In studies in Nigeria, all instars of Zonocerus variegatus (L.) were found to be strongly attracted to flowers of the common exotic composite weed Chromolaena odorata. Experiments in the field and with caged nymphs suggested that the attraction is due to a volatile compound(s) concentrated in the conspicuous stigmas and released when the buds open. Although very palatable, the flowers seemed inadequate as food, and most of the nymphs roosting on C. odorata even during the flowering season had fed on leaves of C. odorata or other plants. Feeding diminished the attraction to the inflorescences in experimental cages, and of the field nymphs attracted between 11.00 and 15.00 h, a significantly higher proportion than on other plants had relatively empty foreguts. The numbers of field nymphs attracted were maximal at 08.00–10.00h and minimal at 11.00–12.00 h. Both in the cages and in the field, interest in the inflorescences diminished after about 17.00 h, when the highest points within reach are being looked for as roosting sites. Reduction of C. odorata around plantations is unlikely to lessen crop damage by Z. variegatus, but insecticides for Z. variegatus control could be applied conveniently to the tops of C. odorata at roosting time during the flowering season.

A silicone membrane was developed to meet the feeding requirements of Glossina palpalis palpalis (R.-D.). Starting with a total of 1050 females, a self-sustaining colony fed on defibrinated pig blood was established. The colony performance in terms of mean daily mortality, mean pupal weight and fecundity was evaluated. With the exception of June 1976, the mean daily mortality ranged between 0·40% and 1·20%. During June 1976, bacterial infections caused a sudden increase in mortality. Escherichia coli and Staphylococcus spp. were predominant in the gut of dead and diseased flies. Pure cultures of either organism caused the same symptoms in teneral flies within one week after uptake of an infected blood-meal. The weight of the offspring significantly decreased with increasing female age. Starting with a mean pupal weight of 30 mg there was a decrease of 4–6 mg over a period of 90 days. The innate capacity for increase in numbers (r-) was calculated based on data from 340 females. The value of rm = 0·0095 would result in a 32-fold increase of the colony in one year.

Adult male Tribolium castaneum (Herbst) secrete an aggregation pheromone that is attractive to both sexes. The responses of T. castaneum to different pheromone concentrations (0.5, 1.0, 2.0, 4.0 and 8.0 mg/septa) were tested in the laboratory. In general, pheromone-baited pitfall and probe traps were over 50% more effective than unbaited traps. A curvilinear relationship between numbers trapped and pheromone concentration indicated that 2.0 mg of pheromone per trap elicited an optimum response. The proportion of marked beetles released in 2.5 m × 0.3 m × 0.4 m trough, filled with wheat and caught by unbaited probe traps, declined with distance from release point, whereas pheromone traps captured a similar proportion up to 2.0 m from the traps. Tracks of T. castaneum responding to different pheromone concentrations in still and moving air in a 2.5 m × 0.4 m olfactometer indicated that the aggregation pheromone stimulated the beetles to walk faster at higher concentrations, to increase the frequency and magnitude of turning and to decrease track reversal distances and distances between turns. The behavioural responses of the beetles to the pheromone in still and moving air were similar, indicating chemotaxis as the major orientation mechanism used by T. castaneum to locate an odour source. The beetles showed greater orientation efficiency within a discrete pheromone plume than a diffuse plume.

Although several factors influence herbivore insect distributions at any particular scale, the most important determinants are likely to differ between species with different life histories. Identifying what these factors are and how they relate to life history forms an important component of understanding the population dynamics of species, and the habitat requirements necessary for their conservation. The pupal stage of two wild silk moth species, Gonometa postica Walker and G. rufobrunnea Aurivillius (Lepidoptera: Lasiocampidae), is the target of harvesting practices that are totally dependent on the availability of pupae from natural populations. Consequently, and partly due to poor knowledge of the species' biology, there is substantial interest in the distribution of pupae among and within trees for both these species. It was investigated whether between- and within-tree pupal distributions in these two species are non-random, and if so, whether there are relationships between pupation site use and tree characteristics such as tree size, available pupation space and branch position. Between-tree patterns in pupal abundance were random in terms of absolute spatial position, but markedly non-random with respect to tree characteristics. The apparent G. postica pupae were aggregated on large larval host plants, whereas the cryptic G. rufobrunnea pupae were aggregated on non-host plants. These patterns reflect the life history differences of the two species. In contrast, at the within-tree scale, branch position, aspect and tree shape influenced pupation site choice similarly for both species. These patterns might be related to microclimate. Documenting between-tree and within-tree patterns in Gonometa pupal distributions is the first step towards explaining pupation site selection, as well as identifying possible evolutionarily selective factors in the species, and generating testable hypotheses from these.

Psila rosae (F.) overwinters in Britain in both the larval and pupal stages. Overwintering pupae formed in October and November at soil temperatures of between 10 and 16°C entered diapause. A period of similar temperature in the laboratory during the prepupal stage also caused pupae to enter diapause. Overwintering larvae continued to feed and gain weight; they pupated in early spring at soil temperatures of 2–8°C but did not enter diapause. The sensitivity to diapause-inducing conditions decreased between November and March, associated with changes in developmental temperatures and pupal weight. The differential effects of temperature on larval, pupal and diapause development together serve to synchronise adult emergence from the overwintering population. The mechanisms which allow overwintering by a variable proportion of larvae and pupae also provide the opportunity for the development of a third generation of adult flies in October and November.

The responses of Glossina fuscipes fuscipes Newstead and other Diptera to carbon dioxide were studied in linear and dense forests along the shores of Lake Victoria, Kenya. Flies were caught in biconical traps and were intercepted with electric nets while in flight near traps. Carbon dioxide dispensed at a high rate (5 l min–1) in linear forest failed to increase the numbers of tsetse attracted to or caught in traps. In contrast, catches of non-biting Muscidae, Stomoxyinae and Tabanidae were improved by up to 11 times. Inside dense forest, carbon dioxide released at half this rate increased both the numbers of female tsetse attracted to a trap and the catches in a trap by about 2–3 times. Catches of male tsetse were, however, not affected. Striking improvements for other Diptera were also realized (up to 102 times). Under a variety of conditions, unbaited biconical traps attracted many Diptera to the vicinity of a trap, but caught few flies due to low capture efficiencies (typically less than 10%). In contrast, efficiency estimates for G. f. fuscipes were good, varying from 37 to 82% in different habitats and seasons. These results are discussed in relation to the search for practical odour attractants for riverine tsetse.

Pediobius furvus (Gah.) (Eulophidae) is a parasite of the pupae of Pyralid and Noctuid stem-borers on graminaceous crops in Africa between 17°N and 17°S. It co-exists with the other pupal parasites Dentichasmias busseolae Heinr. and Procerochasmias nigromaculatus (Cam.) (Ichneumonidae) and Hyperchalcidia soudanensis Steffan (Chalcididae), but it is more abundant below 4000 ft where P. nigromaculatus does not occur. Mating follows a courtship dance, and oviposition occurs in any part of the host pupa. The life-cycle is completed in 18–20 days at 30°C, and up to several hundred adults may emerge from a single host pupa, the most suitable pupae being 2–3 days old at the time of oviposition. Longevity was improved when sucrose was provided as food. Host pupae outside the stem were parasitised, but puparia of Diptera and cocoons of Apanteles sesamiae Cam. (Braconidae) were not parasitised in the laboratory. Pupae formed inside cocoons were not attacked. Pediobius furvus has become established in Madagascar on Sesamia calamistis Hmps, and is considered promising for biological control of graminaceous stem-borers in other countries.

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.

A trail pheromone, methyl 4-methylpyrrole-2-carboxylate (M4MP2C), of Atta texana (Buckley) was tested in the laboratory as a possible component of attractive poison bait for the leaf-cutting ants A. cephalotes (L.), A. sexdens (L.) and Acromyrmex octospinosus (Reich). For all three species, M4MP2C when impregnated onto paper discs increased pick-up of the discs. It also increased pick-up by Atta sexdens of a citrus-pulp bait. The addition of M4MP2C made them easier to find, although at high concentrations it was repellent. It did not affect the average number of ant investigations before the bait was picked up. The pheromone remained on citrus-pulp bait in active concentrations for approximately four days. To test -the effect of M4MP2C as a foraging stimulant for A. cephalotes, an apparatus was constructed in which the ants passed in single file over a transparent section of the trail where they were counted with a photoelectric cell. When bait impregnated with M4MP2C was placed on the foraging table, large increases in activity were recorded away from the nest but only small increases were recorded in the nest and at the nest entrance. When air containing M4MP2C vapour was injected into the fungus chamber, an increase in activity was recorded at the nest entrance, but this increase was not repeated when known amounts of the pheromone impregnated onto baits of filter-paper discs were added directly to the fungus chamber. It is suggested that factors other than M4MP2C are also involved in the stimulation of foraging activity. The experiments suggest that M4MP2C could play some part in the formulation of an attractive bait for the control of leaf-cutting ants.

Earlier work in Nyanza Province, Kenya, had led to the conclusion that riverine communities of Glossina palpalis fuscipes Newst. were permanently hungrier than lake-side communities. This was based on analysis of catches (percentage of teneral flies in the whole catch, and percentage of females among non-teneral flies) and on a behaviour criterion (percentage of non-teneral males caught on the party), but subsequent observations in the two types of habitat, in which a different area was used to represent the lake side, showed the lake-side flies to be slightly smaller than the riverine flies and not to differ in fat content, and a further investigation was accordingly made.

Puparia were collected on three dates between January and March 1958 and their surface area measured. A measure of the thoracic surface and fat content was taken of all adults emerging. Non-teneral flies were collected, for comparison, about two weeks later than the puparia.

In all samples, the riverine puparia were significantly larger than those from the lake side, and flies that emerged showed a comparable difference in size, but not in fat content corrected for size. Non-teneral riverine flies were slightly larger than lake-side ones but the difference was less than half that shown by the puparia and the teneral flies obtained from them. Evidence is adduced to show that this discrepancy is due to elimination of the lower size-groups in the lake-side community. Estimates of fat content of non-teneral flies support the conclusion that the lake-side community was under stress as compared with the riverine one, and analysis of available fly-round data from the lake side also suggests stress conditions.

The lake-side results are at variance with those from the site used in the earlier work. Available meteorological data show that the average temperature during February and March is 2°C. higher at the present site than at the former; such difference may directly cause the stresses that appear to be operating in the present instance.

The results suggest that the percentage of non-teneral males caught on the party has a real meaning in terms of nutritional status, and that it is also a very responsive indicator, but that the proportions of tenerals and of female nontenerals may not be simply related to the nutritional state as had hitherto been supposed.

Over 3,000 examples of G. palpalis were age-grouped and dissected for T. vivax over a period of a year. The incidence of infection throughout was highest in Age-group 3 and lowest in Age-group 1. There was a marked seasonal fluctuation, the incidence being highest during the months of heavy rainfall, i.e., August to October, and lowest in the driest.

It has been suggested that the rise in the rate of infection during the rains is merely due to the increasing average age of the fly population, but by the method of age grouping it is shown that this is not the case.

The degree of infection in G. palpalis in Sierra Leone is comparable with that of G. tachinoides in Nigeria.

It is not thought that the seasonal variation in the incidence of infection can be ascribed to changes in the type and abundance of food. The true cause of the fluctuating incidence of infection like the source of infection is unknown.

The failure to recognize seasonal differences in the rate of infection has led to some important practical misconceptions.

Hydroxamic acids (Hx) contained in wheat are active mutagens which play an important role in the defence of the plant against aphids. Random amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR) dominant markers were used to assess genetic variability in the aphid Sitobion avenae (Fabricius) in relation to hydroxamic acid levels in their host-plants. Colonies of aphids belonging to a single RAPD–PCR profile were grown on different host-plants differing in their Hx content under greenhouse conditions. The RAPD–PCR phenotypic pattern showed the appearance of two new RAPD–PCR variants after four to five generations of exposure to wheat cv. Chagual (high Hx levels), one after exposure to wheat cv. Huayún (low Hx levels), and none after exposure to oat (lacking Hx). Differential appearance of new RAPD–PCR aphid phenotypes also occurred on field-grown wheat. While the overall phenotypic ‘richness’ diminished during the season, the number of RAPD–PCR phenotypes decreased on cv. Huayún and increased on cv. Chagual. The preferential appearance in the field and in the greenhouse of new RAPD–PCR phenotypes of S. avenae on cv. Chagual is discussed on the basis of mutagenesis induced by hydroxamic acids and by the products of their transformation within the aphid. Aphid abundance is interpreted in terms of antixenosis and antibiosis by hydroxamic acids. The appearance on cv. Chagual of phenotypes first detected on cv. Huayún was accounted for by intercrop migrations.

Herbivorous insect species with narrow diet breadth are expected to be more prone to genetic differentiation than insect species with a wider diet breadth. However, a generalist can behave as a local specialist if a single host-plant species is locally available, while a specialist can eventually behave as a generalist if its preferred host is not available. These problems can be addressed by comparing closely related species differing in diet breadth with overlapping distributions of insect and host populations. In this work, diet breadth, genetic diversity and population differentiation of congeneric aphid species from southern beech forests in Chile were compared. While at the species level no major differences in genetic diversity were found, a general trend towards higher genetic diversity as diet breadth increased was apparent. The aphid species with wider diet breadth, Neuquenaphis edwardsi (Laing), showed the highest genetic diversity, while the specialist Neuquenaphis staryi Quednau & Remaudière showed the lowest. These differences were less distinct when the comparisons were made in the same locality and over the same host. Comparison of allopatric populations indicates that genetic differentiation was higher for the specialists, Neuquenaphis similis Hille Ris Lambers and N. staryi, than for the generalist N. edwardsi. Over the same host at different locations, genetic differentiation among populations of N. edwardsi was higher than among populations of N. similis. The results support the assumption that specialists should show more pronounced genetic structuring than generalists, although the geographical distribution of host plants may be playing an important role.

Species distribution models (SDMs), which are well established in many fields of biological research, are still uncommon in the agricultural risk analysis of pest insects. To exemplify the use of SDMs, we investigated the influence of environmental factors on the occurrence of Hyalesthes obsoletus Signoret (Hemiptera: Cixiidae). The planthopper is the only known vector of the grapevine yellows disease ‘bois noir’. The study was conducted in 145 locations in the Baden region of southwest Germany. The planthopper was surveyed on host plant patches, consisting of stinging nettle and/or bindweeds. We used a stratified modelling framework where (1) species presence–absence data were related to an extensive environmental dataset using logistic regressions; and (2) different types of average models were developed based on an information theoretic method. The results show that the incidence of H. obsoletus is associated to above- as well as below-ground environmental factors, particularly to the amount of fine soil and average annual precipitation. This result was consistent across all average models. The relative importance of other environmental variables was dependent upon the average model under consideration and thus may vary according to their intended use, either the explanation of habitat requirements or the prediction and mapping of occurrence risks. The study showed that SDMs offer a quantification of species’ habitat requirements and thus, could represent a valuable tool for pest management purposes. By providing examples of current issues of grapevine pests in viticulture, we discuss the use of SDMs in agricultural risk analysis and highlight their advantages and caveats.

Mortality estimates are central to understanding tsetse fly population dynamics, but are difficult to acquire from wild populations. They can be obtained from age distribution data but, with limited data, it is unclear whether the assumptions required to make the estimates are satisfied and, if not, how violations affect the estimates. We evaluate the assumptions required for existing mortality estimation techniques using long-term longitudinal ovarian dissection data from 144,106 female tsetse, Glossina pallidipes Austen, captured in Zimbabwe between 1988 and 1999. At the end of the hot-dry season each year, mean ovarian ages peaked, and maximum-likelihood mortality estimates declined to low levels, contrary to mark-recapture estimates, suggesting violations of the assumptions underlying the estimation technique. We demonstrate that age distributions are seldom stable for G. pallidipes at our study site, and hypothesize that this is a consequence of a disproportionate increase in the mortality of pupae and young adults at the hottest times of the year. Assumptions of age-independent mortality and capture probability are also violated, the latter bias varying with capture method and with pregnancy and nutritional status. As a consequence, mortality estimates obtained from ovarian dissection data are unreliable. To overcome these problems we suggest simulating female tsetse populations, using dynamical modelling techniques that make no assumptions about the stability of the age distribution.

Tribolium castaneum is one of the most economically important insects that damages stored products. The effects of several infested or uninfested raw feed materials (wheat bran, coarse wheat meal, corn feed flour), feed products (compound feed for pigs and for laying hens) and flour mixed with brewer's yeast on the food-searching behaviour of T. castaneum adults were studied in a total of 48 combinations. Preference and olfactometer tests revealed that all the tested uninfested and intraspecific infested substrates were significantly more attractive to T. castaneum than the control (represented by part of an arena or olfactometer arm without substrate). We determined that all infested substrates were 2–9 times more attractive than uninfested in the preference test, while in the olfactometer test, they were 3–8 times more attractive. In comparing the attractiveness of the infested and uninfested substrates, in both tests wheat bran was found to be the most attractive substrate to T. castaneum adults and coarse wheat meal the least. The results of the present study contribute to our knowledge of how raw feed materials and products influence the behaviour of T. castaneum and their susceptibility to infestation, and indicate the possible utilization of wheat bran in monitoring processes of T. castaneum in pest management programmes.

Experiments were conducted with Trinidad strains of Oryzaephilus surinamensis (L.) and O. mercator (Fauv.), the average sizes of which were smaller than those given in the literature. Limited observations on their biology on cereal products showed that whereas the egg-production of O. mercator was comparable with that recorded by other workers under similar conditions, that of O. surinamensis was much lower.

Larvae of both species were able to complete their development on raw and yellow-crystal sugar, but there was a high mortality among those of O. surinamensis. Both species showed very low oviposition rates on sugar and this, together with a high larval mortality, would indicate that infestations of O. surinamensis on these products would die out. O. mercator, on the other hand, could multiply very slowly. Oviposition rates rise rapidly when females return from sugar to cereal products.

Unrefined sugars should accordingly not be disregarded as sources of Oryzaephilus infestation, especially in the humid tropics.

In this short report it is proposed to deal exclusively with the blood-sucking insects and other Arthropods which are, or may be, implicated in the transmission of disease in man and animals. In this connection, however, certain aspects, geographical and geological, are necessarily involved, but these will be introduced only when considered to be directly relevant to the main issue.

The inability to distinguish the females of East African Synphlebotomus spp. (P. martini Parrot, P. vansomerenae Heisch, Guggisberg & Teesdale and P. celiae Minter) was a major constraint on epidemiological studies of visceral leishma niasis (VL) in the region. An intensive morphometric study of two sympatric Synphlebotomus spp. (P. martini and P. celiae) in a VL focus of southern Ethiopia based on both isofemale broods and wild-caught parent specimens (identified by their male progenies) showed that laboratory-bred females were separable by eight morphological characters, but only two (labrum length and labrum length/wing length ratio) successfully distinguished the wild-caught parent females of the two species; the latter were used to identify wild-caught Synphlebotomus females from southern Ethiopia (Aba Roba) during subsequent epidemiological studies. A further difference between the two species was seen in the length of the spermathecal ducts.

It has been stated by Malloch and other authors that the superficial differences between the various species of Simulium in the adult stage are often so minute as to be discernible only after a very careful study of the genus. Previous studies had led the writer to believe that the characters of the pupal respiratory filaments would prove to be of constant specific value, but further investigation has caused this view to be modified with regard to the actual branching, though the structure of the chitinous wall and the general appearance still seem to be constant specific characters.