The characteristics of the high and low density forms of noctuid moths, including Spodoptera exempta (Walker), exhibiting a density-dependent phase polyphenism have frequently been discussed in relation to migration. However, the only previous (unpublished) demonstration of an effect of larval phase on adult flight performance, using a tethered-flight technique, was invalidated by the recent discovery that the principal determinant of flight potential in S. exempta is genetic. When the incidence of prolonged flight was measured in moths derived from genetically-matched (full-sib) samples, there was a clear increase in long flights by females derived from the high-density gregaria phase larvae compared with those from solitaria phase larvae. The reasons for the apparent absence of a similar effect in males is not clear, but it is possible that the tethered-flight technique provides a less reliable index of flight capacity in this sex. The characteristics and significance of phase polyphenism in migratory noctuids are discussed. It is suggested that, in S. exempta and possibly some other comparable species, the high-density phase is adapted to accelerate re-dispersal after populations become concentrated, in order to escape the detrimental consequences of high larval densities.

These studies were made in Uganda on the islands and shores of Victoria Nyanza, in territory which had been depopulated some years before on account of tsetse-fly and sleeping sickness. They were begun in October 1913, and extended over two full years, of which eighteen months were spent in the fly belt on Victoria Nyanza, and three months on a tour into Bunyoro, where for the time being (the spring of 1914) Glossina morsitans was the centre of greater attraction as a possible vector of human trypanosomiasis. Seven tours were made from headquarters at Entebbe—the shortest, of three days only, being interrupted by the War, and the longest, of eight full months, being much prolonged by the War.

The unspecialised portion of the shell and the cap of Rhodnius eggs are impermeable to almost all hydrophilic and lipophilic liquids. If water and very small ions pass through the chorion they must traverse a wax layer on the inside of the shell. Certain corrosive materials, e.g., glacial formic acid, may pass through the shell slowly.

These conclusions, based on experiments with pieces of shell, have been confirmed in ovicidal experiments. A range of materials with widely differing properties enter the embryo only through the micropyles, of which there are approximately fifteen in the rim of each shell. At least one micropyle must be traversed to kill an egg but many eggs were killed when only one had been penetrated.

A cement, applied by the female at oviposition, may occlude the outer orifice of a micropyle. The properties of the cement are described; it appears to be a tanned protein. Cement deposits are much more copious on the eggs laid by younger females. Such eggs are more resistant to ovicides because penetration is delayed. This increased resistance is more pronounced when oleophilic liquids are used owing to the rapidity with which they kill eggs from older females. The random distribution of cement is one cause of the variability of replicates in ovicidal tests.

A detailed investigation has been made of factors governing liquids traversing the micropyles. Hydrophilic liquids invade the outer lipophilic part of the micropyle slowly; the displacement of air is the most important factor and small changes in the wetting power of the liquid make little difference to the rate of entry.

Aqueous liquids aie absorbed into the protein lining of the inner portion of the micropyle. They reach the wax layer on the inside of the shell by migrating into and through the inner protein layer. The area which is invaded increases linearly with time. Mortality, therefore, increases as the square of the time of immersion, but it is proportional to the increase in concentration of a solute if the period of immersion is constant.

Oleophilic liquids wet the micropyle actively. They may by-pass air and flow rapidly to the wax at the inner end of the tube. Wax solvents kill very quickly and are much more toxic than other lipophiles.

Water in the micropyle and shell may affect the entrance of either type of liquid. In general it increases the toxicity of aqueous solutions and retards the entry of oils.

Wax-emulsifying materials added to aqueous solutions do not produce great increases in toxicity. They are “filtered out” at the protein lining of the micropyle and do not reach the wax layer for a considerable period of time.

The effects of the aphicide pirimicarb on the foraging behaviour of the aphid parasitoid Diaeretiella rapae were investigated in the laboratory, using aphid-infested and uninfested, young oilseed rape plants. Female parasitoids spent significantly less time foraging on plants sprayed with pirimicarb within the previous 24 h than on untreated plants, regardless of the presence of aphid hosts. Whilst foraging on sprayed plants, parasitoids spent relatively more time walking than they did when foraging on untreated plants. On sprayed plants foraging parasitoids tended to avoid leaf surfaces, thereby reducing the chances of encountering aphid hosts whilst on the plant. These sublethal effects of the aphicide on foraging parasitoids would considerably reduce their impact on aphid populations which survived in a crop after spraying. This has important implications for the control of aphids, such as Myzus persicae, which have developed pesticide resistant strains.

Long term changes in the size of populations of the tsetse Glossina pallidipes Austen and G. longipennis Corti were monitored over a 12 year period at Nguruman in south-western Kenya. Tsetse populations were subject to droughts of varying intensity and, from 1987, to trapping, initially by a research organization, and later by a community-based development project. Populations were mainly sampled using odour-baited biconical traps, with data from other monitoring traps corrected accordingly. Mark–release–recapture studies were carried out to relate trap catches to absolute population size, and to quantify movement between subpopulations. Trypanosomiasis incidence rates in a herd of local cattle were also monitored for much of this period. Trap catches were shown to be well correlated with estimates of absolute population size, with no evidence of any seasonal change in trap efficiency. The intensity of trapping and level of seasonal immigration appeared to be the main determinants of population trends, with effective control being achieved when traps were well maintained. Movement between the two lowland subpopulations was shown to be greater for females, and to be inversely related to temperature. An analytical model was used to investigate the responses of a partially isolated population to trapping pressure. Predictions of a deterministic simulation model demonstrated that the observed changes are consistent with an adult trapping mortality of 4–8% per day, and immigration of 100,000 G. pallidipes females per month in the long rains (April and May), 5000 per month in the short rains (November), and about 500 per month during the dry seasons. Trypanosomiasis incidence in local cattle was greatly reduced during the period of community-based tsetse control. When tsetse were sampled exactly where the cattle were grazing, disease incidence was shown to be linearly related to G. pallidipes catches. Arguments for trap resistance and residual populations were examined, and found to be inconsistent with the data. The future for tsetse control by the Nguruman community is considered.

The use of the random amplified polymorphic DNA (RAPD) polymerase chain reaction to characterize individual Lucilia sericata Meigen from southern England was evaluated. Some simple techniques which allowed the preservation and extraction of DNA to be optimized without the complications of transporting liquid nitrogen were investigated. The RAPD results show that closely related L. sericata, including those from a single strike, can be readily distinguished from each other on the basis of their RAPD profiles resolved using electrophoretic analysis; profiles were defined with ten random primers. Analysis of these RAPD data using a similarity coefficient method and a recently developed randomization test to detect the non-random association of alleles at different loci, allowed the genetic homogeneity of L. sericata within southern Britain to be explored. This study shows that while a number of factors can complicate the use and interpretation of RAPD fragments as genetic markers, RAPD fingerprinting can be a valuable technique for studies of intraspecific genetic variation in L. sericata.

Amplification of the second internal transcribed spacer (ITS2) of ribosomal DNA was used to compare seven samples of the Tetranychus kanzawai Kishida–T. hydrangeae Pritchard & Baker mite complex from five different countries: Australia, the Congo, Indonesia, Japan and the USA. No morphological differences were detected between these mites and their ITS2 sequences displayed strong similarity except for a small nucleotide divergence of 0.2% in specimens from Australia and Indonesia. Reciprocal crosses and backcrosses between mites assumed to be T. kanzawai and T. hydrangeae respectively showed reproductive compatibility. Fertile hybrid females were obtained in all cases, indicating conspecificity of the mites tested. It is concluded that T. hydrangeae is a synonym of T. kanzawai. The evidence suggests that T. kanzawai originated in South-east Asia and probably spread throughout the world on Hydrangea spp. cuttings.

Pheromone and light traps have often been used in ecological studies of two major noctuid pests of agriculture in Australia, Helicoverpa armigera and H. punctigera. However, results from these two methods have rarely been compared directly. We set pheromone and light traps adjacent to or amongst cotton and various other crops for 10–11 years in the Namoi Valley, in northern New South Wales, Australia. Catches in pheromone traps suggested a major peak in (male) numbers of H. punctigera in early spring, with relatively few moths caught later in the summer cropping season. In contrast, (male) H. armigera were most abundant in late summer. Similar trends were apparent for catches of both male and female H. armigera in light traps, but both sexes of H. punctigera were mostly caught in mid-summer. For both species, males were more commonly caught than females. These catch patterns differed from some previous reports. At least three generations of both species were apparent in the catches. There was some evidence that the abundance of later generations could be predicted from the size of earlier generations; but, unlike previous authors, we found no positive relationships between local winter rainfall and subsequent catches of moths, nor did we find persuasive evidence of correlations between autumn and winter rainfall in central Australia and the abundance of subsequent 1st generation H. punctigera moths. Female H. punctigera were consistently more mature (gravid) and more frequently mated than those of H. armigera. Overall, our results highlight the variability in trap catches of these two species and question the use of trap catches and weather as predictors of future abundance in cropping regions.

The genus Encarsia Förster includes parasitoid species that are effective natural enemies of whitefly and armoured scale insect agricultural pests. Within this genus, several species groups have been recognized on the basis of morphological similarity, although their monophyly appears uncertain. It is often difficult to separate morphologically similar species, and there is evidence that some species could in fact be complexes of cryptic species. Their correct identification is fundamental for biological control purposes. Recently, due to unreliability of morphological characters, molecular techniques have been investigated to identify markers that differentiate closely related species. In this study, DNA variation in an ~900 bp segment of the mitochondrial cytochrome oxidase subunit I (COI) gene was examined by both sequencing and PCR–RFLP. Two pairs of species that are difficult to distinguish morphologically were analysed: Encarsia formosa Gahan and Encarsia luteola Howard, belonging to the luteola group, and two populations of Encarsia sophia (Girault & Dodd) from Pakistan and Spain, belonging to the strenua group, recently characterized as cryptic species. High sequence divergence and species-specific restriction patterns clearly differentiate both species pairs. Parsimony analysis of the nucleotide sequences was also performed, including Encarsia hispida De Santis (luteola group) and Encarsia protransvena Viggiani (strenua group). Two monophyletic clades supporting the two groups of species considered were resolved. The results of this study support the use of the COI gene as a useful marker in separating species of Encarsia, for which morphological differences are subtle. Moreover, the COI gene appears potentially useful for understanding phylogenetic relationships in this genus.

Bioassay data for a reference strain of Nasonovia ribisnigri (Mosely), exhibiting similar responses to proven susceptible strains of Myzus persicae (Sulzer) and Aphis gossypii Glover, were used to assess insecticide resistance in two suspected resistant strains and nine field strains of N. ribisnigri originating from lettuce in the UK. Results showed widespread but varied levels of resistance to pirimicarb, lower and also varied resistance to pyrethroids and organophosphates, and no significant differences in response to imidacloprid. In some strains, resistance was associated with an intensely-staining esterase band disclosed by polyacrylamide gel electrophoresis (PAGE). However, no direct relationship between esterases and resistance has yet been established. There was no biochemical evidence of an altered acetylcholinesterase contributing to pirimicarb resistance in these strains.

Research on aphid-parasitoid associations was carried out in Chile in 1979–80 and 1991–92 on the biological control of the cereal aphid pests Metopolophium dirhodum (Walker), Sitobion avenae (Fabricius), and Diuraphis noxia (Mordvilko). The introduced parasitoid species, Aphidius ervi Haliday, A. rhopalosiphi De Stefani Perez, A. smithi Sharma & Subba Rao, A. uzbekistanicus Luzhetski, Ephedrus cerasicola Starý, E. nacheri QuilisPerez, E. plagiator (Nees), Monoctonus nervosus (Haliday), Prnon gallicum Starý, P. volucre (Haliday) were all recovered in cereal and other ecosystems. Most of the parasitoids had adapted well and some of them had even extended their host range; ecological relationships were all found to extend beyond those of the target pests. The parasitoid complex, which had developed from the indigenous and introduced species, was found to be successful in preventive biocontrol and the endemic fauna of Chile was not affected.

The literature on the history and biology of the cassava mealybug in Africa Phenacoccus manihoti Matile-Ferrero is reviewed, and reports on the search for natural enemies of this species in the Neotropics for biological control purposes are summarised. Further records of the distribution of P manihoti in Africa are presented. A new closely-related species of Phenacoccus, P. herreni sp. n., which causes distortion to cassava in the Neotropical Region is described, and a key is provided to separate it from P. manihoti and from a similar species from the Neotropical Region, P. surinamensis Green, which apparently does not occur on cassava. P. surinamensis is redescribed and illustrated.

A method of obtaining locust eggs which could be expected to be deficient in carotene is described. It involved rearing a parental generation on an artificial diet which, because of certain pigmentation abnormalities it induced, was probably itself deficient in carotene.

Using crowded hatchlings of Locusta migratoria (L.) from eggs thus modified, it was shown that they were sensitive to dietary carotene, whereas hatchlings from normal eggs were indifferent. The absence of carotene was marked by inferior growth, lessened activity and most notably by an extremely different coloration in both hoppers and adults. Without carotene, melanisation was absent or greatly reduced and in many cases the integument developed a greenish-blue colour. With carotene, heavy melanisation occurred in the hoppers, and the colour of the adults was characteristically gregarious.

It was concluded that in normal eggs the amount of carotene present is usually sufficient to mask the expression of a dietary deficiency during nymphal growth, but that with normal eggs having low amounts of carotene, a dietary deficiency might become apparent as it did with modified eggs.

It is suggested that the blue colour of modified Locusta hoppers reared without carotene is due to mesobiliverdin, a prochromogen of insectoverdin, the green pigment of the solitaria phase of locusts. Insectoverdin itself could not be formed because it contains carotenoids, and these were absent from the diet. The effect of extreme deprivation of carotene is therefore to induce solitaroid tendencies, notably in regard to colour (suppression of melanin and production of mesobiliverdin) but also in regard to activity.

Crowded hoppers of Schistocerca gregaria (Forsk.) reared on synthetic diets lacking carotene usually had turquoise-blue blood by the fifth instar. It was shown, by the electrophoresis of yellow, green and blue bloods in parallel, that the blue chromoprotein of blue blood is the same as the blue chromoprotein of green blood. Its prosthetic pigment must therefore be mesobiliverdin.

The abnormalities of coloration which arise in crowded Locusta and Schistocerca when deprived of carotene are normal in the solitary phase. Moreover, they resemble those abnormalities of coloration consequent upon the implantation of additional corpora allata into gregarious hoppers. The implications of this are discussed in relation to the validity of phase criteria, and an attempt is made to relate these findings to hypotheses on the humoral regulation of phase.

Two experiments were done to examine the predation of thrips, and the movement of Orius laevigatus Fieber and Neoseiulus cucumeris (Oudemans) in the presence and absence of two supplemental food sources, pollen and the fungus Trichoderma viride. The presence of pollen led to a 55% reduction in predation of the thrips by N. cucumeris and a 40% reduction in thrips predation by O. laevigatus, in experiments using single predators. The presence of fungus had no significant effect on thrips predation by either of the natural enemy species. Movement of the natural enemies was examined in a multiple predator experiment, and this showed that O. laevigatus was more likely to remain on the plant in the presence of thrips and when supplemental food, either pollen or fungus, was present. For N. cucumeris, there was no association between the presence of thrips and the mite, with the majority of the mites being found on the leaves where pollen was present. Although the single and multiple predator experiments were done at different times, the indications are that the predation rates of the N. cucumeris do not differ greatly between the two experiments, suggesting that there may be a potential interference effect between the mites, which is not present for O. laevigatus. The significance of these results for the use of supplemental food sources in biological control is discussed.

The egg production of females of Ixodes ricinus (L.) was found to be closely related to the engorged body weight. The relationship was due almost entirely to the size of the blood-meal. Smaller ticks seemed to be slightly more efficient than larger ones in converting their blood-meal to eggs. Ticks, especially larvae, that overwintered in diapause did not survive as well as those that fed and then moulted in the same year. Larvae that fed and entered diapause early in the autumn did not survive as well as those that fed later in the season. A very high proportion of tick eggs hatched, either in the same year as they were laid or after overwintering. Almost all nymphs and adults became active and climbed to the top of the tubes after moulting. Although most larvae appeared to become active, only about half of them reached the tops of the tubes. This is thought to be a reflection on the fact that larvae are adapted to parasitise small rodents. It is suggested that winter temperatures may play an important part in determining the mortality rate of larvae that overwinter in the engorged state.

A comparison is made of the distribution, breeding, migration and population dynamics of Schistocerca cancellata (Serville) in South America and S. gregaria flaviventris (Burmeister) in southern Africa. The annual patterns of breeding and migration are strongly influenced by the weather and its seasonal variations. Breeding is confined to the summer rains, and outbreak regions lie in the driest parts of the distribution areas, where habitats are unstable but where high reproductive capacity allows the occasionally abundant rains to lead to plagues. The long dry season is passed in the mobile, downwind-displacing adult stage, survival being assisted by flexibility of rates of sexual maturation and of egg development. Some comparisons are made with S. gregaria gregaria (Forskål).

Aphis gossypii Glover is a polyphagous aphid pest with a worldwide distribution. However, there is evidence that on a global scale the name A. gossypii is being applied to a number of forms with different life cycles and/or host-plant associations. Morphometric variation of A. gossypii samples from crops and non-cultivated plants in many parts of the world was examined, to determine whether this variation is correlated with the hosts from which the aphids originated. Samples of A. gossypii were collected from Cucurbitaceae and Malvaceae in Europe, and from Compositae in various parts of the world. Morphometric data for 13 parameters measured from 97 clonal lineages (728 specimens) and 27 field-collected samples (313 specimens) were analysed by a series of canonical variates analyses, using the field sample/clonal lineage as grouping factor. Clonal lineages were reared on a common host in controlled conditions to standardize the effect of host and environment on morphology. The analyses provided a clear morphometric separation of the aphids originating from Compositae and those collected on Cucurbitaceae and Malvaceae, regardless of the geographical origin of the aphids and the host plant on which they were reared. This indicates that within A. gossypii there are two widely distributed host races or subspecies with different plant family associations. The taxonomic implications are discussed.

Geographic body size variation was analysed in males and females of 19 populations of the South American grasshopper Dichroplus vittatus Bruner spanning 20 degrees of latitude and 2700 m of altitude. Using mean and maximum body length of each sex and factors obtained from principal components analyses of six morphometric linear characters it was shown that D. vittatus followed the converse to Bergmann's rule latitudinally but not altitudinally where no significant trends were observed. For males, variability of body size increased with latitude but not with altitude. Both types of trends were significantly correlated with mean annual temperature and minimum annual temperature (positive correlations), and two estimators of seasonality, the coefficients of variation of mean annual temperature (negative) and mean annual precipitation (positive). Some allometric relationships also showed geographic variation. It is suggested that the observed decrease in size with latitude together with the increase in morphological variability is a consequence of a number of factors: the shortening of the growing season southwards; the increasing seasonality and climatic unpredictability; and the fact that the species exhibits protandry which contributes to smaller and more variable size in males and smaller but more constant body size in females.

An account is given of the development of aqueous gum-chloral mounting media used for mounting small arthropods on microscope slides. Berlese’s fluid is shown to have never been used by Berlese and other formulae are shown to have been randomly attributed to various authors, often incorrectly. Erroneous formulae and modifications to formulae have been followed by subsequent workers without reference to their origin. Details of the five formulae currently recommended in the literature are given and serious problems are shown to have been encountered with all of them by many workers. In many collections throughout the world gum-chloral slides are steadily deteriorating and specimens becoming irretrievably lost. Those workers advocating the use of gum-chloral aqueous media continue to propose alternative techniques in an attempt to overcome the problems they admit still occur. It is recommended that these media be used only for temporary mounts and never for specimens of taxonomic significance.

An examination was made of the movements of Pscudococcus njalensis Laing, the dominant vector of swollen-shoot disease, on cacao in Ghana. The mobile population is composed almost entirely of first-instar nymphs (92%). Movement is initiated at about 23·5°C. and activity becomes more pronounced at higher temperatures. Movement is maximal during mid-afternoon when many hundreds of insects become mobile on heavily infested trees. The density of mobile mealybugs increases from the base of the trunk and reaches a maximum at a few feet below the top of the canopy. Under experimental conditions, nymphs walked at least 28 ft. in search of favourable feeding sites and their dispersion increased proportionately with the number of canopy bridges. On cacao, adults are occasionally carried by the ant, Crematogaster striatula, Emery.

Using insects labelled with radioactive phosphorus, the assumption was confirmed that P. njalensis is capable of walking from tree to tree via the canopies of farmers' cacao. In a plantation of 8-year-old Amelonado cacao, 40 per cent, of the branches were in contact at 4-ft. spacing and about 20 per cent, at spacings between 5 and 7½ ft. No branches were in contact where the trees were spaced more than 12 ft. apart. At the closest spacing, the ratio between the number of mobile mealybugs that reached adjacent contact trees and those that did not was about 9:100, this ratio being reduced to 1 or 2:100 amongst trees growing 5 to 7½ ft. apart.

The significance of the movement of mealybugs in the canopy in relation to virus spread is emphasised. Methods of preventing vector dispersal by pruning, wide spacing and interplanting with a secondary tree crop are discussed. The importance of a closed canopy in preventing attack on the trees by Miridae is stressed.