Emergence of coffee berry borer, Hypothenemus hampei (Ferrari), from infested coffee berries (Coffea arabica) was studied in the laboratory under controlled temperature and relative humidity (RH) regimes. Low humidities (<60% RH, 25°C) provoked rapid evacuation of adults. Emergence was at a minimum at 90% RH. A steady increase in emergence occurred at values from 90 to 100% RH. Emergence was low below 20°C (90 and 100% RH) and increased markedly between 20 and 25°C. There was no significant increase in emergence above 25°C. Using a simple flight event recorder, emergence flight times were found to peak at the time of maximum daily ambient temperatures on successive days. Under constant temperature conditions successive peaks of emergence were not seen. Results are discussed in relation to control and sampling procedures.

Four dispersal phases occur during larval development of Chilo partellus (Swinehoe) on young host plants, phase 1, ballooning of newly hatched larvae when moving from egg batch to plant whorl, phase 2, ballooning of first and second instars which leave the plant whorl in the week after egg eclosion, phase 3, walking prior to stem penetration, and phase 4, walking after stem penetration. In laboratory experiments larval dispersal was density dependent during dispersal phases 1, 3 and 4 and there were clear differences between maize and sorghum in the percentage of migrating lavae and time of migration. Maize plants accommodated many more pupae than sorghum plants which suggests that the distribution of older larvae in the field can be more clumped in maize than in sorghum. Pupal weight descreased with infestation level on sorghum but seemed less affected on maize. Resistance to starvation in four combinations of temperature and relative humidity increased with age. All hatchlings survived six hours′ starvation but with considerably reduced crawling capacity. Seven- and 15-day old larvae were descreasingly affected. Older larvae survived and maintained their mobility after 48 hours. Successful dispersal will depend on host-plant, egg load, and costs of migration; these costs will change with larval age.

We have used a new technique to identify discrete genetic markers in aphids, a family in which biochemical and morphological genetic polymorphisms are rare. The new technique uses the polymerase chain reaction (PCR) to amplify random regions of aphid genomes (random amplified polymorphic DNA) and has been termed RAPD-PCR. We demonstrate the use of the technique in revealing genetic variation in four aphid species, the greenbug (Schizaphis graminum (Rondani)), the Russian wheat aphid (Diuraphis noxia (Mordvilko)), the pea aphid (Acyrthosiphon pisum (Harris)), and the brown ambrosia aphid (Uroleucon ambrosiae (Thomas)). In contrast with allozyme surveys, RAPD-PCR revealed large amounts of genetic variation among individuals in each of these species. Variation was detected among biotypes, populations, colour morphs and even individuals on a single plant. We also explored the utility of RAPD-PCR in the detection and identification within aphid bodies of two endoparasitic wasps, Diaeretiella rapae (McIntosh) and Lysiphlebus testaceipes (Cresson). The use of RAPD-PCR in species diagnostics, parasitoid detection, and population studies is discussed.

Two strains of Helicoverpa armigera (Hübner), resistant to synthetic pyrethroids, were isolated from field populations collected in the irrigated cotton growing areas of northern New South Wales: an isofemale strain, Mfo, and a composite field strain, Field. A series of crosses were undertaken between the Mfo and susceptible strains to determine the genetic basis of the resistance. Dose-responses were obtained by bioassay using topical application of fenvalerate in acetone. Considerable variation in tolerance was observed in both resistant and susceptible strains. In the Mfo strain, the major shift in resistance phenotype (33-fold resistance) was due to a single major gene with incomplete dominance. The resistance phenotype was not diluted by 23 generations of backcrossing. The major resistance phenotype could be eliminated almost completely by the addition of piperonyl butoxide which affects oxidative breakdown of the pyrethroids by mixed function oxidase (mfo) enzymes. Similar results were observed in the Field strain. Monitoring for resistance in field populations will be imprecise because a true discriminating dose does not exist for susceptible and heterozygous resistant individuals.

The sexual behaviour of Heliothis peltigera (Denis & Schiffermüller) was studied in the laboratory. Calling activity was very low during the first five hours of scotophase and then increased sharply, particularly in six-to eight-day old females. Peak activity was observed, in all ages tested, between eight and nine hours into scotophase. Calling in six-day old females was significantly higher than in two-day old females but no significant differences were detected between four-to eight-day old females. Maximal amounts of pheromone were found in the pheromone glands of five-to eight-day old females in the second half of scotophase. Male activity was monitored in a wind tunnel. There was no response to pheromone lures during the first two days, then flying activity increased sharply and maintained its high level until the eighth day. Peak activity was observed between six and eight hours into scotophase. Mating activity was very low during the first five hours of scotophase and then increased sharply, with 61.8% of the observed pairs mating between six and eight hours into scotophase. The sexual behaviour of H. peltigera was very similar to the reported behaviour of the sympatric species Helicoverpa armigera (Hübner) indicating that the reproductive separation of the two species is not affected by temporal factors, but depends mainly on the species-specific pheromone blends.

A hand-applied ‘twist-ti’ pheromone formulation containing the combined pheromones of Pectinophora gossypiella (Saunders) (Gelechiidae), Earias vittella (Fabricius) and E. insulana (Boisduval) (Noctuidae) was used in trials conducted in Pakistan from 1986 to 1988. In plots of cotton ranging in area from 2.8 to 6.0 ha, season-long control of the bollworm complex was achieved using the pheromone formulation applied alone or together with one conventional insecticide treatment, with the conventional insecticide spray programme requring up to five applications of insecticide to achieve a similar level of control. No significant differences were found in yield estimates from plots treated with pheromones compared with plots receiving conventional insecticide treatments. Significantly higher levels of boll infestation and lower yield estimates occurred in control plots where neither pheromones nor insecticides were applied.

The electrophoretic mobility of the enzyme glutamate oxaloacetate transaminase (GOT) on cellulose acetate plates was compared among sibling species of the Myzus persicae (Sulzer) group (M. persicae, M. nicotianae Blackman, M. antirrhinii (Macchiati)). M. persicae itself is monomorphic for GOT-1 (genotype ff), whereas European populations of M. nicotianae are polymorphic for this enzyme, with two forms of slightly different mobility (alleles s, f). In the samples of M. nicotianae examined, M. persicae-likeff genotypes were rare and heterozygotes (sf) were in large excess, even in samples from Greece where M. nicotianae has a regular holocycle (i.e., annual sexual reproduction). In North America, where M. nicotianae is probably entirely anholocyclic, samples of both red and green colour morphs of this species were found to be heterozygous for GOT-1. The enzyme difference can thus provide a means of distinguishing most individual specimens, including trapped alatae, of M. persicae and M. nicotianae. The anholocyclic taxon M. antirrhinii appears to be a fixed heterozygote for GOT-1 and thus resembles most M. nicotianae, but can be distinguished electrophoretically from both M. persicae and M. nicotianae by its distinctive pattern of esterases.

Studies on Culicoides spp. biting midges in south-west Scotland in 1991 revealed that Culicoides impunctatus Goetghebuer, the dominant species throughout the season (May-September), was bivoltine, with a generation period of six weeks. Unseasonal climatic conditions during much of June resulted in a low proportion of first generation females surviving to the parous stage and a reduction in the overall, expected size of the second generation. Distinct behavioural phases of the female midges, such as resting, dispersal and host-seeking, were shown to be directly related to parity states (determined by fat body condition and ovarian development) during the gonotrophic cycle. Female flight activity increased after laying the first, autogenous egg batch, whereas males never flew far from the emergence site. The mean parous rate formula was used to calculate the survival rate of second generation nulliparous females, which was 0.57 per gonotrophic cycle.

Seasonal changes in the distribution of the tsetse flies, Glossina pallidipes Austen and G. longipennis Corti, along a transect from riverine thickets out into open plains were monitored along with tsetse density, climatic factors, vegetation and host abundance. Dispersal of tsetse into open country was quantified using the mean spread. During and after the rains both species extended their distribution out into open country up to at least 3.5 km from riverine thicket areas. The mean spread of G. longipennis was greater than that of G. pallidipes. The spread of males and females was very similar, as was the spread of different age categories of parous females, but nulliparous flies and females carrying second instar larvae were under-represented in samples from open areas. This seasonal dispersal can be accounted for by random diffusion with an average root mean square displacement of about 175 m per day. Observed degrees of spread were best correlated with humidity conditions prior to sampling, but multiple regression models suggested that host abundance, vegetation as measured by Normalised Difference Vegetation Indices (NDVI), and, in the case of G. longipennis, tsetse density, were also factors in determining the degree of spread. The significance of these findings in relation to tsetse control is discussed.

A description is given of the life history, biology and feeding habits of the cetoniine beetle Pachnoda interrupta (Olivier) (Coleoptera: Scarabaeidae) studied in pearl millet (Pennisetum glaucum) fields in north-west Mali. The third instar larva of this beetle, reared from the progeny of field captured adults, is also described and figured. Yield losses to a range of beetle densities (1–5 and 10 beetles/head) on millet heads have been estimated to range from 9 to 48% in caged trial experiments. The regression equation generated from these data may be used to establish economic injury thresholds and predict losses resulting from varying beetle densities.

Anagyrus mangicola Noyes, a primary parasitoid of the mealybug Rastrococcus invadens Williams, a pest of fruit crops in West Africa, was studied under controlled conditions at 27°C and 75% r.h. Data are given on the larval stages, their morphology and duration of immature development. The sex ratios of emerging parasitoids, adult longevity, host stage preference, the relationship of the size of the emerging parasitoid to host stage and development time are also investigated.

Insecticide resistant Myzus persicae (Sulzer) employ increased esterase activity to detoxify insecticides by hydrolysis and sequestration. The amount of esterase, and hence resistance, in individual aphids can be determined by measuring either overall naphthyl acetate hydrolysis in crude homogenates, or the specific enzyme responsible (E4 or FE4) after electrophoresis or immunological isolation. The ability of a total esterase assay, done in microplates, to discriminate between susceptible (S) aphids and resistant variants (R1, R2) with different amounts of E4/FE4, was compared with the resolving power of the more elaborate immunoassay technique. The immunoassay gave the better discrimination between variants, resolving them all with greater than 95% confidence, with particularly good separation of R1, from S. The microplate assay using crude homogenates, although a poorer discriminator, identified most of the very resistant (R2) aphids, and provided a robust and widely accessible method for broadly representing the resistance of field populations.

Genetic methods to eliminate females prior to releasing sexually sterilized males in sterile insect technique programmes generally involve the translocation onto the Y chromosome of a readily selectable gene (here designated F). However, such strains often show instability with regard to sexual dimorphism. Concerted attempts to determine the most probable causes of such instability have rarely been successful, and appropriate countermeasures have generally not been implemented. We have developed a computer model which simulates the progression of instability in such strains. Here we simulate the effects of contamination in association with a range of genetic and biological parameters and assess the patterns and rates of progression of the ensuing instability. A single event of contamination alone was found to contribute relatively little to the progression of instability and invariably resulted in an equilibrium within the population. However, strong effects were produced by reduced fitness and mating competitiveness of both the f/f genotype and the translocation carriers, a reduction in the parameters involving the f/f genotype resulting in the virtual elimination of f/f, while a reduction in the translocation parameters had the opposite effect of virtually eliminating the F/ – phenotype. The sex ratio was affected only by a change in the relative fitness of the f/f genotype and the translocation. Several characteristic patterns contributed to distinguish clearly the effects of contamination from those of male recombination in unstable genetic sexing strains. With such knowledge appropriate measures may be taken to counter or alleviate the effects of instability in mass reared genetic sexing strains.

Pupae and larvae from various recorded hosts of the cecidomyiid Asphondylia gennadii (Marchal), a pest of carob on Cyprus, are found to be anatomically similar. These are redescribed and illustrated. The species appears to be a Palaearctic generalist species analogous to the Nearctic Asphondylia websteri Felt. Asphondylia capsici Barnes (Syn. n.) is considered a new junior synonym of A. gennadii. An unnamed soybean pod gall midge in Japan appears also to be identical to A. gennadii.

Chemical signals produced by leaves of stinging nettle (Urtica dioica), goat willow (Salix caprea) and tomato (Lycopersicon esculentum) attracted Anthocoris nemorum Linnaeus in a Y-tube plexiglass-walled olfactometer. A. nemorum reacted to odours of chloroform extracts of tomato foliage but not to water or methanol extracts. On the other hand, methanol or water extract of U. dioica attracted A. nemorum, but it was not attracted to chloroform soluble fractions of this plant. Adult A. nemorum could not distinguish between odour released by the aphids Myzus persicae (Sulzer) or Brevicoryne brassicae Linnaeus (Homoptera: Aphididae) and leaf odours emitted by Brussels sprout (Brassica oleracea). However, A. nemorum reacted to and distinguished between odours coming from either Tetranychus urticae Koch or T. cinnabarinus Boisduval (Acari: Tetranychidae) and from clean French bean (Phaseolus vulgaris) leaves.

Adult grasshopper (Orthoptera: Acridoidea, Tetrigioidea Tettigonioidea) assemblages were sampled at four localities in south-eastern Shoa, around Debre Zeit, Ethiopia, between August 1986 and September 1988. Three localities were followed for the whole period but the fourth locality was followed only between August 1986 and July 1987. Samples were taken fortnightly from both black and light soil fields of tef and wheat crops, each in three replicates. The fauna consisted of twenty-nine taxa of both short- and longhorned grasshoppers, twenty-six of which are identified to species. Over 70% of the species belong to Acrididae and most of them are either pests or potential pests of cereal crops. Species richness, diversity and dominance within and between sites and seasons did not differ much during the two year period. The composition and structure of the assemblage was relatively constant. Despite fluctuation in abundance, dominant and common species remained common and rare species rare. Aiolopus longicornis Sjöstedt was most dominant. Some species are more abundant on black soil than on light soil and vice versa. The results are compared to grasshopper assemblages studied elsewhere.