The validity of the MLD (Minimum Lethal Dose) as a practical concept for measuring toxicity, despite its obvious lack of precision, is discussed. Its use has justification.

The 48-hour MLD of acetone-water suspensions and oil films of DDT and dieldrin for early fourth-stage larvae of Anopheles gambiae Giles have been measured.

The results show A. gambiae to be relatively resistant to DDT.

In acetone-water suspension dieldrin appears to be about six times as toxic as DDT. In oil solutions this difference is more marked, the ratio being in the neighbourhood of 20:1.

The Garden Chafer, Phyllopertha horticola (L.) is the chief British representative of a type of world-wide pest. The following summary concerns the adult and its reproduction under laboratory conditions.

Adult feeding affects neither the number of eggs produced by the ovaries (productivity) nor the number laid (fecundity). Productivity depends entirely on the amount of fat-body stored away by the third-instar larva before hibernation.

The adult stage lasts about three weeks (3 to 35 days) in both males and females. Starvation shortens the life by a day or two. Females which lay no eggs (barren) are usually short-lived, i.e., they die before oviposition is due to start, and comprise 14 per cent, of the population.

The fat-body is exhausted and the eggs are all matured by about the end of the first half of the adult stage. Oviposition and feeding apparently do not begin until the manufacture of eggs is completed. Individually, oviposition lasts five or six days (1 to 23 days), the more eggs laid, the longer does the oviposition period usually last. The female dies two or three days (0 to 10 days) later. Starved females have a rather shorter oviposition period. Unmated females may lay a few non-viable eggs just before they die.

The average female lays 13 eggs (0 to 46 eggs). More than 70 per cent, of females lay all or nearly all of the eggs manufactured from the fat-body. Apart from barren females, there is no significant difference in length of life between females that lay all of their eggs and those that lay only some.

Females are larger than males, being on the average 1·2 to 1·3 times heavier. Productivity and fecundity are positively correlated with female body weight (which is, of course, proportional to weight of fat-body). Thus regressions may be calculated such as:

F = 0·113W − 6·60

where F = number of eggs laid and W = weight of pupa in milligrammes. Female pupal weights vary from 80 to 310 mg. Body weight is not associated with the occurrence of barrenness. If all individuals always fulfilled themselves, a population would increase eight-fold annually.

There is not the slightest evidence of a fixed oviposition pattern. Four eggs may take nine days to lay while 27 may take only 24 hours. The same number of eggs may take a longer or shorter time to lay in larger or smaller driblets, the numbers of eggs and the intervals between them being apparently quite random.

A female burrows down at a different point each time she has eggs to lay. At each burrowing she deposits her eggs within a radius of one inch from the vertical line passing through her entrance hole on the soil surface. Eggs are laid singly in small cavities about quarter of an inch apart (3/16 to 1 in.).

Eggs hatch out in 4 to 6 weeks at temperatures of 15 to 17°C. Eggs failing to hatch vary between 4 and 28 per cent, of the total laid. They comprise both unfertilised eggs and, to a lesser extent, eggs which have been fertilised but die from other causes. The proportion of unfertilised eggs increases with the age of the female at oviposition.

The Garden Chafer, Phyllopertha horticola (L.), has three larval instars, the third ending in hibernation, which gives way to a prepupal stage. The development cycle occupies 12 months and only one generation is present in the soil at any time. From a study extending over five years, 1948 to 1952, the cycle from egg to adult in the English Lake District may be outlined as follows:—

At the earliest, oviposition starts in the latter half of May. In soil 3½ in. deep, eggs are laid at an average depth of 1½ in. (range ¾ to 2½ in.). Other authors report that where the soil is sufficiently deep, the maximum egg depth may extend to four inches in the Lake District and even eight inches elsewhere. The eggs are spaced about a quarter of an inch apart (max. 1 in.), each in a tiny earthen cavity, all more or less directly below the point where the female enters the soil. Incubation of the individual egg averages five weeks.

The first instar occupies individually about three weeks on the average; the second instar about four weeks; and the third instar, up to the beginning of hibernation, eight to ten weeks. On the average also, first-instar larvae begin to appear in a population about the first week of July, second instars about the fourth week of July, third instars about the fourth week of August, and the earliest hibernators about the third week of October. Except for a few stragglers occasionally in early December, the entire population is generally hibernating by the end of November. The hibernation is a true diapause.

A detailed description of the method of feeding is given. The larva consumes plant roots which it obtains by tunnelling through the soil. Since its natural habitat is pasture land, grass roots are the main food. It probably also eats invertebrate carrion occurring by chance in its path. The first and second larval instars are given over to growth, the third and final is occupied mainly in storing up fat-body. This store has to suffice for maintenance during the remainder of development and also for the entire egg or sperm production.

On hatching, the larvae feed at about 1½ inches (¾ to 2½ in.) depth in the soil, i.e., at egg-level. As they grow, however, they ascend until latterly, as third instars, they are feeding about ½ inch (¼ to 1 in.) from the surface. This progressive rise is probably dictated by the increasing need for a more copious food supply. With the possible exception of a very prolonged drought, weather has no effect on the level at which larvae feed.

Larvae hibernate at 2 inches (0·8 to 3·8 in.) below the surface of soil 4 inches (2·3 to 6·0 in.) deep, i.e., well above the “ pan ” (gravel bed, or rock). In other localities other authors have recorded hibernation at the same as well as greater depth in deeper soils. The existing data are insufficient to show what governs the choice of depth in the soil.

On the average, prepupation begins in a population about the end of March and, individually, lasts between three and four weeks; pupation begins in the third week of April and lasts about four weeks. The pupa lies inside the last larval exuvium in the hibernation cell. Sex can easily be discerned in the pupa. There are always rather more males than females in a field population, considerably more in some years. Pupal sex ratios ranged from 1·13 to 1·89. On the average, male pupation precedes female by one day or a little more.

Behaviour after the splitting of the pupal skin is the same in male and female. At first, for about four days (1 to 7), the adult remains motionless in the hibernation cell. Then, alternately burrowing and resting, it ascends to the base of the sward in about two days (¼ to 4). At the sward base it now halts for about two days (½ to 6) before emerging into activity upon the sward surface for the first time; this halt of two days may be prolonged by one or more days if weather is unsuitable when a beetle is ready to become active. In toto, given no weather hindrance, the individual transit from cell to sward surface usually occupies rather more than one week (7·7 days, range 6·0 to 8·5). On the average, the first active beetles are seen in the last week of May but may be as early as the third week of May or as late as the second week of June, according to the weather. The male precedence over females in development is maintained from pupation onwards, hence the first males are always active upon the sward at least one day before the first females.

It takes some considerable time for all the individuals in a population to accomplish the change from any one particular stage of development to the next. There are, however, never more than two successive stages in the soil at the same time. The period of overlap of two stages in the population fluctuates widely (8 to. 41 days) from step to step in the development cycle. This is the result of the seasonal rise and fall in the soil temperature, and of diapause. The overlap, which is really a measure of range of developmental age among individuals, contracts to the minimum (8 days) as the population approaches maturity. This facilitates mating.

The host specificity of R. sanguineus (Latr.), 1806, sens, sir., and R. secundus Feldman-Muhsam, 1952, in Israel was studied.

It was found that 81 per cent, of R. sanguineus, sens, lat., found on the dog was R. sanguineus, sens, str., and 19 per cent. R. secundus, whereas on cattle, sheep and goats, 97, 94 and 91 per cent., respectively, were R. secundus and the remainder R. sanguineus, sens. str.

It is suggested that this situation exists also in other countries in the Near East, since R. secundus was very common in material from Algeria, Turkey, Yugoslavia and Iraq.

The problem of transmission of disease by R. sanguineus, sens, lat., should be re-investigated in the light of recent taxonomic data.

Further analysis of results obtained from a study of populations of Coccinellids on three plots of Vicia faba infested with Aphis fabae Scop, at Rothamsted during 1952 are presented. The distributions of coccinellid egg batches and older larvae (mostly 3rd and 4th instars) on bean stems of five arbitrary classes of aphid infestation, emphasise the differences in the manner of increase of the predator and prey populations considered here; at the same time, the results throw light on the oviposition behaviour of the adult Coccinellids.

The degree of correlation between coccinellid egg batches and Aphids on the plots (as indicated by regression analysis) varied inversely with the size of the aphid populations on the plots. On one plot, where Aphids were extremely numerous, this correlation was negligible; on the two other plots, where Aphids were less abundant, the correlation was more marked, being highest at the plot where the aphid numbers were lowest. The degree of correlation between egg batches and Aphids was determined apparently by the rate of increase of aphid numbers. It is pointed out that while these coccinellid populations increased additively (by immigration of ladybirds to the beans), populations of A. fabae increased multiplicatively (by reproduction) and at much higher rates.

During the early stages of the aphid infestations on the bean plots, when aphid-infested stems were comparatively few, there was no statistically significant association between coccinellid eggs and the presence of Aphids on the bean stems; but when all stems had become infested, egg batches tended to occur most frequently on the stems with the most Aphids. From these and other observations it is concluded that the female Coccinellids do not need the stimulus of the presence of Aphids before laying their eggs on beans, and that they concentrate on well-infested bean stems where they tend to stay and feed on the Aphids and probably oviposit on those stems. The distributions of older coccinellid larvae (3rd and 4th instars) indicate that they, too, tend to concentrate on well-infested stems.

The oviposition habits of the female Coccinellids are discussed in relation to the feeding problems of the newly-hatched larvae.

Difficulty is being experienced in obtaining natural regeneration of Juniperus procera in the Daloh Forest, Erigavo, British Somaliland due to infection of the seed by an unidentified species of Megastigmus. In 1953, Mr. A. R. Tribe succeeded in breeding specimens from infested seed, and this material, together with a subsequent collection by Mr. J. J. Lawrie in January 1954, has been used as the basis of the following description.

Early last year five females of a species of Eupelmid were received from Mr. B. A. O'Connor of the Department of Agriculture in Fiji, where they had been bred in the previous November from eggs of the Phasmid, Graeffea crouanii (Le Guillou). Although this Phasmid, which is a pest of the coconut crowns, bad been bred many times before, no such parasite had occurred previously. As this species was unknown to the author, more material was requested.

The need having arisen for a small, conveniently situated warm room for the maintenance of mosquitos in a constant environment, the cabinet described below was constructed by the authors at a relatively small cost, and set up in a laboratory-class room (35 ft. x 45 ft.). The warm room, being detached and moveable. entailed no structural alterations or installations.

The distribution of the Sudan HALTICINAE is given, together with brief notes on the food-plants and habits where known, and a key to the species.

Some 39 species, within 19 genera, are known to occur. Many are of minor economic importance, but three can be ranked as major pests. These are the two cotton flea-beetles, Podagrica puncticollis Weise and P. pallida (Jacoby), and Phyllotreta cheiranthi Weise on cruciferous vegetables.

Hands of warm-skinned Caucasian individuals were significantly more attractive to Aëdes aegypti (L.) than cool-skinned individuals. An artificially cooled hand is very much less attractive than a normal one.

Hands of Negroes were significantly more attractive than those of Orientals, and both were significantly more attractive than those of Caucasians. Hands of dark-skinned Caucasians were significantly more attractive than those of light-skinned Caucasians.

Warmer skins were more attractive even if combined with a lighter skin hue, in Caucasian subjects. Thus skin hue is secondary to skin temperature in deciding the attractiveness of Caucasians.

Hands of individuals with low moisture output were significantly more attractive than those of high moisture output. A hand induced to perspire freely was significantly less attractive than the normal hand.

A new genus, Austrotortrix, is erected for Teras postvittana Walker, the Apple Leaf Roller or Light Brown Apple Moth, a common pest of apple and Citrus in the coastal regions of Australia, and in Tasmania and New Zealand.

Two new synonyms of A. postvittana in addition to those already recorded are given.

As there are several species in Australia closely resembling postvittana, making identification difficult, descriptions of the genitalia of postvittana are given as these provide the best means of positive identification.

Apart from the type species, postvittana, ten other species are assigned to the new genus.

A simple method for culturing Culicoides nubeculosus (Mg.) in the laboratory is described, the medium used for rearing the larvae being a mixture of powdered mud from near a farm byre, dried autolyzed yeast and powdered charcoal, in the proportions 25:3:2. A layer of the mixture 4 mm. deep was spread over the bottom of unglazed earthenware pots, 6 in. diam. x 1 in. high, and just covered with water. After about three weeks in an insect-proof cage in the open, the pots were brought into the laboratory, the temperature of which was maintained at 20°C. except for brief periods in very hot or very cold weather. Each pot was stocked with from 70 to 220 newly hatched larvae, derived from a single batch of eggs laid on moist filter-paper discs in 3 x 1-inch glass mating tubes by adults that had been fed on human blood and provided with raisins. The surface of the medium became covered with a growth of bacteria, algae, fungi, and protozoa, which provided a source of food for the larvae. These made shallow burrows in the substratum from which they partially emerged to feed and in which they pupated. About 45 per cent, of those introduced emerged successfully as adults.

The incubation and pupal periods lasted 3–6 and about 4–7 days, respectively. The time taken for larval development varied greatly between individuals from the same batch of eggs, and also between batches started at different times of year. The complete life-cycle of examples started as larvae in January–September was thus 3–8½ weeks, the period over which emergence occurred amongst a single batch being 1–5 weeks; the corresponding figures for those started as larvae in October were 6–18 and 2 to nearly 12 weeks.

The behaviour in the various stages is briefly described.

Investigations on the Akah river, in the 4th Division of Sarawak, showed 13 species and one variety of Anopheles to be present. A. l. leucosphyrus Dön., the principal malaria vector, was the only species common in houses.

A. l. leucosphyrus has a strong preference for human blood and feeds throughout the night, with a peak of activity soon after midnight. Both fed and unfed mosquitos rest indoors on the walls but the latter become increasingly scarcer later in the night. Most individuals rest low down (62% below 3 ft., 96% below 5 ft.) but only a negligible percentage remains in the house after daybreak. Observations suggest that many females spend quite long periods resting outside the house before entering and that entry is almost entirely through windows and other openings in the walls; very few enter the space below the house. There is also evidence of two separate stimuli, or levels of activation, one bringing the mosquito to the bait and one initiating the act of feeding.

Wet weather was accompanied by an abrupt increase in catches of A. l. leucosphyrus and dry weather by a decrease—this is thought not to be due to any effect on breeding places. During the wet period, females entered earlier and tended to rest to a greater extent before feeding.

Mosquito larvae derived from eggs laid in earthenware pots in various habitats on the site of University College, Ibadan, in Nigeria were collected over a period of 26 months.

Anopheles gambiae Giles, Aëdes aegypti (L.) and Culex (Lutzia) tigripes Grp. were the species most frequently collected.

The relation of these results to the fluctuation in the populations of the species concerned is discussed. It seems unlikely that pot collections give results which can be directly related to the numbers of mosquitos in the field, but they can elucidate questions of mosquito biology and behaviour.

Mealybug populations (Pseudococcus njalensis Laing) originally present in piles of slash infected with the virus of swollen shoot of cacao are usually small. It is suggested that many of the insects leave the trees at an early stage in the development of infection.

Slash piles offer conditions which induce mealybugs to remain within them. The piling of infected slash retards the rate of wilting of the cut wood and consequently retards the rate of migration of the mealybug population. The construction of piles protects the mealybugs from direct insolation and rainfall and leads to the persistence of the population on the cut wood. The colonies which survive the longest are those in the lower part of the heaps where death and desiccation of the material is most delayed.

Mealybugs continue to live and to reproduce within heaps of slash for as long as nine weeks or more. Reproduction of the mealybugs is stimulated as the tissues of the felled trees become wilted and the resulting first-instar nymphs contribute numerous participants to such migration as does occur. There is evidence from laboratory experiments that these insects are not potential vectors.

The concentrating of mealybugs in slash piles produces no increase in the population of Coccinellid or Cecidomyiid larvae within the piles.

Mealybugs are capable of walking quite rapidly for long distances over smooth surfaces. They become incapable of movement when starved for a few days and the majority die within a week. A soil surface seriously impedes the progress of mealybugs which leave the slash heaps and this effect is more marked with the nymphal stages. Even on clean-weeded soil the rate of travel is slow and few. if any, insects can travel over appreciable distances in the period during which the virus may persist within them. Results of preliminary experiments were confirmed by the use of insects labelled with radioactive phosphorus.

Some of the ants, which become associated with slash piles and which remain in attendance of the residual mealybug population, carry mealybugs, but the number of insects transported in this way is of little practical significance.

The establishment of migrating mealybugs on seedlings and mature cacao is poor even in the presence of their attendant ants.

All these factors make the possibility of infecting healthy trees from infected slash extremely remote. There is accordingly no reason to believe that the efficiency of “ cutting out ” is seriously reduced by the movement of vectors from the infected trees which are cut out.

Without the co-operation of farmers in supporting the removal of contact trees no further recommendations can be advanced to improve the present method of control of swollen shoot.

Tinea pellionella (L.), commonly known as the Case-bearing Clothes Moth or Fur Moth, is of world-wide distribution and is of considerable economic importance. It has been recorded on a variety of substances, particularly those of a keratinous nature. In India, it has been found as an important pest of woollen textiles. Its life-history and habits have been systematically investigated at different levels of temperature and humidity.

The incubation period is 4 to 5, 5, 6 to 7 and 6 to 7 days at 21·5, 25, 30 and 32·5°C., respectively. Temperatures higher than 32·5°C. have been found lethal to eggs. Humidity has no effect on the incubation period. Percentage viability of eggs is greater at lower than at higher temperatures.

Both temperature and humidity have been found to influence the larval development and the number of larval instars. Irrespective of temperature, higher humidities favour shorter larval development and the shortest larval period is at 25°C. and 90 per cent. R.H.

Woollen materials impregnated with yeast are more suited for the larval development than those not so treated. Larvae do not exhibit colour preference. Woollen fabrics dyed with Cloth fast orange G 4 per cent, manufactured by “ Ciba ”, however, inhibit the growth of freshly hatched larvae.

The behaviour of the larvae to direct sunlight has been studied. The rôle of (a) diffused light alternated with darkness, (b) darkness, (c) temperature and (d) humidity on the extent of damage caused by the larvae has been investigated. Under the conditions of the experiments, the amount of damage in continuous darkness was significantly greater than in alternating light and darkness, and that at 90 per cent. R.H. significantly greater than at 30 per cent., but there was no significant difference in the amount of damage at 27·5° and 32·5°C., respectively, and 90 per cent. R.H.

The mode of pupation has been described. The pupal period has been studied and found.to occupy 18 ± 0·4, 10·3 ± 0·16 and 10·3 ± 0·33 days at 21·5, 25 and 30°C. and 90 per cent. R.H., respectively. Humidity has no effect on this period.

The effect of temperature and humidity on (a) the preoviposition, oviposition and postoviposition periods and (b) number of eggs laid by a female has been studied. The life-span of the male and female, the relationship between the weight of the female at emergence and fecundity (which was highly significant) on the one hand and length of life (which was not significant) on the other has also been investigated. Sex ratio between females and males has been found to be 2·6:1. Three to four generations in a year have been recorded at 26 ± 8·0°C. and 82 ± 10 per cent. R.H. when the larvae are fed on woollen fabrics impregnated with yeast.

Literature, mainly Indian, pertaining to the recorded hosts of Bracon hebetor Say and B. brevicornis Wesm., and on the taxonomy of the two species, has been reviewed. Observations on different morphological characters, including the male and female genitalia, which have been used in establishing the identity of the two species, have been made. A large number of B. hebetor specimens reared in Bangalore on Corcyra cephalonica (Stnt.), Ephestia cautella (Wlk.), Adisura atkinsoni Moore and those collected in food-grain godowns, and of B. brevicornis reared on C. cephalonica and E. cautella in Bangalore, on Nephantis serinopa Meyr. from Coimbatore (South India), on Pyrausta nubilalis (Hb.) from Canada and on cotton bollworms (?) from Delhi (North India), have been examined.

Differences in colour, relative proportions of antennal joints and punctation on the abdomen have been found to be variable and as such are not to be depended upon for distinguishing the two species. The number of antennal joints which has hitherto been considered to be the decisive character by which the two species may be separated is also not reliable as there is a wide range of variation even in the progeny of a single pair of parents. Above all, the fact that the two species interbreed and give rise to fertile offspring, which also show a fairly wide range of variation in the number of antennal joints, proves that the two are identical, and there is no ground to treat them as two distinct species, at least so far as the Indian specimens are concerned, for which Bracon hebetor Say is the valid name.