The dispersal of Microctonus hyperodae Loan, an introduced parasitoid of the South American grassland pest Listronotus bonariensis Kuschel, was measured in Canterbury, New Zealand. Considering all directions, the mean annual dispersive increment was 1.9 ± 0.9 km year–1 as measured in the winters of 1993, 1994 and 1995. The parasitoid’s ground distribution suggested that its movement was biased towards the south-west indicating probable wind-borne dispersal. The overall relatively low rate of dispersal was thought to be related to the inhibitory effects of M. hyperodae parasitism on L. bonariensisflight. A generalized linear model fitted to percentage of L. bonariensisparasitized took a simple form, with a quadratic increase in weevil infection, that with time, gradually decreased. The build-up of parasitism at the release site was significantly greater than the rates at the other sites measured in this study (P< 0.001) with a ratio of release site: dispersal site rates of 1.33: 1. The simplicity of the fitted generalized linear model indicated remarkable uniformity in both parasitism build-up and dispersal from one year to the next; this finding indicated that all dispersal was ‘natural’ and unassisted by human activity. Despite such modest dispersal rates, by the winter of 1996, five years after its release, the parasitoid had spread geometrically over an area of c. 140 km2.

The attack rate by the parasitoid Apanteles glomeratus (L.) on laboratory-reared larvae of Pieris rapae (L.) exposed for 3–4 day periods in a kale field in Massachusetts was greater when five larvae rather than two were placed on plants. The attack rate was greatest if host larvae were in the first instar when placed in the field, and little or no attack occurred when second- or third-instar larvae were exposed. The co-occurrence of unoccupied P. rapae larval feeding sites on plants where larvae were exposed reduced attack rates. Parasitism rates in trap-host larvae and in field-collected larvae (counting only cases in which the parasitoid was still in the egg stage) did not differ as estimators of recruitment to the population of parasitized hosts either in terms of total recruitment achieved per host generation or in the temporal pattern of the recruitment. In both simple and multiple linear regressions, the density of young P. rapae larvae (either parasitized or not) was the strongest correlate of parasitoid recruitment for the whole season, whereas average air temperature was the strongest correlate in the last month of observations (September).

Seasonal abundance of fleas infesting small mammals was studied from July 1975 to August 1976 in a grassland in Lake Nakuru National Park, Kenya. Ten species of rodents and two species of shrews were live-trapped 935 times. The Nile grass rat (Arvicanthis niloticus) was the most abundant species, with 233 individuals captured 690 times, forming 73·8% of all captures. From these grass rats, 4247 fleas were collected, including Dinopsyllus lypusus Jordan & Rothschild (n = 2596), Xenopsylla bantorum Jordan (n = 1396) and Ctenophthalmus calceatus cabirus Jordan & Rothschild (n = 255). D. lypusus and C. calceatus cabirus were more abundant on Nile grass rats during the rains, while ×. bantorum became more abundant during the dry season and peaked during the early part of the rains. The potential for plague transmission by fleas between Nile grass rats probably exists all year. The potential for transmission to people living in close proximity to these rodents may be highest during the seasonal peak of X. bantorum, at the end of the dry season.

Oryctes rhinoceros (L.) is a major pest of coconut palms in Papua New Guinea but has a limited distribution within the country. Pre-release monitoring showed that no baculovirus disease was present in the country prior to its importation. A consignment of O. rhinoceros larvae infected with a baculovirus disease was imported into Papua New Guinea from Western Samoa in 1977. The virus proved highly infectious to both larvae and adults of the local population of O. rhinoceros. During 1978 and 1979, adults were perorally infected with the baculovirus and released at nine sites on Manus Island, four sites on New Ireland and twelve sites on the Gazelle Peninsula of East New Britain. The infected adults were active disseminators of the virus into the field population, and the virus became established at nearly all the release sites. The shortest time between virus release and recapture of newly infected adults from a release site was eight weeks. Three different examples indicated the virus spread at approximately 1 km/month. During a fourteen-week period in the early establishment phase, significantly more females than males were collected in traps but a significantly higher percentage of the males was infected.

The age-composition of mosquitos biting at different times and levels was investigated in Zika Forest, Uganda. The four species studied were Mansonia aurites (Theo.) group (material mainly of actual M. aurites (Theo.) but probably including some examples of M. microannulata (Theo.)), Aedes africanus (Theo.), A. ingrami Edw. and Culex annulioris Theo. In each case the biting cycles of nulliparous and parous females were computed separately.

The material examined came from eleven 24-hour catches made by Dr. A. J. Haddow. Samples were taken at seven levels, at 20-ft. intervals, from the ground to a height of 120 ft. The top of the canopy was at 70–80 ft.

In each species the biting cycles of nullipars and pars were closely similar, both at the preferred level and at all levels combined. In only one case (that of the group of M. aurites) was there a significant and consistent difference in the average age of females at different levels, there being a relative excess of older females above the canopy, as found previously in M. fuscopennata (Theo.). This difference persisted throughout the period of biting activity.

These and other recent findings are briefly discussed. It is concluded that the hypothesis which relates the form of the mosquito biting cycle to the age-composition of the biting population and to the larval habitat of the species concerned cannot be accepted as a valid generalisation.

The encyrtid parasitoid Apoanagyrus diversicornis (Howard) (formerly known as Epidinocarsis diversicornis) failed to establish itself in Africa where it was introduced, in addition to A. lopezi De Santis for the biological control of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero. Apoanagyrus lopezi is a better competitor and available evidence suggests that competition prevents the coexistence. Yet, both parasitoid species were reared from P. manihoti in the same locality in their native South America. Competition should prevent coexistence on P. manihoti in South America as well as in Africa. We investigated how A. diversicornis persists in South America. The use of alternative hosts could explain its persistence. We aimed at finding possible alternative hosts for A. diversicornis that can serve as a refuge from competition with A. lopezi. The existing information on the distribution of A. lopezi and A. diversicornis and their known hosts in South America is reviewed. Candidate alternative hosts for A. diversicornis were selected and tested. Alternative hosts should at least be suitable for development of A. diversicornis and unsuitable for development of A. lopezi. Only Phenacoccus herreni Cox & Williams met these requirements. Phenacoccus madeirensis Green, P. solani Ferris and Ferrisia virgata (Cockerell) were unsuitable hosts for both species. In cages with continuous parasitoid populations under strong interspecific competition, A. diversicornis did significantly better if half the population of P. manihoti was replaced by P. herreni. This supports the hypothesis that P. herreni can serve as an alternative host for A. diversicornis in South America and that its presence enhances coexistence of A. diversicornis and A. lopezi. Phenacoccus herreni is absent in Africa.

Densities of four herbivorous insect species were compared on field beans (Phaseolus vulgaris) grown in monoculture and those grown in relay intercropping with winter wheat. In three years of study in New York State, population densities of Empoasca fabae (Harris) and Aphis fabae Scopoli were significantly less in plots intercropped with winter wheat than in those grown in monoculture. In contrast, intercropping was associated with greater densities of Lygus lineolaris (Palisot de Beauvois) and Systena frontalis (F.). An increased density of L. lineolaris may be an economic risk factor in beans intercropped with wheat because only this species of the four studied feeds exclusively on the flowers and developing seed pods.

The biology of three West African ambrosia beetles, Trachyostus aterrimus (Schauf.), T. ghanaensis Schedi and T. schaufussi schaufussi (Strohm.) is described on the basis of studies made in China and Nigeria, and notes are given on the six other species and subspecies of Trachyostus that have been taken in West Africa.

All species of Trachyostus are confined to forest areas in West Africa. some of the species extend into montane and swamp forest, but the genus is most abundant in lowland rain forest. It is suggested that susceptibility to desiccation of the young larvae and of the ambrosia fungus is the principal factor in limiting Trachyostus species to forest areas. Two species, T. ghanaensis and T. interstitialis Schedl, are confined to the forests between Sierra Leone and Ghana, but the remaining species are found throughout the lowland forest of west Africa.

Host selection by species of Trachyostus depends mainly on the taxonomic status of the host, the condition of the tree, and the time of year. The genus as a whole is considered very selective. T. ghanaesis attacks living trees of only one host species, selecting individual trees and favouring the most vigorous. All other species of Trachyostus normally attack felled trees of a wide range of host species, but show preferences for those of a small number of plant genera. Attack on living trees by species other than T, ghanaensis occurs in the dry season. It is suggested that T. ghanaensis is sensitive to subtle changes in tree condition, while the remaining species require a more drastic change before attacking such trees.

The process of nest initiation and establishment is described for ome species. Species of Trachyostus differ from other tropical Platypodids in that the length of time elapsing between nest initiation and the emergence of the first young adults is exceptionally long. This is thought to be mainly due to the ambrosia fungus requiring a long time to establish itself on the gallery walls of the nest.

All species of Trachyostus are active in daylight hours. Emergence of young adults from the nest occurs only in daylight and is dependent on a drying atmosphere. Falling light intensities probably contribute towards ending emergence in the late afternoon. The thresholds of humidity and illumination for emergence of T. schaufussi schaufussi appear to be higher than those of T. aterrimus.

Nests of T. aterrrimus and T. schaufussi schaufussi remain functional for about nine months, but those of T. ghanaensis can still be active after four years. The protracted nest duration of T. ghanaensis is apparently a consequence of the habit of this species of attacking living host trees in which the rate of development seems to be slowed down. Only a small proportion of the nests initiated by species of Trachyostus are successful. In T, ghanaensis this high failure rate is attributable to failure of the ambbrosia fungus, but in the other species insect nest-associates and predators are apparently the main causes.

The habits and life-history of T. ghanacnsis can only be compared with those of one other Platypodid, Dendroplatypus impar (Schedl), a Malaysian species. Both species attack only living trees, and show a high degree of host selection. The intensity of attack on the host tree by these species is very low, and the life-cycle of each seems to take a long time for completion.

An illustrated description is given of the construction details of a stable trap in Jamaica to catch Anopheline mosquitos. This trap is of knock-down type, which is more portable than many traps used for the same purpose.

Mosquito “ catches ” from stable traps are a means of obtaining information for planning anti-Anopheline work in a new area. These “ catches ” can be carried out with regularity and can give data to indicate the need of strengthening control measures to deal with the seasonal emergence of different mosquitos in specified zones.

The area in which the Health Officer of Kingston requires information about the prevalence of Anophelines is so extensive that nearly fifty regular mosquito catching stations should be visited at least twice a month. In order to obtain the needed data with the present staff, the writer recommends the simultaneous use of six portable stable traps.

1. Algae are ingested by many species of mosquito larvae and appear to form an important part of the food of these larvae.

2. The algae are digested in the gut, but the digestion is often by no means complete.

3. It is quite possible that the rôle played by the algae may also be assumed by other forms of organic matter, for larvae may be reared to maturity in solutions containing little or no algae.

4. Different algae react differently in the guts of the larvae, some being noticeably digested and some hardly at all.

5. Those algae which are digested the most are easily stained and are forms of low osmotic pressure.

6. Cytological investigation revealed no character that indicates that algae are an especially nutritious diet.

This work was carried out at the Farnham House Laboratory of the Imperial Institute of Entomology, Buckinghamshire, under the guidance of Dr. P. A. Buxton, to whom my thanks are due.

Adults of Autographa gamma (Linnaeus) make regular, seasonal migrations into areas where they are unable to breed continuously. Individuals migrate into Britain each spring, and after one, two or three generations, offspring of the spring migrants return to over-wintering areas in North Africa and the Middle East. The larvae are highly polyphagous and have been recorded damaging many crops, especially Brassica spp. Insects usually migrate during the adults' pre-reproductive period (PRP). The length of this period is therefore an index of migratory potential since individuals with longer PRPs have more time to express their capacity for flight and to travel further. Individuals reared outside in Britain in autumn have longer PRPs than individuals reared outside in summer. Laboratory experiments show that PRPs are extended at low temperatures and under short photoperiods and there is some evidence that PRPs are also extended under gradually decreasing photoperiods. By extending PRPs in response to environmental conditions typical of Britain in autumn, individuals are able to increase their potential for pre-reproductive migratory flight and therefore their potential for reaching suitable overwintering sites further south.

1. The thermal constant and the zero of the velocity curve have been determined for each of the pre-adult stages of Tortrix postvittana, Walk. The experimental methods are described. The thermal constant for the eggs is 153 day degrees C. and the zero of the velocity curve 4·80°C. The corresponding constants for the larvae are 469 day degrees C. and 8·05°C, and for the pupae 182 day degrees C. and 5·93°C.

2. The experimentally determined constants and the mean monthly temperatures have been used to calculate the peak of the flight period of the adult moths at Huonville, Tasmania, during the 1935, 1936 and 1937 seasons. In three cases out of four the calculated dates approximate very closely to the observed dates for the peak of the flight period.

3. The results of observations on the number, duration and head-widths of the larval instars are given. The majority of larvae fed on young apple leaves had four instars. A greater proportion of the larvae fed on mature apple leaves had more than four instars. The length of larval life at 25°C. is significantly longer for both male and female larvae when they are fed on mature leaves. The head width of the final instar of four-instar female larvae is significantly greater than that of the final instar of four-instar male larvae. Food quality has no apparent influence on the head width of the final instar of either male or female larvae.

4. At 25°C. the length of larval life of female larvae is significantly longer than that of male larvae when both are fed on the same food ; the same tendency is exhibited at other temperatures. The separate velocity curves for male and female larvae are not significantly different in slope. The difference between velocity values for male and female larvae at the mean temperature approaches significance.

5. Larval mortality increases rapidly at temperatures above 30°C. and 100 per cent, mortality occurs at 35°C. Starved larvae at low temperatures and high humidities show a tendency for the survival time to increase with the size of the larvae. Final instar larvae under these conditions can survive for two and a half months.

Deposits of deltamethrin suspension concentrate (s.c.) on Terylene net and cotton cloth were bioassayed in Zimbabwe by exposing them to fed, female Glossina pallidipes Austen, using a 45 s contact with cloth and a brief collision with net. On textured yarn net, the effective life of deposits produced from immersion in 0.1% deltamethrin was longer than on flat yarn net, apparently because the textured net held more insecticide and the insecticide was lost more slowly. The addition of an absorber for ultra-violet light (0.1% 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid) did not significantly extend the effective life of deltamethrin deposits on cloth or net. Applying deltamethrin s.c. as a 0.6% suspension to cotton cloth produced mortalities of <90% for 300 days. Applications of 0.8% deltamethrin on cotton cloth and textured net produced mortalities of <70% for 12–16 months and 9 months, respectively, compared to 4–10 months and 5–7 months, respectively for applications of 0.1% deltamethrin. Chemical analyses indicated that the longer effective life of the 0.6–0.8% was due to a higher initial amount of insecticide and a lower rate of loss. It is suggested that for controlling tsetse in southern Africa, all-cloth targets sprayed with 0.6% deltamethrin s.c. will have an effective life of ca. one year.

Primary pests such as Rhyzoperta dominica may increase the contents of dockage, dust, and frass in grain mass. Although it has been suggested that frass can affect the population growth of stored product pests and ecological interactions among primary and secondary pests in stored grain, this has not been validated experimentally. Therefore, this work experimentally tested the hypothesis that R. dominica wheat frass may support population increases in secondary pests such as Tribolium confusum, T. castaneum, and Oryzaephilus surinamensis for the first time. The effect of frass on secondary pest performance was compared with the effects of various physical qualities of wheat grain (i.e., intact grain kernels, grain fragments, flour, grain + frass) and an artificially enriched control diet (milled wheat kernels, oat flakes, and yeast). The results showed that the clean intact grain kernels did not support the population growth of any tested species, and the nutrient-rich control diet provided the best support. Frass was a significantly better food medium for O. surinamensis and T. castaneum than flour or cracked grain, while T. confusum performed equally well on flour and frass. Our results showed that in terms of food quality and suitability for the tested species, frass occupied an intermediate position between the optimized breeding diet and simple uniform cereal diets such as cracked grain or flour. The results suggest that (i) the wheat frass of primary pest R. dominica is a riskier food source for the development of the tested secondary pests than intact or cracked wheat grain or flour; (ii) frass has the potential to positively influence interspecific interactions between R. dominica and the tested secondary pests; and (iii) wheat grain should be cleaned if increases in R. dominica populations and/or accumulated frass are detected.

Development rates of the aphid, Brachycaudus rumexicolens (Patch), a recent arrival in Australia and a potential biological control agent against weeds in the family Polygonaceae, were measured over a range of constant temperatures. The theoretical lower limit for development is 6.4°C and the upper limit 32°C. Maximum fecundity per day was reached at 19°C. The rate of increase peaked at about 28°C giving a population doubling time of less than two days. These values were used with the current distribution to develop a CLIMEX model to predict the potential world distribution of the aphid. The model predicts that the aphid has suitable periods of population growth in autumn and spring, and that survival is unlikely over summer in most of south-western Australia where the aphid has the potential to contribute to the biological control of the polygonaceous weeds, Emex and Rumexspecies. The model predicts that years with cool summer temperatures and late summer rains in south west Australia, such as in 1990 when the aphid was first abundant, will be particularly suitable for aphid development. These conditions occurred twice between 1985 and 1995. To increase the effectiveness of the aphid as a biological control agent of weeds in other years, augmentation by provision of alternative hosts and/or the release of mass reared individuals during autumn is proposed.

One of the most important pests of rain-grown cotton in the Sudan is the genus Dysdercus (Pyrrhocoridae) of the Hemiptera Heteroptera. Upon the introduction of cotton into the southern provinces of the Sudan, these insects appeared in great numbers, and in certain districts threatened to render impossible the growing of the crop. In 1926 work was started on the bionomics and control of the cotton-stainers by Cowland & Ruttledge, who were working respectively in the Nuba Mountains and the Fung provinces. Later the crop in the Nuba Mountains proving to be the more important of the two, the study of these insects was confined to that region. Mr. Ruttledge followed Mr. Cowland as entomologist in the Nuba Mountains, and the writer followed Mr. Ruttledge in 1928. The results of the preliminary investigations of Cowland & Ruttledge formed a valuable base from which the writer continued the work.

This review of investigations of Lygus simonyi, Reut., was originally written early in 1944 as a handing-over report, and was not intended primarily for publication. As I was then about to leave Uganda, it seemed desirable to place on record, for the information of my successors, the work which I and others had done, even though the investigations were still in an early stage. Since then, the opinion that publication of the report would be useful as a basis for future work has been expressed by the Empire Cotton Growing Corporation and others, and I have therefore agreed to publish it in spite of my consciousness of many shortcomings in it.

Development and survival of an erigonine spider, Erigonidium graminicolum (Sundevall) (Araneae: Linyphiidae), were studied at seven constant temperatures ranging from 15°C to 35°C. Plotting development rates (reciprocal of mean times for development) and survival rates (expressed as percentages) against the different constant temperatures indicated that E. graminicolum is well adapted to low temperatures, but sensitive to high temperatures. Juvenile development occurred over a wide range of constant temperatures, but the survival rate was low at the upper and lower extremes. All eggs died before hatching at the highest tested temperature (35°C). There were statistically significant differences between males and females in juvenile and pre-imaginal development times. Juvenile development time decreased as temperature was raised to 32°C, but increased at 35°C. The mean duration of pre-imaginal development (egg to adult) varied from 94.4 d at 15°C to 23.8 d at 32°C. Considering development rate and survival, the most favourable temperature range appeared to be 15–32°C. For all life stages, graphs obtained by plotting the reciprocal of development times against temperature could be described by the six-parameter rate function of Wang et al. (1982). Temperature-independent distributions of normalized development times were approximated by a cumulative Weibull function. Frequency distributions of development times changed with temperature; they were almost uniform at 15–20°C, more symmetrical at 25–28°C, and somewhat skewed to the right at 30–32°C. The sum of effective temperatures (SET), and lower development threshold (LOT), were established for all life stages of E. graminicolum. Survivorship curves varied with temperature and, on average, were Type III.

An airborne radar system able to measure insect density profiles and the orientation of individual insect targets was developed using standard components. Using the system, typical moth targets, with a radar cross-section of 1 cm2, can be detected to a range of about 1 km. Signals from 48 separate height bands, each 15 m deep, are recorded on three analogue data channels. Analogue outputs related to aerial population per hectare can be viewed in real-time. Signals recorded during recent field work show an inclined layer over a track length of 30 km, with target orientation profiles at two positions along the layer. The strongest orientation occurred in regions of wind shear. Airborne entomological radar powerfully complements existing techniques by virtue of its mobility, providing unique opportunities to study the spatial organization of migration, to track features as they develop and to survey large areas.