The cereal rust mite Abacarus hystrix (Nalepa), a significant pest of grasses, has been regarded as one of a few exceptions among eriophyoid mites with reference to the pattern of host plant utilization. At least 60 grass species have been recorded as its hosts. Thus, the mite has long been considered as a host generalist in which host specialization would not be likely to evolve. However, recent studies have revealed that host-associated specialization is possible in A. hystrix. Here, we aimed to discriminate between the three populations of A. hystrix associated with the different hosts (namely quackgrass, ryegrass and smooth brome) on the basis of mitochondrial (COI) and nuclear (D2 region of 28S rDNA) DNA sequences. The phylogenetic trees obtained with the maximum likelihood analysis of both COI and D2 region data sets showed that host-adapted strains of A. hystrix form distinct clades. Furthermore, on the COI nucleotide tree, the quackgrass- and brome-associated strains were internally divided each into two well-supported monophyletic clusters. The nucleotide D2 region data set tree showed that brome-associated strain is polyphyletic in origin. There is clear co-variation of DNA results with earlier morphological and ecological traits, as well as the results of crossing experiments. We showed that reproductively incompatible strains of A. hystrix exhibit more than 20% sequence divergence in the COI gene and 0.2% sequence divergence in the D2 28S rDNA. Our results did not confirm the placement of three host-associated strains of A. hystrix within one, ostensibly generalist, species.

To elucidate how thrips feed, the mouthparts of Limothrips cerealium (Hal.) were examined in dead specimens by scanning electron microscopy and plasma-ashing, and in living specimens by cinematography as individuals fed through a transparent membrane on clear liquid containing small polystyrene latex particles that made its flow visible. Close contact with the food substrate was maintained by the labral pad. The single mandible was used to pierce the membrane and was then withdrawn rapidly and replaced by the maxillary stylets, which formed a tube with either a terminal or sub-terminal opening into which food was drawn by cibarial pumping at 2–6 pulsations/s. Oscillations in the surrounding fluid caused by such pumping were detectable up to 58 μm from the maxillary opening. Feeding persisted from a few seconds to up to half an hour, and when complete the stylets were withdrawn either rapidly and together, or more gradually by sliding one against the other. Whole chloroplasts up to 6 μm in diameter were ingested even though the diameter of the maxillary tube was about 1 μm. The thrips consumed the contents of ruptured plant cells at about 8·5 × 1O-5 μl/min, equivalent to almost 12·5% of their body weight per hour. Probing and feeding removed the surface wax from leaves, and the cuticle was so exposed that it often wrinkled. Leaf cells beneath a pierced epidermal cell were usually emptied completely, and little seepage from the wounded tissue occurred after stylet withdrawal. After intensive feeding, many mesophyll cells were totally destroyed and others showed extreme plasmolysis; grana sacks were contorted and large starch grains formed due to desiccation. Above such internal damage the epidermal cells collapsed, and the outer cuticle wrinkled and appeared silvery before turning yellow and brown.

The biological consequences of mating interactions between indigenous and exotic biotypes of Bemisia tabaci (Gennadius) in Australia were studied using a combination of field and laboratory experiments. The key results of the interaction between the B and eastern Australian biotypes were reduced population increase, a marked increase in the proportion of male progeny, fewer eggs produced by females paired with males of different biotype and no difference in the numbers of eggs per unmated female and females paired with males of the same biotype. In addition, there was no change in the proportion of eggs hatching, mixed biotype pairs spent more time courting than single biotype pairs and a low level of hybridization in field cages and small containers was observed. These observations suggest three possibilities. The first is the ‘distracting male hypothesis’ in which mating pairs made up of different biotypes apportion more time to courtship and less time to egg laying than single biotype pairs. The second invokes the ‘single-locus complementary sex determination model’ in which the production of non-viable diploid male zygotes may explain the reduction in eggs laid. The third is cytoplasmic incompatibility between biotypes caused by Wolbachia. The results also suggest that the geographical distribution of clusters of related biotypes both overseas and in Australia may be explained by between-biotype interactions leading to the formation of parapatric populations.

Day and night sampling of windborne arthropods at a height of 200 m above ground was undertaken at Cardington, Bedfordshire, UK, during July 1999, 2000 and 2002, using a net supported by a tethered balloon. The results from this study are compared with those from the classic aerial sampling programmes carried out by Hardy, Freeman and colleagues over the UK and North Sea in the 1930s. In the present study, aerial netting was undertaken at night as well as daytime, and so the diel periodicity of migration could be investigated, and comparisons made with the results from Lewis and Taylor’s extensive survey of flight periodicity near ground level. In some taxa with day-time emigration, quite large populations could continue in high-altitude flight after dark, perhaps to a previously underrated extent, and this would greatly increase their potential migratory range. Any trend towards increases in night temperatures, associated with global warming, would facilitate movements of this type in the UK. Observations on the windborne migration of a variety of species, particularly those of economic significance or of radar-detectable size, are briefly discussed.

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

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

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

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

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

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

Emigration of moths of the Noctuid Spodoptera exempta (Wlk.) from their developmental sites occurred within a few hours of emergence, and captive moths have lived in semi-outdoor conditions for several weeks. Flight has been recorded at all times of night in the Kenya highlands, and has shown a very marked association, seasonally, nightly and even hourly, with rain; it has been observed at temperatures down to 13°C, and inferred at temperatures several degrees lower, so that over the greater part of eastern Africa flight activity is very unlikely to be restricted by low temperatures.

The breeding season of S. exempta differs markedly and consistently in different parts of eastern Africa; outbreaks of larvae recorded over the past forty years in Kenya, Tanzania and Uganda have been confined to November-July (very largely to December-May), alternating with those recorded over the past twenty years in Ethiopia, which have been confined to March-December (very largely April to August). The progressive establishment of a network of fifty light-traps in these countries since late 1962 has repeatedly recorded the arrival of invading moths before the first infestations of larvae, and has also provided evidence of a strikingly complete seasonal evacuation of much of the region; all traps in Kenya and most of those in Tanzania have revealed a period of several months in every year without a single moth of S. exempta.

Seasonal successions of moth catches and outbreaks of larvae have provided repeated evidence of a progressive northward movement of populations of S. exempta, developing in March in Tanzania and Kenya, and extending across Ethiopia, in some years as far as northern Eritrea by June. The extent of these inferred displacements is consistent with the evidence so far available on behaviour and other factors affecting range of flight, which has been examined in as much detail as the limited data permit.

Evidence of a return migration southwards to Kenya and Tanzania is relatively scanty. There are some indications of a north to south sequence of moth catches and outbreaks; the heaviest infestations in Kenya and Tanzania during the four-year period of detailed study were preceded by the largest catches so far recorded at the relevant time of year in Ethiopia; and in several years the first moths arriving in Kenya and Tanzania, in November-December, have appeared with the onset of the north-east monsoon, representing the southward movement of the intertropical convergence zone. Conversely, appearances of moths towards the northern limits of their inferred seasonal migration, in Ethiopia and around the Gulf of Aden in June, have shown an analogous association with the establishment of the south-west monsoon, i.e., with the northward movement of the intertropical convergence zone. Brief reference is made to evidence of seasonal migration in other parts of Africa; possibly in some years the eastern African populations may be supplemented by migrants from the south.

Two recorded moth ‘ swarms ’ have been associated with weather systems characterised by particularly vigorous wind-convergence. It is suggested that wind-convergence may have contributed to the density of the ‘ swarms ’ and of the subsequent infestations of larvae.

The overall effect of the seasonal changes in distribution which have been demonstrated is to bring the population into areas experiencing seasonal rains. Such a pattern of seasonal migration is likely to be of particular survival value for grass-eating insects, and such concentration of the insects as may be attributable to the associated wind-convergence may be significant in relation to the status of such insects as pests of cereal crops.

Records in the literature of long-range geographical displacements of some other Lepidoptera have been found to be associated in a similar manner with analogous systems of wind and weather in other parts of the world.

The paper includes a review of the published literature on the biology of the Cigarette Beetle, Lasioderma serricorne (F.). A list is given of foods on which this species has been found breeding. Information on the duration of the various developmental stages is tabulated and the data on oviposition are summarised. Observations are collected together on the rate of increase of the species in warehouses, on the number of generations per year, on sex ratio, on the use of traps to catch adults and on the spread of the pest and the damage that it causes. The lengths of exposure to various high and low temperatures that are required to give a complete kill of the species are tabulated, and the known natural enemies are listed.

Original work includes a morphological comparison of L. serricorne and the closely related common storage species Stegobium paniceum (L.). The experimental work consists of a study of the life-cycle of L. serricorne on wheatfeed over a wide range of combinations of constant temperature and humidity. Development was possible from just under 20°C. to 37·5°C. at favourable humidities. Larvae died at 90 per cent. R.H. at 37·5°C. The lower humidity level for development was under 25 per cent. R.H. at 30°C. but change of temperature, both up and down, raised the lower humidity limit so that, at 20°C. and 37·5°C., all larvae died at 40 per cent. R.H. When fed on foodstuffs such as groundnuts, which contain less water than wheatfeed at all humidities, the effects of low humidity are more rigorous. The effect of a number of foodstuffs on the length of the developmental cycle was investigated. The duration of larval instars on wheatfeed at 30°C. and 70 per cent. R.H. was found. The adults obtained in the experiments were weighed. The heaviest insects were obtained at 25°C. and 100 per cent. R.H. Higher temperatures and low humidities reduced weight. Females were heavier than males. The sex ratio was unity.

The oviposition rate was investigated at 70 per cent. R.H. over a wide temperature range. Under all conditions the eggs were laid quickly. At this relative humidity, no fertile eggs were laid at 37·5°C. and few pairs laid at 20°C. The total number of eggs laid per female at 20°C. was low, otherwise temperature had little effect on the number of eggs laid, but the rate of oviposition was increased by high temperature. The theoretical rate of increase at 70 per cent. R.H. was calculated for several temperatures and shown to increase with temperature up to 35°C.

The conclusions on the distribution and multiplication of the species which can be drawn from the laboratory results are discussed.

The close association of Anopheles gambiae Giles with humans and its females’ ability to live on human blood alone suggest that females may ignore sources of sugar in favour of human blood as a source of energy. They have limited energy reserves at emergence, and at 27°C both sexes generally die if they do not feed during night 1, 24–36 h after emergence. Food preferences during this critical period were tested by measuring responses to volatiles from honey and soiled socks, which served as surrogates for nectar-related and human-related volatiles in a wind-tunnel olfactometer. Both sexes responded more strongly to honey than to human volatiles, and given a choice, preferred honey over human volatiles. After 5 days of sugar access and maturation, males continued to prefer honey volatiles, whereas females changed behaviour, responding almost exclusively to human volatiles. Night 1 experiments also demonstrated that: (i) females previously having had sugar during the night of emergence responded more strongly to human volatiles; (ii) large-bodied mosquitoes of both sexes responded more strongly to honey than small-bodied ones; and (iii) females were equally responsive to honey in both early and late scotophase but were slightly more responsive to human volatiles in late scotophase. These results indicate that for a female’s first meal, sugar is a viable option and is preferred when nectar-related stimuli are strong. This supports field evidence that sugar-feeding is a significant component of A. gambiae female behaviour.

A Belgian field strain (MR-VP) of Tetranychus urticae (Koch) (Acari: Tetranychidae) exhibits different levels of resistance to four frequently used METI (mitochondrial electron transport inhibitor)-acaricides, i.e. tebufenpyrad, fenpyroximate, pyridaben and fenazaquin. Resistance factors for these compounds were 184, 1547, 5971 and 35, respectively. A 23.5-fold increase in 7-ethoxy-4-trifluoromethylcoumarin O-deethylation activity suggested that metabolic resistance through elevated levels of cytochrome P450 dependent monooxygenase-activity is a possible resistance mechanism.

However, synergism studies with different metabolic inhibitors revealed some contrasting resistance mechanisms between the METI-acaricides. Tebufenpyrad resistance could only be synergized after pre-treatment with the monooxygenase inhibitor piperonyl butoxide (PBO), whereas pyridaben resistance was strongly synergized both by PBO and the esterase inhibitor S,S,S-tributylphosphorotrithioate (DEF). Resistance levels to fenpyroximate could neither be suppressed by PBO nor by DEF. Although METI-acaricides are structurally related, these findings probably reflect a different role of esterases and mono-oxygenases in metabolic detoxification between these compounds. The overall lack of synergism by diethylmaleate (DEM) suggests that glutathione-S-transferases are not an important factor in resistance to METIs.

Reciprocal crosses between susceptible females and resistant males showed no maternal effect, and resistance to METI-acaricides was inherited generally as a dominant trait. Backcrosses with F1 females revealed striking differences in the mode of inheritance. Although resistance to fenpyroximate and pyridaben was under monogenic control, resistance to tebufenpyrad was under control of more than one gene.

A method for continuously rearing cabbage root fly, Erioischia brassicae (Bch.) is described.

Adult flies fed on sucrose, brewers’ yeast and yeast hydrolysate laid an average of 220 eggs per female when caged together in large numbers and 376 eggs per female when caged singly. Egg viability was 86 per cent. Egg hatch was severely reduced by relative humidities of less than 90 per cent, and the embryo became more susceptible to desiccation as it matured. The larvae were reared on swede, and maximum survival was obtained when the swedes were inoculated with an optimum number of eggs calculated from the ratio of 1 egg: 1.6 g. of swede. Different ratios were obtained from turnip and winter radish indicating that survival was probably related to the nutritional value of the rearing medium as well as to its availability. An average of 68 per cent, of the eggs placed on swede produced pupae that were equivalent in size to wild pupae. The fecundity of the flies was directly related to pupal weight and to the availability of protein in their diet. Adult longevity was reduced more by mutual disturbance than by any other factor.

The autumn return migration of the beet armyworm Spodoptera exigua Hübner and other insects in northern China was observed with radar and with a simultaneously-operated searchlight trap and ground light-trap at a site in Langfang, near Beijing. The searchlight trap was found to be an efficient tool for trapping migrants and, operated alongside a ground light-trap, could distinguish migrant from locally-flying species. It was confirmed that S. exigua and some other species were high-altitude nocturnal windborne migrants during September and October in northern China. Maximum density of moths typically occurred below 500 m, and strong layering was often observed at about 200 m above ground level in airflows that would carry the moths towards the south. Descent of S. exigua in the vicinity of the radar site in late September was often associated with rain.

Generalist predators contribute to pest suppression in agroecosystems. Spider communities, which form a substantial fraction of the generalist predator fauna in arable land, are characterized by two functional groups: web-building and cursorial (non-web-building) species. We investigated the relative impact of these two functional groups on a common pest (Sitobion avenae, Aphididae) in wheat by combining a molecular technique that revealed species-specific aphid consumption rates with a factorial field experiment that analyzed the impact, separately and together, of equal densities of these two spider functional groups on aphid population growth. Only cursorial spiders retarded aphid population growth in our cage experiment, but this effect was limited to the initial aphid-population growth period and low-to-intermediate aphid densities. The molecular analysis, which used aphid-specific primers to detect aphid DNA in predator species, detected the highest proportion of aphid-consuming individuals in two cursorial spiders: the foliage-dwelling Xysticus cristatus (Thomisidae) and the ground-active Pardosa palustris (Lycosidae). The results suggest that manipulating the community composition in favour of pest-consuming functional groups may be more important for improving biological control than fostering predator biodiversity per se. Agricultural management practices that specifically foster effective species or functional groups (e.g. mulching for cursorial spiders) should receive more attention in low-pesticide farming systems.

The autumn migration of the rice leaf roller moth, Cnaphalocrocis medinalis Guenée, in eastern China was studied at two sites (one in southern Jiangsu Province and one in northern Jiangxi Province), using radar and aerial netting. It was confirmed that C. medinalis is a high-altitude nocturnal windborne migrant, with large numbers of moths taking-off at dusk and flying continuously for several hours. Migration was post-teneral and the females had immature ovaries. Maximum densities of the moths typically occurred between 250 and 550 m above ground, and layering was intense on some nights. Moth layers often occurred at an altitude where there was a wind-speed maximum. In early September, migrant C. medinalis from southern Jiangsu Province were carried on the winds in an approximately westward direction. However, the winds prevailing in late September and October took migrants from both sites towards the south-west or south. Forward trajectories for C. medinalis and other insects emigrating from northern Jiangxi during October indicated that they were able to reach the tropical rice-growing areas near the south China coast, where year-round breeding would be possible. Incidental observations on the migratory flight of other lepidopteran pests, including Mythimna separata (Walker), Spodoptera litura (Fabricius), Ctenoplusia agnata (Staudinger) and Agrotis ipsilon (Hufnagel) (all Nocturidae), Spoladea recurvalis (Fabricius) and particularly Omiodes indicata (Fabricius) (both Pyralidae) are presented.

A synoptic view is given of the data amassed by WHO, with technical assistance from the Imperial College of Science and Technology, on the origins of blood-meals in Anopheles samples collected from 1971 to 1978. Attention is focused on the proportion of each sample found to contain human blood and on the problems of interpreting from this the human blood index or degree of biting-contact with man exhibited by vector populations. The difficulties of overcoming bias in sampling, which are formidable in unsprayed areas, are further compounded where the dwellings are treated with a slow-acting residual insecticide which knocks down many engorged mosquitoes before they can be collected from their daytime resting places. There is evidence to suggest that the host-selection patterns of those vectors which are ‘opportunistic’ feeders may be heavily influenced, even from village to village or from month to month, by the changing availability of alternative hosts, particularly cattle. This suggests in turn that the possibilities of manipulating the degree of mosquito-man contact by encouraging deflection to animals (zooprophylaxis) or by measures to afford a degree of personal protection should not be under-estimated by malaria strategists. It may sometimes be found less difficult to reduce the vector’s human blood index than it is to measure it, but in view of the epidemiological importance of this parameter, suggestions are put forward for improving entomological field practice in this area. They include a quantitative survey of the biotopes available to the mosquito population as diurnal shelters, a longitudinal survey of the densities of blood-fed females per biotope, and a survey of the numbers and the respective distribution of people and domestic animals available as hosts. The work-load entailed by such a thorough form of investigation, to be repeated where necessary at different seasons of the year, underlines the necessity to concentrate efforts on a small number of localities, carefully chosen for the malaria situations they represent and the vector populations they support. A large-scale blood-meal sampling programme, confined to these selected localities, is most likely in our estimation to yield information of value for controlling malaria vectors.

The literature on age-grading techniques of adult insects, published since 1968, is reviewed. The techniques described include those which deal with changes in the reproductive system, as well as somatic changes which take place with age. They also include techniques based on changes induced by wear and tear. Follicular relics found in different orders of insects are described, and their origin, fate and relative usefulness in age-grading studies are discussed. Attention is drawn to the formation of anomalous, or aberrant dilatations, particularly ones formed as a result of follicle resorption. The suitability of the various techniques to the study of different insect species is compared, and the advantages of using more than one type of age-grading method in the study of one species are discussed. Enough detail of each technique is given to permit field workers to choose and apply the technique most suitable for the study of the insect of their choice, and for the degree of accuracy required by them. Lists of species which have been studied by particular age-grading techniques, or combinations of them, are given. Finally, examples are cited of the types of problems entomologists have sought to solve, often successfully, using age-grading methods.

The diversity of beetle assemblages in different habitat types (primary forest, logged forest, acacia plantation and oil palm plantation) in Sabah, Malaysia was investigated using three different methods based on habitat levels (Winkler sampling, flight-interception-trapping and mist-blowing). The overall diversity was extremely high, with 1711 species recorded from only 8028 individuals and 81 families (115 family and subfamily groups). Different degrees of environmental changes had varying effects on the beetle species richness and abundance, with oil palm plantation assemblage being most severely affected, followed by acacia plantation and then logged forest. A few species became numerically dominant in the oil palm plantation. In terms of beetle species composition, the acacia fauna showed much similarity with the logged forest fauna, and the oil palm fauna was very different from the rest. The effects of environmental variables (number of plant species, sapling and tree densities, amount of leaf litter, ground cover, canopy cover, soil pH and compaction) on the beetle assemblage were also investigated. Leaf litter correlated with species richness, abundance and composition of subterranean beetles. Plant species richness, tree and sapling densities correlated with species richness, abundance and composition of understorey beetles while ground cover correlated only with the species richness and abundance of these beetles. Canopy cover correlated only with arboreal beetles. In trophic structure, predators represented more than 40% of the species and individuals. Environmental changes affected the trophic structure with proportionally more herbivores (abundance) but fewer predators (species richness and abundance) in the oil palm plantation. Biodiversity, conservation and practical aspects of pest management were also highlighted in this study.

1. The work was carried out in Bwamba County, Uganda, a district where human yellow fever has recently occurred. It consisted mainly of 24-hour catches in banana plantations and rain forest combined with climate observations.

2. It was found that forest was cooler and moister by day than a banana plantation while the plantation was cooler and moister than the open air. By night, however, the climate of all three environments was strikingly similar.

3. Methods used in making 24-hour catches and large scale routine catches are described. Trials with trap nets showed these to be less efficient than hand catching.

4. Experimental catches showed that Aëdes simpsoni, the only species known to be a vector of yellow fever in Bwamba, bites mainly in coffee gardens, maize fields and the thinner parts and edges of banana plantations. It is scarce in fully exposed situations. It occurs within the edges of primeval rain forest. It prefers human blood to that of goats, fowls, and monkeys, and attacks the head and shoulders selectively.

Experiments were carried out on the flight pattern of unfed female mosquitoes in an area of the Gambia adjacent to mangrove swamps. The mosquitoes were trapped in flight by the use of ramp-traps as they approached natural or simulated baits. The traps were arranged in series in four avenues of cleared bush, radiating out at right angles to each other. The baits were installed either at the centre of the cross formed by the avenue or at the outer end of one avenue. Trapping was carried out at six ranges simultaneously, extending from 5–80 yd (4·5–73 m) distance from the bait. The baits were either two small calves or carbon dioxide emitted from a cylinder at a rate equivalent to the expiration rate of the animals. A series of catches with no bait was also made.

Avermectins administered to cattle for control of parasitic infections by injection or slow-release bolus are excreted in the faeces and have a variety of harmful effects upon Diptera and Coleoptera that develop in cow-pats: these effects are reviewed. Diptera Cyclorrhapha are severely affected, the extent of the response depending on the drug concentration in the dung. At high levels, larvae are killed or paralysed while at lower levels their metamorphosis is inhibited. At very low levels, adult emergence is reduced and a significant number of imagines show morphological abnormalities. These responses are induced by concentrations of avermectins well below levels occurring in faeces after routine treatment. Diptera Nematocera are less sensitive than Cyclorrhapha but larval and pupal development are affected at higher dose levels. Larval dung beetles and some immature adults cannot survive in the pats of recently dosed livestock. Mature adult beetles are more resistant, but contact with treated dung leads to impaired reproduction. Dung eliminated up to 5 weeks after cattle have been treated with a single injection or up to 14 days after topical dosing shows harmful activity against dung insects, and ivermectin-containing pats retain much of their toxicity after several weeks exposure on pastureland. The impact on dung insects is more pronounced and of longer duration when ivermectin is delivered daily at 40 μg per kg cow by sustained-release bolus. Following topical or injection treatments, the rate of cow-pat degradation (measured by actual loss of biomass) is significantly delayed. When cattle are treated with a bolus delivering 40 mg ivermectin per kg cow per day, their dung remains intact on grassland for at least three months. The conclusions drawn from the various papers on these effects are compared and contrasted. In particular, attention is drawn to the general failure to recognize the importance of delayed reactions to non-lethal doses of avermectins, and to our lack of consideration of long-term consequences for cow-pat insects and the wider implications for ecology.

The method of measuring relative humidity by matching the colours of tissue paper impregnated with cobalt thiocyanate has now been made more convenient by the commercial production of impregnated paper and coloured glass standards.

Although the method as used straightforwardly is not at all precise, it is especially useful for the measurement of humidity in small or relatively inaccessible spaces, e.g., cracks in floors, air spaces in stored grain, under bark, or inside small tubes, etc., and for general use when elaborate equipment cannot be employed.

A piece of the paper is exposed to the humidity to be measured, preferably for two hours, then mounted on white opal glass in oil (liquid paraffin) and matched, in a simple comparator, against the coloured glass standards. When matching is done at a temperature other than 20°C., corrections are required as tabulated.

Tables of error are given, showing the range of variation from different causes, with estimates of 95 per cent, confidence limits. To cover all the sources of variation normally affecting the measurements under various conditions, limits up to ±5 are allowed for relative humidities down to 70 per cent.; these limits increase at lower humidities to a maximum of ±15, about 30 per cent. Various ways of avoiding errors are described, and it is shown that if special precautions are taken the method can be used with considerable accuracy, particularly at relative humidities above 65 per cent.