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 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.

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.

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.

Copris diversus Waterh. is a brood-caring dung beetle from Africa, the females remaining in the nest with their brood balls until the young emerge. A technique was developed which allowed access to the nest without interrupting nesting behaviour, so that beetles and nest contents could be observed and dung could be added into or removed from the nest at specific times. At 27°C, if more dung was added to the nest in the first three days after the start of brood care, most beetles continued oviposition. Resorption of the terminal follicle started some time between the third and twelfth days of brood care, and while the terminal follicle was resorbing the beetles did not revert to breeding if supplied with additional dung. Subsequent follicles were also resorbed if brood care was allowed to continue beyond ten days, but their resorption did not impose a lengthy delay in breeding. Oviposition resumed 17 to 21 days after the start of brood care, irrespective of when the dung was added. Development of new follicles following follicle resorption took three to seven days, and thus the resorption of the terminal follicle must have taken about seven to fifteen days.

In studies in the Zambezi Valley of Zimbabwe, Glossina morsitans morsitans Westw. and G. pallidipes Aust. were captured on electric nets at various points around stationary targets. The distribution of flies was affected by wind direction, wind speed and the presence or absence of an attractant odour consisting of carbon dioxide and acetone. The distributions suggested that tsetse attracted to baits by visual stimuli alone fly first to a point just downwind of the baits, where the perception of odour is important in host recognition. Changes in the distribution of catches when odour was used suggested that the distributions could form useful indices of assaying attractant odours in the field. Data for Muscidae, Tabanidae, Asilidae and Hymenoptera are also presented.

The establishment and survival of larvae of Chilo partellus (Swinh.) on two sorghum cultivars in the six days after hatching was investigated in the field in India. During this period relatively few larvae are present outside the whorls of the plants, and the numbers present six hours and three days after hatching are proportional to the numbers hatching. The number of larvae in the plants declines during these first three days, but subsequently is stable. Some dispersal to adjacent plants occurs during this period and, at the plant spacing used, approximately seven plants were infested by larvae from a single egg-mass of 40 eggs. The relative susceptibilities of the two cultivars, IS 1151 and IS 2205, altered with the age and size of the plants. This is a vulnerable period in the life-history of the insect and attention should be focused on it in developing resistant cultivars, but because the susceptibility of the plants changes with age it is important to decide the age at which protection would have the greatest economic value.

The climbing behaviour of newly hatched larvae of Chilo partellus (Swinh.) on sorghum plants was studied in the laboratory and in the field in India. The upward movement is directed by light, while the final downwards movement into the whorl is probably a response to the contrast of light above and dark below. Many larvae fail to reach the whorl, and success is reduced by high winds and rain, and by some physical features of the plants. Two sorghum cultivars, IS 1151 and IS 2205, differed in the extent to which larvae successfully reached their whorls, and their relative susceptibilities altered with age.

Cyrtobagous singularis Hust. was recorded from Brazil, Paraguay, Uruguay and Argentina in association with six species of Salvinia (aquatic ferns). Field observations and laboratory studies in Brazil and Australia showed that C. singularis severely damaged S. molesta and that the weevil is suitable as a control agent for this weed in tropical and subtropical areas in Australia. In host-specificity studies using 46 plant species that occur in Australia, development of the immature stages took place only on S. molesta. Minor leaf scarring occurred on sweet potato when in contact with water, but starvation tests excluded this plant as a possible terrestrial host. Adults fed, but were unable to reproduce, on water lettuce (Pistia stratiotes). The high degree of host specificity indicated that establishment of this weevil in Australia is without risk to non-target plants. C. singularis was first released and became established in Australia in 1980.

A major component of the sex pheromone of Dacus oleae (Gmel.) has recently been identified as a spiroacetal. The use of this compound as a lure for use in the development of a monitoring trap for that species is described. Polyethylene vials gave a slower release rate of the spiroacetal than rubber septa or microfibres, but even in polyethylene vials a loading in excess of 10 mg was required (optimum 20 to 25 mg) to obtain catches in delta traps which were comparable with those in unbaited vertical yellow sticky traps. In studies in an olive grove near Granada, Spain, a 25-mg spiroacetal lure used with a vertical yellow trap gave catches of males of D. oleae which were four times as great as those in delta traps with the same lure or in unbaited yellow traps. The height of the trap had no apparent effect on catch. Previously recorded components of the sex pheromone did not prove to be effective when combined with the spiroacetal. Combined monitoring of Prays oleae (Bern.) and D. oleae, using their respective pheromones in the same trap, appears to be feasible with delta traps.

Baseline toxicity measurements established discriminating concentrations of pirimicarb and demeton-S-methyl guaranteed to kill susceptible examples of Aphis fabae Scop., Sitobion avenae (F.), Metopolophium dirhodum (Wlk.) and Rhopalosiphum padi (L.) in the dip-test, the FAO-recommended method for detecting resistance in aphids. There was no evidence for resistance to either insecticide in field-collected populations of aphids from various parts of the UK or amongst variants of S. avenae characterised by staining their esterases after electrophoresis. New, simple techniques for rearing large numbers of colonies of cereal aphids are described.

The development of adults of Nilaparvata lugens (Stål) reared on one susceptible and one resistant variety of rice plants of different ages was compared. Throughout the range of plants tested there was an overall trend for the newly moulted adult to synthesise and store a reserve of lipid and to lose most of the stored glycogen accumulated during the nymphal stage. N. lugens has two wing morphs, and whilst lipid deposits were greatest in the macropterous ‘migrant’ males, in females it was the brachypterous ‘reproductive’ insects that had the highest lipid deposits and also the greatest residual body weight. However, because of their lower body weight, the macropterous females had the greater percentage of lipid. Both flight willingness and the percentage of macropterous females showing flight-orientated physiological development increased with the age of the host-plant. Both survival and migration potential were lower in insects reared on the resistant rice variety compared to those reared on the susceptible variety. The pattern of post-flight resynthesis of fuels suggests that more than one major migration is unlikely.

The biology of Bubas bison (L.) was studied in southern France. It was active from September to the end of May. Adult emergence lasted from September to January; 8 % of the female population was parous and laying eggs in September, and 100% were parous from February to the end of June. Females exhibited extraovariolar egg resorption, which may have been a response to adverse conditions. Eggs laid in October, November, February and March hatched synchronously in May. Adults resulting from eggs laid in March emerged in early September. The rate of oviposition varied from 0–03 egg/day in January to 0·5 in March. Females stopped laying eggs for three weeks in January. The structure of the nests formed from buried dung brood-masses was studied. Each brood-mass contained two eggs, one at each pole. About 12 brood-masses were formed under each dung pad in October 1981. The mean length of each mass was 96 mm and the dry weight 10–5 g. The mean number of masses in a nest was 24, with a mean number of 4–9 nests under each dung pad. The dry weight of dung buried under a pad in October 1981 was 1239 g, 66–6%, of the mean dry weight of an experimental dung pad. B. bison has the potential for recycling large amounts of dung in climatic areas of Australia equivalent to southern France.

The numbers of mealybugs and other Homoptera on 96 cocoa trees in Ghana were assessed by examining four branches from each tree. The trees were then felled and examined in detail. Ten species of mealybugs, eight other coccoids, an aphid and a psyllid were recorded. Ninety–five of the trees were infested with mealybugs, 66, 90 and 69 trees, respectively, with Planococcoides njalensis (Laing), Planococcus citri (Risso) and Phenacoccus hargreavesi (Laing). Stictococcus sjostedti Ckll., a species of Gascardia near G. zonata (Newst.) and Mesohomotoma tessmanni (Aulm.) were found on 70, 68 and 48 trees, respectively. The remaining 14 species were found on fewer than 48 trees. All species other than Pseudococcus calceolariae (Mask.) and Ferrisia virgata Ckll.) were most prevalent in the canopy. In the field, mealybug densities recorded on shoots underestimated true levels by an average of 95%. Branches were as effective as whole trees for detecting mealybugs, but less effective for other Homoptera. Branches were suitable sample units for estimating population densities of mealybugs, stictococcids and psyllids. All species of mealybug other than F. virgata infested vegetative buds. An average of 21.7% of buds on the youngest shoots were infested. Samples of buds can be used for detecting mealybug infestations.

Eighteen strains of the complex of Culex pipiens L. from Africa, Asia and Europe were bioassayed for resistance to chlorpyrifos and electro-phoresed and stained for esterases. Susceptible strains showed only low activity esterase bands. The resistant strains of C. quinquefasciatus Say from hot countries (Liberia, Nigeria, Sri Lanka, Tanzania, Thailand) all showed the same two high intensity esterase bands (Rm 0·60 + 0·82). Different patterns of high esterase were found in resistant C. pipiens strains from cooler localities in Nairobi, Kenya (Rm 100), and Mont-pellier, France (Rm 0–50). Selection experiments on strains originally polymorphic for resistance and esterase pattern showed, without exception, that high esterase remained associated with resistance, and it is concluded that the association is almost certainly causal and not merely due to genetic linkage. The high intensity esterase bands were probably due to alleles of the loci Est-l, Est-2 and Est-3, separated by crossover distances of approximately 2·4 and 5·5 units, respectively. Strains monomorphic for what appeared to be the same high esterase pattern varied markedly in resistance level. Enzyme assays showed a direct relationship between levels of enzyme activity and resistance. Bioassays with fenthion and chlorpyrifos revealed differences in the relative resistance of C. quinquefasciatus from Colombo (Sri Lanka) and Dar-es-Salaam (Tanzania). Despite these differential degrees of cross-effectiveness, it is concluded that high intensity esterases are reliable indicators of organophosphate resistance in mosquitoes of the C. pipiens complex, although the possibility of other resistance mechanisms means that the lack of abnormally active esterases does not necessarily indicate the absence of resistance.