Some aspects of the biology of Callosobruchus subinnotatus (Pic) were investigated at controlled conditions. Temperature and relative humidity were found to have effect on oviposition, development and longevity of adults. The best condition for oviposition was 30°C, 80% r.h. at which the mean number of eggs laid was 135.8 and the worst condition was 35°C, 50% r.h. at which 61.1 eggs were laid per female. Oviposition lasted very long at 25°C and was too short at 35°C. Relative humidity favoured oviposition at 30 and 35 but not at 25°C. The beetles were found to be positively phototactic as more eggs were laid at 12 hr light and 12 hr dark (105.1 eggs) and continuous light (98.6) than at continuous darkness (43.0).

Duration of development was shorter at 35°C than at other temperatures investigated. The shortest developmental period was at 35°C, 80 % r.h. (23.2 days) while longest was at 25°C, 50 % r.h. (42.6 days). While development was shorter at 35°C, more progenies were produced at 30°C and the rate of increase was better enhanced at 30°C. Adults were heavier when reared at lower temperatures and high humidities than at high temperatures and low humidities. Adults lived longer at lower temperatures and high humidities than at higher temperatures and lower humidities. The females were heavier and lived longer than the males.

The permanent mass rearing of rice stem borer, Chilo zacconius in West Africa; rice stem borer, Chilo suppressalis, in Asia and Europe; and sugar-cane stalk borer, Chilo sacchariphagus, in Asia and Indian Ocean was perfected in the laboratory to enable us multiply some parasites such as Apanteles spp., Goniozus procerae, Tetrastichus spp., Trichospilus spp. or the tacbinids, Diatraophaga striatalis and Lixophaga diatraeae.

The principal difficulties appear during mating of several hosts and parasites, development of pyralid young larvae or when it is necessary to protect reared insects or artificial medium against pathogens.

Plotting the movement of air through typical tsetse habitats in Zimbabwe revealed that it is liable to change direction by over 90° within a few metres. In winds of < 1 m/sec, there was a negative correlation between windspeed and the wind's tendency to meander, whether in thick bush or out in the open. And at the mean windspeed of wet season mopane woodland (0.3 m/sec), the wind changed direction by c. 15°/sec. Accordingly, host odour does not move downwind in simple trajectories that tsetse flies could easily follow. Even 5 m from a source, odour (modelled with smoke) approached a notional tsetse fly for a quarter of the time from >90° away from the true source direction. Also, air turbulence at common tsetse resting sites generates much nonsense information about the “true” direction of any odour-bearing wind. The suggested answer to how tsetse manage to find distant, invisible hosts, in spite of this confusing information from the wind, is that they progress by a biased random walk which is the outcome of their upwind anemotactic responses to odour-bearing wind and the proportion of the time for which the wind does blow in the “correct” direction. Computer simulation shows that this might work in principle.

Several experiments were conducted with Rhipicephalus sanguineus, Dermacentor variabilis and Amblyomma maculatum during which degrees of resistance by rabbits to infestation were quantified. Manifestations of resistance were measured through estimations of “Decreased Tick-Weight Index”, “Decreased Engorgement Period Index” and “Reject Index”. Degree of resistance was evaluated through estimation of Tick Resistance Index. The degree of resistance of rabbits to infestation with each of the three tick species was found to increase with the number of reinfestations. Fully engorged ticks induce the same degree of resistance as partially engorged ones. Nymphal ticks induced higher resistance than larvae, but the resistance conferred by both immature stages was lower than that conferred by adults; previous exposure of rabbits to adults enhanced the degree of resistance against subsequent nymphal or larval infestation. There was cross-resistance between A. maculatum, D. variabilis and R. sanguineus. Resistance induced in rabbits waned with time; rabbits became non-resistant to ticks 12 weeks after the last infestation. Resistance to tick infestation was transferred to rabbits through passive transference of serum from resistant animals. The importance of these observations to the epidemiology of field infestation of animals with ticks is discussed.

Laboratory and field methodologies for screening for resistance against Chilo partellus on sorghum and maize are reviewed in relation to the insect biology, plant phenology and insect-plant interaction. The value of field and laboratory techniques in achieving the goal to produce resistance varieties and hybrids is discussed. Recommendations for future work are made.

Tsetse colonized either for laboratory studies or for release in S. I. T. programmes are assumed to be healthy and geneticallyw similar to flies in natural populations. However, insect colonies are subjected to many of the same evolutionary forces that influence genetic changes in natural populations, i.e. drift, selection, hitch-hiking, mutations, assortative mating and immigration. The influence of these on genetic structure of tsetse fly colonies is outlined, and examples are presented from several species. There is little or no evidence for adaptation during the early phases of laboratory colonization of five species of tsetse. A model is presented indicating that with as little as a 5% fitness difference between males, some colonies have existed long enough to have undergone significant changes in the relative numbers of males having “standard” and “enhanced” fitness. Slight changes in heterozygosity of colonized flies is documented by comparing colonies and field-collected flies and by comparisons within colonies over periods of several generations or years. An example of hitch-hiking is illustrated with the closely linked genes Sr (sex ratio) and Est-X in Glossina morsitans submorsitans. A possible interaction between alleles at these loci is discussed. A summary is presented of polyacrylamide gel electrophoretic methods for monitoring 16 polymorphic loci distributed among the X chromosome and autosomes of tsetse.

Stem borers are major insect pests of rice in Africa. The utilization of varietal resistance in the management of these pests, has great economic potentials, as it involves no extra cost to the farmer and is also free from environmental hazards. Investigations into the sources of resistance to the African rice striped borer, Chilo zacconius, some possible factors associated with host plant resistance and the benefits derived from growing resistant varieties are briefly reviewed.

Laboratory studies were carried out to determine the effect of high larval densities of Plodia interpunctella (Hubner) on the development and survival of the moth in two food media. Mortality was found to be higher when reared on groundnuts than on artificial diet. Mortality was between 6.6 and 13.3% when larval densities were below five larvae on 3 g of both groundnuts and the artificial diet in 75 × 25 mm tubes. At higher larval densities (10 or more larvae on 3 g of medium) mortality ranged from 22.5 to 60% on the artificial diet, and on groundnuts it was between 30 and 65%. In both media, development period was prolonged and weights of moths at emergence was lower when larval densities were greater than 10 per tube.

When high densities were experienced between the first and the fourth instars individuals had protracted development, high mortality at larval stage and reduced weights of emerged adults and those subjected to high densities only at the final instars were less significantly affected. It seems that the fourth larval instar is the stage most sensitive to high densities.

Tsetse flies have been eradicated from an area of 48,000 km2 in Zimbabwe since 1981. The main approach has been pesticidal control, involving ground spraying, aerial spraying, cattle dipping and artificial bait techniques, in some circumstances in combination. This represents a change in tactic from the pre-independence period when control relied solely on ground spraying. Factors which have influenced choice of technique are discussed in the paper, including scale of trypanosomiasis problem, technical limitations of the technique, cost-effectiveness and environmental considerations.

Ground spraying, the mainstay of tsetse control operations in Zimbabwe prior to 1980, is becoming increasingly unfavourable because of high logistical requirements and environmental reasons, but remains an effective technique under a wide range of circumstances. Aerial spraying has proved very effective for management of crisis situations but is comparatively expensive, capital intensive in hilly terrain and less effective against Glossina pallidipes than G. morsitans. Vector control by applying insecticide (deltamethrin) to cattle appears technically feasible at a very competitive cost. This is a most promising technique in areas where there are already cattle and few wild hosts.

Control of tsetse using odour-baited and insecticide-treated screens has proven technically feasible in a wide range of terrain, and appears economically competitive with ground spraying. Both technical and financial performance of the technique are still being improved. Bait technology offers scope for the new approaches to the control of the fly and defence of cleared areas from reinvasion.

The feeding behaviour of third-instar larvae of Chilo partellus appear to be mediated by a complex profile of chemicals present in the whorls of sorghum. These chemicals were extracted sequentially into hexane, ethyl acetate and methanol. Methanolic extracts showed greater feeding stimulation than ethyl acetate extracts and these in turn showed greater feeding stimulation than hexane extracts. Extracts derived from a more susceptible cultivar IS 18363 showed greater feeding stimulation than extracts from a less susceptible cultivar IS 2205.

Phagostimulatory compounds present in ethyl acetate and methanolic extracts include phenolics and sugars, respectively. Combinations of these sets of phagostimulants synergize to give enhanced feeding activity of third-instar larvae. Chromatographic examination of extracts of IS 18363 and IS 2205 showed quantitative rather than qualitative differences: the more susceptible cultivar IS 18363 had higher phenolic and sugar contents than the less susceptible cultivar IS 2205. These results suggest that Chromatographic quantification of the different sets of phagostimulants might constitute a basis for resistance screening of different cultivars of sorghum.

Pyramidal traps (8000) have been set up against Glossina fuscipes fuscipes to control Trypanosoma rhodesiense in Busoga. In order to understand the pattern of tsetse/human contact, the collection of data on the density, spatial distribution and mobility of flies has been related to the dynamics of human trypanosomiasis in Busoga. As for T. gambiense, few reasonable correlations between global fly densities and incidence of the disease have been found. However, field observation with a recording time of seasonal variations of movements of people and animals associated with particular habitats, remains the key to understanding the transmission of the disease.