A novel non-destructive method was devised for studying the development of insects hidden within individual wheat grains using a standard nuclear magnetic resonance (NMR) spectrometer. The development of Sitophilus granarius (L.) at 25°C and 70% RH was studied from egg-laying to emergence by NMR, X-radiography and weighing. The results of the three methods correlated quite well. Neither the NMR nor the X-radiation appeared to harm the insects. The NMR method did not usually detect the insects until they were in the third larval instars, but after that the areas of the two NMR peaks observed with each infested grain followed a pattern which was readily interpreted in terms of the insect development. The major NMR peak was found to be due almost wholly to water and the minor peak to lipid, and the size of the major peak obtained with adults was close to that expected on the basis of their water content. The movement of some of the insects within the grains was observed for short periods and appeared to be characteristic of each developmental stage. Preliminary work with a less sophisticated NMR machine showed that it is possible in a single scan to detect ten grains infested with S. granarius larvae in a batch of 500 grains, but further work is required to see whether single eggs can be detected. The results obtained in this study were sufficiently encouraging for a wide variety of other areas to be suggested in which use of NMR might help to solve some entomological problems.

Descriptions of the three sibling species of the Anopheles farauti complex in Australia, A. farauti Laveran (formerly A. farauti No. 1), A. hinesorum Schmidt sp.n. (formerly A. farauti No. 2) and A. torresiensis Schmidt sp.n. (formerly A. farauti No. 3) are provided. These species form a part of the punctulatus group, which contains the major malaria vectors in the southwest Pacific. Morphological markers are described for adult females, fourth instar larvae and pupae which identify most specimens, and are in keys.

The red spider, Oligonychus coffeae (Niet.), persists in all stages of its development on a few old leaves and ‘ janams ’ (small leaves at the base of the shoot) of tea bushes during the cold weather, and this persisting population is primarily responsible for the attack in the spring.

In pruning, a great many of the old leaves (including janams) are removed from bushes, and, concomitantly, the red spider. Pruned tea is, therefore, less attacked than unpruned tea or ‘ skiffed ’ tea (where just a little is cut off the tops of the shoots) in which comparatively more leaves are left on bushes.

Catches of Prostephanus truncatus (Horn) and Teretriosoma nigrescens Lewis from 205 pheromone trapping stations in Mexico were compared and related to climate and habitat. Prostephanus truncatus numbers differed between regions and over time with significant interaction between the two. An overall peak in captures occurred between August and November but this was not apparent in Veracruz and Chiapas. Catches of T. nigrescens also differed but effects were less distinct. The peak in P. truncatus catch was related to monthly rainfall and, with a time lag, minimum temperature in the drier, upland regions, but poorly matched in Chiapas and Veracruz. Prostephanus truncatus abundance was predicted from climatic and habitat data during the periods March to 3 July, and 31 July to November. A regression equation derived from temperature, humidity and rainfall, explained 82% of the variance in the P. truncatus catch in the later period. Local habitat made only a small addition to this model. The best correlate of T. nigrescens numbers was the catch of P. truncatus, but it was less abundant relative to P. truncatus as P. truncatus became more numerous and where annual r.h. was above 70%. Predicted abundance of P. truncatus from the regression model is compared with predictions from laboratory studies of reproductive potential under different climatic regimes. While laboratory studies predict high survival in hot, humid areas, the trap data showed higher catches in cooler, more temperate regions. Possible reasons for these differences and implications for the spread of P. truncatus in Africa are discussed.

Field surveys, manipulative field experiments and laboratory studies were employed to study the behaviour and development of a large coreid, Amorbus obscuricornis (Westwood), in response to changes in the architecture/foliar quality of Eucalyptus (Myrtaceae) hosts in Tasmania, Australia. Following tree decapitation and subsequent regrowth, A. obscuricornis nymphs were only associated with coppiced hosts. Eucalypts coppiced naturally by wild fire were found to carry significantly more nymphs than non-coppiced conspecific hosts. In contrast, adult A. obscuricornis were found on both coppiced and non-coppiced hosts. The foliar quality of coppiced hosts was superior to that of non-coppiced hosts; being softer, having a higher moisture content and a lower C/N ratio. Field collected fifth instar nymphs were heavier when collected from coppice vs. noncoppice; but in bagged shoot experiments second instar nymphs gained less weight on coppice than non-coppice. It is suggested that because coppice is softer the shoots may deteriorate (i.e. wilt) more quickly than non-coppice shoots. Through different exposure regimes, it was confirmed that first instar nymphs need only water to ecdyse, while feeding is initiated in the second instar. Differences in the nutritional requirements of first and second instar nymphs were reflected in their behaviour. First instar nymphs did not discriminate between conspecific hosts on the basis of whether they were coppiced or not, whereas second instar nymphs preferentially chose coppiced conspecific hosts. The findings of this work are discussed in the context of the plant vigour and resource regulation hypotheses.

Temperature is considered to be an important abiotic factor influencing insect reproduction. Despite the importance of Plutella xylostella L. (Lepidoptera: Plutellidae) as a pest of brassicaceous crops worldwide, the effects of temperature on its reproduction are not well understood. We evaluated the effect of constant temperatures ranging from 10 to 32.5°C on the reproduction of P. xylostella and developed an oviposition model for the species. The model combined temperature-dependent parameters of total fecundity, age-specific oviposition rate and age-specific survival. Additionally, we modelled population growth as a function of temperature. The estimated parameters allowed us to discuss the possible consequences of global warming on P. xylostella distribution. Temperature affected the length of pre-oviposition after adult emergence, oviposition period, longevity, total fecundity and egg viability. The model predicted that both daily egg production and length of oviposition period decreased at temperatures below 15°C and above 25°C. Population growth increased linearly with temperature in a range from 10°C to 25°C; however, the model predicted a reduction in population growth at temperatures above 28.6°C. Data suggested that temperature plays a critical role in P. xylostella reproduction, and subtle differences in average temperature could have an impact on its population growth. This is especially important in the context of global climate change, which in turn could alter the distribution and abundance of the pest in some regions of the world.

Changes in host preferences are thought to be a major source of genetic divergence between phytophagous insect taxa. In western Europe, two sympatric taxa, O. nubilalis (the European corn borer) and O. scapulalis, feed mainly on maize and hop or mugwort, respectively. These two species may have diverged without geographic isolation after a host shift of ancestral populations onto maize or another cultivated species (e.g. sorghum). A previous study using inbred laboratory strains revealed that the two species differ in their oviposition choices in maize-mugwort tests. We sampled four natural populations in France (two of each taxon) and tested their oviposition behaviour toward four of their main host plant species: maize, sorghum, mugwort and hop. O. nubilalis females showed a very high preference for laying their eggmasses on maize, whereas O. scapulalis females displayed a more balanced range of preferences. O. nubilalis females were attracted slightly to sorghum, suggesting that this plant is an accidental, rather than a regular and ancestral host plant of O. nubilalis. One important result arising from this study is the significant proportion of eggs laid by both Ostrinia species on hop. This may explain why some stands of hop are sometimes not only infested by O. scapulalis but also by O. nubilalis larvae, a situation preventing assortative mating based on microallopatry. Hence, further studies must be conducted to see whether the host preference in the genus Ostrinia might be linked to assortative mating by a mechanism that is not mediated by the host plant.

To elucidate the host preferences of tsetse, an observer followed animals as they wandered in woodland infested with Glossina morsitans morsitans Westw. From 55 to 88 landings by tsetse and 0·2–3·0 engorgements were seen per hour on ox, dog, bushpig and adult warthog, as against 14 landings and no engorgements on warthog 2–5 months old and 0·3–1·7 landings and no engorgements on impala and bushbuck. Many of the landings and most of the engorgements on adult suids occurred near the eye but this region was not attractive with other animals and young warthog. Unsuccessful attempts were made to determine the attractive stimuli from the eye region of adult suids.

In Southeast Asian tropical rainforests, two events, severe droughts associated with the El Niño-Southern Oscillation and general flowering, a type of community-wide mass flowering, occur at irregular, supra-annual intervals. The relationship between these two supra-annual events and patterns of insect population fluctuations has yet to be clearly elucidated. Leaf beetles (Chrysomelidae) are major herbivores and flower-visitors of canopy trees, affecting their growth and reproduction and, in turn, affected by tree phenology; but their population fluctuations in the Southeast Asian tropics have not been extensively investigated. We examined population fluctuation patterns of the 34 most dominant chrysomelid species in relation to the two supra-annual events by conducting monthly light-trapping over seven years in a lowland dipterocarp forest in Borneo. Our results showed large community variation in population fluctuation patterns and a supra-annual (between-year) variation in abundance for most of the dominant chrysomelids that was significantly larger than the annual (within-year) variation. Specifically, in response to a severe drought in 1998, chrysomelid species exhibited different population responses. These results show that population fluctuations of individual species, rather than the entire assemblage, must be analyzed to determine the effects of changes in environmental conditions on the structure of insect assemblages in the tropics, especially in regions where supra-annual environmental changes are relatively more important than seasonal changes.

Four putative knockdown resistance (kdr) mutations have been documented in the voltage-gated sodium channel (VGSC) gene of Cimex hemipterus from several countries. However, no information regarding kdr mutations in any Chinese tropical bed bug population is available to date. In this study, a double-mutation（M918I + L1014F）kdr allele was identified in six C. hemipterus populations across Guangxi Zhuang Autonomous Region of China. The frequency of this allele was 100% in all the six examined populations. In addition, only two cytochrome c oxidase I (COI) gene haplotypes, with one synonymous nucleotide variation, were identified in a total of 48 individuals from six locations. The fixation and broad geographic distribution of this resistant allele questions the continued use of pyrethroids in the treatment of tropical bed bug infestations. The very low genetic diversity within and among these populations indicates that these bed bugs may have a single origin.

Cotton growing landscapes in Australia have been dominated by dual-toxin transgenic Bt varieties since 2004. The cotton crop has thus effectively become a sink for the main target pest, Helicoverpa armigera. Theory predicts that there should be strong selection on female moths to avoid laying on such plants. We assessed oviposition, collected from two cotton-growing regions, by female moths when given a choice of tobacco, cotton and cabbage. Earlier work in the 1980s and 1990s on populations from the same geographic locations indicated these hosts were on average ranked as high, mid and low preference plants, respectively, and that host rankings had a heritable component. In the present study, we found no change in the relative ranking of hosts by females, with most eggs being laid on tobacco, then cotton and least on cabbage. As in earlier work, some females laid most eggs on cotton and aspects of oviposition behaviour had a heritable component. Certainly, cotton is not avoided as a host, and the implications of these finding for managing resistance to Bt cotton are discussed.

Over the past 40 years there have been marked shifts in arable farmland management that are widely believed to have had a considerable impact on flowering plants and invertebrates and the small mammals and birds that rely upon them. It is not yet possible to predict the dynamics of plants and invertebrates either with past or future changes in farmland management. This study investigates whether a basic invertebrate classification, formed of broad trophic groups, can be used to describe interactions between invertebrates and their resource plants and evaluate management impacts for genetically modified, herbicide-tolerant (GMHT) and conventional herbicide management in both spring- and winter-sown oilseed rape. It is argued that the analyses validate trophic-based approaches for describing the dynamics of invertebrates in farmland and that linear models might be used to describe the changes in invertebrate trophic group abundance in farmland when driven by primary producer abundance or biomass and interactions between invertebrates themselves. The analyses indicate that invertebrate dynamics under GMHT management are not unique, but similar to conventional management occurring over different resource ranges, and that dynamics differed considerably between spring- and winter-sown oilseed rape. Thus, herbicide management was of much lower impact on trophic relationships than sowing date. Results indicate that invertebrate dynamics in oilseed rape are regulated by a combination of top-down and bottom-up trophic processes.

Studies were carried out at Jilaal Moogi, south-eastern Somalia, of the responses of Glossina pallidipes Austen to traps and targets. F3 traps caught three times as many tsetse as a biconical trap. Baiting F3 traps with acetone (released at 5–50 000 mg/h), butanone (10–50 mg/h) or octenol (0·05–5 mg/h) either alone or as mixtures did not affect the catch significantly. The catch was increased by 1·6 times (P<0·05) by releasing a mixture of 4–methylphenol (at 0–2 mg/h) and 3-n-propylphenol (0·04 mg/h), and by four times by releasing a mixture of acetone (500 mg/h), octenol (0·5 mg/h) and the two phenols. Baiting a target enclosed in an electric net with the combination of acetone, octenol and phenols increased the catch only 1·3 times, (P>0.05). Baiting an electric net plus target with natural ox odour increased the catch 1·8 times (P<0·05). A pthalogen blue (peak reflectivity = 40% at 450 nm) target caught 1·7 times as many tsetse as a black target (P<0·01) and a standard blue (reflectivity = 29%) target caught 7·4 times the catch of a yellow one (P<0·001). The results are compared with published data from Zimbabwe, Kenya and Mozambique, and it is noted that the level of response of G. pallidipes in Somalia to host odours is lower than elsewhere.

A survey of the parasites of aphids that occur on lettuce was made in two localities, in the Midlands and northern England, respectively, and a list of these parasites compiled.

A study was made of the Braconid parasite, Monoctonus paludum Marshall, in relation to its host, Nasonovia ribis-nigri (Mosley), on lettuce. Techniques for observing the parasite's behaviour towards various species of aphids are described and methods of conducting experiments on breeding success in species other than N. ribis-nigri are given.

1. The object of the investigation is the study of possible methods of control of injurious insects in pine areas in Britain, with special reference to bark-beetles and to Myelophilus piniperda, L., in particular.

2. Reference is made to the economic status of the pine beetles in Britain as compared with other countries, and it is pointed out that in this country control measures must be of a more intensive character than in countries where large tracts of natural forest occur.

3. An analysis of the various types of damage caused by Myelophilus is made, and it is shown that although the actual amount of damage caused in any particular year may at the time appear comparatively slight, the effects of successive outbreaks are cumulative, and frequently result in a great reduction in the value of the crop.

4. The occurrence of bark-beetle outbreaks and the conditions under which they occur are briefly described.

5. The factors influencing the pine beetle population are discussed, and it is pointed out that the effects of climatic and physical conditions on the development of the host-plant under forest conditions are of fundamental importance in determining the density of the bark-beetle population in standing pine woods. It is stated that apart from abnormal increase brought about by exceptional breeding facilities as a result of fire, windfall, and felling operations, the conditions favouring the increase of bark-beetles and wood-boring insects in pine forests are considered to be mainly due to exceptionally favourable conditions for vigorous growth during the early stages of the crop's development, resulting in large numbers of trees being suppressed and killed in the pole stage, by rapidly increased shade as a result of the abnormal development of predominant trees. This is inevitable when Scots pine plantations are formed on soils too rich and situations too favourable. On the other hand, exceptionally favourable conditions for bark-beetle development occur when conditions are unfavourable for the healthy development of the crop owing to bad drainage conditions and water-logging of the soil.

6. The effect of overcrowding among the brood is considered to be one of the most important factors in the limitation of the bark-beetle population. Examples of how this factor operates are given and it is shown that the practical application of this factor can be brought about by the limitation of the supply of suitable breeding material.

7. The relative value of various parasites and predators as factors in the control of bark-beetles is discussed.

It is considered that pathogenic organisms are of little importance in the control of bark-beetles, as although these organisms may cause an epidemic when the pest has reached its maximum abundance, the object of our control measures must always be to prevent the bark-beetle population from approaching that stage of density.

Evidence is cited from the literature as to the effects of Nematode worms in reducing the egg-laying capacity of bark-beetles. It is suggested that the difference in the results obtained by various writers may have been influenced by the state of the insects at the time the observations were made, since the state of development of the reproductive organs of bark-beetles varies considerably during different stages, and although they sometimes appear to be shrivelled, they are capable of recuperation after a period of feeding. In any case it is impracticable to utilise Nematode worms in control measures, and it seems probable that their usefulness as parasites of bark-beetles will be neutralised by their effects upon the Coleopterous predators.

A list of the Hymenopterous parasites of pine beetles found during the progress of the investigation is given, together with notes on their relative abundance, and their importance as controlling factors is emphasized.

A list of the Coleopterous predators found associated with the bark-beetles is given with notes on the most important species. It is pointed out that some species of Coleopterous predators are probably more injurious than beneficial owing to the destruction of parasite larvae ; Thanasimus formicarius and Elaterid larvae are examples. On the whole, the Coleopterous predators are considered to be of even greater importance than Hymenopterous parasites as agents in the control of bark-beetles.

The larvae of several species of Diptera are very numerous in the bark-beetle brood-galleries. A list is given of the species which have been identified. Although listed as predators of bark-beetles, these Diptera are regarded as being of greater importance as destroyers of parasite larvae and are therefore being studied with a view to their possible elimination.

The economic status of birds in relation to bark-beetle control is briefly discussed, and it is pointed out that although under certain conditions birds do undoubtedly destroy large numbers of adult bark-beetles, it is probable that this useful work is counterbalanced by the destruction of parasite larvae in winter. On the whole, birds are not regarded as being of importance in the control of pine beetles in Britain.

The effects of competition between different species of bark-beetles is discussed, with special reference to Crypturgus cinereus, Hbst., and its influence in the control of Myelophilus minor.

8. A detailed description is given of some large-scale thinning experiments which have been in progress in the New Forest since 1933.

The scheme on which the experiments are based is the result of observations carried out by the writer over a period of years during which he noted that parasites and predators of the pine beetles are most numerous in young pine stands in the pole stage, previous to the first thinning operations. The conviction was formed that under those conditions a state of biological control existed which might, under favourable conditions, be continued throughout the rotation of the crop. One of the necessary conditions for the maintenance of a permanent resident population of parasites and predators is the presence of a permanent host population. This, in turn, necessitates a continuous supply of suitable breeding material. The density of the host population is largely governed by the quantity of suitable breeding material available, and the requirements of an increasing bark-beetle population demand a corresponding increase in the amount of suitable breeding material from year to year; so long as this increase in suitable breeding material continues, the host population is maintained at a higher level than that of the parasites and predators. When, however, the supply of suitable breeding material ceases to meet the requirements of the increasing bark-beetle population, a point is reached where overcrowding of the brood takes place. The intersection and intermingling of the larval tunnels facilitates the work of destruction by the predator larvae and the balance is, for a time, turned in their favour. The increased density of the host population also favours the increase of the parasites at the expense of the host. Limitation of the supply of suitable breeding material also results in a high rate of mortality among the bark-beetle larvae. The combined effects of the increased parasite and predator population, accompanied by overcrowding in a limited supply of food material, will result in a sudden reduction in the bark-beetle population, which is followed by a corresponding reduction in the parasite and predator populations. It will be seen, therefore, that under natural conditions there is a considerable fluctuation in the rise and fall of the numerical ratio of the host population and that of the parasite and predator population. The time occupied by each cycle may be extended over a considerable period of years, the peak of each host infestation giving rise to a periodic outbreak, corresponding with the period of maximum density of the crop. The automatic opening up of the canopy results in a temporary reduction in the amount of suitable breeding material. Under silvicultural conditions, however, the sudden increase of available breeding material produced when a thinning takes place and the material is allowed to remain on the area provides abnormally favourable conditions for the sudden increase of the bark-beetle population, and an outbreak is precipitated. The occurrence of these outbreaks has led to the popular belief that the remedy lies in what is called “ clean forestry.” In theory, the elimination of all suitable breeding material would solve the bark-beetle problem, but in practice the method is often impracticable when large areas of forest have to be dealt with, as is clearly demonstrated by the frequency with which bark-beetle outbreaks occur as a result of thinning operations.

The object of the experiment was, therefore, to devise a method by which the state of biological control can be continued throughout the rotation, by the provision of the amount of breeding material necessary to maintain a permanent population of hosts which would be kept at a level of economic control by the parasites and predators, and at the same time to bring into practical application the factor of overcrowding as an automatic governor to check any undue increase of the bark-beetle population. The results of the experiments are given in detail, and it is shown that the rate of growth of the crop is a decisive factor.

A scheme is outlined for the study of the use of billets and trap-stems.

Reference is made to operations which tend to upset the balance of insect populations.

Control measures in felling, burnt, and windfall areas are also discussed.

Endrosis lactella is widely distributed in Britain, where it is a minor pest of stored products, especially of grain and seeds.

The incubation period of the egg varied between 42 days at 10°C. and 6·0 days at 26°C. It was almost unaffected by changes in relative humidity.

Survival of eggs was low at high temperatures and low humidites, and the mean survival from complete batches of eggs at 70 per cent. R.H. 25°C. was 44 per cent. The highest survival recorded was 81 per cent.

On a diet of middlings the larval stage lasted 133 days at 90 per cent. R.H. 10°C, and 38 days at 90 per cent. R.H. 25°C. No adults were reared from larvae grown below 80 per cent. R.H. At 90 per cent. R.H. and 25°C. there were 7 instars.

On various foodstuffs at 90 per cent. R.H. 20°C, duration of the larval stage varied between 40 days on dead moths and 109 days on macaroni. Survival to the adult stage varied between 75 per cent. on whole wheat and 20 per cent. on groundnuts.

The pupal incubation period was 58 days at 10°C. and 10·4 days at 25°C, and was approximately the same at all humidities.

The time required for complete development from egg to adult was 235 davs at 10°C. and 62 days at 25°C. (90 per cent. R.H.).

There was a significant correlation between the weight of a female moth at emergence and the number of eggs laid. Egg output was lower at 25°C. than at 15°C, was not significantly affected by relative humidity, but was increased by provision of drinking water. Weights of females varied from 2·9 mg. to 9·4 mg. and egg output from 14 eggs to 231 eggs.

The sex ratio of the adults in the dried grass culture was found to be 1 male to 23 females.

Longevity could not be correlated with weight in all experiments, but, in the case of mated females, was dependent upon temperature, humidity and availability of drinking water. The mean adult life in days was 3–0 at 30 per cent. R.H. 25°C.; 5·0 at 90 per cent. R.H. 25°C.; 9·1 at 90 per cent. R.H. 15°C.; and 8.9 at 70 per cent. R.H. 25°C. + drink. Mated males were very short-lived (2–4 days at 70 per cent. R.H. 25°C).

The only important predator was the mite, Cheyletus eruditus, which attacked the young larvae.

The distribution and movement of 1st instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae on whole garden pea (Pisum sativum L.) plants were determined in glasshouse trials. This economically-important herbivore attacks a wide variety of agricultural, horticultural and indigenous plants. To investigate the mechanisms underlying larval intra-plant movement, we used early-flowering and wild-type plant genotypes and placed eggs at different vertical heights within the plants, one egg per plant. Leaf water and nitrogen content and cuticle hardness were measured at the different plant heights. Of 92 individual larvae, 41% did not move from the node of eclosion, 49% moved upwards and 10% moved downwards with the distance moved being between zero and ten plant nodes. Larvae from eggs placed on the lower third of the plant left the natal leaf more often and moved further than larvae from eggs placed in the middle or upper thirds. The low nutritive value of leaves was the most likely explanation for more movement away from lower plant regions. Although larvae on flowering plants did not move further up or down than larvae on non-flowering plants, they more often departed the leaflet (within a leaf) where they eclosed. The final distribution of larvae was affected by plant genotype, with larvae on flowering plants found less often on leaflets and more often on stipules, tendrils and reproductive structures. Understanding intra-plant movement by herbivorous insects under natural conditions is important because such movement determines the value of economic loss to host crops. Knowing the behaviour underlying the spatial distribution of herbivores on plants will assist us to interpret field data and should lead to better informed pest management decisions.

Ants act simultaneously as predators and as hemipteran mutualists, and thereby may affect the composition and population dynamics of a wide arthropod community. We conducted ant-exclusion experiments in order to determine the impact of ants on the infestation levels and parasitism of three of the most important citrus pests of western Mediterranean citrus: the honeydew producer Aleurothrixus floccosus Maskell (woolly whitefly) and the non-honeydew producers Aonidiella aurantii Maskell (California red scale; CRS) and Phyllocnistis citrella (Staiton) (citrus leafminer). The study was conducted in three commercial citrus orchards, each one dominated by one ant species (Pheidole pallidula, Lasius grandis or Linepithema humile) during two consecutive growing seasons (2011 and 2012). We registered a significant reduction of the CRS densities on fruits in the ant-excluded treatment in the three orchards and in the two seasons, ranging from as high as 41% to as low as 21%. Similarly, the percentage of shoots occupied by A. floccosus was significantly lower in the ant-excluded plots in the orchards dominated by P. pallidula and L. humile. No significant differences were registered in the percentage of leaf surface loss caused by P. citrella between ant-allowed and ant-excluded treatments in any case. We found no significant differences in the percent parasitism between ant-allowed and ant-excluded treatments for honeydew and non-honeydew producing herbivores. These results suggest that: (i) ant management should be considered in order to reduce herbivore populations in citrus and (ii) mechanisms other than parasitism (e.g., predation) might explain the differences in herbivore infestation levels between treatments.

We followed lifetime trajectories of reproductive allocation in Coleomegilla maculata females of three different size classes produced by rearing beetles on three different daily larval feeding regimes (30 min, 6 h or ad libitum access to eggs of Ephestia kuehniella). We hypothesized that small females would produce fewer and smaller eggs than larger females and that reproductive effort would decline with female age. Females were mated with a male from the same treatment and then isolated with ad libitum food for their entire adult lives. Egg size increased over time in all treatments; small females started off laying the smallest eggs, but increased egg size more rapidly than larger females, until all treatments converged on a similar egg size around the 20th day of oviposition. Large females realized a larger proportion of their fecundity early in life, but smaller females increased daily fecundity over time. Reproductive effort (egg mass/body mass) did not decline over 30 oviposition days; it remained constant in large females, but increased among small and medium females, suggesting gradual compensation for larval food deprivation. An increase in egg size with maternal age may be an adaptive strategy to maximize fitness on ephemeral patches of aphid prey, assuming females reproduce in a single aphid outbreak and that offspring produced later in the aphid cycle experience greater competition and risk of mortality compared to those produced earlier. We demonstrate for the first time in Coleoptera that dynamic changes in both egg size and number occur as a function of female age and illustrate that such changes are constrained by larval feeding histories via their effects on maternal body size.

Dissections of over 93,000 grass stems obtained by random core-sampling of natural grasslands at a site in Berkshire largely confirm earlier conclusions regarding the associations of different species of dipterous stem borers and grasses. Allowing for the number of stems of each grass species per unit area, the densities of larvae were greatest in Anthoxanum odoratum, Poa and Lolium and lowest in Dactylis glomerata. Oscinella frit (L.) was less abundant than Cetema spp. and Opomyza germinationis (L.); it was not found in D. glomerata but was most abundant in Lolium and Festuca. Sampling showed that overwintering larvae of O. frit suffer at least 50 per cent, mortality between September–December and January–March.

Previous studies have largely concentrated on populations in different species of grasses, but it is advantageous to consider the production of O. frit in terms of short (grazed or regularly mown) grasslands and long grasslands (hay fields, uncut commons and rough grazing); comparisons of figures obtained by core-sampling for larvae and emergence traps for adults indicate a production from short grassland and long grassland of about 11 and under 1 overwintered adult per sq. yd., respectively. Having regard to the greater productivity of common leys, dominated by Lolium and Poa, a national average for the first figure would be 15. There is little increase from generation to generation in grassland populations during the year, in contrast with the situation in oats.

From tentative estimates of the acreages and productivities of the different sources of O. frit in England and Wales as a whole, it is clear that the majority of the adults of O. frit are produced by grasslands in the spring and summer and by the oat panicles in the autumn, the latter population being much the greater. As O. frit is a migratory insect, such a conclusion is especially significant and indicates that during the autumn the ‘ population pressure ’ in the grasslands will be very different to that during other seasons.