—The possible immune responses of insects to some abiotic agents were reviewed. These agents include insecticides, insect growth regulators, antibiotics, inert particles and miscellaneous substances of particulate and non-particulate nature. The significance of studying the immune response of insects to abiotic agents in relation to insect control, together with the link between the immune response of insects to both abiotic and biotic agents is discussed.

In a sub-Saharan African context, limited natural resources, infectious diseases, including those transmitted by arthropod vectors, and chronic exposure to food contaminated with mycotoxin-producing fungi which, among others, are vectored by insects, are among the major constraints to human health. Thus, pest control should be an important component in human health improvement projects. It appears that the advantages of preventive over curative methods are rarely recognised in Africa, with more emphasis being given to the search for the ‘silver bullet’ than to integrated control approaches. Integrated pest management (IPM) systems can be assigned to different decision-making levels as well as to different integration levels, combining ecological (individual pest species, species communities, species assemblages) and management (crop, cropping systems, farms, communities) levels with the respective control systems. These levels produce a highly structured environment for decision-making, in which the use of modern information technology is important. Case studies show that IPM systems are developed and implemented at four integration levels, whereby most work is done on the lowest integration level, addressing a single pest or pest complex attacking a particular crop, group of livestock or human population, and the respective control measures undertaken. Coordinated efforts to develop and implement supplementary IPM systems at higher levels are concluded to be important elements in integrated pest management and a further contribution to human health improvement and poverty alleviation.

Fluoride accumulation and the relative fluoride loading of different body parts in the wild mulberry silkworm (Bombyx mandarina M.), mulberry geometrid (Pathonandria atrineata B.) and mulberry silkworm (Bombyx mori L.) near fluoride pollution sources in the main sericultural region of China were studied. The results showed that the insects had an increased fluoride accumulation if compared to their feed, and that there were wide differences between the different insect species with the same feed and within the same polluted site. The digestive tract of the insect retained much higher fluoride content than other body parts. Moreover, a highly significant correlation was found between fluoride content in the studied insects and that of the mulberry leaves on which they were collected. Of the three insects studied, the mulberry geometrid appears to be most adapted to environmental fluoride, while the domestic silkworm is the least able to tolerate high fluoride levels, experiencing high mortalities at 94.3 mg/kg.

Mulberry (Morus spp.) was found to be the most sensitive plant to air-borne fluoride pollution among six plants studied in polluted areas, and could be a useful bioindicator to monitor environmental pollution. The highest fluoride content was found in the oldest leaves, and in plants growing closest to and downwind from the pollution source.

Data on insects as food in sub-Saharan Africa were collected by reviewing the literature and conducting interviews in a number of African countries. A list of about 250 edible insect species from Africa was compiled. Of these, 78 percent are Lepidoptera (30%), Orthoptera (29%) and Coleoptera (19%), and 22 percent Isoptera, Homoptera, Hymenoptera, Heteroptera, Diptera and Odonota. Insects are rich in protein, vitamins and minerals, and a good source of iron and B-vitamins. Examples of insects being toxic are given, but often traditional methods are used to remove the poison. Whether or not insects are eaten depends not only on taste and nutritional value, but also on customs, ethnic preferences or prohibitions. The harvesting of insects is often done by women. The way of collecting depends on insects' behaviour. For example, inactivity at low temperatures enables easy catching of locusts and grasshoppers in the morning. Night flyers (termites, some grasshoppers) can be lured into traps by light and some insects like palm weevils can be attracted to artificially created breeding sites. Some species (crickets, cicadas) can be located by the sound they make. A number of tools are used to facilitate capturing such as glue, sticks, nets and baskets. Because most insects are only seasonally available, preservation by drying is often practised. Some examples of how to prepare them as food are given from important insect groups.

To manage insects in the interest of food security more attention should be given to environmentally sustainable harvesting methods. They should be made better available throughout the year by developing improved conservation methods or by farming this minilivestock. Considering the economic, nutritional and ecological advantages of this traditional food source, its promotion deserves more attention both from national governments and assistance programmes.

To simplify and improve the effectiveness of human trypanosomosis control efforts as well as reduce their cost, it is desirable to identify high-risk sites for transmission of trypanosomes by tsetse flies to humans. The authors propose a simplification of the risk index previously developed by Laveissière et al. (1994). The simplified index has been developed in Côte d'Ivoire and validated in Cameroon. Unlike the old index which required determination of the flies' daily survival rate, the calculation of this new index requires only the knowledge of the proportions of teneral flies and of flies that have fed on human blood, from the population caught in the various biotopes.

The use pattern of alternative host plants by Maruca vitrata was investigated in southern and central Benin. Among the wild host plants, Pterocarpus santalinoides, Pueraria phaseoloides and Centrosema pubescens were found to be key relay hosts during the long dry season, Lonchocarpus sericeus and L. cyanescens were the most important hosts during the main rainy season, while Tephrosia platycarpa was an essential relay host during the short wet season in between. Cowpea was the major cultivated host plant and can sustain M. vitrata all year round, if available. However, this pest was able to maintain high population levels exclusively on wild hosts without needing to switch to cultivated crops. The relevance of these findings and their implications for the control of M. vitrata are discussed.

The study reported here evaluated the distribution, relative abundance, and malaria transmission potential of Anopheles mosquitoes at 30 sites representing different ecological strata in western Kenya. Seasonal variation in anopheline densities and transmission potential, as expressed by Entomological inoculation rates (EIR), was investigated. Of the 6491 indoor resting anopheline mosquitoes collected at the 30 sites, 91.3 % (n = 5926) were An. gambiae s.l. and 8.7 % (n = 565) were An. funestus with an average house density of 6.58 and 0.63, respectively. Analysis of the data indicated significant variation in mosquito densities between study sites, species and season. High densities of both An. gambiae and An. funestus were recorded in the northern and northeastern parts of the district, while generally low densities were recorded in the south. Anopheles gambiae s.s. and An. arabiensis comprised 60.3 % (n = 3573) and 39.7 % (n = 2352) of the total number of An. gambiae s.l. mosquitoes collected, respectively. The composition of the An. gambiae s.l. sibling species showed temporal and spatial variation. Entomologic inoculation rates were estimated at 1.55 and 0.12 infective bites per person per month for An. gambiae s.l. and An. funestus, respectively. This study reveals considerable seasonal and site-specific variation in vector distribution, composition and transmission potential. Application of control interventions must therefore consider seasonal variations since the vectorial system changes quite rapidly over a short period of time.

Mites are known to live in a diverse number of habitats, but only recently have they been collected in large quantities from the tropical canopies, where they have a diverse feeding habit.

We studied the canopy oribatid mites from five localities of Mexican oak species. Foggings with a natural pyrethrum in aqueous solution were employed to obtain the arthropods living on the canopy of the oaks. Specimens were taken from two collections made in February and August of 1997.

The total number of mites obtained with the two foggings was 5824 specimens. Most of them (95%) were collected during the rainy season and only about 5% during the dry season. The Mesostigmata were represented by 194 specimens, Prostigmata by 849 and the Cryptostigmata (or oribatids) were by far the most abundant, with a total of 4781 specimens. This group represents only 3% of total mite abundance during the dry season and 97% during the rainy season.

Quercus crassipes harboured more oribatid mites during the dry and rainy seasons, and the most important mites in abundance and frequency were Camisia sp., Phauloppia sp. and Scapheremaeus sp.

The effects of four different neem formulations (Neemros®, Neemroc EC®, Neemroc Combi and Saroneem) and a combination of Neemros® with a synthetic acaricide (Mitac®) on the twospotted spider mite (Tetranychus urticae Koch) were compared with Mitac® on tomato (Lycopersicon esculentum Mill.) leaf discs in the laboratory, The following LC50 were determined: Neemroc EC® 12.9 ml/1, Saroneem 5.8 ml/1, Neemroc Combi 1.0 ml/1 and Mitac® + Neemros® 1 ml/1 + 17.6 g/1. No LC50 was determined for Neemros® since the highest mortality observed was 11.4 %. The combination of Mitac® and Neemros® resulted in the highest mortality after 24 hours (83.3 %), followed by Neemroc EC® (78.3 %), Saroneem (53.4 %), Mitac® (50.8 %), Neemroc Combi (38.9 %), the control (4.5 %) and Neemros® (0.0 %). All neem formulations also caused repellence and oviposition deterrence in T. urticae.

We have previously described a bloodmeal-induced molecule (lectin-trypsin complex) from the midgut of the tsetse fly, Glossina longipennis, with both lectin and trypsin activities (Osir et al., 1995). In this paper, we report on the isolation of a similar molecule from the midguts of Glossina fuscipes fnscipes and provide direct evidence for its involvement in the development of African trypanosomes. The molecule (native Mr ∼65,700) has two non-covalently linked subunits, Mr ∼28,800 and Mr ∼35,700. The native molecule was found to be capable of inducing differentiation of bloodstream-form trypanosomes into procyclic (midgut forms) in vitro. In the assays, specific antibodies against procyclin were used to monitor the transformation of the bloodstream-form trypanosomes into procyclic forms. This induction was specifically inhibited by D-glucosamine. Cis-aconitate was also capable of inducing the transformation process with the same efficiency as that of the lectin-trypsin complex. While increasing the concentrations of the lectin-trypsin complex (≥100 μg protein/ml) in the incubation assays resulted into higher transformation rates, it also led to high parasite mortality. These results provide evidence for the involvement of the midgut lectin-trypsin complex in the differentiation of bloodstream-form trypanosomes within tsetse midgut.

The effect of artificial infestation of the spiralling whitefly, Aleurodicus dispersus Russell at 0, 1, 2, 3, 4 and 5 pairs on caged potted pepper (Capsicum spp.) plants at 2 weeks after planting (WAP), representing the nursery stage, and 6 WAP, representing the field stage, was studied in a screen house. Increasing insect density resulted in a corresponding increase in damage to the leaves, measured as leaf drop. Yield reduction was inversely proportional to the whitefly population, with highly significant correlation coefficients. For instance, yield reductions were 8.8 and 36.5% with 1 and 5 pairs of adult whitefly respectively at 2 WAP, and 7.5 and 32.1% with 1 and 5 pairs respectively at 6 WAP. The chlorophyll, sugar, ash, protein and crude fibre contents of the leaves decreased with increases in level of infestation, although infestation had no significant effect on the nutrient contents of the fruits. The significant impact of A dispersus on vegetative growth, yields and chemical contents of leaves confirm it as an economic pest of pepper in Nigeria.

Based on the systematic study of the nature of symptoms and extent of damage, a rating scale of 1 (healthy plant) to 9 (deadheart) was developed to allow the screening of maize genotypes for resistance to the pink stemborer, Sesamia inferens (Walker). The maize plants were separated into three distinct groups, namely least susceptible (1–3 score), moderately susceptible (4–6) and highly susceptible (7–9).

We studied the mite complex—consisting of Tetranychus cinnabarinus (Boisduval), T. urticae (Koch) and Aculops spp.—on three varieties of carnation (Finesse, Optima and White Barbara) in a flower farm in Kenya. Over a period of 24 months, those carnations established in a soilless substrate (pumice in gunny bags) harboured on average less than five mites per leaf as compared to over 20 per leaf on plants established on bare soils. This was the case whether the crop was judiciously or prolifically sprayed with acaricides. The study further established that the economic gain was the same when lower volumes of pesticides were used, whether sprayed judiciously or prolifically. The variety White Barbara generally harboured higher mite numbers than Finesse or Optima. Furthermore, there were fewer rejections, and higher market value when plants were established on pumice substrate compared to bare soils. The study further showed that planting in pumice holds promise for mite control in flower farms. Furthermore, predatory natural enemies of the pest mites, including phytoseiid mites and Orius spp., were conserved in plots where pumice was used with minimum spray.

Experiments were conducted to assess the effect of four plant growth regulators (PGRs), namely coumarin, kinetin, gibberellic acid (GA3) and indole-3-acetic acid (IAA), on the development of the melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). All four compounds exerted growth-and development-inhibitory effects on the fly. Coumarin was most potent, followed by kinetin, GA3 and IAA. The first and second instars of the fly were more sensitive than the third instar. Treatment with the PGRs also prolonged the fly's developmental period, reduced percentage emergence and increased percentage of abnormal flies emerging. At the higher concentrations tested (125, 625 and 3125 µg/ml) coumarin, kinetin and GA3 caused 100% mortality in first instars.

The biological hypothesis that female parasitoids can adjust their fecundity schedule according to host availability, and tradeoff longevity with fecundity was tested in a thelytokous oophagous parasitoid, Trichogramma brasiliensis Ashmead (Trichogrammatidae: Hymenoptera) parasitising the rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). The tradeoff between early and late reproduction revealed that this wasp was able to exploit practically all available hosts during the first day or first few days of adult life. During spells of host unavailability, it was able to adjust its fecundity schedule accordingly. There was a negative relationship between survival and reproduction. Adult females survived shorter (10 days) when an unlimited supply of hosts was present, but longer (16 days) when no hosts were provided. These observations suggest the potential suitability of T. brasiliensis for inundative releases even in conditions of fluctuating host availability.

Studies were conducted in farmer's field, Lambwe School of the Deaf, and Mbita Point Field Station of ICIPE (ICIPE-Mbita) in western Kenya during the long rains of 2001 and 2002 to assess the impact of a diversionary stemborer management strategy on the pest's predators. Treatments consisted of a maize monocrop (control) and an intercrop of maize and desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as trap crop around the field (‘push-pull’) in the farmer's field and Lambwe School of the Deaf. Sudan grass, Sorghum vulgare sudanense (Pers.), was used in place of Napier on the station. A combination of sticky traps, direct observation and hand-collection methods were employed. Predator groups encountered included 12 families from 7 insect orders and 4 families from one arachnid order, with most of the foregoing represented in both maize monocrop and ‘push-pull’ plots. A Cheilomenes sp. and Chrysopa sp. were, however, recovered from ‘push-pull’ plots only. Ants, earwigs and spiders were the main predators encountered. Both overall and individual group populations of these predators as well as ant diversity were significantly higher in ‘push-pull’ than monocrop plots in all the sites during the vegetative, flowering and mature maize growth stages (P < 0.05, t-test). The results thus indicate a numerical enhancement of stemborer predators by use of this habitat management system.

The resistance of 63 tomato (Lycopersicon esculentum Mill.) accessions to the twospotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), was investigated in screen house experiments and compared to Money Maker, a T. urticae-susceptible variety widely grown in Kenya. The number of motile mite stages 12 days after inoculation with 5 adult female mites was significantly lower than in the control variety (Money Maker) in seven accessions (Marglobe, Roma-VF, 94 RT 330, Continental Michel, Early Pearson, ARP 366–4 and 94 RT 316). Egg numbers were significantly lower than in the control in 14 accessions (Marglobe, Cal-J-VF, Roma-VF, Beauty, 95 RT 315, 93 KT 20, EC.3504,94 RT 313, EC-1193, Continental Michel, Early Pearson, ARP 366–4,94 RT 316 and Malawi Local 3). This study reveals the existence of resistance to T. urticae in the tomato accessions.