The spread of human trypanosomiasis towards Central Africa from sources in the Congo at the beginning of the present century, has been linked to population changes and movements between the affected states.

The re-appearance of the disease in this part of Africa during the last 10 to 15 years raises again the question of how this disease is propagated. Although present day population movements are not so pronounced as those at the beginning of the century, these are significant population movements along major lines of communication (large rivers particularly). Of equal importance are disease foci which straddle national boundaries. Migrant populations (fishermen from Nigeria and displaced persons or refugees) also play important roles in the dispersal of the disease.

Even within certain foci, the mobility of rural populations helps to sustain the endemicity of the disease over large areas.

The risks of introducing or increasing trypanosomiasis must not be neglected when populating new areas and when developing agro-industrial complexes which require large labour forces.

A total of 39 strains of Anopheles stephensi, an important urban malaria vector, were collected from various parts of India and maintained in the insectary for this study. Based on the egg-float ridge number, 19 strains were classified into ecological variants and 32 strains were exposed to chlorpyrifos and propoxur to investigate their resistance status. Filter paper containing freshly laid eggs was taken, the ridge numbers on the floats were counted under the microscope, and strains were classified into ecological variants. Of the 19 strains, 18 were of ‘type form’, with ridge numbers ranging from 15 to 21. The Papareddipalya (PRP) strain belonged to the ‘intermediate form’, with 14 to 17 ridge numbers. Larval bioassays were carried out according to the procedure of the WHO. For chlorpyrifos, the lowest LC50 value was 0.00107 mg/l (Padmanabhanagar strain) and the highest value was 0.0403 mg/l (GOA-A strain). Furthermore, the lowest LC90 value was 0.00368 mg/l (Delhi strain) and the highest was 0.1746 mg/l (GOA-A strain). For propoxur, the lowest LC50 value was 0.00029 mg/l (Goraguntepalya strain) and the highest value was 0.0037 mg/l (JP Nagar strain). Moreover, the lowest LC90 value was 0.00094 mg/l (Goraguntepalya strain) and the highest value was 0.0115 mg/l (JP Nagar strain). The tolerance values ranged from 1.26 to 37.68 for chlorpyrifos and from 1.34 to 12.77 for propoxur. All the type forms were from urban and semi-urban locations, and the intermediate strain was from a semi-urban location. The bioassay results indicated that the strains of An. stephensi were more susceptible to propoxur than to chlorpyrifos.

The population of green spider mite Mononychellus tanajoa (Bondar) was monitored on cassava for 52 weeks (mid October 1979 to mid October 1980) at Moor Plantation, Ibadan, Nigeria. Mite population was found to be high in the dry season (80.1 ± 57.7 per leaf) and low in the wet season (15.2 ± 13.5). There was a linear relationship between mite population and the weather factors investigated. The relationship was positive in the cases of temperature and radiation, and negative in those of rainfall and humidity. The high mite population in the dry season was attributed to the high temperature (27.9 ± 1.26°C) and radiation (39.1 ± 7.86) conditions which favoured development of the different stages in the life cycle of the mite. The low population in the wet season was attributed to the adverse effects of high rainfall (56.31 ± 33.14 mm) and humidity (87.29 ± 2.36%) on the mites. Seasonal fluctuations in mite population was attributed to the physiological condition of the host plant.

Interest in the study of parasitic Hymenoptera has been revitalized consequent to recent emphasis on biological control and the role that the parasitoids play in effective biological control methods. However, our knowledge of the species of parasitic Hymenoptera, and their host associations is rather imperfect, and the family Ichneumonidae is no exception. The potential that parasitic Hymenoptera offer in the control of unwanted pests, and thereby increase agricultural output, cannot be utilized unless basic taxonomic and biological studies on them are fully supported and funded.

The known species of Ichneumonidae at the present moment are approximately 19,000, which is only about 10% of the estimated number of species occurring in the world. Most species occurring in the tropical countries are unknown. The described number of species from various regions are approximately 7000 in Eurasia, 4500 in Indo-Australian area, 3500 in North America, 2000 in South America, and about 2000 in tropical Africa.

The African ichneumonid fauna is rich and diverse, but very few areas have been intensively and extensively explored. Certain countries like Malagasy Republic and Zaire have been more extensively explored than the others, but recent studies indicate that species diversity is much greater than what we know today. Catches made in limited areas by using Malaise traps in places like Kampala, Uganda during 1964–1965 and in Freetown, Sierra Leone during 1969–1970 increased the number of species 300–400 per cent.

The effect of covering post-harvest banana stumps with soil on banana weevil Cosmopolites sordidus (Germar) oviposition levels was investigated at three locations, Sendusu, Kawanda Agricultural Research Institute (KARI) and Ntungamo district of southwestern Uganda. In the first experiment oviposition levels were assessed in a banana system comprising growing plants and residues. Oviposition increased on sword suckers, reaching a peak 1–7 days after harvest and decreased thereafter. In the second experiment conducted on farmers' fields, corms received 70% of the eggs and pseudostems 30%. The area 5–10 cm below the collar received 27% of the eggs, the area 0–5 cm above the collar 30% and the area 5–10 cm above the collar 0.3%. The remaining eggs (43%) were laid 0–5 cm below the collar. The effect of stump height and covering the stumps was evaluated in both the wet and the dry seasons at Kawanda and Ntungamo. Cutting stumps to the ground level alone had no effect on oviposition. Covering post-harvest banana stumps reduced C. sordidus oviposition in the wet but not in the dry season.

Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20–25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants. There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.

Laboratory and field assays carried out so far indicate that microsporidian pathogens, especially Nosema spp., may be exploited for the management of the spotted stalk borer Chilo partellus and possibly other Chilo spp. Several formulations have been tested for the application of Nosema spores in the field for borer management. Significantly high levels of control were achieved when the pathogen was sprayed on plants infested with borer larvae, compared with unsprayed plots. Sublethal dosages of Nosema spp. reduced the biological performance of C. partellus, as indicated by reduced fecundity in infected females, high mortality in pre-imagines as well as in the filial generations, and reduced lifespan. There was also a high level of deformity in the surviving adults. Such debilitating factors would subsequently result in a reduction of population levels.

In sugar-cane pests, granulosis viruses have been observed to cause high natural mortalities in C. infuscatellus and C. sacchariphagus. Field infestation has been reduced by the application of the virus. Further, the presence of polyhedrosis viruses in C. partellus, and Chilo iridiscent virus in C. suppressalis, points towards the possibility of using this group of pathogens in Chilo control.

Field tests were carried out to compare the performance of a new tsetse trap, the Nitse (I and II) with the biconical, F3 and NGU traps respectively at the Yankari Game Reserve, Bauchi State, Nigeria. The game reserve harbours Glossina palpalis, G. tachinoides and G. morsitans submorsitans species. The biconical trap was used as the standard. The sites had been cleared of vegetation; they were 5–10 m away from vehicle paths and about 100 m apart. Each trap was moved rotatingly until all traps were exposed to each of the five sites. Traps were emptied each morning after 24 h and the tsetse sorted according to species and sex. The data on the different trap catches were analysed using the one-way ANOVA and the multiple range test via the SPSS statistical package. The performance of the Nitse I on G. tachinoides in one area with high tsetse density was significantly better than that of each of the three traps. But for G. m. submorsitans, Nitse I and the biconical trap performed better than only the F3 (P ≤ 0.05) in the high density area. Only the biconical performed significantly better than the F3 trap in an area with low tsetse density. The new Nitse trap was more effective for G. tachinoides than for G. m. submorsitans.

Two monoclonal antibodies (Mabs), that react in an enzyme linked immunoabsorbant assay, were generated against Aedes aegypti vitellin. One of these Mabs, VIIG9 that reacted predominantly with a 64 kDa component of Ae. aegypti yolk protein, also recognized 68 kDa and 66 kDa components in the yolk proteins of Culex sitiens and Cx. annulirostris, respectively. Mab VIIG9 has been used to detect vitellin or vitellin precursors in gravid female and non-blood fed nulliparous female mosquitoes as a possible age grading method. The presence of polyclonal and monoclonal antibodies to vitellin in the blood meal did not affect the fecundity of Ae. aegypti.

Biochemical approaches have been used to enhance the potency of Bacillus thuringiensis against Plodia interpunctelia. Tests were made with different classes of chemical compounds, characterizedby being safe, non-toxic to man, and cheap in price. Among the tested inorganic salts, calcium carbonate, calcium oxide and zinc sulphate were found to increase the potency of B. thuringiensis δ-endotoxin by 2.5-, 1.9- and 2.7-fold, respectively. With the nitrogenous compounds, the amino acids serlne, arginine, alanine and teucine enhanced the endotoxin effect by 52-, 3.6-, 13- and 1.1-fold, respectively. Also, among the protein solubilizing agents, EDTA and sodium thloglycollate led to a 100- and 2.6-fold Increase in the potency. Formic acid was highly effective among the organic acids used in enhancing the potency, followed by malk acid, with 4.8- and 2.4-fold increase, respectively.

Soil samples collected from six localities in Pakistan—Peshawar, Quetta, Loralai, Sibi, Lahore and Sheikhupura—were screened for insecticidal Bacillus spp. Bacillus coagulane, B. megaterium and B. alvei, which constituted 50%, 33% and 17% of the Bacillus isolates respectively, were isolated and their toxicity was evaluated against larvae of the house fly, Musca domestica (Diptera: Muscidae). The most toxic bacterial isolate of the three was B. alvei (98.7% mortality) and the least toxic was B. megaterium (89.3% mortality). Extracts of experimental larvae showed the presence of strains of the respective species of Bacillus in all cases, indicating that the observed mortality in the house flies was caused by the Bacillus species.

At 25°C and 70% r.h. larvae of Spodoptera exempta develop faster and pass through five instars on star grass, Cynodon dactylon (L.); Pers. maize, Zea mais L.; and Kikuyu grass, Pennisetum clandestinum Chiov. whereas on guinea grass, Panicum maximum Jacq.; and Setaria plicatilis (Hochst.) Hack, the development is not only slower, but the larvae pass through six and seven instars, respectively. Samples of larvae reared on the former grass species suffer high mortality only at the first and the last instar stages so that the distribution of per cent mortality is U-shaped. On the latter host plants, the mortality during the first instar stage is equally high and continues through the subsequent instars with no obvious peak towards the end of the larval life. The samples on C. dactylon and Z. mais had much higher growth indices than those on P. maximum and S. plicatilis. C. dactylon is a preferred natural food plant of S. exempta in the field, and these investigations demonstrate its value and importance.

There are 43 identified insect pests of sugar-cane in Mauritius, of which several are important enough to warrant control measures. However, insecticides are not used for this purpose. All the insect pests of sugar-cane are controlled biologically. This includes traditional biological control using parasites or predators, as well as more recent biology-based methods like the use of resistant cane varieties, sex pheromones, etc.

Mauritius has the distinction of being the first country on record to have successfully introduced a natural enemy, namely the Minah bird, specifically to combat a pest—the Red Locust, Nomadacris septemfasciata, in 1792.

Very few of the insect pests in Mauritius are indigenous; most of them are exotic, having been accidentally introduced into the country, one way or the other. Some of the important ones include: spotted stem borer (Chilo sacchariphagus), armoured scale (Aulacaspis tegalensis), white grub (Clemora smithi), white grub (Heteronychus licas), soft scale (Pulvinaria iceyi), armyworm (Leucania loreyi) and pink borer (Sesamia calamistis).

The introduction of various natural enemies from different parts of the world has been made over the years with different degrees of success. In all, there are presently a total of 102 species of parasites and predators controlling 43 species of sugar-cane insect pests.

With sugar-cane spread out over most of the island and representing 90% of all cultivated land, close vigilance over the important pest populations, and swift counter measures as appropriate, is required. This task is being performed efficiently and successfully by the Mauritius Sugar Industry Research Institute.

Ten sorghum genotypes at three plant growth stages were evaluated for antibiosis component of resistance to Peregrinus maidis expressed in terms of survival, duration and population build-up of nymphs as well as longevity and fecundity of adults. Support of nymphal survival and continued succession in mortality was evidenced on IS 18676, IS 18677 and IS 19349, indicating the influence of antibiosis factor(s) which again was supported by their prolonged duration. The growth index was consistently low at three plant growth stages on IS 18676 and IS 19349, but the genotype, IS 18677 did not express consistency on 45 days old plants. Greater longevity of adult females over males was consistent at different growth stages. Low fecundity was predominantly noticed on IS 18676, while reduced longevity was pronounced on IS 18677 and IS 19349 which was reflected in low population build-up at 15 and 30 days after infestation, when infested with 25 or 50 neonate nymphs. All these parameters contributed together suggest that antibiosis levels in IS 18676, IS 18677 and IS 19349 proportionately increased with plant age and the variability at different growth stages may be attributed to the differences in host genotypes and greatly aid as potential donors in resistance breeding programmes.

A number of resistance sources have been identified against two major pests of sorghum, viz the sorghum shootfly, Atherigona soccata Rondani, and the stem-borer, Chilo partellus (Swinhoe). These identified sources of resistance were generally tall, late maturing and poor yielders. Two of these identified sources of resistance, viz. BP 53 and M 35-I, have been utilized in the breeding programme, by crossing with dwarf exotic types, which are highly susceptible to both the pests, but are agronomically desirable varieties. The crosses thus obtained were screened for their reaction to the two pests. An extensive screening programme was carried out under heavy levels of shootfly and stem-borer infestation from 1968 to 1980, which resulted in the identification of nine advanced generation derivatives possessing moderate to high levels of resistance to both shootfly and stem-borer as well as desirable agronomic characters.

The derivatives with M 35-I, as one of the parents showed more resistance to shootfly as compared to derivatives with BP 53, as one of the parents. However, in the case of resistance to stem-borer, the reverse was true.

Studies on the effect of various diets on development, longevity and fecundity of Oxycarenus gossypinus were conducted in the laboratory at temperatures of 25–33°C. The mean periods of nymphal development when reared on seeds of okra, kenaf, roselle and cotton were 15.5, 15.7, 15.8 and 18.1 days, respectively.

Mated males lived longer and in decreasing order on okra (59.2 days), roselle (57.5 days) and kenaf (57.3 days) than on cotton (43.5 days). Mated females also lived longer on okra (41.4 days), kenaf (40.1 days) and roselle (39.3 days) than on cotton (32.5 days).

Mated females reared on okra seeds laid significantly the highest mean number of eggs per female per day (15.05 ± 0.87 eggs). But the mean number of eggs oviposited when fed on seeds of kenaf (12.9 ± 1.01 eggs) and roselle (10.9 ± 1.18 eggs) was not significant.

The persistence of 34 formulations in the green (G) and red (R) berries of C. arabica var. typica, infested with female adult H. hampei were assayed by a dip-technique. The 3-day LC50 values in G and R (figures in parentheses) berries for thiodan EC 35 were 0.00284 (0.00327), and the relative ratio of values for other formulations were: perfekthion 1.2 (2.1) > carbicron 1.6 (2.3) > basudin 3.5 (3.2) > actellic 4.0 (3.6) > decis 4.1 (3.7) > thiodan EC 3 4.2 (4.2) > bidrin 5.8 (5.0) > malathion 5.8 (5.1) > lindane 5.8 (5.6) > ciodrin 5.9 (5.6) > folimat 6.0 (6.0) > belmark 6.2 (6.3) > aldicarb 8.0 (9.7) > nexion 11.0 (12.0)>kelthane 13.5 (15.4) > tiovel 14.6 (16.3) > dursban 15.6 (22.0) > chlordane 17.8 (23.8) > methomyl 21.5 (24.3) > aldrin 25.1 (24.9) > supona 27.2 (26.5) > dimilin 29.0 (27.5) > methoxychlor 31.7 (92.2) > chlorfenvinphos 35.8 (92.5) > dieldrin 41.2 (93.8) > phosdrin 65.0 (94.7)>sevin 104.2 (118.0)> nexagan 106.4 (121.9) > bimarit 196.4 (301.7) > azodrin 271.2 (410.4) > fenitrothion 448.3 (417.0) > chlorpyrifos 448.8 (614.3) > gardona 514.6 (703.1), -fold more than the thiodan EC 35 values.

The 7-day LC50 values for 29 formulations were ca 10–82% less than those of the 3-day values; the decrease in the values for leading formulations being thiodan EC 35 13.4 (8.3), perfekthion 6.5 (39.9), carbicron 12.4 (10.6), thiodan EC 324.3 (16.4), malathion 35.2 (25.7), lindane 82.1 (76.9) and tiovel 59.6 (67). The values for the 17 least toxic formulations (except dimilin and bimarit) showed ca 27–88% decrease during the last 4 days of observations.

Studies on the population dynamics and species composition of the sorghum stemborers Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Sesamia sp. were conducted at Melkassa, Rift Valley of Ethiopia, during the 1990 and 1992 cropping seasons. Chilo partellus at 92% dominated the species composition. Busseola frisca made up 7.7% and Sesamia calamistis less than 1% of the borers. Occurrence of partellus declined with delay in planting until the third planting ( early June to early July) then increased during late planting in July. Busseola fusca alone, however, tended to increase in numbers with delay in planting. In Melkassa area, early planting in July could be considered as the most suitable, with low borer numbers, damage symptoms and resulting in fewer stalks with peduncle damage. Grain yield was also higher during early planting in July while the lowest yield was obtained during late planting in July. Weather factors showed no consistency but relative humidity seemed to have a significantly negative correlation with insect numbers in the last two plantings in 1992.

The ability of males of Ephestia cautella to mate and transfer sperms aftergamma radiation as 5–6–day old pupae was investigated. The results indicate that gamma radiation had no significant effect on mating, sperm transfer and percentage of egg hatch.