fore suggested.

Among several parasites received by the Imperial Bureau of Entomology from different countries, the following three parasites and hyperparasites of the pink boll-worm, Platyedra gossypiella, Saund., proved to be new and are described here as they may be of interest in the biological control of this cotton pest.

Several studies have shown the negative effects of mature plant resistance (MPR) on aphids in sugar beet, which is correlated to the formation of black deposits in their stomach. However, the underlying mechanism of MPR still needs to be elucidated, by understanding the toxicity effects of MPR on aphids and the role of the plant phenological stage and the environment. Here, we report that MPR in sugar beet does not only affect Myzus persicae mortality rate and the formation of a black deposit in the aphid stomach, but also aphid fecundity and behaviour. In addition, experiments in climate-controlled and field settings showed quantitative variation in MPR to M. persicae between six genotypes of sugar beet. Our results indicate that environmental effects, such as temperature, play a major role in MPR and underscore the importance of proper climate-controlled experiments for investigating MPR. In climate-controlled experiments, 83.3% of aphids on old leaves developed a black deposit, in contrast to only 16.8% of aphids on young leaves. This shows that not only plant age, but also leaf age plays a major role in the intensity of MPR. Further research will be needed to identify the underlying mechanism, before MPR can be used as a viable and sustainable solution to aphid pests in sugar beet.

Adult olive fruit flies Bactrocera (Dacus) oleae Gmelin were exposed for 24 h to 25 × 10 cm polyester target devices, impregnated with 3% a.i. triflumuron (2-chloro-n-[[[trifluromethoxy]phenyl]amino]carbonyl]benzamide), a chitin synthesis inhibitor, formulated in 10% w/v sugar solution and air-dried. Treated insects were tested for egg hatch inhibition and larval mortality. Inhibition of egg hatch and F1 larval mortality depended on the sex exposed and the elapsed time after exposure. Egg hatch was reduced to 37.6% and F1 larval mortality reached 100% when both exposed sexes were mated. Exposure of one sex prior to mating resulted in a lower level of egg inhibition and larval mortality; but exposure of females was more effective at inhibiting egg hatch and larval survival than exposure of males in these crosses. In flies exposed once, the residual activity of triflumuron decreased gradually, fifteen days post-exposure egg hatch and larval mortality reached 62% and 44% respectively. Target devices aged under natural conditions reduced egg hatch to an average of 39% and inhibited completely larval development for a period of four months.