The results of field trials in the UK are reported, investigating the hypothesis that the disruption of proleg clasping in lepidopteran larvae by sublethal doses of the formamidine pesticide chlordimeform contributes significantly to a control mechanism. Pieris brassicae (L.) was used as a model pest. Topically dosed third-instar larvae, placed on cabbage plants, became excited and many fell. Although the behavioural symptoms were reversible within 24 h, fallen larvae rarely re-established themselves on the plants. The ED50 halving the initial population was similar to the ED50 for proleg disruption, emphasizing the importance of the latter as a major cause of the former. Arthropod or bird predation was not shown to increase following chlordimeform treatment. However, inclement weather did enhance the detaching effect of treatment and also its delayed effects on larval development and survival.

In studies in Western Australia, temperatures in air and one- and two-litre pads of cattle dung set out weekly and ranging from one to 20 days old were measured hourly for 438 days over all seasons, producing 1437 day x dung-pad observations. Daily maximum temperatures (and hence thermal accumulation) in cattle dung pads could not be accurately predicted using meteorological data alone. An accurate predictor of daily maximum dung temperature, using multiple regression analysis, required measurement of the following factors: maximum air temperature, hours of sunshine, rainfall, a seasonal factor (the day number derived from a linear interpolation of day number from day 0 at the winter solstice to day 182 at the preceding and following summer solstices) and a dung-pad age-specific intercept term, giving an equation that explained a 91·4% of the variation in maximum dung temperature. Daily maximum temperature in two-litre dung pads was 0·6°C cooler than in one-litre pads. Daily minimum dung temperature equalled minimum air temperature, and daily minimum dung temperatures occurred at 05.00 h and maximum temperatures at 14.00 h for one-litre and 14.30 h for two-litre pads. Thus, thermal summation in a dung pad above any threshold temperature can be computed using a skewed sine curve fitted to daily minimum air temperature and the calculated maximum dung temperature.

The effect of dung burial by the African dung beetle Catharsius tricornutus De Geer on the survival and size of the dung-breeding African fly Haematobia thirouxi potans (Bezzi) was examined in the laboratory at 25°C using 1-litre pads of cattle dung. The experiment included a set of dung pads which were exposed to infrared radiation for 12 h per day to mimic the heating effect of solar radiation. C. tricornutus is a large (1–2-g live weight) dung beetle, and moderate numbers can completely bury dung pads within 24 h of pad colonization. Dung burial was proportional to the number of pairs present (range 0–8 pairs per pad), but the level of burial was reduced in the presence of infrared radiation. Dung pads lost moisture with time, and the rate of desiccation of unburied dung increased with the amount of dung burial and under infrared radiation. Mortality in the immature stages of H. t. potans increased with increasing levels of dung burial and with exposure of pads to infrared radiation. The timing of addition of dung beetles (i.e. before or after egg hatch) did not affect fly survival. At moderate levels of dung burial, fly larvae were killed directly by beetle activity and at high levels of dung burial, fly larvae also perished due to an unfavourable physical environment associated primarily with moisture stress. Infrared radiation killed immature flies and increased the level of moisture stress. There was a low level of survival in dung buried by the beetles under these unnatural laboratory conditions. Stunting of surviving flies was associated with reduced levels of moisture in the core of the unburied dung and was observed when the level of dung burial was >60% in ambient conditions and >40% under infrared radiation.

A total of 134 species of Coleoptera (100 of staphylinids, 13 of hydrophilids and 21 of histerids) was extracted from pads of cattle dung placed in four contrasting habitats in both Hluhluwe Game Reserve, Natal, South Africa, and the surrounding pastoral regions. Pads were exposed to colonists for 24 h on eight occasions over one year. Forty-six species and species complexes were captured in numbers sufficient to permit analysis of their distribution patterns. Of 27 species significantly influenced by vegetation type, 22 were more abundant in unshaded situations and five more abundant in situations shaded by high profile vegetation. The total numbers of individual predatory staphylinids were evenly distributed between vegetation types, but members of coprophagous staphylinid and other predatory taxa were more numerous in unshaded situations. Of 13 species significantly influenced by soil type, six were more abundant on clay and seven more abundant on deep sand. The total numbers of individual coprophagous oxyteline staphylinids were greater on clay than on sand, but the members of predatory taxa, including staphylinids, were evenly distributed across soil types. Of 14 species showing significant seasonal changes in abundance, 13 were more abundant in hot wet months and one in cool dry months. The total numbers of hydrophilid individuals were greater in the cool dry season, but the other taxa were active predominantly in the rainy season. Most species were present in similar numbers in both the game reserve and pastoral regions. Enclosure of dung pads within wiremesh cones to exclude large dung-burying beetles resulted in reduced colonization by most beetle species regardless of their size.

Large colonies of holocyclic Rhopalosiphum padi (L.) were sampled in May-June in 1985 and 1986 from the principal host, Prunus padus, in various parts of Britain, mainly in the south-east. They were tested electrophoretically using nine enzymes representing 14 putative genetic loci. Only two loci (14%) were polymorphic (GOT, glutamate-oxaloacetate transaminase, and SORDH, sorbitol dehydrogenase), the remainder being monomorphic. Allele and genotype frequencies at each locus were generally similar both spatially and temporally, and genotype frequencies were close to Hardy-Weinberg expectations. The low level of genetic variability may reflect population bottlenecks which have purged most of the variation and which have been imposed by the distribution of P. padus, especially in the south of Britain where the tree is generally scarce. In addition, it is probable that adverse climatic conditions directly affect winter survival of anholocyclic populations of the aphid and thus also reduce variability. In the long term, such bottlenecks would tend to preclude the maintenance of effectively neutral enzyme variants that arise within populations. The similarity of allele and genotype frequencies may reflect the highly migratory behaviour of R. padi. Thus, in southern Britain, where P. padus is generally much rarer in comparison with the north of the country, R. padi inter-population gene flow is still sufficient to alleviate the influences of genetic drift and possible directional selection on the allelic variation that remains.

Clones of Sitobion avenae (F.) collected in southern England in 1983 and 1984 were subjected to sexual-inducing conditions in the laboratory (12 L:8 D photoperiod at 15°C and/or 8 L:16 D photoperiod at 12°C). Most clones were continuously parthenogenetic under these conditions; some clones produced males only (androcyclic), and the same behaviour was observed under field conditions in the autumn of 1983. In contrast, over 90% of the clones collected from Scotland in 1984 were holocyclic (i.e. cyclically parthenogenetic). Fundatrices from intra- and interclonal matings were obtained. Those from interclonal matings were significantly more fecund than fundatrices from intraclonal matings. Examination of the descendants of these fundatrices indicated that both life-history strategy and migratory tendency were genetically-determined.

In the ecologically sensitive Sahel of West Africa, two major crop pests, Helicoverpa armigera (Hübner) and Heliocheilus albipunctella (de Joannis), are attacked by Cardiochiles variegatus Szépligeti and C. sahelensis sp. n., respectively. The twelve Cardiochiles species present in the Sahel are revised, and a key is given for their identification. Five of these species (C. calvus sp. n., C. coelofrons sp. n., C. exiguurus sp. n., C. nixoni sp. n. and C. sahelensis sp. n.) are described, and C. striatus Brues is made a synonym of C. punctatus Szépligeti. Host relationships of the genus worldwide are discussed and the host records, principally involving Pyralidae and Noctuidae, collated. The known biology is summarized from the literature on the North American species C. nigriceps Viereck, and a comprehensive bibliography on the genus is given.

Dans la région écologiquement difficile du Sahel de l'Afrique de l'Ouest, on a découvert que deux importantes variétés d'insectes nuisibles à la culture, Helicoverpa armigera (Hübner) et Heliocheilus albipunctella (de Joannis), sont attaquées respectivement par Cardiochiles variegatus Szépligeti et C. sahelensis sp. n. Les douze espèces de Cardiochiles qui se trouvent dans la région du Sahel sont réétudiés, et une clé est formulée afin de les identifier. Cinq de ces espèces (C. calvus sp. n., C. coelofrons sp. n., C. exiguurus sp. n., C. nixoni sp. n. et C. sahelensis sp. n.) sont décrites, et C. striatus Brues devient synonyme du C. punctatus Szépligeti. Les rapports universels de ces genres d'hôtes sont discutés ainsi que la comparaison des rapports d'observation, principalement en ce qui concerne les pyralides et les noctuides. La biologie actuelle est resumée de la littérature sur l'espèce C. nigriceps Viereck nord américain et une vaste bibliographie du genre est présentée.

The rate at which gregarious nymphs of Schistocerca gregaria (Forskål) lose the tendency to form groups after different periods of isolation was measured. There was a marked loss of social grouping after isolation for 24 h. The fall in level of grouping was highly significantly correlated with the number of days the nymphs had been isolated. Further experiments showed that the extent of loss of grouping behaviour could be significantly modified by the length of time the nymphs spent in crowded conditions before they were isolated, but the density during previous crowding did not have a consistent effect on reduction in grouping. It had been previously considered that S. gregaria nymphs lose very little of their gregarious tendency once it is acquired; this is now shown not to be the case. The behaviour of this species is very responsive to the social environment, whether the locusts are learning to form groups or are losing that tendency.

A dense layer of large insects in windborne, migratory flight was observed by radar in the Tilemsi Valley in Mali between about 23.00 and 02.00 h on 10–11 October 1978. The volume density, height of flight, area density, displacement speed and direction, orientation and migration rate were determined for the overflying insects. Light-trap catches and radar signatures provided strong evidence that the pest grasshopper Diabolocatantops axillaris (Thunberg) contributed to the overflying layer. Other species contributing probably included Oedaleus senegalensis (Krauss) and possibly Ochrilidia spp. For D. axillaris, the migration can be regarded as a search for overwintering sites by adults in reproductive diapause, and thus is an example of C. G. Johnson's Class III migration. Estimated trajectories placed the probable source areas of the overflying grasshoppers in the Gourma, about 150 km west-south-west of the radar site. Migration direction was approximately downwind, but the grasshoppers showed a degree of common orientation towards the east-south-east, which added a southwards component to their displacement. At 02.30 h on the same night, a very dense line-concentration associated with a wind-shift moved across the radar site, and insects still in flight probably became entrained in this wind convergence zone and added to the line-concentration. Other evidence of long-distance, windborne migration in D. axillaris was adduced from records of captures on ships at sea, mainly off the West African coast. The consequences of downwind displacement and concentration for grasshopper ecology and pest management are discussed. The migration behaviour of D. axillaris and other grasshopper species probably reduces migration losses by the efficient location of new habitats and forms an essential part of life-history strategies for survival in a sahelian environment.

The synthetic attractant pheromone 6-acetoxy-5-hexadecanolide in a formulation of 20 mg containing 5 mg of the active (−)-(5R,6S)-isomer in an effervescent tablet produced a high, positive overall response by gravid females of Culex quinquefasciatus Say when the mosquitoes were exposed to the pheromone in established breeding sites in western Kenya. Significantly more females (82%) oviposited around the pheromone source compared to a control. The activity of the pheromone persisted in the established breeding place for four days after application. The addition of the insect growth regulator S-31183 (2-[1-methyl-2-(4-phenoxyphenoxy)ethoxy]pyridine) to the formulation did not affect the activity of the pheromone. Newly-made breeding sites exposed domestically were not attractive initially for oviposition by gravid females but, after 18 days, they became more attractive. Trays treated with synthetic pheromone diverted females from similar unbaited trays exposed within 10 m. A sample of larvae taken from a site treated with pheromone and insect growth regulator showed 100% mortality by the pupal stage. Thus, the efficacy of the pheromone has been demonstrated for the first time in the field and the possibility of using this material in combination with a ‘safe’ insecticide confirmed.

Seasonal patterns of abundance of Musca vetustissima Walker and scarabaeine dung beetles were measured at Busselton in south-western Australia for two years before and three years after, the introduction and establishment of two species of summer-active dung beetles, Oniticellus pallipes (F.) and Onthophagus binodis (Thunberg). Previously, only a single winter-active native dung beetle species, O. ferox Harold, occurred in this area. The mean dry weight of dung beetles trapped in December (early summer) was unaffected by the establishment of the additional species, and fly populations remained high. In January, however, dung beetle dry weight increased more than 60-fold and M. vetustissima abundance fell to 12% of its previous value, essentially halving the duration of major fly problems in the area. Virtually no flies emerged from cattle dung after December, when dung beetle activity reduced egg-adult survival of M. vetustissima to only 0·5%. It is proposed that better M. vetustissima control could be achieved in much of south-western Australia by introducing additional dung beetle species that are abundant in November and December.

Inundative releases of the indigenous egg parasitoid Trichogrammatoidea cryptophlebiae Nagaraja were made against Cryptophlebia leucotreta (Meyrick) in two sweet orange orchards in the Transvaal lowveld, South Africa. The rate of parasitism was raised to similar levels in the two release areas, but there was a significant decrease in crop damage in only one of them. Although the larval population was twice as large in a control orchard, the losses there were compensated for by a larger total crop. Three explanations for the different performances of the parasitoids are examined. Movement away from release areas was not apparent. Rates of parasitism at the tops or bottoms of trees or at the four cardinal aspects were not significantly different overall but should have been to compensate for the linear increase in numbers of host eggs with height, and the larger numbers on the warmer northern and eastern sides of trees. Parasitism was higher at the tree tops than at the bottoms in the orchard that lost the least fruit. The stochastic processes governing host-egg distribution on fruit were also important. Pest density was higher in the release areas than the control, and eggs were distributed more contagiously in the orchard with the most crop loss.

Through repeated sampling in maize planted on different dates over different seasons in South Africa, it was shown that damage by Busseola fusca (Fuller) to plant parts other than the whorl had an important influence on yield. Damage to plants in the period after tasselling was shown to be important. The number of larvae in the plant was a weak estimator of expected yield losses.

Treatment of rice fields in Sri Lanka with monocrotophos at 10 mg/litre or pirimiphos-methyl at 0·1 mg/litre gave a selective advantage to larvae of Anopheles subpictus Grassi and A. nigerrimus Giles carrying the oxidase- and acetylcholinesterase-based resistance genes, respectively. However, this selective advantage was apparent for less than ten days after spraying. There was no mortality of any larval instar with monocrotophos 12 days after spraying, and no fourth-instar larval mortality with pirimiphos-methyl 17 days after spraying. The chemical degredation curves for these compounds indicated that this short duration of efficacy was due to the instability of the compounds in water under field conditions. In contrast, the new growth regulator S-31183 (2-[1-methy1-2-(4-phenoxyphenoxy)ethoxy]pyridine) sprayed at 0·1 mg/litre conferred no selective advantage to larvae with either resistance mechanism and had a total efficacy period of at least 71 days. This difference can be attributed to the greater toxicity of the growth regulator and its slower chemical degradation under field conditions when compared to the organophosphates.

Groups of gravid females of Lucilia cuprina (Wiedemann) in a 1-m3 cage flew upwind in response to sheep placed upwind of the cage. No downwind flight or other response was observed to sheep placed downwind of the fly cage. Flystruck sheep stimulated the greatest accumulation of flies on the upwind cage wall (46% of the caged flies), followed by sound wet sheep (29%) and sound dry sheep (19%). All sheep tested caused significantly more flies to accumulate on the upwind wall than did controls consisting of either no bait or a man placed upwind (14%). Struck sheep elicited significant upwind movement of flies at distances of up to 20 m; sound, dry sheep did so only up to 10 m. It was concluded that L. cuprina is able to orient from a distance in response to volatile sheep kairomones; kairomones from dry sheep are augmented by wetting or the presence of cutaneous myiasis, as indicated by an enhanced fly response. The experiments performed did not exclude a role for visual or thermal cues in blowfly orientation to sheep.

The development and testing of a bioassay system to evaluate the potency of floral odours as mediators of long-range floral nectar source location by mosquitoes are described. The bioassay is quantitative and behaviourally discriminating, upwind flying and landing acting as indices of behavioural activity over the 24-h light:dark cycle. In initial tests, the responses of Aedes aegypti (L.) to the flowers and floral odours of ox-eye daisy (Leucanthemum vulgare) were investigated. A. aegypti exhibited a biphasic diel cycle of nectar-feeding behaviour and landed on modified flowers that retained either their disc or ray florets. Most significantly, the mosquitoes responded in a similar way to the odour of L. vulgare in the absence of visual stimuli or nutritional cues. They did not respond to solvent extracts of ox-eye daisy flowers.

Opisina arenosella Walker is a defoliating pest of coconut in Sri Lanka. A first attempt was made to understand its population dynamics. Analysis of records of population outbreaks throughout the country from 1965 to 1985 revealed cycles in the population of approximately one generation period, giving the population the appearance of partially discrete generations. There was also evidence for longer cycles of six-month period. Outbreaks occurred throughout the coconut-growing regions of Sri Lanka, and the numbers of outbreaks per year in different provinces were sometimes correlated, indicating a common, probably climatic, triggering mechanism. Parasitism remained high throughout the outbreaks and there was some evidence that pupal parasitism increased towards the end of an outbreak. A working hypothesis that explains the population dynamics of O. arenosella and the origin of outbreaks is presented.

The influence of natural enemies on the population growth of Diuraphis noxia (Mordvilko) in wheat fields in eastern South Africa was investigated. Since the natural enemies were not present in the initial stages, the apparent mortality observed must have been due to other causes. During the logarithmic phase of aphid population growth, predators, in particular the coccinellid Hippodamia variegata (Goeze), had a slight inhibitory effect on growth. During the decline phase of the aphid population, the potential population size was reduced by as much as 52% by predation. The most abundant parasitoids, Aphidius colemani Viereck and Diaeretiella rapae (M'Intosh), had a negligible effect. Although natural enemy populations showed functional responses to increases in Diuraphis noxia numbers, they did not prevent the latter from attaining and exceeding economic injury levels.

A wind-tunnel bioassay system, developed previously for the evaluation of long-range host-location stimuli, was used to investigate the responses of Anopheles arabiensis Patton to floral odours. Mosquitoes were found to respond by flight and landing to Achillea millefolium inflorescences and also to the odour of A. millefolium in the absence of visual stimuli. An air-entrainment technique was used to extract floral odours for biological and chemical testing. Both sexes of Anopheles arabiensis were found to respond to the floral odour extract. The major component of the floral odour was tentatively identified as a cyclic or bicyclic monoterpene.

The attractiveness of cattle urine to Glossina morsitans morsitans Westwood and G. pallidipes Austen was shown to be entirely attributable to the phenolic components which it contains. Four of the eight naturally occurring phenol derivatives (3- and 4-methylphenol, 3-ethylphenol and 3-n-propylphenol) were electroantennographically active, induced upwind flight in wind-tunnel bioassays and increased trap catches in field tests in Zimbabwe. One of the minor components, 2-methoxyphenol, had little antennographic activity but induced upwind flight in the wind-tunnel and appeared to be repellent in field tests.