Polyculture can help stabilize agroecosystems against frequent and severe pest outbreaks. An overview of the published data highlights ecological relationships among weeds, nematodes, arthropods, sugar-cane mosaic virus (SCMV), and the sugar-cane crop itself. Whereas individual studies commonly depict weeds as being either “good” or “bad”, this review is a synthesis of the variable roles and interactions of weeds in sugar-cane in order to provide a realistic perspective on the possibilities of weed interactions in sugar-cane agroecosystems. Conservation of weeds in Louisiana sugar-cane has resulted in more diversified arthropod fauna, higher natural enemy populations, and reduced damage by the sugar-cane borer, Diatraea saccharalis (F.). Weed competition and SCMV infection have each been associated with altered sugar-cane free amino acid accumulations that appeared to play a role in reducing populations of selected phytophagous nematodes. The combination of both weed and SCMV stress factors, however, have been shown to favour higher sugar-cane nematode populations. Although some weeds are alternate hosts for SCMV and its aphid vectors, and ratoon stunting disease (RSD), weed growth has not been linked with higher phytophagous nematode infestations or incidence of RSD. Weeds, if kept below economically competitive densities, may be ecologically and financially sound assets to sugar-cane pest management tactics.

The millet stem borer, Acigona ignefusalis Hampson, can cause total crop failures when severe infestations occur such as happened in northern Nigeria in 1984. Research at the Institute for Agricultural Research at Samaru has shown that various millet types and varieties exhibit different levels of susceptibility to the stem borer, although no resistant varieties are yet available. Infestation and damage by the stem borer are strongly influenced by date of planting and rate and time of nitrogen fertilizer. The effect of mixed cropping with sorghum depends on the spatial arrangement of the component crops in the mixture as well as on the insect population pressure. Systemic insecticides, particularly granular carbofuran, have been found to control the stem borer more effectively than contact insecticides like carbaryl. Seed dressing with carbofuran has been found to be ineffective. Some natural enemies of the stem borer have been identified but their role in lowering damage to millet is minimal. The destruction of infested stems before the beginning of the rainy season is a very important control measure against the insect. The possibilities of integrating these various methods for stem borer control are discussed.

Cellular and humoral immune responses against arthropod vector antigens in invertebrate hosts affect vector physiology and significantly modulate the transmission of pathogens. This phenomenon may be the basis for novel methods of disease control based on immunization against arthropod antigens. Current research in this field is briefly reviewed.

A study of the mosquito fauna of the Mwea Rice Irrigation Scheme, Kenya, carried out during 1984 and 1985 identified 13 species, with Anopheles gambiae s. l. comprising 65.71% of the total collection. X-chromosome identification of 652 semi-gravid females resulted in 649 (99.5 %) positive identifications of An. arabiensis, implicating it as the noxious member of the An. gambiae complex present. Inversion polymorphism of chromosomes 2Rb and 3Ra karyotypes was studied in one village population. Seasonal population changes were found to be heavily dependent on rice field surface water. Artificial irrigation for rice farming greatly extended the breeding period per year by linking up the two wet seasons. Adult females fed more frequently on bovids than humans. The mean percentage gonotrophic condition of all females caught in the villagesof Karima, Thiba, Mucii-wa-Urata and Rurumi by pyrethrum spray-sheet collections, miniature light-traps and exit window traps was 69 % bloodfed, 18 % unfed and 13 % gravid. These proportions were statistically shown to be within predictable limits over time and space. The sporozoite infection rate in adult females was 0.55% by manual dissections and 1.2% by the ELISA technique.

Thirty-five pearl millet cultivars of short, medium and long maturity cycle were screened in Senegal during 1985–1986 crop seasons to study field reaction to the attack of stalk borer, Coniesta (Acigona) ignefusalis Hmps.; spike worm, Heliocheilus (Raghuva) albipunctella De Joannis; millet midge, Geromyia penniseti Felt; head smut, Tolysporium penicillariae Bref; and ergot, Claviceps fusiformis Lov. Insect and disease incidence varied considerably depending upon cultivar maturity cycle. Least susceptible cultivars were IBV-8001 and P8 against spike worm; Zalla, NKK, P8 and M2D2 against head smut, and Ex-Darou against ergot. Cultivation of IBV-8001 has been suggested in northern and central Senegal. However, studies on identification and utilization of resistance sources of wide genetic diversity and multilocational tests may be necessary.

It is now nearly a century since systematic research started on tsetse, the principal vector of animal trypanosomiasis or “nagana” and human “sleeping sickness”. This major research effort was the consequence of the outbreak of a traumatic epidemic of sleeping sickness which swept through Uganda and what is now western Kenya in 1901, leading to the depopulation of that region through death and out-migration; the then colonial government appointed a Royal Commission to find a lasting solution to this tropical disease of crucial social and economic importance. importance. In spite of large-scale control campaigns carried out since that time in many parts of Africa—by colonial governments (British, French, Portuguese, and Belgian) in the first half of this century; and since then by specialized agencies of international organizations (the Food and Agricultural Organization of the United Nations, the International Atomic Energy Agency, etc.), and several aid agencies (U.S. Agency for International Development, The Netherlands Government, the Canadian International Development Agency, etc.)—the lasting solution to trypanosomiasis and tsetse vector control which we started seeking some 90 years ago still eludes us.

Trypanosoma congolense and T. simiae have been the two recognized species within the subgenus Nannomonas. T. congolense is pathogenic to cattle and the small ruminants but not to pigs, while T. simiae causesdisease only in plgs. The two species are difficult to distinguish from each other because both share the same developmental cycle in the tsetse and are broadly similar morphologically. However, their isoenzyme and DNA characteristics are quite different. Even more confusing is the fact that T. congolense itself is composed of a number of “strains”, or types; historically the different types of T. congolense were often considered as separate species by different workers.

Now isoenzyme and DNA charaterizatlon show that T. congolense is composed of at least three different types, which are probably equivalent to subspecies. Furthermore, evidence for another species within the subgenus Nannomonas has come recently from isolates from tsetse midguts in The Gambia.

Specific DNA probes have now been produced for the different kinds of Nannomonas. With these, it is now possible to identify the different infections from midgut dissections of wild tsetse. This should now facilitate an elaboratestudy to determine the distribution and prevalence of the different types across Africa, their association with the different species of tsetse, and the significance of each in the causation of disease in domestic livestock. The information gained will also help clarify the taxonomic status of each type within the subgenus.

Sources of information on the biology and ecology of Chilo species are reviewed on a world-wide basis, with emphasis on the major pest species which are stem borers of rice, maize, sugar-cane, sorghum and other cereal crops and grasses. Information on geographical distribution, host plants, general biology, ecology and population dynamics is summarized for the main species, especially for C. partellus (Swinhoe), C. suppressalis (Walker), C. infuscatellus (Snellen), C. sacchariphagus (Bojer), C. auricilius (Dudgeon), C. zacconius Bleszynski and C. agamemnon Bleszynski. Other species are also noted, including C. diffusilineus (de Joannis), C. panici Wang and Sung, C. terrenellus Pagenstecher, C. polychrysus (Meyrick), C. plejadellus Zincken, C. niponella (Thunberg) and C. orichalcociliellus (Strand). Requirements for additional and better organized information are identified.

Quality assessment and control of artificially reared insects has been traditionally linked to how well the insects perform in their “intended role” or their “fitness for use”. This paper suggests that quality should be defined more in terms of success in survival and colonizing ability. It is argued that the rearing facility should be regarded as an “ecological habitat”. Differences between wild and artificially reared insect populations are therefore due to the different effects and demands placed on the insects by the two habitats. Assessment of quality and its subsequent control should be based on biological parameters that are constant in the two habitats like the larval critical weight (Lcw).

The importance of the gram pod borer, Helicoverpa (=Heliothis) armigera (Hiibner) and the earhead bug, Calocoris angustatus Lethierry in the sorghum panicle was assessed. Gram pod borer consumed 2. 364 g of dough stage grains from fourth instar to pupation. A total of 74. 50 grains were damaged during the complete larval period. Grain loss was 14. 32 and 29. 42 g respectively when 50 and 100 nymphs per panicle were confined. When the two species occurred together grain loss was more than the sum of the loss due to each species alone.

In two study seasons, viz. summer (March to May) and “kharlf” (August to October) 1984 at Bangalore, India, populations of Aphis craccivora Koch on cowpea increased rapidly with crop growth and their peak coincided with peak pod formation. The activity of predatory coccinellids started 1 to 3 weeks after the appearance of aphids. The peak predator population more or less coincided with the peak aphid population. Highly significant positive correlations were found between weekly aphid and predator populations in the two seasons. The prey to predator ratio reached higher values 2 weeks after the incidence of the aphid, during peak pod formation stage and at the time of harvest. Amongst the predatory coccinellids, Menochilus sexmaculatus (F.) was predominant in both seasons constituting 77–88% and 83–95% of total predator population during summer and “kharif”, respectively. The study demonstrated a prey-dependent predator growth, often lagging behind that of the prey, pressing the need for alternate control methods that can be integrated into the management strategy considering the weather factors such as rainfall.

The application of nucleic acid hybridization techniques in the identification of most protozoan parasites, using species-specific DNA probes, has recently been described by several investigators. Species-specific DNA probes have been employed in the characterization of trypanosome infections in cattle and tsetse from Uganda. Most infections revealed by our DNA probes were mixed. Using these probes, a mixed infection with Trypanosoma brucei, T. vivax and both savannah and Kilifi types of T. congolense was revealed in one cow. This mixed infection could not have been detected by any of the classical parasitological methods. Isolates made from natural field infections, which had been passaged in laboratory animals, were found to consist of homogeneous trypanosome species. This was demonstrated in all of 47 stabilates which were homogeneous infections either of savannah type T. congolense or T. brucei.

The method of sample preparation for DNA probe analysis was modified to suit field conditions. The samples, which were spot-blotted onto nylon filters and either immediately denatured or left undenatured, could be kept at room temperature for 1 month with only a moderate loss of hybridization signal intensities. Although hybridization signals were visible in undenatured samples, those seen with the samples that had been denatured were clearly more intense. This approach eliminates the need for liquid nitrogen and/or an incubator in the field. The simplicity, sensitivity and specificity of this diagnostic technique using species-specific DNA probes, make it an important tool for future studies of the epidemiology of African trypanosomiases.

Biological and morphometric studies of the different stages of Lucilia caesar, were carried out using three rearing media prepared from local materials as the test media, and the standard Snyder's medium as control. The materials for the test media were: (i) Garri, soybeans, palmwine and liver (GSPL), (ii) Garri, soybeansand palmwine (GSP) and (iii) Pap, nono, cabbage and liver (PNCL). The Snyder's medium consists of milk, yeast and bacto agar (M Y A). There was no significant difference in the duration of larval instars and adult emergence for the blowflies reared in the standard, PNCLand GSPL media. For blowflies reared in GSP, duration of larval and adult stages was prolonged by about 48 hr and 5 days respectively, when compared with the flies reared from the other three media. The average length and width of each larval stage reared from the four media were not significantly different. Morphometrics of the adults showed that those reared from the GSPL and control media were longer, heavier, and laid significantly more eggs per female than adults reared from PNCL and GSP media. The GSPL medium was considered to be the most suitable alternative to MYA.

A survey of the parasites, parasitoids and predators of the nymphs and adults of Oedaleus senegalensis showed that three dipterous insects and a red mite were common parasitoids of the grasshopper. Seven arthropod species were observed preying on the nymphs. Among the vertebrates, two reptile species, one amphibian and 20 species of birds were observed preying on both the nymphs and adults of the grasshopper.

Five mutants for seed coat colour from the faba bean, Viciafaba L. variety BF 2/2 (Beladi) were tested qualitatively and quantitatively for tannin content. The susceptibility of the mutants to Bruchidius incarnatus (Boh.) and Callosobruchus maculatus (F.) was also evaluated. All seed coats contained tannins (0.75–3.75%). The darker the colour the lower the tannin content. Cotyledons with testas removed were devoid of tannins. The thickness of the seed coats ranged from 0.146–0.155 mm, however, differences among mutants were not significant. Faba seeds were more suitable for the multiplication of B. incarnatus than C. maculatus. The poor performance of the latter was manifested as low fecundity, high mortality and longer developmental period. It was concluded that selection for white coloured faba seeds should not be discouraged on the basis of its assumed susceptibility to bruchids.

Lepidopterous stem borers constitute one of the major constraints to cereal crop production in southern Africa. Chilo partellus Swinhoe, is an economically important stem borer of maize and sorghum. Current research status on C. partellus is reviewed and substantial advances in the distribution, bioecology and control strategies are discussed. Present work on the assessment of crop losses, elucidation of mechanisms of resistance, development of resistant crop cultivare, feasibility of biological control measures and the implementation of other stem borer management methods are reported. Further areas of research into the management of C. partellus are identified.