The ability of the African trypanosomes to vary their surface coats of glycoprotein antigens during infections of susceptible host animals has prevented the development of vaccines employing cell surface proteins, as is being attempted with other parasitic protozoa (see Cohen, 1986). Since the phenomenon of antigenic variation in protozoa was the subject of another symposium, of the five papers presented in this symposium one dealt with the possibility of sexual phenomena occurring in trypanosomes, one with the transmission of the organisms by tsetse to vertebrate hosts and one with the characteristics of the trypanosomes isolated from man. The fourth paper described the vertebrate host response to the parasites and the fifth described the control of such infections by chemotherapy.

Studies were conducted with Ugandan isolate of Coelomomyces stegomyiae against mosquito larvae. Aedes aegypti first instar larvae was most susceptible (99.8%) within 6 days, and the fourth instar was least susceptible (44.4%). Culex quinquefasciatus suffered 70% mortality within 10 days. Mortality rates were 92.5% for Culex tigripes, 70% for Culex duttoni, 89.5% for Aedes africanus, 89.9% for Anopheles gambiase and 97.3% for Aedes simpsoni. There was no infection when two species of the predatory mosquito Toxorhynchites were exposed to infection. A few adults emerging from an infected larval population were found infected when dissected. Other mosquitoes that pupated died and the pupae were found infected. Infected females were produced by 19.2% of the fresh pupae exposed. The importance of the results in biological control is discussed.

Eight potato cultivars, viz, Anett, Desiree, Feldeslohn, Kerr's Pink, Kenya Baraka, Roslin Eburu, Roslin Gucha and Roslin Tana were tested in the field to compare their susceptibility to aphids. Despite the variation in results, Anett, Kerr's Pink and Desiree were identified as the most susceptible cultivars. The experiments revealed that Roslin Tana was a comparatively resistant cultivar useful for reference in further work.

There were no significant correlations between leaf area, glandular hairs and alate aphids with the number of apterae aphids on the eight potato cultivars. Resistance of Roslin Tana to aphids was, therefore, not due to the morphological characteristics of the cultivar, but probably to some physiological factor(s).

From early March 1981 to late May 1982, the aphid population trend on 2-year-old Raphia hookeri palm plantation in Nigerian Institute for Oil Palm Research Benin, was studied in relation to ambient weather conditions. The population, taken from the central ‘spear’ and leaflets of Raphia, where it is most abundant, was high from March to April 1981. This declined to a low level in July and August 1981 following a heavy rainfall. Another peak was observed in September, but this however declined gradually to a very low level at the end of March 1982. However, in mid-April, there was an incipient peak which was quickly lowered again in early May by larvae of the ladybird, Platynaspis sp. The number of adult alatae correlated positively with the total aphid population on spear and leaflets (r = 0.68). There was no direct relationship between the measured environmental factors and the aphid population fluctuation.

An economic threshold on fresh cabbage affected by Plutella xylostella (L.) and Crocidolomia binotalis Z., based on visual estimates of defoliation and a determination of this damage on the marketable yield was developed. An initial survey of unprotected cabbage field for determination of general levels of number of holes caused by feeding of both the lepidopterous pests formed a prerequisite for conducting visual damage threshold experiments. Maintaining a low visual damage threshold of up to 1.0 mean hole (mean of two leaves) on the wrapper leaves, after initial protection of primordia, was found to be an effective alternative in reducing present reliance on weekly or fortnightly sprays for the control of both the pests on cabbage. The possibility of eliminating precupping sprays is supported by the study since the larval populations causing damage to either outer leaves or leaves about to cover the head did not reduce the yield to a significant extent. The use of thresholds based on larval counts of either P. xylostella or C. binotalis failed to give enough lead time during scouting and resulted in loss of marketability.

This paper combines some of the results from three studies that explain the system by which the gut of Phlebotomus papatasi is maintained bacteria free. This system includes an antibacterial factor in the crop (diverticulum) and feeding behaviour which determines selective routing of meals. When feeding by piercing animal skin or plant tissue, in a ‘blood feeding’ mode, the uncontaminated meals of both sources enter the midgut directly. Free-solution sugar-meals which may contain contaminants, enter the crop where they mix with the antibacterial agent. Feeding on plants is also described.

A millet farm was divided into five treatment plots of three replicates. The population of the grasshoppers was assessed by flushing and the percentage leaf damage on the millet was estimated by visual grading of the defoliated area. Weeding discouraged oviposition and reduced the vegetative shelter and the population of the grasshoppers. The unweeded plots had high levels of defoliation and low grain yield of millet relative to the weeded plots. Oedaleus spp were the most numerous grasshoppers and probably caused the greatest damage on pearl millet. The common weeds on the farm were Brachiaria xantholeuca, Cenchrus biflorus, Ipomoea vagans and Mitracarpus scaber.

Endocytosis is the process by which a cell ingests material (solute, paniculate, living cells) and encloses it in a membrane-limited vacuole, the endosome. Protozoa may ingest or they may become ingested. In the latter case they may serve as food for the ingesting cell or they may, as parasites, survive and multiply at the expense of the ingesting cell. The present symposium was concerned with two topics: (1) endocytosis by free living protozoa, and (2) endocytosis of parasitic protozoa. In both cases the initial result of endocytosis is the formation of an endosome, whereas the further fate of the ingested contents differs (Fig. 1); in the first instance the contents are digested by the action of hydrolytic (lysosomal) enzymes and in the second instance the ingested parasite avoids digestion and becomes adapted to parasitism.

This report summarizes the contributions to a symposium held at the VII International Congress of Protozoology in Nairobi. Within the cell cycle of different ciliates, stages and modes controlling cell cycle length are described. In addition, cytoplasmic factors as well as genes related to meiosis are demonstrated. These factors are effective in some unrelated organisms. Several lines of evidence indicate that there is a close connection between the control of meiotic and of mitotic events.

Four instars of Cerataphis palmae (Ghesquierei) ( = Cerataphis variabilis H.R.L.) were identified from laboratory-bred and field-collected alatoid and apterous immatures through morphometric studies. These were distinguished most readily by the number and shape of antennal segments, body size, degree of development of the thorax, the presence or absence of wing pads and crenulations on body margin.

Larval dispersal and establishment of Chilo partellus (Swinhoe) was studied on different maize cultivar combinations at the whorl stage. Dispersal was increased 2-fold when the infested cultivar ICZ2-CM (resistant) was surrounded by the more susceptible Inbred A, and decreased when Inbred A plants were surrounded by ICZ2-CM. A negative relationship (r = 0.89) was found between the proportions of larvae establishing on infested plants and those unaccounted for. The influence of a cultivar on increased larval dispersal could be exploited in resistance breeding strategies. The possible role of such an effect in pest management strategies is discussed.

The diagnosis of visceral leishmaniasis must be based upon a demonstration of the parasite in tissues of the patient. The best diagnostic test is a splenic aspirate, which is safe, highly sensitive and specific if the technique described in this paper is used and both smears and cultures of the aspirate are performed. Peripheral blood and nasal exudate have parasites in smears and/or cultures in 75 and 40% of Kenyan visceral leishmaniasis patients, respectively. Sodium stibogluconate (Pentostam) is the preferred treatment for visceral leishmaniasis. Recent Clinical Research Centre trials of different schedules of treatment with sodium stibogluconate are discussed. Currently, we recommend sodium stibogluconate, 20 mg/kg once daily for 30 days, for initial treatment. For patients who have not responded to initial treatment with sodium stibogluconate or have relapsed after initially responding to this treatment, we recommend sodium stibogluconate, 20 mg/kg once daily for 60 days. Further studies are now underway comparing the combination of allopurinol plus sodium stibogluconate versus sodium stibogluconate alone for unresponsive or relapsed patients.

Amylase, sucrase and cellulase were detected in the alimentary canals of workers and soldiers of Amitermes evuncifer Silvestri, but only sucrase and cellulase were found in the alimentary canal of the alates. Enzyme activities varied in different parts of the alimentary canal. That high enzyme activities were observed in the guts of the workers (than those of the soldiers) is due to the fact that the workers forage for food which they digest partially before feeding other members of the colony through trophallaxis. The presence of enzymes in the alimentary canals of alates and soldiers indicates that the partially digested food, from the workers, undergoes further digestion in their systems.

Various planting patterns of cabbage and tomato were investigated to assess whether such a cultural practice could fcring about reduction in the incidence of Plutella xylostella (L.) and Crocidolomia binotalis Z. on cabbage. No reduction in the larval incidence of both the pests was observed when different combinations of cabbage and tomato were planted at the same time. A slight reduction in the incidence of both the lepidopterans had ensued in all the planting patterns, when cabbage was planted 15 days later than tomato. Maximum reduction, however, was observed following planting pattern of one row cabbage and one row tomato (cabbage planted 30 days later than tomato). It is further opined that this type of cultural practice cannot be used as a sole control measure for both the pests, since the marketable yield of cabbage recorded in the promising intercrop combination was well below the attainable yield that could be expected when insecticide sprays are undertaken on pure cabbage. Significant reduction in net return was also obtained following this cultural practice as compared to cabbage receiving insecticidal sprays based on different management programmes.

Assessment of the damage potential of Cydia ptychora (Meyrick) was carried out in Ife Brown cowpea at different levels of larval infestation and different pod growth phases. The results showed that C. ptychora caused significant shrivelling in pods of Ife Brown cowpea when infested with either one, two or three first-instar larvae per pod at either the young or mid-fill growth phases, relative to the corresponding controls. A significant reduction in seed yield was also recorded in plants subjected to an infestation level of either one, two or three first-instar larvae per pod at both mid-fill and mature pod growth phases. Thus, an infestation level of one first-instar larva per pod at either the mid-fill or mature pod growth phases would be adequate for intensive screening of cowpea varieties for resistance to C. ptychora, using Ife Brown as a standard for comparison.

The nutrition, growth, development and mortality of the cotton leafworm, Spodoptera littoralis, were followed on six different artificial diets. As compared with the reference diet of Poitout et al. (1972) (Entomologia exp. appl.15, 341–350), our new media exhibit some interesting technical features:

(1) The agar is replaced by a new gelling substrate of which two types exist: Korano gels 400 and 411.

(2) These gels allow the preparation of a dry, sterile and ready-to-use mixture in convenient plastic packings. The powder is obtained by grinding the insoluble components and the nebulization of the soluble ones. When needed, the powder is simply added to hot distilled water (60–70°C) and stirred.

Different conditioning processes have been tested and this work was carried out to ensure that the two Korano gelling powders have the same biological quality as agar. The prepacked diets have proven to be very easy to store and to handle, and overall they are quite efficient and time-saving. Furthermore, they are much cheaper than the laboratory-prepared control diet. They supported the complete and normal development of S. littoralis, and even at a slightly better rate than agar-containing diets (M1 and M2b diets).

The unique habitats of marine environments including some organically rich, but physically variable, benthic environments, and the rather uniform, regionally stable, open ocean environments have both produced species of biomineralizing protozoa of remarkable size ranging from several hundreds of microns to several millimetres (for solitary forms of foraminifera and radiolaria for example). Some colonial radiolaria are several centimetres in diameter and may reach lengths of over a metre for filiform species. These larger, free-living protozoa aften harbour algal symbionts and exhibit unusual adaptations to enhance their survival in their unique habitat and to stabilize, if not enhance, their association with their algal symbionts through structural and physiological modifications to complement the unique requirements imposed by animal–algal associations.

The distribution of canine leishmaniasis and figures on infection frequency in countries bordering the Mediterranean Sea are given. The clinical picture and most common laboratory findings are reviewed. Leishmania infantum is the aetiological agent of both human and canine forms of visceral leishmaniasis. The proved or suspected vectors of L. infantum are listed and mention is made of wild animals (fox, rat) as possible primary reservoirs of the parasite. Finally, the methods of investigation and control of canine leishmaniasis are discussed.

A comparison was made of the relative abundance of three species of black-fly pupae colonising three natural substrates in the River Assob, in central Nigeria. Simulium hargreavesi, S. squamosum and S. vorax preferred trailing roots, whereas S. cervicomutum, S. unicomutum and S. impukane preferred dead leaves and to a lesser extent, rocks.

In order to see whether this was a preference between cylindrical and flat surfaces, polythene strips were compared with polythene strings and a smooth surface was compared with a rough one. Results are presented for the three most abundant species S. squamosum, S. hargreavesi and S. cervicomutum. All markedly avoided the rough string. S. squamosum and S. hargreavesi preferred smooth strings, whereas S. cervicomutum had no significant preference between smooth strips and strings (although slightly preferring strips). These findings are discussed in relation to natural habitats and sampling bias.