Biotypes B and Q of Bemisia tabaci (Gennadius), collected from the islands of Tenerife and Majorca respectively, were exposed to competition conditions on tomato cv. Marmande in the laboratory. Both biotypes were established in single and mixed cultures at different densities. Increased mortality of biotype Q females and immature instars was observed together with a lower rate of fecundity and progeny size compared to biotype B, when reared in single or mixed cultures. The female:male sex ratio of F1 individuals of biotype Q was higher in single than in mixed cultures. However, the sex ratio of F1 individuals of biotype B was the same in single and mixed cultures, suggesting reproductive interference. Whitefly density did not affect interspecific interactions. It had a moderate effect on developmental rate of both biotypes, and on mortality of immature instars and progeny size of biotype B only. The results indicate that under laboratory conditions the studied biotype B should displace biotype Q.

Life-cycle variation, involving alternative methods of overwintering (holocycly and anholocycly), is found in many important pest aphids, and may have considerable ecological, genetic and economic significance. The occurrence of life-cycle variation in Myzus persicae (Sulz.) in different parts of the world is reviewed. The holocycle of M. persicae, with sexual reproduction and overwintering of eggs on Prunus, occurs in the temperate regions of every continent, and although anholocycly is widespread in warm climates there are indications that the potential for sexual reproduction may be retained throughout the whole range of the species. The environmental factors involved in the determination of sexual morphs are considered. Photoperiodism provides the timing mechanism for sexual morph production, and the photoperiodic response is probably tuned to different regional conditions and buffered against other environmental variables within certain limits. The only other environmental factor clearly implicated in sexual morph production is temperature, and an attempt is made to correlate the global pattern of life-cycle variation in M. persicae with temperature differences between regions, by dividing the world into six zones delimited by selected isotherms. The overall pattern of life-cycle variation can be explained largely on the basis of climatic differences between zones, and the effects of these differences on gene and genotype frequencies within the species. Clones of androcyclic character seem to be widespread and, although genetically isolated anholocyclic biotypes undoubtedly exist, androcyclic clones could be the principal source of parthenogenetic overwinterers in all parts of the world where life-cycle differences exist within populations.

Collections of siricid-infested coniferous trees were made in 150 localities in 19 European countries, Turkey and North Africa to obtain parasites and parasitoids of siricids for use in the biological control of Sirex noctilio F. in Australia. During this work, information was obtained on the distribution and biology of 8 siricid species (S. noctilio, S. cyaneus F., S. juvencus L., Urocerus augur (Kiug), U. gigas. (L.), U. sah (Mocs.), U. fantoma (F.), Xeris spectrum (L.)) and 7 parasitoids (Rhyssa persu.asoria (L.), R. amoena. Gray., Pseudorhyssa maculicoxis (Krchb.), Megarhyssa emarginatoria (Thnb.), Ibalia leucospoides leucospoides (Hochenw.), I. rufipes drewseni Borries, Odontocolon geniculatum. (Krchb.)). Data are presented on distribution, flight periods and sexratios (determined from emergence records), factors leading to the susceptibility of timber to siricid infestation and the types of timber and host tree species infested. Levels of parasitism by the various parasitoid species, determined from emergence records, are given. Localities are assigned to bioclimatic categories, and their siricid and parasitoid species are classified in relation to the climatic criteria. The ecological status of S. noctilio is discussed in relation to its establishment in Australia.

A few years ago a paper appeared in this Bulletin (Buxton, 1931) describing methods of controlling and measuring humidity. Since that paper was written, we have evolved a number of improvements which tend to make the methods easier in practice, though none of them are novel in principle. It is now known that humidity has diverse and unpredictable effects on many insects. In experimental work it is advisable that humidity should always be measured and controlled even if it is not a factor in the experiment. Moreover, workers should state what method of measurement or control they have adopted.

Multivariate techniques, principally the method of canonical variates, were used to investigate morphological variation within and between populations of the group of Myzus persicae (Sulzer) from North and South America, Europe, Africa and Asia. The scores on the first canonical variate of samples from tobacco in North America, the Mediterranean region, the Middle East, Africa and Sri Lanka all grouped consistently when compared with samples from other host-plants, even after aphids from tobacco had been reared for up to seven years on a non-tobacco host. Thus there is a widely-distributed tobacco-adapted form, closely related to M. persicae but with its own characteristic morphology. Morphological discriminants are given for the recognition of apterous and alate viviparae of this tobacco form, which is given the name M. nicotianae sp. n. Both M. persicae and M. nicotianae have 2n = 12, and both are frequently heterozygous for apparently the same autosomal translocation, which they must have acquired independently. M. nicotianae is presumably isolated from M. persicae by being permanently parthenogenetic. In Japan and Central Asia, however, aphids of the M. persicae group on tobacco can produce sexual morphs; the taxonomic status of these latter populations is still unclear. Multivariate comparison of European and North American populations of dark green aphids of the M. persicae group with 13 or 14 chromosomes in somatic cell nuclei instead of the normal 12, led to the conclusion that these all belong to one morphologically variable taxon, M. antirrhinii (Macchiati). Keys are provided to the apterous and alate virginoparae of the species of the M. persicae group in America.

L. sericata, L. cuprina, Ch. rufifacies, C. stygia and C. augur have been bred through many generations in captivity. These flies were bred in artificial light as well as in sunlight. Inbreeding had no effect upon activity, fecundity or length of life.

A diet of protein is necessary for the maturation of ova but not of spermatozoa.

Oviposition is not strictly associated with a suitable larval environment, but is more in the nature of a response to a tactile stimulus. Copulation appears to provide an essential stimulus for oviposition.

No evidence of parthenogenesis has been obtained and unfertilised females did not lay eggs.

The maximum oviposition observed was 3,171 ova by a hybrid Lucilia. This fly lived 94 days.

A total oviposition of 2,373 ova was observed in a L. sericata. Both parent flies lived 77 days.

The number of ova a fly can produce at one time is dependent on its size and thus on the amount of food obtained in the larval stage.

The sex-ratio for Lucilia is very close to 1 : 1. Starvation in the larval period did not have a marked effect on the sex-ratio.

It is possible to cross the two closely related species of Lucilia, and the cuprina characters appear to be dominant. It is unlikely that this cross occurs in the field.

Applications of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae have traditionally been targeted against soil insects. Nonetheless, research over the last two decades highlights the potential of such agents against above-ground pests under certain circumstances. A general linear model was used to test for patterns in efficacy among 136 published trials with Steinernema carpocapsae Weiser, the most common species applied against foliar and other above-ground pests. The focus was on field and greenhouse assessments, rather than laboratory assays where relevant ecological barriers to infection are typically removed. The model showed differences in nematode treatment efficacy depending on the pests’ target habitat (bore holes > cryptic foliage > exposed foliage) and trial location (greenhouse > field studies). Relative humidity and temperature during and up to 8 h post-application were also predicted to influence rates of nematode infection obtained. Conversely, spray adjuvants (both wetting agents and anti-desiccants) and nematode dosage applied (both concentration and use of consecutive applications 3–4 days apart) did not explain a significant amount of variance in nematode performance. With reference to case studies the model is used to discuss the relative importance of different factors on nematode efficacy and highlight priorities for workers considering using entomopathogenic nematodes to target pests in novel environments.

The chief aims of the survey and an important conclusion reached during some preliminary work are briefly stated. This latter was the recognition of two distinct nest types—the wet nest, exposed to rain, and the dry nest, sheltered from rain.

The methods used to examine materials and record results are described. They were closely similar to those described in a previous publication.

The insect fauna is listed under three headings: (a) ectoparasites of birds, which includes 12 species; (b) scavengers, including 66 species; and (c) predators, comprising 14 species. Figures are given for the frequency of occurrence and the abundance of the more important nidicole species, abundance being given as an arbitrary estimate. The importance of each as a pest is also briefly stated, and detailed records are given for uncommon or particularly interesting species.

The mite fauna is dealt with in a similar manner. It includes one ectoparasite, 10 scavengers and 11 predators.

The basic composition of nests and the temperature and humidity conditions within them are described briefly and the possible influence of these factors upon the nest fauna is discussed.

The species of the dry nest community are classified, according to their feeding habits, as ectoparasites of birds, scavengers and predators, and according to their status in the nest, as regular, occasional and incidental inhabitants. The distribution of the group of species which truly characterises this community is discussed.

Peach shoot volatiles were attractive to mated female oriental fruit moth, Cydia molesta (Busck), in a dual choice arena. No preference was observed between leaf odours from the principle host plant, peach, and the secondary host plant, apple. Twenty-two compounds were identified in headspace volatiles of peach shoots using gas chromatography–mass spectrometry. Green leaf volatiles accounted for more than 50% of the total emitted volatiles. A bioassay-assisted fractionation using different sorbent polymers indicated an attractant effect of compounds with a chain length of 6–8 carbon atoms. The major compounds of this fraction were tested either singly or in combinations for behavioural response of females. Significant bioactivity was found for a three-component mixture of (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol and benzaldehyde in a 4:1:1 ratio. This synthetic mixture elicited a similar attractant effect as the full natural blend from peach shoots as well as the bioactive fraction.

The time during which prey remains are detectable in the gut of a predator is an important consideration in the interpretation of molecular gut-content data, because predators with longer detectability times may appear on the basis of unweighted data to be disproportionately important agents of prey population suppression. The rate of decay in detectability, typically expressed as the half-life, depends on many variables; one that has not been explicitly examined is the manner in which the predator processes prey items. The influence of differences in feeding mode and digestive physiology on the half-life of DNA for a single prey species, the Colorado potato beetle Leptinotarsa decemlineata (Say), is examined in two predators that differ dramatically in these attributes: the pink ladybeetle, Coleomegilla maculata (DeGeer), which feeds by chewing and then ingesting the macerated material into the gut for digestion; and the spined soldier bug, Podisus maculiventris (Say), which physically and enzymatically processes the prey extra-orally before ingestion and further digestion in the gut. In order to standardize the amount of DNA consumed per predator, a single L. decemlineata egg was used as the prey item; all predators were third instars. The PCR assay yields estimated prey DNA half-lives, for animals maintained under field temperatures, of 7.0 h in C. maculata and 50.9 h in P. maculiventris. The difference in the prey DNA half-lives from these two predators underscores the need to determine detectabilities from assemblages of predators differing in feeding mode and digestive physiology, in order to weight positives properly, and hence determine the predators' relative impacts on prey population suppression.

A close association exists between the ant Oecophylla longinoda (Latr.) and the scale insect Saissetia zanzibarensis Williams.

Several factors cause the scale to be rare in the absence of the ant. Contamination by honey-dew and sooty moulds prevents increase of the S. zanzibarensis population above a relatively low level, while, in addition, insect parasites and probably predators virtually exterminate the scale. A fungal parasite may destroy honey-dew-contaminated S. zanzibarensis under humid conditions.

The attendant O. longinoda prevents contamination of the scale by honeydew. It gives absolute protection from Coccinellid predators and, although parasitism by Coccophagus spp. and predation by Eublemma spp. is not prevented, the mortality of S. zanzibarensis which they cause is thought to be of little significance.

O. longinoda workers benefit S. zanzibarensis in other ways. They remove débris from the scale clusters; they transport the nymphs and establish them at suitable feeding sites. The effect of these benefits is most marked when the ant population is high relative to that of the scale.

The silken shelters built by O. longinoda over S. zanzibarensis clusters protect the ant during adverse weather and may only incidentally benefit the scales.

S. zanzibarensis and other honey-dew-producing Homoptera are the major food source for O. longinoda. Other sources are sufficient to maintain only relatively low populations of the ant.

The effect of temperature on the growth rate and survival of the immature stages of Aëdes aegypti (L.) was studied by rearing them at each of a series of constant temperatures from 14–38°C. in water to which adequate food (bakers' yeast) was added. Larvae were hatched, by immersing eggs in water, in four successive groups with an interval of six hours between each, and six hours after the last group hatched, and every 24 hours thereafter, those surviving in each group were recorded and transferred to fresh water and food, the exuviae remaining being recorded. The average time at which any given stage was reached was taken as the mid-point of the 6-hr. period within which the number of individuals that had completed the previous stage reached 50 per cent, of the total that finally did so.

The curve relating temperature and time of development from newly hatched larva to adult is hyperbolic, except at the extremes. The later the instar, the lower is the temperature at which growth is most rapid. The threshold of development was between 9° and 10°C., the developmental zero 13.3°C., and the average thermal constant (between 16° and 32°C.) 2,741 degree-hours. The highest and lowest temperatures permitting development from newly hatched larva to adult were 36° and 14°C., respectively. The average durations of the four successive larval stages and the pupal stage, expressed as percentages of the time taken for newly hatched larvae to reach the adult stage, were 14.6, 13.9, 17.5, 33.3 and 20.6, respectively.

The within-field spatial distribution of some common farmland arthropods from the Carabidae, Araneae and Collembola was assessed using two-dimensional grids of pitfall traps distributed across whole winter wheat fields. In the first year, the extent to which arthropod capture was influenced by location within the field and sampling intensity was examined using a nested grid design (1.5 m, 7.5 m and 30 m spacings). In the second year, distributions within two different-sized winter wheat fields were compared. Spatial pattern and association between arthropods and weed cover were analysed using SADIE and trend surfaces were used to visualize distributions. Many of these arthropod groups exhibited aggregated distributions within the fields in clusters larger than 30 m across, demonstrating that the numbers captured will vary depending on the location of sampling within a field. Amara species, Bembidion lampros Herbst, Carabidae and Lycosidae were predominantly found within 60 m of the field edge. Nebria brevicollis Fabricius and Pterostichus madidus Illiger were found within the field in patches of one and two hectares, respectively. Linyphiidae were relatively homogeneously distributed across the fields. There was some evidence of clustering by Collembola. The spermophagous Carabidae and Lycosidae were positively associated with the degree of weed cover. SADIE analytical techniques were useful for identifying the importance and location of patches with greater and less than average numbers, although a minimum of 36 sample points is recommended.

1. Mosquitos often recover completely after showing the preliminary symptoms of DDT poisoning.

2. The effect of contact with DDT on the activity and distribution of mosquitos has been studied in a small cage, exposure times being kept below that necessary to kill the insects.

3. The duration of single resting periods on DDT-treated surfaces was several times shorter than resting periods on untreated surfaces, provided the mosquitos had had no recent access to DDT.

4. Mosquitos that had been in recent contact with DDT rested only slightly longer on untreated than on DDT-treated surfaces.

5. Mosquitos excited by DDT moved preferentially toward light.

This paper presents a key to the larvae and pupae of 28 species of Culicoides found in Britain and to larvae and pupae of the genera Stilobezzia, Serromyia and Ceratopogon including the subgenera Ceratopogon and Isohelea. The keys are supplemented by descriptions of the larvae and pupae, including photographs of the fourth instars and figures of the so-called “hypopharynx” —the true epipharynx—of most of the larvae and by figures of specific characters of the pupae. Twenty-eight species of Culicoides larvae are described:—C. albicans, C. chiopterus, C. circumscriptus, C. cubitalis, C. cunctans, C. delta, C. fascipennis, C. grisescens, C. halophilus, C. heliophilus, C. impunctatus, C. lupicaris, C. maritimus, C. nubeculosus, C. obsoletus, C. odibilis, C. pcdlidicornis, C. pictipennis, C. pseudochiopterus, C. pulicaris, C. punctatus, C. riethi, C. salinarius, C. scoticus, C. simulator, C. stigma, C. truncorum, and C. vexans. The descriptions of the pupae include all the above, with the addition of C. parroti.

An analysis has been made of the breeding preferences of Culicoides and it was found that species could be placed in one of six groups depending on the larval habitat. The six categories were:— (i) Bog, (ii) Fresh Water Marsh, (iii) Swamp, (iv) Mud, (v) Salt Water Marsh and (vi) Dung.

The vertical distributions of seven species of Culicoides larvae are given. There are marked differences between the species in this respect.

In Zimbabwe, the catches of Glossina morsitans morsitans Westwood and G. pallidipes Austen in traps were increased by up to three times by releasing 1-octen-3-ol at 0·05–50 mg/h or acetone at 5–5000mg/h near traps, but in some circumstances 1-octen-3-ol at 5–50 mg/h reduced catches. Carbon dioxide at 0·02–20 litres/min increased catches by up to ten times. A mixture of all three chemicals increased the catches by up to 60 times. Each of the three chemicals attracted both species of flies from a distance; carbon dioxide also enhanced trap-entering and alighting responses. Acetone with 1-octen-3-ol can increase by several times the numbers of flies that contact visual baits suitable for exposing them to insecticide. Data for other Diptera are also presented.

The host range of major fruit fly pests in Central Tanzania was evaluated from October 2004 to October 2006. Samples of 48 potential hosts were collected and incubated for fruit fly emergence. Bactrocera invadens was the dominant species in incidence expressed as the ratio of infested to total number samples collected, as well as infestation rate, expressed as number of flies emerging per unit weight. Eight new host fruits are reported. Infestation by native pests, such as Ceratitis capitata and C. cosyra, was minor compared to B. invadens. Ceratitis rosa was the dominant species in temperate fruits, and Cucurbitaceae were mainly infested by Bactrocera cucurbitae, a specialized cucurbit feeder. Among commercial fruits, high infestation incidences were observed in mango and guava, but they decreased throughout the fruiting season. Low infestation rates were observed in all Citrus species and in avocado, indicating these fruits as poor hosts for the studied fruit fly pests in this region. Widespread availability and abundance of fruit species studied here ensures year-round breeding of B. invadens. Seasonal infestation differs, with mango being the most important host in October to January, while guava being important from February to August. Tropical almond showed very high incidence and infestation rate for B. invadens and might act as an important reservoir host, bridging the fruiting seasons of mango and guava. Soursop acts as an important host for C. cosyra after the mango season. Ceratitis capitata is a pest of minor importance of the commercial fruits studied in this region.

In order to test their ability to survive the winter in unheated buildings, 68 species of storage and domestic insect pests were exposed throughout one or more winters in wooden screens and various outbuildings at the Pest Infestation Laboratory, Slough, Bucks.

Generally, cultures containing all developmental stages were exposed. The chief aim was to demonstrate some survival or else the complete failure of the culture; conclusionsabout single stages were added where possible.

The ability or failure of a species to overwinter may be affected by the following factors, which are discussed: cold-hardiness, effects of previous conditions, differences between strains or races within a species, severity of the winter, length of period of exposure, moisture conditions, type of building, protection by materials in storage, biological heating of the immediate environment.

The shortest experiment lasted 16 days, the majority for about six months.

The distribution of ants in a 2·25-ha cocoa plantation at the University of Ghana Agricultural Research Station, Kade, was recorded in December 1970. The 44 species of ants found could be grouped as dominant, co-dominant, sub-dominant and nondominant. Oecophylla longinoda (Latr.) and Macromischoides aculeatus (Mayr) were mutually exclusive as were six Crematogaster spp.; the latter were also exclusive of O. longinoda and M. aculeatus. Camponotus acvapimensis Mayr became dominant under insolated conditions, and Platythyrea frontalis Emery for reasons unknown. The distribution of these ant species in cocoa plantations resembles a three-dimensional mosaic which is preserved by their aggressiveness and by competition for food and nesting sites. It is suggested that this mosaic is due to vegetative succession.

The work described in this paper forms part of an investigation into the conditions which influence the breeding of Pieris brassicae (L.) in captivity. Observations have been made on the behaviour of the females at the time of oviposition, on factors which influence oviposition, on the appearance and weight of the eggs and on their fertility and hatching.

Females which are ready to lay seek out green surfaces and, as they respond eagerly to plants from which they are separated by glass, it seems that plant odour plays little part in the attraction. Once they have alighted, however, the insects drum on the surface with their fore legs to test its suitability. Normally they lay only on plants which contain the mustard-oil glucosides, but they have been observed to oviposit on broad bean (Vicia faba), on which the larvae do not survive. Sinegrin applied to green paper stimulates the female to lay. Provided she is standing on an acceptable surface she will oviposit on any other surface, for example, filter paper or glass. The eggs are normally deposited on the under surface of the leaves. This is largely due to a preference for the physical underside but the insects also seem to prefer the morphological under surface of the leaf to the upper surface. When laying an egg, the female locates one previously laid with the tip of her abdomen and so builds up the regularly arranged batches.

The females lived and oviposited as well in small cages as in large cages. They laid more eggs per day, and more eggs in a batch, at 30°C. than at 20°C. Both numbers increased until the female was about six to seven days old and then declined. Oviposition occurs at low light intensities. Fertilised females laid very many more eggs than virgin females. Oviposition occurred two to three days after copulation, and most females oviposited six or seven times in eight days. The number of eggs laid by starving insects is low: it is higher for insects given water or one per cent, honey solution and very much higher for insects given ten per cent, honey solution. Sucrose solutions are as satisfactory as honey solution.

When first laid, the eggs of P. brassicae are yellow in colour and become more orange as they develop. Some batches of newly laid eggs are of a distinctly darker yellow than others but, as it is believed that the eggs are fertilised only just before oviposition, it seems that this colour difference cannot be due to the eggs being in somewhat different stages of development. The number of ribs on the shells seems to vary in different cultures.

Batches of eggs which are laid within an hour of each other may begin to hatch several hours apart, and the time taken for all the eggs in one batch to hatch was found to range from two hours to about seven. A fertilised female lays scarcely any infertile eggs. The fertility after one mating falls below 100 per cent, after about 14 days, but normally the female mates again before this time. Temperature naturally affects the time taken by the eggs to hatch. The shortest time was about 3¾ days at 28°C.; the longest observed was 17 days at 12·5°C.

The eggs cannot be stored for more than ten days at 3·5°C. and 50 per cent, relative humidity. Eggs will develop and hatch at very low humidities. If the eggs are detached from the surface on which they are laid by the use of acetone their capacity to develop and hatch in air dried over phosphorus pentoxide is substantially reduced.