Experimental huts fitted with window traps, of the same basic design as those described by Thomson (1948), modified for Malayan conditions, were used in studying the behaviour and mortality of A. maculatus in relation to DDT and BHC. Other species of Anophelines formed a large proportion of the human bait trap catch but rarely entered the huts.

In untreated huts, A. maculatus fed at all hours of the night with a peak between 9 p.m. and midnight. The large majority left before 8 a.m. in search of outdoor resting places, at least 50 per cent. before dawn. It appeared that attraction to light was the strongest, but not the only factor influencing exit from the huts.

Large numbers of Culicines (mostly Culex fatigans) were recovered. In untreated huts about 80 per cent. were blood fed ; 28 per cent. were in the window traps.

DDT (33 per cent.) and BHC (“ Gammexane P530 and P520 ”) water dispersible powders were tested.

An application of 100 mg. DDT and 20 mg. γ BHC (P530) per sq. ft. was unsuccessful, due in part to the small numbers of mosquitos recovered. No conclusions are drawn from the results.

DDT at 200 mg. and BHC (P520) at 40 mg. γ isomer per sq. ft. were both effective for at least 12 to 16 weeks against A. maculatus. With DDT, 63 per cent. initial, and 83 per cent. 24-hour corrected mortalities were recorded over 16 weeks. With BHC, though the initial mortality dropped from 100 per cent. in weeks 1–4 to 19 per cent. in weeks 12–16, the 24-hour mortality, almost 100 per cent. for weeks 1–10, was still 88 per cent. for weeks 12–16.

DDT apparently had little effect on the feeding of A. maculatus ; with BHC there was a reduction in the percentage fed.

DDT was relatively non-lethal to C. fatigans, but had a marked irritant effect driving them into the light trap and the biting rate was reduce to 45 per cent. BHC killed all C. fatigans which entered for 2 weeks but most of its toxic effects were lost by the eighth week. The biting rate was reduced to 27 per cent. for weeks 1 to 8 and the majority of mosquitos were recovered in the light trap.

Ants, cockroaches, spiders, etc., were found to affect the number of mosquitos recovered and special precautions had to be taken against losses.

The results suggested that BHC when freshly applied acts as a repellent to mosquitos.

Mansonia uniformis was shown to be susceptible to both DDT and BHC residual deposits.

In 1932, Clark investigated the exotic and indigenous insect relationships with Pinus radiata in New Zealand, recording six species in the former group and 19 in the latter. Three previously unrecorded insect associations are now added to this list.

A brief historical account is given of the spread of the Eucalyptus Snout Beetle, Gonipterus scutellatus Gyll., fron Australia, its country of origin, and of the utilisation of its natural parasite Anaphoidea nitens Gir. for its control on the African mainland.

The discovery of G. scutellatus in Mauritius is described. Its entry was effected between 1935–40, and by 1944 it was threatening Eucalyptus plantations over the whole island.

A. nitens was introduced in 1946 from East Africa. Establishment was extremely rapid and two years later G. scutellatus was effectively controlled.

Notes are given on the bionomics of both host and parasite under Mauritian conditions.

Ecological data are briefly discussed.

All stages of Tineola bisselliella were subjected to temperatures between 30°C. and 43°C. for periods varying between a few hours and a number of days.

Although humidity was not an important factor, it was controlled at 70 per cent., and various other humidities were used at some of the lower temperatures.

Complete mortality occurred at relatively low temperatures, 41°C. for four hours being lethal to all stages of the insect.

The eggs appear to be the most resistant stage. Some are able to hatch at 35°C. and some to survive exposure of four hours at 40°C.

Development through the entire life-cycle is possible at 33°C.

Pyrgomorphella arachidis, sp. n.

♂ (Type). Of medium size, slender, finely rugulose.

Antenna of 17 segments, shorter than head and pronotum together, thick, slightly flattened and scarcely broadened at the base. Fastigium of vertex long, parabolic, ratio of its length to the width between eyes, 1·8. On the lateral sides of head behind the eyes there is a series of callosities forming a longitudinal stripe, which continues on to the lateral lobe of pronotum.

Wood-and-fibre-board huts fitted with one-way entry and exit traps were sprayed with DDT and BHC wettable powders at dosages 3·3 and 1·5 times the dosages reported by Muirhead Thomson in Tanganyika. Mud huts similar to his design were sprayed at 1·4 times his dosage of DDT and 1·1 times his dosage of BHC. Catches of Anopheline mosquitos continued for 16 weeks.

In the first-named huts kills of A. gambiae were 97 per cent. for both treatments. Kills of A. funestus were 100 per cent. and 97 per cent. for DDT and BHC respectively.

In the mud huts kills of A. gambiae were 62 per cent. and 98 per cent. for DDT and BHC respectively. For A. funestus kills were 78 per cent. and 93 per cent. in the same order.

The advantages claimed for the wood-and-fibre-board huts include :—

(a) freedom from ants, which may remove dead mosquitos.

(b) ease of catching live adult mosquitos.

(c) rigid construction of exit trap.

(d) lack of adventitious exits other than exit trap.

A block of a mile and a half of riverine forest on the Kuja River was separated from other riverine bush by clearings of 2 and 3 miles. Clearing costs are recorded.

An attempt was made to exterminate G. palpalis in the block by hand-catching. This failed, because the clearings did not exclude immigrant G. palpalis.

More G. palpalis could be caught from boats on the river than from paths beside the river.

Two attempts were made to prevent G. palpalis from crossing the clearings :—

(a) by stretching hessian screens treated with DDT right across the river.

(b) by placing large numbers of DDT treated “ trap-screens ” in the clearings. Neither had a decisive effect.

No evidence was found to indicate that hand-catching would not work in a completely isolated block, but it appears to be quite impracticable to isolate a block of G. palpalis bush on a permanent river.

A method for the routine quantitative estimation of mealybug populations on cacao trees is described and the results obtained from 24 successive monthly samples are tabulated.

The quantitative results obtained are of such variability that only gross differences in population density are shown as statistically significant.

From a series of analyses based on the survey data the following conclusions have been reached with regard to P. njalensis, the most important mealybug vector of swollen shoot virus :—

(a) The species is almost invariably attended in the field by Crematogasterine ants, the most important ant species building protective carton tents over the mealybug colonies.

(b) Crematogaster density is closely correlated with mealybug density and the ants construct their carton tents in relation to the numbers of mealybugs to be protected. Some of the arboreal Crematogasterine groups investigated are shown to be consistently associated with higher mealybug populations, and to have a more advanced tent building habit, than others.

(c) Tree to tree variation in mealybug density is shown to be largely dependent on the identity of the dominant ant group.

(d) No direct correlation is apparent between mealybug density and incidence of swollen shoot though populations in areas devastated by virus are usually smaller than in areas in which virus is actively spreading.

(e) The factors of importance in the natural control of P. njalensis populations have been discussed in some detail. It is clear that the species is maintained by ant protection at a density level considerably above that prevailing amongst closely related pseudococcid species which are not ant attended to the same extent. At this level of “ protected steady density ” balance is maintained partly by losses during crop harvesting, and partly by swollen shoot rendering the host plants unsuitable as feeding stations. It is concluded, however, that natural enemies must, in the last analysis, be responsible for maintaining balance.

(f) Since the protected density of P. njalensis is a direct result of ant associations it follows that factors tending to control the attendant ant species will have a delayed effect on mealybug density. In this respect it is believed that Oecophylla, which is strongly negatively correlated with Crematogaster spp., is of importance. Any attempts that may in the future be made to control the mealybugs by killing the ants will have to be designed as specific against the Crematogasterini and non-lethal to Oecophylla and the other large predatory ants common on cacao.

The question of the attractancy of water-vapour, carbon dioxide and candidate attractant compounds was investigated by the use of an olfactometer emitting freely into a 360-cu. ft. cage filled with female adult Aëdes aegypti. Moist air (85 per cent. R.H.) was found to attract 3–5 times as many mosquitos as dry air (15 per cent. R.H.). A moistened billiard-ball was found to attract about seven times as many mosquitos as a dry one, the result being similar whether black or white balls were used. The attractancy was reduced and even reversed at very high room humidities.

The addition of 10 per cent. CO2 to a dry air stream approximately doubled its ability to bring mosquitos within 0·5 inches of the olfactometer port. Its addition to a moist air-stream did not significantly increase its attractancy. Pure CO2 vapour proved to be no more attractive than dry air, and several times less attractive than moist air.

A number of chemical compounds found in body exudations, and some housefly attractants, were tested in the olfactometer for their effect on Aëdes adults. None were consistently attractive, and many were significantly repellent. However, sweat itself proved significantly attractive at a low vapour concentration, while significantly repellent at a high concentration.

A number of liquid mosquito repellents were assessed for vapour repellency power in an olfactometer mounted in a very large cage filled with females of Aëdes aegypti. They were also tested for their knockdown power in fumigation bottles. Their vapour pressures were determined by the Ramsay-Young method.

All the liquids showed vapour repellency, and in 39 out of the 42 tested this effect was highly significant. The highest vapour repellency ratings were shown by compounds already known to be the most effective repellents.

Although the more volatile compounds such as citronellal tend to show the highest repellency ratings, nevertheless compounds of low vapour pressure such as indalone, DMP and isobornyl morpholinoacetate may also show high vapour repellency. It is concluded that vapour repellency, although in the first instance dependent upon volatility, can vary independently of vapour pressure, so that compounds may be found which afford not only a long protection period due to their nonvolatility, but also a high vapour repellency due to the potency of the comparatively few molecules that are volatilised.

The vapours of most of the repellents were found to induce knockdown of mosquitos, but there was no correlation between the speed of this process and the vapour repellency of the compounds.

Information about the recorded distribution of the tick, Rhipicephalus sanguineus (Latr.) was accumulated in the same way as that gathered and mapped by Buxton (1941) for certain fleas. The search of the literature which was begun by Miss Benzian was continued by me to January, 1949. Besides the examination of original papers the following were consulted : Review of Applied Entomology, Series B, Tropical Diseases Bulletin and Zoological Record.

The movement of weevils in a mass of grain was investigated using metal pipes 4 ins. in diameter. These grain columns were broken down into samples. It was found that the predominant movement of weevils was towards the bottom.

The major factor affecting movement was tightness of packing but although tight packing restricts movement it does not prevent oviposition. Small insects move more easily in grain than bigger ones and also show a greater tendency to move downwards. Increase of moisture content which increases the amount of airspace also increases the ease of insect movement.

The results of experiments giving the weevils a choice of moisture content were somewhat contradictory. This is partly due to the choice of the weevil being affected by the humidity it experienced prior to the test and partly due to the moisture choice being overridden by the greater attraction of the end of the grain column. On the whole, however, damper grain appears to be preferred to dry grain.

In the field, owing to the tighter packing, movement is likely to be more restricted than in these experiments. The tight packing will prevent much of the downward penetration of weevils observed in these experiments but some such movement may occur on the walls and posts. Where insects are originally placed in the centre of a bulk of grain they will often be immobile but will lay eggs and be liable to cause heating. It is clear that the insects will tend to move toward the edges of the bulk and remain there.

Experiments have been carried out on the insecticidal action of p-, m- and o-iodo-nitrobenzene and their dichlorides. The real toxicity of these substances was estimated with the micro-injection method of Dresden, the contact action with the petri-dish method of Krijgsman & Berger. The real toxicity of the p- compounds appeared to be somewhat higher than that of their isomers. The dichlorides showed a somewhat higher toxicity than the other compounds. The contact action of the p- compounds is much higher than that of their isomers. This is caused by considerable differences in permeation velocity. The position of the iodine atom affects the permeation velocity very considerably but has much less influence on the real toxicity. It is suggested that the enhanced effect of the p- position on the permeation velocity is a general rule.

P-iodo-nitrobenzenedichloride shows such a high permeation velocity that it must be considered as a promising contact insecticide despite the fact that its real toxicity is low as compared with several other modern insecticides.

Perfusion of the isolated heart of Periplaneta americana with caffeine, digitalin, acetylcholine, nicotine and lobeline shows that the pacemaker of this heart is different from the “ myogenic centre ” of the vertebrate heart.

The action of strychnine, morphine and apomorphine on this heart preparation affords evidence of the existence of a neurogenic pacemaker.

This pacemaker is stimulated by suitable concentrations of acetylcholine, nicotine, lobeline and pilocarpine, while it is inhibited by atropine. Acetylcholine and tetraethyl pyrophosphate show a synergistic action. Atropine and tetraethyl pyrophosphate, like acetylcholine and curare, show an antagonistic action. These results prove that the neurogenic pacemaker possesses cholinergic properties.

Adrenaline stimulates the insect heart and ergotamine inhibits it, thus suggesting that the insect heart probably also has adrenergic properties.

On the basis of the present work and the results obtained by other investigators, a theory is put forward that the heart mechanism of most arthropods consists of a neurogenic pacemaker with adrenergic properties, controlled by a cholinergic accelerating nerve. This mechanism bears some resemblance to the sympathetic nerve system of vertebrates.

Rotenone strongly counteracts the action of acetylcholine, tetraethyl pyrophosphate, nicotine, lobeline, pilocarpine and digitalin on the insect heart. Its point of action, however, remains obscure at the moment.

The opposing action of rotenone and tetraethyl pyrophosphate is an indication that a combination of these insecticides for pest control is not to be recommended.

Losses from Pink Bollworm (Platyedra gossypiella) and from Spiny Bollworm (Earias insulana) were studied in the American Upland cotton crop grown on Zeidab pump irrigation scheme in the Northern Province of the Sudan. In 1948, a year of normal attack, 12·9 per cent. of the estimated potential yield was destroyed by bollworms. Pink Bollworm was responsible for 10·7 per cent. or a loss of 135 pounds of seed cotton per acre. Spiny Bollworm damaged 2·2 per cent. or 28 pounds per acre.

Four-fifths of the total yield is derived from the bottom crop which is harvested before the end of September and consists of high grade seed cotton. The other fifth is produced as a top crop and consists of low grade seed cotton ripening in October and November. Only 3·5 per cent. of the bottom crop is lost on account of Pink Bollworm as against 33·3 per cent. of the top crop. The corresponding figures for Spiny Bollworm are 1·6 per cent. and 4·1 per cent.

Some factors influencing the extent of pink bollworm attack are outlined. The Zeidab crop escapes serious damage through rapid maturity and even growth. Correct agricultural management is of great importance. Attack by Laphygma exigua in the seedling stage may result in increased damage by Pink Bollworm in the ripening crop.

The origin of the initial pink bollworm infestation is discussed. Available evidence, which is not conclusive, suggests that local carry over of the dead season may not be sufficient to account for the initial infestations observed in the crop.

Atmospheric water vapour saturation deficit appears to influence the duration of larval diapause in Pink Bollworm in the northern Sudan. Maximum emergence of moths from resting larvae in three areas occurs at or near the lowest saturation deficit of the year. The possibility is discussed that the degree of fixity of the diapause may be related to the gradient of the saturation deficit curve during the development of the resting larvae in the crop, a rising curve being associated with a well fixed diapause which lasts until the saturation deficit falls, and a falling curve being associated with a poorly fixed diapause which does not last but begins to break at once.

Four species of Haemagogus have been found in Brazil, the commonest and most widely distributed being H. spegazzinii.

Keys and diagrams are given to facilitate the identification of the Haemagogus of this country.

Two of the proven vectors of sylvan yellow fever, H. capricornii and H. spegazzinii, can be distinguished one from another only by their male terminalia.

Specimens of the new species here described were received by the Commonwealth Institute of Entomology, London, from Mr. J. R. Williams, Entomologist of the Department of Agriculture, Mauritius, who reported it to be predacious on the Galerucid, Schematiza cordiae Barb., which has been introduced there to control the weed, Cordia macrostachya.

An experiment on a semi-practical scale was made to determine the effectiveness of DDT treatment to a new house, in quelling an infestation of bed-bugs introduced with untreated furniture. Two small huts were constructed, one being finally treated with DDT, the other acting as a control. Rabbits introduced nightly represented the hosts and infested rabbit-hutches the furniture.

Forty adult bugs were introduced on the infested hutches in each hut. In the untreated chamber, the bug population soared up to over 400 in six months. In the treated hut the population remained at 10 to 20 up to the end of the experiment (28 weeks) ; these bugs remained in the untreated hutch. Translating these results to practical conditions, it appears that a bug colony might persist in an untreated bed in a room sprayed with DDT. However, the wandering bugs would be destroyed which would severely check population growth and prevent a heavy and widespread infestation.

Observations in the untreated hut indicated the decline of the first generation adults, the rise and decline of the second generation and emergence of the third.

A few preliminary tests with marked bugs proved that these insects do not usually return to the same site after going to the host to take a meal.

Aëdes leucocelaenus transmits yellow fever virus readily in the laboratory and has twice been found infected in nature.

Except in south Brazil this species is much less common than Haemagogus spegazzinii among day-biting sylvan mosquitos captured with human bait.

A. leucocelaenus has a wide distribution throughout the forested area of this country.

As a natural vector of jungle yellow fever in the northern part of Brazil it is of secondary importance when compared to H. spegazzinii.

A method is described for observing the numbers of ants foraging on the surface of of the ground by attracting them to baits of raw meat. The general area is described briefly and sites were selected for the work in three types of country.

A total of 50 baits were laid on each site in July and October. Pheidole sculpturata and P. crassinoda were the most abundant ants found on the baits. These were active mainly in the morning and evening, fewer ants were found at midday during the dry season. Comparing the numbers collected on the baits, more Pheidole were found in July than in October, and in July more ants were found on the unburnt grey soil sites than elsewhere. On the red soil sites there was a difference between burnt and unburnt country only in October, when more ants were found on the red soil in unburnt country. Pheidole is compared with three other genera of ants commonly found on the baits.

The food of Pheidole is mainly grass seeds ; some reference is made to the supply of grass seeds in different types of country and the relation between this and the numbers of foraging ants.