Serial exposure of a susceptible laboratory strain of Phthorimaea operculella (Zell.) recently obtained from the field to granulosis virus over six generations produced a 140-fold increase in LD50. The evidence suggests that this was due to a change in frequency of a resistance gene within the population. An attempt to select for even greater resistance in an already highly resistant laboratory strain resulted in only a small increase, due mainly to reduced variability in response of the population. The implications of resistance to viral insecticides developing under field conditions are discussed.

The biology and economic status of aphids attacking rice throughout the world is reviewed, as is the literature concerning other aphids found in or near irrigated rice fields but not usually infesting rice. Altogether, 37 species of aphids belonging to seventeen genera are considered. The aphids are dealt with in two similar–sized groups according to their feeding sites, namely root–feeding and leaf–, stem– and ear–feeding species. Aphis craccivora Koch and Myzus persicae (Sulz.) are regarded as ‘occasional rice aphids’ as they are found on rice occasionally but do not regularly infest rice plants. A. gossypü Glov. is treated as a ‘rice aphid’ although its occurrence on rice plants is also sporadic. In addition to the literature survey, additional information is given based on field collections and observations, on the rice aphid component of more than 18 000 aphids trapped in yellow pan traps, on the natural enemies reared and collected and from laboratory experiments in Japan. Unpubished information was also extracted from the data labels of the British Museum (Natural History) aphid collection. The ecological relationships between rice aphids and aphids associated with weeds near irrigated rice fields in the Yamaguchi area of Japan is discussed. Three of the rice aphids were found on 22 species of weeds and the three ‘occasional rice aphids’ also occured on 22 species of weeds. A total of 43 species of weeds harboured aphids.

The effects of vegetative cover and soil type on the abundance and distribution of 50 species of scarabaeine dung beetle were examined during three successive days in January 1979 in Hluhluwe Game Reserve, South Africa. Pitfall traps baited with bovine dung were set at intervals of 20 m in a transect across a 20–ha patch of grassveld surrounded by Acacia bushveld. One end of the transect was on clay–loam soil and the other on sandy loam. In all, 32 936 specimens were caught, representing 71 species from 22 genera. Thirty–two species were diurnal and 18 were crepuscular or nocturnal. Twenty–six species were more abundant in bushveld than in grassveld, and eight species were more abundant in grassveld than in bushveld. Soil type influenced the relative abundance of 23 species. The degree of habitat specificity varied widely between species. During overcast weather, both bushveld and grassveld species became abundant in the transitional zone between bushveld and grassveld where the light intensity was similar to that in bushveld on a clear day. It is suggested that light intensity is one characteristic by which beetles recognise bushveld and grassveld.

Schistocerca piceifrons (Wlk.) is the swarming locust of tropical America. It has until recently been confused with closely related species and has usually been misidentified as S. paranensis (Burm.). The biological information that can definitely be attributed to this species is reviewed and is supplemented with some original observations. The invasion area of the locust includes Mexico, Central America, Colombia, Venezuela, Guyana, Ecuador and Peru. Permanent populations are known from the Yuc´tan Peninsula, northern Honduras, the Pacific coast of Central America and the highlands of Peru. There are two subspecies, S. piceifrons piceifrons, known from Mexico and Central America, and S. piceifrons peruviana Lynch Arrib., from Peru. S. piceifrons exhibits phase polymorphism in nymphal colouration and adult morphometrics. The femur length/maximum head width (F/C) ratio is most effective in separating the phases. There are two generations a year. Immature adults of the second generation survive the dry season. Its habitat is subclimax mosaic communities in areas where the natural vegetation is dry tropical woodland. Plagues are believed to have originated when swarms formed in the permanent breeding areas. Records of susceptible crops and natural enemies are given, and the behaviour of hopper bands is described.

The natural predators of Culex pipiens L. and C. torrentium Mart, in artificial containers and ponds were studied in southern England, using serological techniques. The antisera were from rabbits immunised by injections of saline extracts of the species of Culex into the inguinal lymph nodes and made relatively more specific by absorption. The gut contents or whole individuals of 1098 potential predators were smeared on to filter paper and tested. The most important predators in the ponds were Odonata nymphs while those of artificial containers were larval Dytiscidae. Diptera and Araneae preyed on emerging adults. The length of time a mosquito meal remained detectable in the gut of predators varied from a minimum of 8 h for the newt Triturus vulgaris to 24 h for the zygopteran Ischnura elegans (van der Linden). The results of laboratory tests indicated that the anisopteran Sympetrum striolatum (Charp.) was potentially more important as a biological control agent for larval culicines in ponds than the zygopteran Coenagrion puella (L.).

The seasonal population trends of the immature stages of Aedes africanus (Theo.), an important vector of yellow fever virus and other arboviruses, were studied in Zika Forest, Uganda, for two years during 1974–75. Data were collected from natural breeding places in tree holes and from bamboo pots placed 80 cm above the ground. Developing larvae and pupae were present at all times of year, and there were monthly, seasonal and annual fluctuations in density. These fluctuations followed the seasonal distribution of rainfall and were more marked in the natural breeding places, which were subject to irregular fluctuations in water level, than in the bamboo pots, which were constantly supplied with water. Thus, in addition to the drought-resistant eggs whose erratic hatching by instalments could ensure the presence of A. africanus throughout the year, there are probably also present at any given time females that are capable of ovipositing. As a measure of the seasonal population changes, it was found that both the percentage of positive containers index and the mean number per container index were almost equally sensitive.

Detailed data from a preselected release site in Tanzania were collected preparatory to testing the insect sterility concept against Glossina morsitans morsitans Westw. The site was at Mkwaja Ranch, a north-eastern coastal cattle-ranching enterprise, in which about 195 km2 was encompassed by a 1-km-wide fly barrier constructed at an average cost of $37/ha. Weekly surveys of flyround transects spaced 1 km apart were conducted over a 14-month period. The estimated male density of G. m. morsitans in the release site was about 630/km2 and for G. pallidipes Aust., 255/km2. The only other species of tsetse found was G. brevipalpis Newst., which was restricted to drainage areas during periods of low rainfall.

Night migrations of insects above the surface boundary layer were studied by direct observations with an entomological radar, and by direct aerial sampling with a kite-borne net, in an area in New South Wales inhabited by large fledging populations of Chortoicetes terminifera (Wlk.). The aerial catches and radar echo-modulation observations suggested that the majority of migrants detected by the radar were locusts, and this conclusion was supported indirectly by light-trap catches and by observations of take–off at dusk. Night flights of locusts began at dusk with a mass take-off and continued on a diminishing scale until about midnight. Displacements were all approximately downwind and to the north, under the influence of a southerly airflow which prevailed throughout the six-day study period. A quantitative radar observation procedure was used to estimate locust aerial densities and migration rates, and to observe the variations of these quantities with height and time; typical and extreme values for all the principal migration quantities are presented. The flight paths of the locusts were estimated from radar observations of target tracks, and probable source areas at distances of up to 200 km to the south were identified; a major overflight which probably originated 150 km away was detected on one occasion. Northward movements of C. terminifera during anticyclonic conditions may help to explain how populations are redistributed in the periods between the long-range southward invasion movements for which this species is well-known.

As part of a programme to test the sterile insect technique against Glossina morsitans morsitans Westw. in Tanzania, two aerial applications of endosulfan were applied to a 195-km2 test area. The applications were made with a 28-day interval to provide an initial reduction in the target species prior to the release of sterile males. A Cessna 310 aircraft equipped with a rotary atomiser and operating at night was used to apply the insecticide at a dosage of about 20 g/ha. Flyround surveys within 48 h following the spraying operations indicated that a 100% reduction of G. m. morsitans adults was achieved in both applications, while G. pallidipes Aust. was reduced by 91 5% in the first and 100% in the second.

Studies conducted in Zika Forest, Uganda, on the breeding interactions between Aedes africanus (Theo.) and two mosquito predators, Toxorhynchites brevipalpis conradti Grünb. and T. kaimosi (van Som.), revealed a significant reduction in the numbers of A. africanus larvae and pupae in tree holes that were also inhabited by the predator larvae. There was a tendency for seasonal peaks in numbers of A. africanus to be followed two months later by peaks in Toxorhynchites spp. Cannibalism appeared to play an important role in the regulation of the population size of the two species of Toxorhynchites. The implications of these results in relation to the possible use of Toxorhynchites mosquitoes for biological control of A. africanus and other mosquitoes breeding in tree holes are discussed.

Experiments were carried out to determine whether Oryzaephilus surinamensis (L.) was attracted to water on a wick suspended in an arena. When insects were preconditioned at 25, 50, 75 or 100% RH, they were attracted to the water source. Those preconditioned at 50% RH gave the greatest response and those preconditioned at 100% RH, the least. Measurement of the humidity changes in the arena caused by adding a wick containing 5 Μ1 of water showed that the gradient between the edge and centre was steepest at the start of an experiment when insect activity was also greatest. About 30 min after a wick had been placed in the arena, virtually all the water (about 94%) had evaporated, the humidity had equalised over the arena and the insects were no longer attracted to the wick. This behavioural response is discussed in relation to the insects' environment.

From estimates of the most likely egg–laying dates of 53 outbreaks of Spodoptera exempta (Wlk.) in East Africa, and from estimates of the likelihood of rainstorms (20 mm or more a day) at the outbreak sites around those dates, it is shown that concentrated laying by moths leading to outbreaks early in the season (January to March) in 1974–75 was associated with rainstorms at the time of oviposition. However, there was no such association in April and May. The mechanism of association is unknown; moths may be concentrated whilst airborne, or they may reach and stay in limited areas wetted by rain, where new grass growth might be expected.

Species records of Sphingidae taken in Trinidad were kept from 1968 to 1979. Seventy–five species and one subspecies were taken, including several new records for the island. The numbers of sphingids taken in Robinson light–traps equipped with 125–watt mercury–arc lamps were recorded over a period of eight years at St. Augustine, Trinidad, and the data analysed. The species abundance distribution was found to be well–fitted by the log–normal series. Data were examined for trends and periodicities, and the variance was found to be largely accounted for by three principal factors. A long–term decline in catch was observed in one trap due to the growth of screening vegetation. Annual variation in catch was found to correlate with the annual pattern of precipitation, with higher catches during the rainy season, although some species differences were detectable. Monthly variation in catch was found to correspond with the cycle of lunar illumination, being significantly depressed with increasing brightness. Interspecific differences in the response to moonlight were also detected. The influence of screening effects on the observed periodicities is discussed in relation to the siting of the traps. Times of commencement of flight activity were recorded, and the relationship between time of capture and activity is discussed. Apart from one species, the sex ratio of captured sphingids was significantly male-biased. Data from three traps were compared with each other and with those from other tropical locations.

A field trial of the sterile insect technique was conducted in Tanzania using males of Glossina morsitans morsitans Westw. that were reared, irradiated and packaged at Tanga. The experimental site was a 195–km2 area 110 km to the south. Following two applications of endosulfan as an aerosol at an interval of 28 days, irradiated puparia of G. m. morsitans were released twice weekly at stations distributed throughout the experimental site. Each of the 120 release stations was serviced every 14 days with puparia which produced sterile adults synchronously within 30 min after placement. Over the 15–month experimental period, an average of 81% control of G. m. morsitans was obtained, whereas G. pallidipes Aust., against which no releases were carried out, recovered to prespray levels within five months. The released sterile insects were found to be highly competitive and to survive well in the field. Immigration of indigenous flies from outside the perimeter barrier surrounding the experimental plot provided a continuous influx of fertile flies that provided the nucleus of the 19% residual population. Under operational conditions, the prevention of migration should result in the elimination of an indigenous G. m. morsitans population subjected to the combined stress of population reduction by two applications of endosulfan aerosols and sequential releases of sterile males.

The effect of a single flood irrigation cycle on the number of adults of Musca vetustissima Wlk. emerging from cattle dung was examined in the field in south-western Australia. Sets of fresh dung pads were exposed to natural oviposition on the day after a flooding and then every three days until the next flooding, 21 days later. The emergence of flies was compared with that from equivalent sets of dung pads in an adjacent unflooded but otherwise similar pasture. The age-stages most susceptible to drowning were post-feeding larvae and pre-emergent puparia. Reduced fly emergence from dung placed in the irrigated pasture one day after the first irrigation was attributed to suppression of oviposition by the wet conditions. Overall, there was a reduction of 57% in the number of flies emerging in the irrigated pasture compared with the unflooded control.

The effects of feeding by groups of 0, 15, 30, 45, 60, 75 or 90 adults of Empoasca dolichi Paoli per plant on the growth and yield of caged Prima and Ife Brown cowpea plants infested 14, 21 or 28 days after planting were studied in Ibadan, Nigeria. Caging had no significant adverse effects on yield. E. dolichi caused severe hopper-burn in plants infested 14 days after planting. The mean pre-flower-opening stage lasted 42–1, 38–0 and 39–0 days in Prima and 446, 407 and 423 days in Ife Brown plants infested 14, 21 and 28 days after planting, respectively, the first figure for each cultivar being significantly different from the other two. The mean yields were 23 3, 28 5 and 298 pods per plant for Prima, and 350, 48–1 and 437 for Ife Brown, respectively, the first figure for each cultivar being significantly lower than the other two. The reduction in seed yield in damaged plants infested 14 days after planting ranged from 287 to 413% for Prima and 272 to 56–9% for Ife Brown, the reductions being significantly correlated with scores for feeding damage by E. dolichi.

The immature stages of Musca vetustissima Wlk. in dung pads in south-eastern Australia suffered a high mortality through the actions of a complex array of dung organisms, including dung beetles (scarabaeids), predatory beetles (hydrophilids and histerids) and predatory mites (Macrocheles glaber (Müll.)). At times of high dung beetle numbers, it was possible to demonstrate a relationship between fly mortality and dung beetle numbers. Single-species dung beetle populations appeared to be as effective as multiple-species populations in reducing fly numbers, except that some benefit was derived from a combination of day- and night-flying species. When dung beetle numbers were low, their influence could not be measured because of the high mortalities already caused by the other dung fauna. It is suggested that in those circumstances any mortality caused by the dung beetles may simply have become substituted for an existing mortality caused by other fauna without adding to the total mortality.

In order to see if aeration causes grain beetles to become peripherally distributed in bulks of grain, the positions of adults were recorded 7–10 days after they had been placed in the middle of vertical columns of wheat 1200 mm long and 80 mm in diameter. The columns were held at 10 or 25°C, and a downward current of air was passed through half of them. At 10°C, there were more adults of Oryzaephilus surinamensis (L.) at the ends and fewer at the centre of aerated than unaerated tubes when a high airflow was used, and at 25°C, a similar difference occurred when aeration caused cooling, dampening or drying of the grain. Dampening at 10°C and drying at 25°C caused there to be fewer adults of Sitophilus granarius (L.) at the ends and more at the centre of aerated than unaerated tubes. However, vibration at 10°C encouraged the dispersion of weevils. Rhyzopertha dominica (F.) scarcely moved at 10 or 25°C under either aerated or unaerated conditions.

Males of Phthorimaea operculella (Zell.) less than 24 h old were sterilised with thiotepa by circulatory fumigation in the laboratory and then released in cages in a potato field in New Zealand. Laboratory-reared sterile males, normal males and females were released in different ratios. Sterile males competed successfully in mating to suppress reproduction between laboratory-reared normal males and females. Laboratory-reared sterile males were also released in different numbers into field cages containing the resident population and additional field-collected males and females. The results showed that the sterile males were slightly less competitive than normal ones, but they were effective in suppressing the population in the cages.

A study was made at Hurley in southern England of the hymenopterous parasitoids of the stem-boring larvae of Oscinella spp. and Geomyza tripunctata Fall, in perennial ryegrass plants {Lolium perenne) taken from swards managed in different ways. Six species of parasitoids were identified after their emergence from stem-borer pupae; four of these were also identified in the parasitoid larval form parasitising stem-borer larvae. Parasitism exceeded 45% during 1980 but was only about 20% in 1981. Of the species of Oscinella, larvae of O. frit (L.) were always the most highly parasitised and those of O. vastator (Curt.) the least, irrespective of their frequency of occurrence. G. tripunctata also showed less parasitism than O. frit. The braconid Chasmodon apterus (Nees) was responsible for 95 % of the parasitism in 1980 and 85% in 1981. The higher parasitism in 1980 probably resulted from greater synchrony between the populations of the adults of C. apterus and those of the stem-boring larvae. Samples from eight other sites in the UK gave results similar to those obtained from Hurley.