Different modes of immune reactions of insect vectors of human and animal diseases to nematode and protozoan parasites, fungi, bacteria, viruses and to other biological materials e.g. xenografts are discussed in this paper. Since most of the insect vectors of diseases are adult dipterans with low numbers of circulating haemocytes, their mode of defence against metazoan parasites and fungal pathogens is primarily by means of humoral encapsulation, with little haemocyte participation. Although earlier workers reported that humoral capsules in dipterans were formed without direct participation by haemocytes, this paper reveals increasing evidence of cellular involvement in the formation of humoral capsules, both at the initial and terminal stages of the encapsulation process. The role of phenoloxidase system in non-self recognition and in the process of melanization of haemolymph and capsules formed around parasites and fungal pathogens is also discussed. Immune defence of insect vectors against bacterial invasion by means of haemocytic reactions e.g. phagocytosis and nodule formation and by synthesis and release of humoral antibacterial factors e.g. lysozyme, attacins and cecropins is described and compared with similar reactions reported to occur in other insects. The role of lectins in defence of insect vectors against the parasites they transmit e.g. sandflies against Leishmania, blackflies against Onchocerca and tsetse against Trypanosomes is discussed and the possible mechanisms by which some parasites evade recognition and attack by the vector immune systems are also briefly discussed.

Larval establishment and feeding site selection of Eldana saccharina Walker were studied on maize (Katumani Composite B) and sorghum (Serena). These parameters were defined as the location within the plant of the larva 7 days after hatching; and feeding activity was measured by the extent of stalk tunnelling. In naturally infested maize, more larvae settled in the basal section of the plants between second and fifth node/internode, and in sorghum they settled between fourth and seventh node/internode. In the artificially infested plants of both crops, larvae settled in the middle section of the plant mainly between fourth and seventh node/internode. The neonate larvae first settled in the leaf sheath until they were third instars when they entered the stalks. However, in sorghum stalk entry was limited by stalk wall toughness and waxes on the stalks.

The extent of stalk tunnelling indicated that in maize larval feeding is highest in the internodes whereas in sorghum it is in the peduncles.

A total of 17 species of Hemiptera were collected from sorghum with compact panicles during the 1982 and 1983 cropping seasons at Samaru and Kano, Nigeria. The most important species based on time of appearance and abundance were Eurystyhis rufocunealis, Campylomma angustior and C. subflava. Paramixia suturalisand Taylorilygus vosseleri occurred in high numbers only at Samaru in 1982. Significantly more Orius spp. were collected at Kano. These species represented 95 % of all hemipterans collected.

The number of spiders per panicle were significantly lower at Samaru, up to three per panicle, than at Kano, up to 10 per panicle, in 1983. There was no relationship between the number of spiders and the number of hemipterans at Samaru, but at Kano a significant positive relationship was observed between the number of spiders and the number of immature hemipterans. The spider families Dysderidae, Thomisidae and Salticidae represented 80% of the spiders collected.

Three generations of the maize stalk borer, Busseola fusca (Fuller) per year were observed in maize fields in Southern Ethiopia. However, the third generation was not important on maize. The first generation developed on young maize plants during the wet season (April–July). The second generation occurred in July and majority of larvae went into diapause from September to February while a small proportion pupated in the months of September and October and gave rise to a third generation. Pupation of the diapause larvae was observed in April.

Female moths from the first (non-diapause) generation laid significantly more eggs than those coming from a diapause generation. Longevity of these moths was also significantly longer than the diapause generation. Despite the indicated differences, female moths from both generations laid most of their eggs between the second and fifth nights after emergence. The number of eggs laid and rates of hatching declined with age of moths irrespective of generations.

We studied the distribution of wild Mediterranean fruit flies, Ceratias capitata (Diptera: Tephritidae) in different environments of trimedlure-baited Jackson traps during high fall season populations in Southern Egypt. We found that 98% of females attracted to within aim radius of standard trimedlure (TML)-baited Jackson traps remained on the surrounding foliage without approaching the trap. Also about 30 % of males aggregated there, calling and competing for matings with approaching females. The closest mating occurred 25 cm from a standard trap. The nearest lek formation away from a trap was observed at a distance of 2 m on the same trap tree. The highest captures of males were recorded in the morning after male calling on the foliage reached its daily peak. Jackson traps baited with both protein hydrolyzate and TML on cotton wicks caught as many males, but significantly more females than traps with TML only.

The ability of three anti-juvenile hormone agents (AJHAs) to prevent the juvenile hormone dependent phase of larval-pupal transformation has been investigated. Neck-ligated post-feeding last instar larvae of Spodoptera mauritia were treated topically with different doses of a juvenile hormone analog (JHA) or the AJHAs, tetra-hydro-4-fluoromethyl-4-hydroxy-2H-pyran-2-one (FMev), ethyl-4-[2-(tert-butyl carbonyloxy)butoxy] benzoate (ETB) and ethyl-[E]-3-methyl-2-dodecanoate (EMD). Untreated ligated larvae or those treated with acetone survived for 12 ± 1 days without showing any sign of pupal cuticle secretion. On the other hand treatments of ligated larvae with different doses of JHA induced pupation. Among the three AJHAs tested treatments of ETB promoted pupation. Treatments of ligated larvae with lower doses of EMD induced the formation of larval-pupal intermediates whereas those treated with higher dose moulted into either pupae or larval-pupal intermediates. FMev-treated larvae exhibited a complete inhibition of moulting and metamorphosis. In order to study whether AJHAs would prevent the JHA induced pupation, neck-ligated larvae were treated simultaneously with different doses of AJHAs and 1 μg JHA. Co-application of JHA with different doses of EMD induced pupation in majority of the ligated larvae and thus appears to a certain extent to counteract the effects of treatments of same doses of EMD alone. Co-application of JHA with different doses of ETB elicited pupation in all the surviving ligated larvae. To a large extent co-application of JHA with different doses of FMev failed to induce pupation. The significance of the findings is discussed in the context of the mode of action of these AJHAs.

The effects of applying varying doses of an antibiotic to fifth instar larvae of Philosamia ricini on the silk glands were studied. Transaminases were increased by low doses, while RNA accumulation was reduced after administration of tetracycline. The levels of DNA showed little response to treating with antibiotic. However, the incorporation of amino acids into silk proteins was generally increased. The overall effects on the silk gland was reflected by its weight, cocoon weight, quantity of raw silk and quality of silk. All these indices were improved by administration of tetracycline.

A new eye colour mutant, “Orange eye (Or.)” is described for Ephestia cautella, Baghdad strain. This mutation is inherited as an autosomal recessive mutant. Fecundity of the orange-eyed strain is significantly reduced while its viability is not affected.

Bruchidius atrolineatus Pic is a Coleopteran Bruchid developing in cowpea (Vigna unguiculata Leguminosae) seeds. This insect causes important damage in tropical countries during storage of cowpea seeds. The influence of some volatile sulfur compounds is studied on adults and larvae of B. atrolineatus. Dimethyl trisulfide and diethyl trisulfide produce the highest mortality to adults, eggs and larvae. The toxicity of the sulfur compounds is higher than that of carbon tetrachloride but is less than that of Dichlorvos at a dosage of 500 g/l. It is suggested that the sulfur compounds produced by the leaves of some tropical plants (Alliaceae, Bignonlaceae, Mimosaceae) could be used for control of Bruchid populations in the stored products.

Apanteles flavipes is a gregarious endoparasitoid of Porthesia scintillans. A new method for the estimation of energy available to the parasitoid is presented and used to prepare an individual energy budget for A. flavipes. A. flavipes consumes 13.9 J of the host tissue and assimilates 13.4 J. Production amounted to 10.1 J. Efficiencies of assimilation and production are 96.2 and 753 % respectively. Metamorphic metabolic rate was 0.555 kJ/g/day.

This paper is based on experiences obtained during a joint enterprise between the Social Science Interface Research Unit, of the Crop Pests Research Programme, and the Livestock Ticks Research Programme at ICIPE. Topics bearing on technology design and development are emphasized.

The resource-poor farmer as conceptualized within ICIPE and reinforced by research experience, is by definition a person who operates a diversified system of production in which food security concerns and cash income intakes are crucial.

The family/household provides most of the labour required in production in African farming communities. For this reason, their labour investment into the adoption of novel activities or technological innovation and their assessment of the value of such innovations requiring changes in their normative practice, is appraised primarily in terms of the returns they would get for the additional labour input.

It is noteworthy that much of the so-called family labour is, in fact, female labour. It is therefore arguable that the perception of the women of technological inputs and innovations as profitable, is crucial for the successful adoption and social acceptance of novel technology.

Although agricultural land is in increasingly short supply, it would appear that the crucial limiting factor in production is not a shortage of land per se, since a good number of households do not fully exploit all the agricultural land at their disposal. Labour, and/or cash income to secure additional labour, appears to be the most important constraint to production. This tends to suggest that for future technological interventions in agricultural systems of the rural poor, consideration will have to be given to inputs which optimize the use of family/household labour.

The escalating population growth suggests that focus on women's health and incomes could significantly and qualitatively improve the prospects for the adoption of new and improved technology in areas such as pest and vector control.

Between May 1984 and December 1985, the population of immature stages of Anopheles arabiensis was sampled by the dip method at sites close to two villages in Mwea Irrigation Scheme, Kenya. Larval presence corresponded to rainy seasons and the flooding phase of the rice cycle. No larvae were found during the postharvest dry season. The instar composition, age distribution and survivorship curves for the different stages were determined. Pupal productivity for Mwea rice fields was estimated to be 1% of the total immature population.

Per cent survival, larval period and weight, pupal duration and weight, emergence, adult longevity and fecundity of Heliothis armigera (Hubner) were affected by the pulse species on which it was reared. The pulses could be classified into two groups i.e. pigeon pea and chick pea which were suitable for growth, development and fecundity and black gram, sweet pea, green gram, broad bean and lentil which were unsuitable.

Populations of Rhipicephtdus sanguineus, Dermacentor variabilis and Amblyomma maculatum with high and low oviposition capacities were successfully bred in the laboratory. Mating of male and female ticks which possess high oviposition capacity produced female progenies with high oviposition capacity; male and female ticks which possess low oviposition capacity produced female progenies which possess low oviposition capacity. Crossmatings of males with females of opposite oviposition capacity produced female progenies which acquired the category of oviposition capacity of the males in predominant numbers after fourth and fifth generations. It is suggested that the genetic factor for high or low oviposition capacity is either possessed by male ticks alone or is stronger and dominant in the male over that of the female. This genetic factor is also potentiated by successive crossmatings of males and females possessing opposite oviposition capacities.

The possible application of these results to tick control through the suppression of natural population by field release of laboratory-bred populations of male ticks which possess low oviposition capacity is discussed.

Laboratory studies were conducted on the role of flood on egg development, survival and hatchling weight in the solitary phase of Locusta migratoria migratorioides (Reiche and Fairmaire). Egg development is retarded by flood, particularly if the eggs develop for a long period in ordinary moist soil prior to flooding. Floods are also detrimental to egg survival; eggs that are flooded immediately after oviposition and those flooded when they are about to hatch are particularly susceptible. Egg age at flooding is a major determining factor of hatchling weight; heavier hatchlings are produced if eggs develop in ordinary moist soil for longer, rather than shorter, period before being flooded. Length of flooding period has no apparent effect on hatchling weight.

Effects of nitrogen on stem borer damage in a sorghum/millet m ixture were investigated in Nigeria. Millet and sorghum grain yield as well as stem borer infestation were not significantly influenced by rate and time of nitrogen application. Borer (Acigona ignefusalis) infestation on millet was very severe in 1984, resulting in total crop failure. In 1985, millet produced grains because of lower borer infestation and damage; the yield of sole millet was thrice that of millet in mixture, whereas the sole crop density was twice that in the mixture. Unlike millet, sorghum produced grains in 1984 despite severe damage by Busseola fusca. Sole sorghum yielded five times the mixture in 1984 but two and a half times in 1985. Borer damage was generally more severe in the mixture.

A total of 1244 egg-pods of 12 grasshopper species were collected — 26.7% were from low altitude hills, 23% from Swat valley, 22.1% from Punjab plains, 19.4% from Peshawar region and 8.8% from Potohar plateau. Aiolopus thalassinus was the dominant species comprising 27.7% of the total pods. This was followed by Shirakiacris shirakii (24.5%), Oxya multidentata (13.6%), Trilophidia annulata (9.7%), Spathosternum prasiniferum (9.7%), Atraetomorpha acutipennis(7.4%), Stenohippus sp. (3.8%) and Phlaeoba punteli (1.8%). Others were rare being less than 1%.

Egg-pod density was effected by several closely related factors. Mean annual temperatures (15.6 − 23.4°C) and average precipitation (310 − 2100 mm) of the localities were not the ultimate controlling factors. Parasitism however, appears to play an important role. Highest parasitism of Scelio spp. was 10% on the Potohar plateau where egg-pod population was lowest. A. thalassinus was the most preferred host(41.7%) followed by S. prasiniferum (35.4%), S. shirakii (14.6%), O. multidentata (8.3%), T. annulata and Stenohippus sp. (2.1% each). Soil-type (clay-loam, loam, sandy-loam) and type of vegetation(cultivated area, grasslands) also have a considerable bearing on the microclimate in which the insects live.

Limonoids such as deoxylimonin, obacunone and pedoniti are known to have antifeedant effects against some lepidopteran pests. However, there is no electrophysiological data showing the effect these compounds have on taste receptor cells. This information gap is due to the fact that limonoids are insoluble in water and this makes it difficult to apply the tip-recording technique in an electrophysiological bioassay of limonoids. This problem was solved by dissolving the limonoids in a mixture of 50 % tetrahydrof uran and 50 % aqueous NaCl. Limonoids and sucrose so dissolved were used to investigate responses of Eldana saccharina maxillary styloconic sensilla. The solvent mixture did not appear to damage the taste receptor cells and the taste receptor responses to solutes dissolved in that solvent were reproducible. Sucrose stimulated a cell in the medial as well as in the lateral styloconic sensilla. Deoxylimonin alone stimulated a cell in the medial sensillum but not in the lateral sensillum. When presented with sucrose, deoxylimonin inhibited the sugar receptor cell and this was also true for obacunone.

Conessine, the steroidal alkaloid of Holarrhena antidysenterica Wall, possesses a wide range of activities against four insect species viz. Aedes aegypti, Dysdercus koenigii, Spodoptera litura and Pieris brassicae. In D. koenigii the compound inhibits the egg hatching of treated adults and nymphs. In Ae. aegypti the larval developmental periods are extended, resulting in a high mortality rate. Such effects are produced at very low dosages of 0.5 to lOppm. Antifeedant activity is observed against larvae of S. litura and P. brassicae at concentrations of 0.005 to 0.2 % of conessine.