Regular field surveys were carried out in 2 week intervals in 1986 and 1987 to determine population density, species composition, migration activity of Cicadulina leafhoppers and their infectivity with maize streak virus (MSV) in different ecological locations of southeastern Nigeria: mangrove swamp forest (IITA and RIART station at Onne), deltaic swamp forest (RSUST, Port Harcourt), seasonal swamp forest (Iriebe) and high forest zone (NCRI, Amakama near Umuahia).

Population density was always low during dry season, significantly lower in the rain forest zone and higher in the swamp forest, rapidly rising in the second rainy season in all ecological zones and reaching its maximum before the rains finally stopped. Sharp increase in the population density in Nov. and Dec. may indicate mass migration activity of Cicadulina leafhoppers from already dry areas of adjacent Guinea savanna at that period.

Six species of Cicadulina were collected from most of sampled areas. C. ghaurii was the predominant species in 1986 and 1987, averaging 55.9% for all locations and periods. Its portion was higher in the mangrove swamp forest (Onne) than in the high forest zone (Amakama). The predominance of other species declined in the order: C. triangula (18.2%), C. mbila (17.2%), C. arachidis (5.9%), C. similis (2.8%) and C. hartmansi (0.1%). In absolute values, the portion of individuals out of the total number of leafhoppers collected was for C. triangula 53.7%, C. ghaurii 25.5%, C. mbila 17.3%, C. arachidis 2.3%, C. similis 1.1% and C. hartmansi0.1%. A high population of C. triangula occurred only in the relatively short period in Nov.-Dec, especially in Iriebe and was correlated with the rapid increase of Cicadulina densities in all sampled areas; a high migration activity of C. triangula and C. mbila was confirmed.

Incidence of MSV in the surveyed farmers' field varied between 0–22% in the first rainy season (1987) and 12–25% in the second rainy season (1986). The portion of Cicadulina adults already infected with MSV under field conditions and capable of transmitting MSV to the susceptible maize seedlings varied from 3.3 to 23.3%, with higher values for leafhoppers collected at the end of the second rainy season.

The development and morphometrics of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) were studied on cassava and a description was made of the different nymphal instars and oter biological characteristics. The nymphal instars were distinguished using easily recognisable morphological characteristics. Abnormally developing individuals were also easily recognised. Regression analysis was highly significant between the length and width of nymphal instars modelled collectively indicating two-dimensional growth at least across three nymphal stadia. Males were smaller than females on the basis of body length, wing width and width of the abdomen. The insects showed better development on a Colombian cassava variety as compared to an African variety, Ebwanateraka from Uganda, and consistently showed a higher proportion of males than females (2.33: 1) for early-emerging individuals. Mean developmental period on both varieties was 22 days and the first instars accounted for the major part of the developmental period which ranged from 19 to 29 days. The mean number of eggs/female/day was 4.89. The actual events of first instar eclosion, which can last up to approximately five minutes, were described. The intervals of honeydew flow to the vasiform orifice lasted a minimum mean time of 20.8 seconds and a maximum mean time of 123 seconds.

The flight phenology of the stem borer, Chilo partellus (Swinhoe) at the ICIPE's Mbita Point Field Station (MPFS) and on a nearby farmer's field was monitored using pheromone traps. The relation between pheromone trap catches of males and sorghum plant age, infestation, larval/pupal population density and sorghum cultivars used was examined. At MPFS C. partellus males were caught throughout the year in pheromone traps. Fluctuations of trap catches indicated that the pest completes two main generations on each of the long and short rain sorghum crops. On farmers' fields, males continued to be caught in large numbers after harvest, implying that the pest continues to breed on the sorghum stalks and tillers. Significantly lower observed catches of males occurred only on one (MB-3) of the eight different sorghum cultivars, during the period of 2–6 weeks after plant emergence. In general, positive correlations were observed between the number of males caught in pheromone traps and larval pupal population density, males and percentage plants infested, and males and plant age. However, the pheromone trap appeared to be less effective under high population density, particularly during the flight of the second generation moths, due to competition between pheromone trap and wild females. But the flight phenology as monitored by pheromone traps appeared to reflect major events in population development of C. partellus. Pheromone traps would be useful in detecting C. partellus and for monitoring its flight phenology.

Investigations were conducted in six farm fields (1.5 to 3 ha each) in Burkina Faso with objectives to (1) study adult Smicronyx spp. (Coleoptera: Curculionidae) population dynamics during Striga hermonthica (Scrophulariaceae) seed-pod production, (2) assess the impact of different population levels of Smicronyx spp. on St. hermonthica capsule production and, (3) estimate Smicronyx female reproductive success in seed-pod galls. A Univac portable sampler was used to sample adult Smicronyx spp. and St. hermonthica densities were assessed using aim2 metal quadrat. Fifty St. hermonthica shoots per field were sampled each week. Before the emergence of St. hermonthica, Smicronyx adults were found on nearby Striga éspera (Willd) Benth. fields. Striga hermonthica shoots produced on average ca. 24 seed capsules each, while each female Smicronyx galled from 12 to 32 seed pods. Seed-pod galling alone was not sufficiently high to be considered as a successful reduction factor for St. hermonthica seed production in natural conditions. Smicronyx spp. adult population levels decreased during the St. hermonthica capsule production period. Increased population levels of Smicronyx spp. resulted in higher percentages of St. hermonthica seed-pod galls, suggesting that a ugmentative techniques, if used as part of an integrated control programme could be a worthwhile strategy.

The development of simple models for describing the population dynamics of species with overlapping generations is briefly described. The paper then presents a minimally complex simulation model for tsetse populations in which seasonally varying density-independent mortality, generally applied only to the adult stage, is combined with density dependence acting on both puparia and adults. Density dependence regulates population size within limits determined by an interaction between the strength of the density-dependent relationships and the variability of the seasonal density independence. Population data sets for Glossina palpalis and G. morsitans in Nigeria, and G. pallidipes in Kenya are adequately described by the model. Relationships discovered between the density-independent mortality and climatic variables for the Lambwe Valley data set allow predictions of population changes in other sites on the basis of their climatic conditions. Attempts to predict changes in the population of G.pallidipes in Somalia highlight the difficulties of this exercise. A tsetse's demographic response to climate may vary from region to region, making extensive predictions from local data sets difficult. There seems, however, no need to make more complex models to describe observed changes in tsetse populations.

Various insect pests, of which stemborers are the most widely distributed and damaging, affect about 30 out of the 35 million hectares planted with maize in developing countries. Chemical control, biological control; cultural methods and host plant resistance constitute the four general approaches to stemborer control. The use of stemborer-resistant maize increases farming efficiency by both reducing yield losses from stemborer damage and reducing or eliminating the cost of insecticides and other inputs. In the past, CIMMYT followed conventional breeding methods to develop germplasm resistant to stemborers and molecular technology, quantitative trait loci (QTL) in marker-assisted selection (MAS) to select for improved stemborer resistance in elite lines. More recently, CIMMYT has developed the capacity to produce transgenic maize with resistance factor(s) derived from genes that encode delta-endotoxins derived from the soil bacterium Bacillus thuringiensis (Bt). A sub-tropical source population with multiple borer resistance (MBR population) was developed by recombination and recurrent selection under infestation with four stemborer species. Marker-assisted selection is being used in two African countries to promote the transfer of resistance into elite and adapted germplasm. The Insect Resistant Maize for Africa (IRMA) project is pursuing the transfer of Bt-based resistance to adapted maize germplasm, initially in Kenya, but later to other interested African countries. CIMMYT's varietal release strategy is to pyramid Bt genes into maize populations with existing multigenic pest resistance, in order to enhance both the levels and durability of plant resistance to maize pests. This paper discusses the various approaches used at CIMMYT to develop stemborer-resistant maize germplasm.

The length of the reproduction cycle of Lasioderma serricorne (F.) under ambient laboratory conditions (temperature range 28.0–32°C and 72.5–80.5% r.h.)was shown to depend on the identity and state of division of various cereal grains, cowpeas, groundnuts and dried root crops. Cut dried yams allowed the shortest cycle andwholericethelongest.The rate of population increase by L. serricorne was also assessed and this was maximal when cut wheat and minimal when whole rice was provided. Fecundity was highest with sorghum and lowest with rice as food source. Females of the species lived longer than males.

Two shaving methods, one by using a sharp razor blade and the other a small pair of dissecting scissors, were tested on pods of Vigna vexillata accessions to investigate the effect of trichomes on feeding and development of the pod-bug Clavigralla tomentosicollis Stål (Hemiptera: Coreidae). Electron micrographs of unshaved (control) pods showed that all trichome types (glandular, long non-glandular and short non-glandular) were present on the pod surface. Shaving with a pair of scissors shortened long non-glandular trichomes, with little or no damage to the glandular types. Percentages of seed damage and nymphs surviving to the adult stage were similar (P>0.05) between unshaved and scissors-shaved pods. These pods showed significantly lower (P<0.05) percent seed damage than razor-shaved and solvent-washed pods, whose glandular trichomes were all completely scraped or washed off. The opposite trend was observed for the insect's growth index, indicating that glandular trichomes had a greater influence than non-glandular trichomes on feeding and development of C. tomentosicollis. The present study suggests that the scissor-shaving method would be more appropriate if the effect of trichome length is being investigated, and the more abrasive razor-shaving method if the effect of glandular trichomes is of interest

The major alkanone constituents of the resin of Commiphora rostrata, 2-decanone and 2-undecanone, and a series of structural analogues were bioassayed for their repellency against the maize weevil, Sitophilus zeamais in olfactometric assays. All the aliphatic ketones and aldehydes showed comparable or greater activity than the synthetic commercial insect repellent N, N-diethyl toluamide (DEET). In the 2-alkanone series the C-8 and C-9 compounds demonstrated significantly higher activity than their shorter- and longer-chained congeners. Analogues differing in the relative positions of the carbonyl group, including aldehydes, showed a variable pattern of repellency. Alkanols appeared to be mildly attractive to the weevil. The results support our previous suggestion that the resin constituents may play an allomonal role in the ecosystem where the plant thrives.

The control of Trypanosoma rhodesiense sleeping sickness by clinical methods is often complicated by the existence of animal reservoir hosts which greatly contribute to the persistence of the disease in many parts of East Africa. The control of sleeping sickness should, therefore, include control of the vector and elimination of the reservoir hosts. Another factor which is often ignored, when planning sleeping sickness control measures, is the influence of cultural practices of the resident human population on the epidemiology of the disease in any given location in East Africa. At Lower Kitete, northern Tanzania, trypanosomiasis due to T. rhodesiense is occupational in nature so that many of the individuals are infected in Lossitete Forest while engaged in various activities. The factors favouring infection within the area, and the role played by the cultural practices of the Masai around the area in bringing about the outbreak of an epidemic, are discussed. The importance of understanding the cultural practices and occupational tendencies of the Masai in Lower Kitete, where trypanosomiasis outbreaks have occurred in the last 10 years, is stressed. With such an understanding the management of trypanosomiasis at Lower Kitete may be successful.

Sorghum (Sorghum bicolor) is an important food crop, especially of the semi-arid areas of Asia and Africa. One of the major constraints affecting the popularity of high-yielding hybrids and varieties is their extremely high susceptibility to insect pests.

Painter (1951) has reviewed in detail the work done on resistance in sorghum to the chinch bug (Blissus leucopterus), corn leaf aphid (Aphis maidis) and sorghum midge (Contarinia sorghicola). In the last decade and a half considerable work has been done on resistance to the shootfly (Atherigona seccata), stem borer (Chilo partellus) and sorghum midge (Contarinia sorghicola). By conducting multilo-cation screenings of world germplasm under natural and artificial infestation conditions, not only have promising sources of resistance been identified but a number of them have been utilised in crossing programmes to develop high-yielding resistant cultivars. Some sources with multiple resistance have also been identified.

The mechanisms of resistance in sorghum to the major pests have been investigated. It is seen that the mechanisms are generally complex and the observed field resistance is the total reaction of several components. There are several leads available which justify further intensive work, especially on identifying naturally occurring plant products associated with antibiosis mechanism.

Lepidopteran stem borers account for heavy losses in cereals in areas where they are prevalent throughout Africa. Microsporidia, especially Nosema sp. may be developed for use in the management of this group of insect pests. Studies carried out so far show that the application of Nosema spores may increase yield up to 34% in sorghum when the plants are infested with Chilo partellus eggs and sprayed with the pathogen, and up to 80% in sorghum infested with borer larvae.

The procedure for spore production is simple, and may easily be adapted for small scale industrial production by local or regional communities and organizations. In trials aimed at the mass production of Nosema sp. for the management of C. partellus, a yield of 109 spores/larva has been attained. If this production level can be maintained, then a system that produces only 6000 larvae/day would yield enough cadavers for preparation of 6000 1 daily. At the rate in which the pathogen suspension is applied as foliar sprays in the field, this would be sufficient to treat 5373 ha. If widely adopted, use of microsporidia would revolutionize cereal stem borer management in the tropics.

Urticating spicules of Hylesia moth of Guyana (H. metabus Cramer = H. urticans Floch et Abonnenc) are produced by trichogen and tormogen cells which form a monolayer hypoderm similar to that which produces scales. Urticating spicules are interpreted as modified scales.

Inhabited Macrotermes (Termitidae: Macrotermitinae) mounds in cultivated farms in the humid forest agroecological zones of southwestern Nigeria showed higher clay and silt but lower sand contents than their surrounding soils. These physical characteristics were positively correlated with those of the surrounding soils. The heights and diameters of the mounds were also positively correlated to the level of clay and silt in the surrounding soils, although the correlations were not significant (P > 0.05). Carbon and nitrogen content of 67% of the mounds was lower than that of their surrounding soils. A general increase in exchangeable bases and phosphorous contents of the mound materials compared to those of the surrounding soils was also observed. The pH of mound materials varied between 5.5 and 7.3, with 75% of the mounds having lower pH values than the surrounding soils. The implication of these results on the possible use of mound materials to increase soil fertility is discussed.

The egg follicle C of the left ovary was developing first, indicating reversed ovarian sequences in 5.8, 4.8, 4.2, 2.2, 1.1 and 2.0% newly-emerged female G. pallidipes from pupae kept at 29.5 ± 0.5, 27.5 ± 1.0, 25.0 ± 0.5, 22.5 ± 0.5, 20.5 ± 1.0°C and then maintained at ambient temperature (19 to 31°C) in the local colony. There was a highly significant positive correlation between the frequency of reversed ovarian sequences in flies and temperature in the range 19.5–30.0°C. The incidence of the abnormality was very low (0.2%) in wild-caught females from the Lambwe Valley, probably reflecting the constancy of favourable temperatures in that location. Old females with altered ovarian sequence had apparently both normal pregnancy and alternate maturation of eggs between the ovaries. This appears to be the first report suggestive of a temperature-induced reversed sequential ovarian development in Glossina.

This study on predispersal seed predation of the leguminous species Vachellia abyssinica (Hochst. Ex. Benth.) Kyal & Boatwr., Senegalia senegal (L.) Britton, Vachellia seyal (Del.) P.J.H. Hurter, and Vachellia tortilis (Forssk.) Galasso & Banfi was conducted around Lake Langano and Menagesha Forest in Ethiopia to identify the associated seed predators and determine their impact on seed germination. Eight seed beetles Bruchidius albosparsus (Fåhraeus, 1839), B. aurivillii (Blanc, 1889), B. djemensis Decelle 1971, B. discoidalis (Fåhraeus, 1839), B. sinaitus (K. Daniel, 1907), B. silaceus (Fåhraeus, 1839), B. sp 411, B. simulans (Anton and Delobel, 2003), and one unidentified species of Cerambycidae were found associated with seeds of these Acacia species. These predators damaged less than 9% of seeds of these species, which exhibited lower germination. This study provides unrecorded lists of predispersal seed predators associated with seeds of Vachellia and Senegalia species in Ethiopia, and some associations are new. There is need to assess the distribution, abundance and effects of predispersal seed predators on other Vachellia, as well as other tree species.

Cerconota anonella is the most important pest of the Annonaceae in the Neotropical region for larval damage, which can result in 60 to 100% losses in fruit production. However information on the pest's biology is scarce. This research compared different artificial diets for rearing C. anonella under laboratory conditions (25.0 ± 1.0 °C; 60 ± 5.0% RH and 14 h photophase). Five diets were compared: A (bean, soybean meal, wheatgerm, casein and yeast), B (maize flour, wheatgerm and yeast), C (wheatgerm and casein), D (wheatgerm and soybean) and E (wheatgerm and soybean). In diet E, the amount of wheatgerm was higher than that in dietD. The results indicated that diet E was the most suitable one for the development of C. anonella.

The effect of fly age, sex, and period of starvation on the uptake and development of Trypanosoma congolense infection was examined in Glossina morsitans morsitans. In a study consisting of 1739 specimens of various ages, young unfed 16-hr-old flies and 2-day-old starved flies developed significantly higher mature infections than 2-day-old and 7-day-old flies which had been fed previously on a clean blood meal. Females displayed significantly higher immature infections, while mature infections were recorded more frequently in males, suggesting that females possess a stronger barrier to trypanosome development. The possible factors involved are discussed.