Oligo- and mesotrophic wetlands, such as bogs, fens and swamps, have become more and more restricted in Europe, and wetland species related to them have increasingly been threatened. Due to increasing habitat fragmentation, the exchange of individuals of these species among sites and, as a consequence, gene flow has been reduced or even eliminated. Therefore, we analysed the genetic structure of 11 populations of an endangered stenotopic damselfly, Nehalennia speciosa (Odonata: Coenagrionidae), in Poland and Lithuania by means of allozyme electrophoresis of 14 gene loci. The overall genetic diversity of all populations was low (A: 1.32; H: 2.6%; Ptot: 29.2%), and no significant differences were observed among the different groupings of populations (degree of fragmentation, habitat type and size, population size). The genetic differentiation among populations was also low (FST: 2.0%) and no regional groups were detected. A low degree of isolation by distance was observed for genetic distances. Taking into account these results, the conservation effort for this species should be focused on large local populations and not necessarily on metapopulation structures. Furthermore, N. speciosa could be (re-)introduced in extinct patches and seemingly suitable localities. Genetically, such relocations should be feasible due to the generally high genetic homogeneity of populations.

DDT in odourless distillate was topically applied to individual males and females of the Rothamated wild type of Drosophila melanogaster Mg. The lines for the regression of mortality in probits on log. dosage of DDT for males and females, five days old, were parallel, and males were 1·86 times as susceptible as females. Susceptibility was high in young flies, but rapidly decreased with age, to a minimum at about five days, thereafter increasing rapidly in males and not significantly in females. The need for sexing and standardising age in flies used for toxicological investigations was thus demonstrated.

Respiration rate in untreated flies was measured by a modified Barcroft method. In males it increased with age up to five days, and then decreased; in females it increased with age up to nine days. Variations with age in respiration rate and susceptibility to DDT were negatively correlated.

Laboratory evaluation of alternative insecticides to replace persistent organochlorines in leaf-cutting ant baits is described, based on tests of 40 candidate compounds which were bioassayed with Atta cephalotes (L.) and Acromyrmex octospinosus (Reich). Insecticides having a suitable delayed killing action are listed, together with others which, although highly toxic to ants, had too rapid an action, but could feasibly be modified by using a controlled-release formulation.

A search was also made for alternative bait matrices to replace the expensive and often inadequate materials in current use. Horticultural grade vermiculite with sorbed orange juice as an arrestant was the best matrix tested, being at least as attractive as dried citrus pulp, which was the best previously known matrix.

Treatment of dried citrus pulp bait with propionic acid gave considerable protection against moulds, which spoil stored baits and baits placed in the field, and did not alter the attractiveness of these baits to ants.

Spalgis epius and Cryptolaemus montrouzieri are the two potential predators of different species of mealybugs. However, the mode of their interactions is not known to use these predators together in the field. Hence, we investigated on the possible interactions i.e., cannibalism, intraguild predation (IGP) and competition between the predators in the presence and absence of prey Planococcus citri. In the presence of prey, no cannibalism and predation were observed in both S. epius and C. montrouzieri larvae. A pair of S. epius larvae consumed significantly more number of mealybugs than one S. epius/C. montrouzieri larva or a pair of C. montrouzieri larvae. The predation of S. epius larva by C. montrouzieri larva was significantly more than the predation of C. montrouzieri by S. epius. Conspecific and interspecific egg predation was absent both in S. epius and C. montrouzieri. Cannibalism in C. montrouzieri was more than that in S. epius. The study indicated that C. montrouzieri larvae can be used as an additive along with voracious S. epius larvae under abundant prey population. IGP was asymmetric between the two predators in the absence of prey. Both S. epius and C. montrouzieri larvae can maintain a stable coexistence when prey is abundantly available, however, in the complete absence of prey C. montrouzieri may dominate the guild. This study provides an insight into the possible complex inter- and intraspecific predatory phenomena in the field to use these two predators in the biological control of mealybugs.

A simple density-dependent reinvasion model is described and used to estimate tsetse fly populations on the basis of removal trapping experiments. The model was tested on Glossina fuscipes fuscipes Newstead in the Central African Republic and G. palpalis palpalis (Robineau-Desvoidy) in the Republic of Congo (Brazzaville). The density-dependence is modelled by postulating that the inflow of flies each day is proportional to the deficit relative to the equilibrium population. Non-linear least square techniques were used to estimate the following parameters: the daily capture rate, the strength of the density-dependence, and the equilibrium fly population, at the beginning and at the end of the trapping experiment. The model ignores birth and death rates of flies and is applicable only when a rapid decrease in population occurs over a short period (between 10 and 20 days). Over longer periods one could not ignore the natural growth of the populations as well as other more complex density-dependent mechanisms.

Desiccation resistance was examined in pre-diapause, diapause and post-diapause larvae of the spruce budworm, Choristoneura fumiferana (Clemens), in terms of passive water evaporation under three desiccation conditions: freeze-drying, desiccant-drying at 2°C and desiccant-drying 18°C. Diapausing second instar larvae and post-diapause non-feeding second instar larvae showed strongest desiccation resistance: a significant amount of water was retained after repeated drying under desiccating conditions, while pre-diapause first instar larvae and post-diapause feeding instar larvae lost almost all their water content after one or two drying cycles. A hibernaculum covering had no effect on water evaporation. While dead larvae tended to lose significantly more water than their living counterparts, particularly among first instar larvae, such an impact much weaker among diapausing second instar larvae. Desiccation resistance was lost when post-diapause second instar larvae were allowed access to water while the level of desiccation resistance was maintained or enhanced when the larvae did not have access to water. These results are discussed the context of overwintering ecology of the species and possible mechanisms for the desiccation resistance are also discussed.

The African weaver ant, Oecophylla longinoda, is being utilized as a biocontrol agent and may also be targeted for future protein production. Rearing of mated queens in nurseries for colony production is needed to cater for such demands. Thus, newly mated queens must be collected for use as seed stocks in the nurseries. To collect mated queens efficiently it is important to identify when sexuals occur in mature colonies. We studied the occurrence of sexuals in O. longinoda colonies for 2 years in Tanga, Tanzania, a region characterized by a bimodal rainfall pattern. We found that O. longinoda sexuals occurred almost throughout the year with abundance peaks from January to April. Production of sexuals appeared to be triggered by rainfall, suggesting that populations in areas with long rainy periods may show prolonged mating periods compared to populations experiencing extended dry periods. The bimodal rain pattern may thus cause a low production over a long period. The average yearly production of queens per tree and per colony was estimated to be 449 and 2753, respectively. The average number of queens per nest was 17. Worker abundance declined from January to March with minimum by the end of this period, being inversely proportional to the production of sexuals. In conclusion, mated queens may be collected almost throughout the year, but most efficiently by the onset of the long rainy season when the majority disperse.

Observations in three areas in northern Tanganyika on the day-time resting sites of adults of Glossina swynnertoni Aust. showed that the most important of these was the underside of branches of trees. The number of flies seen on this site represented about one-third of the total population as calculated from the apparent density, and about half of them were on branches 4–9 ft. above ground, 1–4 in. in diameter and at an angle of less than 35° from the horizontal. It is suggested that were an insecticide to be applied to branch sites within these limits, then, since any fly must make six or more flights in the first 18 days of its life, it would be expected to alight on a treated surface at least once in this period. Were a lethal deposit maintained for twice this period, plus the pupal period, control could be effected.

An attempt has been made to assemble the important factors concerned with the atomisation of a kerosene spray and to consider the behaviour of the spray alone, and in its relation with an insect flying through it.

The degree of atomisation attained by the spray gun is dependent upon nozzle design, the spraying pressure, the relative rate of liquid and air flow through the nozzle and such physical properties of the spray fluid as viscosity and surface tension.

All atomisers produce droplets of a variety of sizes which leave the gun with a considerable velocity and are carried along by the air current. At this stage they are at their maximum size and possess their maximum velocity so that the chance of impacting with an insect is great. Later on when the droplets have lost much of their velocity and volume (if they contained a non-volatile insecticide they will have become much more concentrated), they are much less likely to impact. It can thus be seen that a non-toxic carrier can increase apparent toxicity of a spray mist by assisting in the production of the momentum necessary for impaction (David and Bracey, 1944). On the other hand a reduction in the size of the droplet decreases the rate of loss from the air space by precipitation. In connection with evaporation the enormous change in concentration which occurs should be borne in mind. Within a few minutes the smallest droplets will have entirely evaporated, leaving only the non-volatile solute and before this stage is reached the droplet will have become super-saturated. Finally this non-volatile solute will exist as minute nuclei which, when they result from a fairly typical insecticidal formula containing up to say 5 per cent. nonvolatile material, may be so small as to settle only very slowly.

Regarding the response of the insect to the spray mist, it may be said that this depends upon the resistance of the insect and the dose of insecticide picked up. Since the spray mist takes some time to distribute evenly and since it is more easily picked up during or immediately after spraying and by insects in flight, it can be seen that the dose received by individual insects will vary a good deal unless the insects behave identically so that under these conditions there is little correlation between the comparative effect recorded on individuals and their relative innate resistance.

To the above remarks arising out of the theoretical discussion which formed the first part of this paper must be added the following conclusions from the experimental work.

Wolbachia is an intracellular symbiotic bacterium that infects various spider mite species and is associated with alterations in host reproduction, which indicates the potential role in mite evolution. However, studies of Wolbachia infections in the spider mite Tetranychus pueraricola, a major agricultural pest, are limited. Here, we used multilocus sequence typing to determine Wolbachia infection status and examined the relationship between Wolbachia infection status and mitochondrial diversity in T. pueraricola from 12 populations in China. The prevalence of Wolbachia ranged from 2.8 to 50%, and three strains (wTpue1, wTpue2, and wTpue3) were identified. We also found double infections (wTpue1 + wTpue3) within the same individuals. Furthermore, the wTpue1 strain caused weak cytoplasmic incompatibility (CI) (egg hatchability ~55%), whereas another widespread strain, wTpue3, did not induce CI. There was no reduction in mitochondrial DNA (mtDNA) or nuclear DNA diversity among infected individuals, and mtDNA haplotypes did not correspond to specific Wolbachia strains. Phylogenetic analysis and analysis of molecular variance revealed that the distribution of mtDNA and nuclear DNA haplotypes were significantly associated with geography. These findings indicate that Wolbachia infection in T. pueraricola is complex, but T. pueraricola genetic differentiation likely resulted from substantial geographic isolation.

Oedaleus asiaticus Bey. Bienko is a significant grasshopper pest species occurring in north Asian grasslands. Outbreaks often result in significant loss in grasses and economic losses. Interestingly, we found this grasshopper was mainly restricted to Stipa-dominated grassland. We suspected this may be related to the dominant grasses species, Stipa krylovii Roshev, and hypothesized that S. krylovii contributes to optimal growth performance and population distribution of O. asiaticus. A 4 year investigation showed that O. asiaticus density was positively correlated to the above-ground biomass of S. krylovii and O. asiaticus growth performance variables (survival rate, size, growth rate) were significantly higher in Stipa-dominated grassland. A feeding trial also showed that O. asiaticus had a higher growth performance when feeding exclusively on S. krylovii. In addition, the choice, consumption and the efficiency of conversion of ingested food (ECI) by O. asiaticus was highest for S. krylovii compared with other plant species found in the Asian grasslands. These ecological and biological traits revealed why O. asiaticus is strongly associated with Stipa-dominated grasslands. We concluded that the existence of S. krylovii benefited the growth performance and explained the distribution of O. asiaticus. These results are useful for improved pest management strategies and developing guidelines for the monitoring of grasshopper population dynamics against the background of vegetation succession and changing plant communities in response to activities such as grazing, fire and climate change.

1. Primary fly-belts round Makongo consisted of three different vegetational communities: a Cynometra-Vitex association along the main length of the Makongo river, on a clay soil; a Ficus congensis association along the river close to the town, on a sandy soil; and Isoberlinia doka woodland on moist sandy soil north-west and south of Makongo.

2. Secondary fly-belts of less dense vegetation occur in the orchard bush savannah round Makongo, and these are not colonised until the commencement of the rainy season.

3. Glossina tachinoides and G. palpalis both occurred in the riverside communities, and G. palpalis alone in the Isoberlinia woodland.

4. Along the river G. palpalis outnumbered G. tachinoides by 3:1 in the dry season. At the commencement of the rains G. tachinoides increased more quickly than G. palpalis, bringing their numbers very nearly equal, but at the end of the rains there was a decrease in G. tachinoides which restored the original proportion.

5. G. morsitans had been found at Makongo formerly but was not met with at the time of this investigation, its absence being due to the disappearance of the larger antelope from the neighbourhood.

6. Smaller game animals, small mammals and reptiles afforded an adequate food supply for tsetse in the fly-belts, and also passing herds of cattle, as well as natives from the village and travellers.

7. The distribution of G. palpalis within the fly-belts was markedly influenced by the proximity of a cattle road along which herds of cattle passed almost daily, and by village water-holes.

8. During the dry season the primary foci were always found to be the places of greatest relative humidity, and the fly does not tend to move out of these until the general atmospheric humidity has reached a certain fairly high degree.

9. In clearing the fly-belts the removal of all primary foci within a quarter of a mile of the town and of thick bush within 100 yards of water-holes was undertaken. The work lasted from the beginning of February to the end of March 1931.

10. The effect of clearing the Isoberlinia doka woodland was to banish G. palpalis completely, and it never returned to these clearings.

11. On clearing the riverside Ficus congensis fly-belt, G. tachinoides was practically eliminated for the first three months, but reappeared in the clearings in June when there was a general increase and up-stream migration of this fly. G. palpalis remained in this clearing in fluctuating numbers up to June, when observations were suspended.

12. 565 marked tsetse were liberated in the fly-belts immediately previous to clearing. Of G. palpalis 12·7% were recaptured in the clearings and 11% outside the clearings. Of G. tachinoides 5·5% were recaptured in the clearings and 6·8% outside.

Light-trap catches of Heliothis armigera (Hb.) reach peaks during the wet seasons, April and November–January. Initial infestation of seed beans by H. armigera occurs in April–May at the time of flowering of the early-sown crop, the adults probably originating from an earlier generation on maize. Two generations are completed during the main seed bean season, the first on early-sown beans and the second on later beans, and the dry period July–October may be passed in pupal diapause. Damage, caused by the older larvae eating the seeds in the pod, is prevented by spraying the young larvae with DDT (25% e.c. at 3 pt/2 gal spray/acre) (the standard treatment) or endosulfan (35% e.c. at 1½ pt/2 gal spray/acre) at about six weeks after the beans emerge.

Adults of the Pentatomid Nezara viridula (L.) invade bean fields from alternative host-plants at the same time as H. armigera. This species, even in small numbers, causes the loss of young pods and also damages or kills the developing seed. It is not controlled by the standard DDT treatment for H. armigera, but the following insecticides were found to be effective: γBHC 20% e.c. (1¼ pt), dieldrin 18% e.c. (2 pt) and endosulfan 35% e.c. (1½ pt) in 2 gal spray/acre. Where N. viridula and H. armigera are found together, the standard recommendation is endosulfan 35% e.c. (1½ pt/2 gal spray/acre).

The Coreids Acanthomia horrida (Germ.) and A. tomentosicollis (Stål) cause damage similar to that of N. viridula, but are serious only when infestations are heavy. They were found to be controlled by DDT, dieldrin or endosulfan at the rates given above.

Alatae of the bean aphis Aphis fabae Scop, invade bean fields mainly during the first two weeks of the crop, producing apterae which concentrate on the tip of the plants. Damage (stunting, and loss of flowers and pods) is serious only when large populations of apterae are produced on a high proportion of the young plants. The early infestation demands control measures separate from those for the other pests, the most effective being methyl-demeton 50% e.c. (½ pt/2 gal spray/acre) applied 3–4 weeks after emergence. Endosulfan, although promising and far less toxic than methyl-demeton to larvae of the predator Cheilomenes lunata (F.), was discarded on grounds of cost, as was dimethoate. Aphid populations reached a peak during July and August and decreased with the warmer weather in September. A large number of alternative host-plants is listed, but the source of the primary flight into beans is not known.

Melanagromyza phaseoli (Tryon), the life-cycle of which is completed in 23 days, is unimportant on seed beans as it is least abundant during the growing period of the main crop, but may damage plants suffering from water stress. Tunnelling in stems by larvae was controlled by seed dressings of aldrin or heptachlor (both 40% wettable powders mixed with seed at 1:200 w/w).

Ukara Island was selected for studies on the transmission of bancroftial filariasis because it provided a naturally circumscribed area with a substantial human population of which adequate numbers showed miorofilariae. It is a closely-knit and stable community.

Filarial infections also occur in bird, lizard, dog and hyrax (rock-rabbit) on the island. The determination of the vectors of human filariasis thus depends on evidence of different kinds, the present paper considering only the general correlation of microfilarial incidence with the distribution of common domestic mosquitos in villages of the island.

Leaving the Government post on the Amala river, at an altitude of 5,500 feet, on 25th July, I moved down the west bank of the river and camped at a spring known as Ol-otu-lomot, at an altitude of 5,200 feet (see accompanying sketch-map). The next day I moved further down the river in search of an old Masai native, by name Ol-botor-ol-joni, who was reported to be familiar with the places in which tsetse-fly (Endorobo of the Masai) was to be found. I found this old man at the place marked on the map and camped there at an altitude of 5,100 feet.

A study of adult populations of Wheat Bulb Ply, Leptohylemyia coarctata (Fall.), has been carried out in the field by routine sweeping at Rothamsted. It has been observed that the males emerge slightly before the females and that the emergence period may cover at least three weeks in late June and early July. Although the number of males may exceed the number of females at first, the females predominate later in the season due to the shorter life span of the males.

The numbers of flies on the wheat have been found to fluctuate appreciably throughout the day. During the first week of the emergence period the number of flies taken increased steadily throughout the day. After the date of population peak, however, the maximum numbers occurred in the crop in the very early morning and the late evening, which suggested a daily flight dispersion followed by a general or localised return of the flies to the crop. Further study of the data showed that the daily temperature rhythm was only partly responsible for this daily flight dispersion, and that there appeared to be an active return flight to the crop in the evening. Generally the males were more active than the females and did not settle so deeply in the crop.

The temperature threshold for flight was observed to be 12 to 13°C. Winds up to 8 m.p.h. did not appear to affect flight activity, but higher winds, e.g., 15 m.p.h., markedly reduced flight, the flies remaining deep in the crop near ground level. Gale-force winds, however, were observed to produce a permanent depletion in the number of flies infesting Broadbalk field, indicating that the population was probably localised.

Although portions of the populations dispersed fairly rapidly from the emergence sites, recaptures of radioactive flies labelled with 32P indicated that the extent of the dispersions was not very great. The females dispersed more than the males, and were influenced to some extent by the occurrence of wheat in flower. Frequently the flies were found to have congregated on the lee edge of the crop, but other preferred regions have been observed which could not be attributed to the influence of the wind.

The seasonal biting-incidences on man of several species of mosquito inside and outside huts of villages on Ukara Island, Tanganyika, between 7 p.m. and 3 a.m. East African Standard Time are recorded. Anopheles gambiae Giles and A. funestus Giles were by far the most common indoor biters in both of the villages which received study: they were also taken biting outdoors in fair numbers. Tacniorhynchus africanus (Theo.) and T. uniformis (Theo.) were common outdoor biters in a village near a swamp, but were taken in only small numbers off human “bait” in a cone hut.

A study of sleeping arrangements in huts showed that people between six and sixteen years of age were most exposed to the risk of mosquito bites at night, since they were least protected by covers and clothing.

The inhabitants were bitten by Aëdes africanus (Theo.) and Aë. apicoargenteus (Theo.) outdoors by day, and by small numbers of A. gambiae and A. funestus in huts during daylight hours in April.

The results are given in detail of dissections for developing filarial worms in over seven thousand mosquitos. Proboscis infections occurred in A. gambiae and A. funestus. Immature (thoracic) forms were found in A. pharoensis Theo., T. africanus, T. uniformis and Culex antennatus (Beck.).

It is concluded that the biting-habits of A. gambiae and A. funestus point to them as more likely vectors of bancroftial filariasis than other species with developing filarial worms.

1. The ornamentation of the wings in Anopheles funestus, Giles, is variable.

2. Nine distinct arrangements of the wing scales were observed in a random sample of 1,084 individuals.

3. Nearly nine-tenths of the specimens occurred in one group, in which there were dark and pale forms.

4. Variations in wing markings are not solely related to sex or to habitat.

5. The pale form was more prevalent in the wet season and the dark form in the dry season.

6. It is suggested that further study may reveal whether the dark form is the hibernating variety and whether one form is more important as a carrier of malaria than the other, and that these details of wing ornamentation should be recorded in future.

An account is given of the damage caused by adults and larvae of Brontispa longissima (Gestro) to the young unopened fronds of coconut palms in the British Solomon Islands. Normally, only young palms less than 10 years old are severely attacked, but this has interfered seriously with replanting programmes. Full-grown palms suffer severe damage only occasionally; reasons for this difference in susceptibility are suggested.

Earlier reports, that seedlings of Malayan type are more readily and severely attacked than those of Samoan or local origin, were confirmed. A fertiliser treatment had no effect on the growth of the palms or the amount of damage by Brontispa.

Laboratory tests showed that the deposit from a spray of 0·2 per cent. p,p′DDT was completely effective for three–four weeks, that chlordane (0·16%) became significantly less effective in the third and fourth weeks, and that dusts of DDT, alone and with BHC, showed signs of diminished efficiency in the fourth week.

In small-plot trials with sprays of DDT or chlordane, applied at various concentrations and frequencies, the effects of treatment were assessed by counts, at suitable intervals, of living and dead examples of Brontispa, by estimating damage to the youngest open frond, and by measuring the growth of seedlings. DDT at 0·1, 0·2 and 0·3 per cent. of p,p′isomer, and chlordane at 0·08, 0·16 and 0·24 per cent. gave very satisfactory control of a heavy attack of the beetle and suppression of damage. Applications at 10-day intervals were more effective than 3-weekly ones. Similar trials with dieldrin at 0·1 per cent. and DDT at 0·3 per cent. against a light attack were completely effective.

In further trials, direct comparisons were made between DDT at 0·25 and 0·025 per cent., chlordane at 0·16 per cent. and dieldrin at 0·15 per cent. applied at both fortnightly and monthly intervals. The lower concentration of DDT was much less effective than the other treatments. DDT at the higher concentration and dieldrin were equally effective when applied at fortnightly intervals, but at monthly intervals the latter was superior in control of immigrant beetles. This is attributed to its greater persistence. It is concluded that, in the formulations used in this trial, dieldrin is superior to DDT and chlordane.

Further trials with dieldrin at 0·15 per cent. showed that palms subjected to only moderate reinfestation were adequately protected by spraying every six weeks, whilst isolated areas of young palms may be left much longer, probably several months, once the initial population has been controlled. The maximum frequency, under the most adverse conditions, might vary between 2 and 4 weeks, initially. Varietal susceptibility in the coconut does not affect the efficiency of control.

Slight phytotoxicity, indicated by retardation of growth and rate of production of new fronds, was caused by frequent applications of high volumes of spray, but the volume necessary to produce such effect is considerably in excess of that required for satisfactory control. Unnecessarily high volumes and concentrations should, however, be avoided.

The spray was applied to each palm, individually, downwards on to the central spike, where the beetle lives. Equipment capable of delivering a fine, low-volume spray controlled by an efficient trigger tap will use only about 16 cc. spray per palm up to 3 years old. With a low-volume atomiser, this consumption can be reduced to about 6 cc.

An imitation aerial spray gave promising but inconclusive results.

With the proprietary formulations of insecticides used, the addition of a wetting agent was unnecessary.

Field applications were tried out in the Russell Islands on extensive areas of young palms that showed heavy beetle attack. Sprays containing dieldrin or DDT, each in two proprietary formulations, gave excellent and satisfactory results, respectively.

It is concluded that the experiments clearly indicate that very satisfactory control can be achieved at low cost, and that a programme of replanting could be safely embarked upon without fear of the severe losses, due to Brontispa, that have been suffered in the past.

Trajectory analysis was used to determine the direction and extent of windborne migrations of insects trapped in autumn and winter in south-east and east Asia for 12 years between 1968 and 1987. Nearly 2600 trajectories were drawn upwind at 10 m and 1.5 km from 15 catching sites and within the time (⋜60 h), wind speed (⋝5 km h-1) and temperature (⋝10°C) thresholds used, only 5% of the trajectories failed to locate a possible source and over 90% were completed in 40 h or less. The delphacids Nilaparvata lugens Stål and Sogatella furcifera (Horváth) dominated the trap catches (96%) with Cicadellidae (2.3%) and Diptera (0.5%) as the next most numerous. Very few Lepidoptera were reported (<0.3%). Nearly 80% of the trajectories were constructed in the prevailing Winter Monsoon and Trade winds, resulting in a southward displacement of insects towards putative overwintering areas as reported in previous studies. Tropical cyclones in autumn, produced trajectories which differed in both direction and extent from those in the prevailing winds, supporting the suggestion that the contraction of the distribution areas of rice pests at this time of year is the product of a series of movements in different directions. The results suggest that migrations continue throughout the year in the tropics and sub-tropics and indicate that this may be one way the capacity for long distance migration is maintained in some rice pest populations.